Analytical Methodologies for Arsenic, Selenium ... - ACS Publications

Chapter 8

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Analytical Methodologies for Arsenic, Selenium, and Mercury: A Historical Perspective Larry Kolopajlo* Chemistry Department, Eastern Michigan University, Ypsilanti, Michigan 48197, United States *E-mail: [email protected].

Historical interrelationships between mercury, arsenic, and selenium are examined and assessed in terms of their environmental impacts, cold vapor/hydride analytical method development, and emergence of the discipline of chemistry. The narrative is accentuated by highlighting important contributions made by environmental chemistry professionals, and is appropriate for an audience of environmental chemical analysts, chemical educators, students, and teachers.

Introduction The first question one might ask about is why arsenic, selenium and mercury are included together in a paper that takes a historical perspective, and the answer is of course that that all three elements have unleashed upon the environment a veritable Pandora’s Box of appalling impacts while tarnishing the image of chemistry in the process. Studying the history of these elements then presents an opportunity for teachers, students, and analysts to learn about the consequences of pollution, and better appreciate the value of environmental initiatives carried out by agencies such as the U.S. Environmental Protection Agency (1), and the World Health Organization (2). What’s more, for decades in the field of analytical chemistry, each of these three elements has been analyzed by cold vapor and hydride methods. It can also be argued that mercury and arsenic are important to the history of chemistry because they have been known and investigated since antiquity (3). Setting itself apart from all other elements by having a privileged place in alchemy, © 2017 American Chemical Society

Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


mercury played a central role in the subsequent shift from alchemy to chemistry. Understanding mercury in today’s context would allow one to trace how mercury has influenced chemical history. Moreover, the history of chemistry should be important to chemical educators, because the discipline helps students and teachers alike, step back and view the big picture of how science developed, and evolved into separate disciplines. Only then can students and teachers alike appreciate the contributions of diverse geniuses whose drudgery led to stunning scientific accomplishments. Unfortunately, however, studies have shown that there is a history knowledge gap in current U.S. secondary teaching and chemistry programs whose over-crowded curricula focus on content, methods, and clinical experience at the expense of a historical perspective. Kaufman (4) has argued that a historical deficit can lead students to formulate a distorted view of chemistry. Furthermore, while Stock (5) demonstrated that few history of chemistry courses exist across the curriculum, Suay-Matallana (6) noted that that the discipline of chemical history has few independent associations and societies dedicated to it. To bridge that gap in secondary teacher preparation programs, studying the history of these elements can imbue chemical educators with an appreciation of the nature of science (7), including the evolution of pure and applied chemistry, the scientific method, the process of scientific discovery, and the human impact of pollution. There also appears to be little historical information available that addresses the history of environmental analytical chemistry, so important in an unsustainable world. Finally, by studying the history of mercury, arsenic, and selenium, one can also understand how chemical history fits within Kuhn’s (8) theory of scientific revolutions, and how changes in one area cause ripple effects in others. The purpose of this chapter is to frame mercury, arsenic, and selenium within their historical context, to understand their environmental impacts and ensuing analytical method development, to demonstrate the interrelationships between these elements, and to communicate how they have played an important role in the transition from alchemy to chemistry. This will be done by integrating the understanding of mercury, arsenic, and selenium from past to present times in such a way as to be of educational value to chemical educators. By reading this chapter, chemical educators can acquire relevant information to enhance their analytical history curriculum, and understand that the history of mercury, arsenic, and selenium are much more than a linear collocation of successive discoveries, and creation of government agencies.

Alchemy to Chemistry Mercury in Arabic Alchemy In this section will be examined how an understanding of mercury, and arsenic to a lesser extent, influenced the development and understanding of Middle Age alchemy (400 – 1400 A.D.), and how the study of these elements, especially mercury, helped catalyze the transition from alchemy to modern chemistry (9). The term alchemy conflates the study of nature (art, chemistry, medicine, and physics) and metaphysics (astrology, mysticism, and spiritualism) 142 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


into a distinct discipline. Many scholars (10) have supported the idea that alchemy originated in the Middle East between 640 and 1100. There Arabic and Islamic scholars cultivated a strong scientific tradition that had a lasting influence on the arcane, embryonic field of alchemy. For example, today’s commonplace chemical vocabulary contains several terms originating from Arabic alchemy, including for example, alkali (al-qaliy), alcohol (al-kohl), amalgamate, antimony, benzene, borax, elixir (al-iksir), soda, and talcum (11). Furthermore, Arab scholars clearly forged the term alchemy from the definite article al, and kimiye (12). The rich tradition of Arabic alchemy created numerous scholarly manuscripts and lab artifacts, many of which being forerunners of today’s modern instruments, are currently exhibited at international museum collections (13, 14). What’s more, it was Arabic alchemists who devised the theory of the mythical Philosopher’s Stone (15) that could not only transform base metals such as mercury into gold, but when used as an elixir (16), possessed the power to confer immortality. For centuries, alchemy’s consummate but unattainable quest was to synthesize this entity, which today is analogous to the modern theory of the transmutation of metals through radioactive decay. In addition, Arabic alchemy triggered the rise of European alchemy around 1100 (17). Hence the role of alchemy in the Middle Ages relative to other known disciplines is analogous to the role of chemistry as a central science today. Before Arabian alchemists conjured up theories of matter, Greek dogma (18) patently defined matter as being a mixture of four natural elements: earth, water, fire, and air that possessed the four properties of coldness, hotness, wetness and dryness. According to Aristotle’s theory, solar heat caused the earth to emit two types of exhalations, one being cold and moist, and the other hot and dry. When moist exhalations met dry rock, the mixture condensed and converted into metals. In the time of Arabic alchemy, metals were still the most recognized form of matter because they were both abundant, and used for a variety of applications such as jewelry, dining, and weaponry (19). In general terms, it was known that metals could be obtained from ores, and further, that alloys and amalgams could be obtained by mixing melted metals. Moreover, only seven metals were known, and most existed naturally as readily available sulfide ores (20): mercury in cinnabar (HgS), silver in acanthite (Ag2S), copper in chalcocite (Cu2S), lead in galena (PbS), and iron in pyrite (FeS2). Obviously, gold could be found in its elemental state, while tin on the other hand, was found in cassiterite (SnO2). Since tin has a relatively low melting point (232 °C), it could be easily prepared in the pure state by smelting cassiterite (21) in the presence of carbon at low temperatures:

To ancient alchemists, these seven elements must have held a very important place in the universe, and hence they took on a metaphysical status as fundamental principles, not just material building blocks. Of these seven metals, the element mercury, having fascinated scholars since antiquity because of its salient properties, namely the fluidity of water, and the luster and color of silver, hence became known as quicksilver. Thus, alchemists 143 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


imbued mercury with possessing metaphysical properties that led to it playing a crucial role in shaping both the concept and theory of matter. Mercury compounds were even employed by Egyptians as pigments and for gold mining (22). The most common mercury containing mineral was cinnabar (23), composed of mercuric sulfide, HgS, which is a bright red in color. Important cinnabar deposits have been found across the Middle East (24), for example, in Turkey, the Balkans, Spain (Almadén), Egypt (Giza), and in Italy (Tuscany). Mercury could be prepared by heating cinnabar:

Since ancient times, cinnabar was used in red-colored pigments, red lacquers, and until recently, in cosmetics when its use was halted due to recognition of mercury’s toxicity (25). Of all the Islamic alchemists, the scholar Jabir ibn Hayyan (26), who lived from 721- 813 in present day Persia, is unequivocally recognized as the leading figure. Jabir worked as both a pure and applied alchemist, and in addition, introduced experimenting as a laboratory method. Among the mercury compounds that he investigated, Jabir’s manuscripts list mercury(II) oxide and mercury(II) chloride (27). One of Jabir’s most celebrated accomplishments was his theory of metals (28). In general, some of the speculative ideas that led to this theory are as follows. Since during Jabir’s time: (a) most known metals were mainly obtained from sulfide ores, (b) both mercury and sulfur were easily obtained from cinnabar, (c) mercury was a liquid in its natural state, and other metals could be melted and amalgamated with it, and d) because mercury exhibited special properties, then it would have been reasonable for him to infer that each of the seven known metals were composed of just two substances, mercury and sulfur. Jabir thus unveiled his famous mercury-sulfur theory of metals, each containing a different ratio of mercury to sulfur (29). However, in contrast to the above reasoning, perhaps the Jabirian theory of metals was rationalized in analogy to what was understood about mixing colors in ancient times. For example, it was known that orange pigment could be prepared by mixing red and yellow pigments, the resulting hue depending on the ratio of red to yellow. Furthermore, in Jabir’s time, the minerals cinnabar and orpiment were employed as red and yellow pigments respectively. Since mercury was obtained from cinnabar, and sulfur from orpiment, then it would have been reasonable to assume that all metals had a dual nature deriving from mercury and sulfur. Hence Jabir could have assumed that metals possessed a weighted average of the properties of mercury and sulfur, just like in color mixing. However, this seemingly simple theory was very complicated and represented not only a refinement of the Aristotelean scheme, but a comprehensive extension. It was published in his 7th-century treatise titled the Secret of Creation (30) and later in The Book of Explanation (31). Up to Jabir’s time, little progress had been made toward an understanding of matter, but Jabir’s theory established a new 144



paradigm whose legacy would not only dominate alchemy for nearly a millennium, but would provide a research path for future alchemists to follow. Jabir’s mercury-sulfur theory is so important to the history of chemistry that it merits elaboration. Most significantly, in Jabir’s mercury-sulfur theory, Aristotle’s moist and cold exhalations were superseded by mercury while his hot, dry exhalations were replaced by sulfur. According to Jabir, metals formed as growths inside the earth when sulfur rose as fumes, and combined and fused with mercury under the influence of heat. Different metals formed in different types of soils containing different amounts of sulfur. The silver fluidity of mercury was thought to impart the properties of fluidity and metallic luster to metals, whereas sulfur gave rise to hardness and combustibility. Moreover, both gold and mercury were known to be dense substances, and the fluidity of quicksilver was viewed to be analogous to the property of malleability in gold. Therefore gold, exhibiting a bright luster and being malleable, was the most perfect metal since it was obtained naturally as the pure element, contained the most mercury, and the highest mercury to sulfur ratio. On the other hand, the metal lead was deemed the least perfect of all because it exhibited a dull luster, was soft and malleable, and hence contained the lowest ratio of mercury to sulfur. Since iron was hard and combustible, it was also classified as an imperfect metal and therefore contained mostly sulfur. Jabir further explained the difference between gold and silver by proposing that silver was made from white sulfur (probably white arsenic) and mercury, whereas gold was composed of purified red sulfur (probably the mineral cinnabar or realgar) and the brightest (purified) mercury. The idea that gold contained red sulfur could have originated from observations of decomposing cinnabar which has a bright red-gold color. Moreover, since it was also known that smelting produced a purer metal, there was proof of Aristotle’s postulate that heat played a necessary role in the formation of metals (in reality, alloys). Such observations probably led alchemists to the theory of transmutation of metals, attempting to produce for example, gold from tin. Jabir is also given credit for the discovery of aqua regia, an acidic mixture that could dissolve gold; it contains HCl and HNO3 in a 3:1 ratio (32). Although Jabir believed that mercury and sulfur were the basic building blocks of all metals, the alchemist’s sulfur was not necessarily the natural element known today, but instead was a name applied to any combustible or volatile substance such as arsenic. Therefore, although some scholars (33) have proposed that Jabir had postulated a three-component theory of metals consisting of mercury, sulfur and arsenic, in reality, Jabir’s white sulfur proposed as a constituent of silver was probably white arsenic (As2O3). Because white arsenic was viewed as being just another form of sulfur, arsenic could not be a third fundamental component of metals. Yet Jabir’s theory was even more obscure than it appeared, because most scholars agree that Jabir’s sulfur and mercury were not to be literally taken as the natural elements known today (34). They instead represented definite principles, idealized elements or philosophic elements exhibited only by purified essences of the real substances, and in the context of the mercury-sulfur theory, these substances would be described as philosophic mercury and philosophic sulfur. Hence in Jabir’s theory, gold was constituted when a mixture of mercury and 145



sulfur ripened in the recesses of the earth through heating, with that change transpiring through the interaction of the principles of philosophic mercury and philosophical sulfur. While thousands of works are typically credited to Jabir, scholars generally believe that many of his less important manuscripts were actually written by his students, collaborators, and later followers, and therefore this group of scholars became known as the Jabirian Corpus (35). Although Jabir’s theory of metals was later discredited, it was an important step forward toward a theory of matter. Subsequent investigations of Jabir’s ideas also helped unravel the distinction between elements, compounds, and alloys.

Mercury in European Alchemy Following Arabic alchemy was the rise of European alchemy (1100 - 1700) made possible by the transfer of Arabic knowledge through translation of the works of Jabir and others into Latin by medieval scholars, who not only edited some of his manuscripts, but changed Jabir’s name to Geber, its Latin equivalent (36). Although it is normally assumed that European alchemists accepted Jabir’s mercury-sulfur theory of metals, William R. Newman (37) has advanced the opposing viewpoint that not all European alchemists accepted the mercury-sulfur theory of metals, but instead believed that mercury and sulfur were palpable, independent substances rather than philosophic constituents of metals. Bombastus von Hohenheim (1493-1541), or Paracelsus as he is generally known, is the next historical figure who initiated a scientific revolution that connects with mercury (38). He was born in Switzerland but worked throughout Europe, especially in Germany. He was an iconoclastic medical scholar who having spurned the current norms of medical practice, publicly burned accepted manuscripts, which did nothing to ingratiate himself with his peers. However, by reinventing medicine, his innovative treatments for disease are today recognized as revolutionary, although they remained controversial during his time. Paracelsus is now honored as being the first medicinal chemist and toxicologist because he was first to comprehend the human body as an organism controlled by natural (alchemical) processes, and furthermore, he argued that medical practitioners should study and use alchemy to invent new medicines. Hence, Paracelsus was a forerunner of today’s applied pharmaceutical chemists because he pursued, introduced, and studied novel alchemical compounds using experimentally obtained knowledge to treat intractable diseases of the time like syphilis. He even advocated that physicians discover and introduce less toxic medicines, like for example calomel (Hg2Cl2) to replace the more toxic mercury metal (39). Having discovered the concept of dosage, he urged his peers to limit their prescribed amounts of known toxic compounds, especially those containing mercury and arsenic, and to experiment with innovative alternative compounds to mitigate their unwanted side effects. He even prepared ointments by mixing mercury compounds with oil. For example, mercury(II) oxide was made into an ointment used to treat eye and skin problems, and mercury(II) chloride was used as a disinfectant (40). 146



Although Paracelsus established a Kuhnian revolution in medicine, his most important alchemical contribution extended Jabir’s mercury-sulfur theory to the so-called tria prima or three philosophic principles to explain not only metals, but all natural phenomena (41, 42). Paracelsus’ tria prima subsumed: mercury (representing the properties of changeability and fluidity), sulfur (the property of combustibility) and salt (the qualities of permanence, hardness, incombustibility). Furthermore, he wrote that since the toxins causing all disease were controlled by these three principles, then understanding them could lead to novel cures. However, Paracelsus’ theory came with an added religious twist - that his three philosophical principles were under God’s control. Moreover, he drew the analogy that mercury, sulfur, and salt in metals, corresponded to spirit, soul, and body in man. Obviously, this new theory of metals may have hindered scientific progress. Paracelsus also wrote detailed narratives about the philosopher’s stone (43). The next scientific revolution that incorporated mercury, and led by Robert Boyle (44), was made possible by the work of Evangelista Torricelli who constructed the first mercury barometer in 1643 (45). Robert Boyle (1627-1691) was born in Ireland and there he began his experimental studies in 1649. In 1654 he moved to Oxford, England where his major scientific works were published. Notwithstanding his amazing inventions and outstanding work in physics, Boyle was primarily an alchemist who revolutionized the field by initiating a Kuhnian paradigm shift, from alchemy to modern chemistry. Boyle guided (46) the transition in six ways: (a) by moving alchemy away from its metaphysical influences, (b) reopening the question of Jabir’s and Paracelsus’ theories of matter centering on mercury, and furthermore, (c) by invoking corpuscular (particle) theory to explain chemistry, (d) believing that the universe can be explained using mathematics, (e) by founding the lab-based technique known as chemical analysis, and (f) by urging the use of sound experimental techniques. What’s more, Boyle was a pure scientist, investigating compounds for the sake of academic knowledge, and not for example, just in the quest for the Philosophers’ Stone. But how did mercury play such an important role in Boyle’s alchemical work? Firstly, Boyle used a mercury manometer in his studies on the relationship between the pressure and volume of air (47). Secondly, Boyle penned a few papers where he claimed to have transmuted gold into mercury, invoking the term chrysopeia (chrysos meaning gold and poiein meaning to make) to describe his work on transmutation (48), as he still clung to that false and increasingly indefensible notion (49). In this regard, Boyle claimed that he converted lead into gold whose transformative agent was a red elixir whose recipe he never divulged (50). Although several authors have indicated that Boyle investigated mercury compounds for their medicinal benefits and tested his potions on himself, there is scant proof of this in the literature. However, Boyle did write about a mercury medicine for use against worms in children: “Infuse one Dram of clean Quicksilver all Night in about two Ounces of the Water of Goats Rue, destil’d’ the common way in a cold Stoll: And afterwards strain and filter it, to sever it from all Dregs that may happen in the making of it. This quantity is given for one Dose.” (51). 147



In 1661, Boyle described the distinction between alchemy and chymistry in his landmark treatise titled The Skeptical Chymist (52), today generally recognized as the first modern chemistry textbook. Boyle also contributed to technical vocabulary by referring to chemists as chymists rather than alchymists. However, some authors (53) debate the contention that Boyle created a modern definition of a chemical element. Recognizing the difference between compounds and mixtures, Boyle advanced one of his most important contributions, that of rejecting existing theories of matter, including both Jabir’s mercury-sulfur theory, and Paracelsus’ mercury-sulfur-salt theory. However, Boyle did not advance a new or alternate theory. Instead, he sidestepped the question leaving it open to study. By doing so he encouraged alchemists to continue experimentation and to later refute the theory (54). Overall, Boyle laid the groundwork for a modern chemical discipline. The next important scientific connection to mercury led to development of the field of thermodynamics when Daniel Gabriel Fahrenheit invented the mercury thermometer (55) in 1714. Mercury even played an important role in the discovery of oxygen (56) by Joseph Priestley (1733 – 1804), a religious iconoclast who founded Unitarianism. In his famous 1774 experiment, Priestley generated nascent oxygen (57) by decomposing red calx (mercuric oxide) under heat produced from sunlight focused with a 12 inch “burning lens”:

Having proven that sulfur was not produced when mercuric oxide decomposed, Priestley’s work challenged these widely accepted scientific theories: (a) Jabir’s mercury-sulfur theory of metals, (b) the Paracelsian tria prima, and (b) phlogiston theory (58), the idea that a substance called phlogiston, a component of all combustible materials, was released during combustion. What’s more, Priestley’s reaction became a research model for the investigation of other metal oxides like PbO. Carl Wilhelm Scheele (59) who lived from 1742 to 1786 is also recognized as having a played role in the discovery of oxygen in 1771, a few years before Priestly; however, he did not publish his results until 1777 (60). Scheele had also generated oxygen from mercuric oxide, and from other metal oxides as well (61). Priestley later collaborated with Antoine Lavoisier (1743 – 1794) and helped motivate the studies that led to the chemical revolution, and the recognition of Lavoisier as the father of modern chemistry (62). However, from the time of Lavoisier, mercury no longer played a central role in the development of the science. Priestley’s brilliant experimental work on mercury(II) oxide was perhaps the last step preceding the protracted collapse of the unstable, untenable edifice of alchemy. Although some scholars (63) do not agree that alchemy’s convoluted progression led to the discipline of chemistry, there can be no doubt that alchemy was impeding scientific progress, and had to be abandoned. 148



Arsenic It is said that the element name arsenic derives from Persian (zarnikh) and Greek (arsenikos) roots, meaning potent (64). Realgar and orpiment (65) are the chief arsenic containing minerals, and both are sulfides. Orpiment (As2S3) is bright yellow in color and is found in volcanic fumaroles, hot springs, and hydrothermal veins. Significant deposits of orpiment have been found in Turkey, northern Albania, and near thermal pools in sulfuric acid caves of Aghia Paraskevi on the Kassandra peninsula of northern Greece (66). Realgar (α-As4S4), derives from the Arabic rahl al ghar meaning powder of the mine; it forms brilliant red crystals and is sometimes called "ruby sulphur" or "ruby of arsenic". Realgar melts between 307 and 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur. Since ancient times, Greek and Egyptian civilizations, for example, have mined arsenic from its sulfide ores: arsenopyrite (FeAsS), orpiment (As2S3), and realgar. Thus arsenic is widely distributed around the globe. Although in the 5th century AD, Olympiodorus of Thebes is said to have roasted arsenic sulfide to obtain “white arsenic” (As2O3), Jabir is generally given credit for its discovery (67). Jabir was also aware of elemental arsenic which he deposited on copper as a silvery mirror. Today, most commercial arsenic is obtained by heating arsenopyrite (68). The German scholar and alchemist Albertus Magnus (1193-1280) is given credit for the discovery of elemental arsenic in 1250 (69). He discovered arsenic by conducting a chemical reaction between orpiment and soap under heat (70). He further investigated and discovered some of arsenic’s metallic properties. Later in 1649, the German pharmacist Johann Schroeder (71) prepared arsenic by two different methods: (a) heating orpiment with lime, and (b) reducing arsenious oxide with charcoal, and he published his discoveries in the work known as in De Mineralibus (72). Throughout history, arsenic has been employed as both medicine and poison. Although the Greeks used arsenic to treat ulcers (73), Frith (74) wrote that Nero poisoned his step-brother Tiberius Britannicus to become Roman Emperor. In 1365, the Italian City of Sienna passed a law restricting the sale of red arsenic at pharmacies (75). As a health remedy, in the time of Paracelsus, barbers (surgeons) used arsenic to cure wounds, ulcers and other ailments that did not respond to normal treatment (76). In his medicinal formulations, Paracelsus mixed arsenic with saltpeter to concoct potassium arsenate (77), but he also prepared chloride salts of arsenic (78). Such concoctions were used to treat skin diseases and syphilis. Paracelsus also studied arsenic and wrote about how arsenic can transmute red copper into white copper (79). By 1670, potassium arsenate was sold as a general medicine, and alchemists discovered how to make solutions of arsenic by boiling arsenious acid in alkali (80). By 1686, orpiment was mentioned as a medicine used to treat the plague (81). As an internal medicine, later in 1786, a 1% solution of potassium arsenite (KAsO2) became an often prescribed tonic known as Fowler’s solution (82), used until its toxicity was discovered. Scheele generated arsine gas (AsH3) through the heated reaction of As2O3 in a solution containing zinc metal and nitric acid (83). The garlic odor of evolved arsine became a quick test for arsenic. In 1836, James Marsh took Scheele’s work 149 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

and developed a forensic test for arsenic by inventing an apparatus that allowed for the digestion of biological samples, such as stomach contents, in the presence of zinc metal and nitric acid to generate arsine, which was collected and passed through a heated tube, where it decomposed into elemental arsenic that formed a characteristic gray mirror (84).


Selenium Selenium was discovered by Jöns Jacob Berzelius (1779-1848) in 1817 (85), and in the year 2017, the world celebrated its bicentennial (86). One interesting note anecdote (87) regarding selenium’s discovery illustrates the role of serendipity and empiricism in pure and applied science. Sweden has a strong tradition of mining, and Jacob Berzelius’ laboratory in Stockholm became both an R&D and quality control center. Around 1817, Jacob Berzelius formed a business partnership with Johan Gottlieb Gahn to produce sulfuric acid through the lead chamber process in the city of Gripsholm located due west of Stockholm. For this process, cheap iron pyrite (FeS2) was the source of sulfur (pyrite is still used today to generate about one third of sulfuric acid production). One source of pyrite during the time of Berzelius was the Fahlun Mine, located about 160 miles northwest of Stockholm. However, a quality problem unique to pyrite from the Fahlun mine hindered sulfuric acid production. The problem involved formation of a reddish sludge. Since Berzelius insisted on basing his conclusions on sound laboratory science, he analyzed the red sludge through a number of tedious experiments, and found that when combusted, it emitted the distinct horseradish odor of tellurium. However, since tellurium had never been found in Fahlun Mine ores, he continued a further series of painstaking experiments and in early 1818, having reproduced his experimental results in his Stockholm laboratory, concluded that the sludge must contain a new element, which was characterized by its unique physical- (brilliant grayish luster, sublimation properties, azure-blue flame, horseradish odor) and chemical- properties (its unique chemical reactions with metals, oxygen, hydrogen, sulfur, phosphorus, and various salts). Since his results showed that the new element was like tellurium, Berzelius adopted the Swedish name selenium (Greek: selene, moon) for the new element. Hence the element selenium was accidently discovered through analysis of the red sludge that deterred sulfuric acid production.

Toxicity and Safety Although alchemists investigated, employed mercury as a medicine, and endowed it with metaphysical powers, they undoubtedly self-poisoned, not knowing that mercury would be one day viewed as one of the world’s most toxic agents. Today, mercury is ranked #1 on the list of 275 substances in the Substance Priority List as published by the Agency for Toxic Substances and Disease Registry (88) because it poses very significant threats to human health based on known human exposure and toxicity data. What’s more, arsenic and selenium are ranked #3 and #145th (89) respectively on that same list. Mercury and arsenic have 150 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


been major players in promoting the odious public perception of the chemistry profession, a public image problem that carried forward from medieval times when alchemists cloaked their work in secret symbols (90), concealed gold in aqua regia, and were sometimes exposed as cheaters or charlatans (91). Arsenic has also secured the dubious distinction of being the poisoner’s choice since antiquity (92). Furthermore, the notorious reputation of mercury even played a role in the now retracted papers linking autism to the measles, mumps, and rubella vaccine that contained an organic mercury compound as preservative (93). After that well publicized episode, mercury preservatives were quickly eliminated from all U.S. vaccines. In one sense, nature’s periodic table has rigged the reputation playing field against chemists, since most elements have a long list of associated health and safety hazards on their safety data sheets, and because the public is not well versed in chemical knowledge. Today, although there are scant medical applications of mercury, arsenic, and selenium, the FDA (94) lists about 130 products that contain mercury, usually as phenylmercuric acetate, phenylmercuric nitrate, mercuric acetate, mercuric nitrate, merbromin, or mercuric oxide yellow. In some countries, mercurochrome (an organic mercury compound) is still sold as an antiseptic to treat minor cuts and scrapes. Arsenic trioxide is used to treat a rare disease, acute promyelocytic leukemia (95). Selenium is mainly used as a dietary supplement because of its antioxidant properties. Both HIV and Crohn’s disease (96) are associated with low selenium levels. Selenium, as selenium sulfide, is also used in medicated shampoos (97). The World Health Organization cites (98–100) many severe, chronic problems associated with mercury, arsenic, and selenium and their respective compounds. For example, mercury, especially methyl- and ethyl- mercury (101), are well known as potent neurotoxins that harm the central nervous systems of both humans and wildlife. Inorganic mercury and its compounds are known to damage renal systems (102). Moreover, mercury also injures the digestive and immune systems, lungs, skin, and eyes (103). On the other hand, arsenic causes cancers of the skin, bladder, and lungs, and in addition, induces developmental effects, neurotoxicity, diabetes, pulmonary disease and cardiovascular disease (104). It has been found that long term exposure to selenium causes discoloration of the skin, pathological deformation and loss of nails, loss of hair, excessive tooth decay, and other possible cancers (105). The Morbidity and Mortality Weekly Report (106) as published by the Center for Disease Control, stated that mercury spillage was the most frequent school accident between 2002 and 2007, and therefore it is essential that all science educators be familiar with its hazards, although it has been essentially banned in the U.S. K-12 educational system. Because mercury is a trace element in coal, today it is released to the environment when coal is combusted. Hence one major source (107) of mercury in the air and drinking water is residue from coal-fired power plants. In addition, environmental mercury also derives from erosion of natural geologic deposits, discharge from refineries and factories, and runoff from landfills making mercury a priority pollutant on a global scale (108). 151



However, mercury has long been imparted to the environment through many types of product manufacturing and human usage. For example, since antiquity, it has been used in cosmetic formulations like mascara. In modern cosmetic products, phenylmercuric acetate was used as a mascara preservative until recently. Other anthropogenic sources of mercury have included thermometers, barometers, blood pressure devices, switches, and chemical catalysts, all of which when disposed of improperly add mercury to the environment (109). In a disconcerting recent phenomenon, mercury has been used to make an amalgam to extract gold in artisanal (small scale) gold mining (110, 111), and the resulting pollution has resulted in tragic ecological impacts, especially in South America. Throughout history, mercury has also been used in various products that played a major role in causing disease. For example, in the 18th century, mercury(II) nitrate poisoning caused mad hatter’s disease (112) and resultant brain damage to numerous workers. However, the most dreadful episode imaginable, of mass mercury poisoning occurred in 1956 when over 10,000 inhabitants near Minamata Japan ate seafood from Minamata Bay (113) that was contaminated with biomagnified methylmercury from a chemical production facility. Almost 1,800 of the officially recognized affected victims suffered an agonizing death. The biomagnification of mercury and selenium is a game changer for pollutants because it causes damaging secondary and third-order effects throughout the food chain. In aquatic ecosystems, for example, bacteria and zooplankton convert mercury (II) to methylmercury that concentrates in fat tissue, most affecting top predators like swordfish which have the highest concentrations (114). More recently, the alarm has been raised that methyl mercury is hyper-accumulating in rice (115). Selenium like mercury, can be biomagnified by a factor of 200,000 (116). Being the 20th most abundant element in the earth’s crust, arsenic leaches into groundwater (117) from its widely distributed natural mineral deposits. On the other hand, anthropogenic sources of arsenic contamination include: wood preservatives, coal-fired power plants, and the manufacture of semiconductors (118). In the U.S., although most public water systems have measured arsenic levels in the 2 to 10 ppb range, Western states, and parts of the Midwest and New England have higher concentrations (119). For example, it has been reported that in Fallon, Nevada arsenic has been found at 80 ppb (120). A tragic example of arsenic groundwater contamination (121, 122) took place in the Ganges Delta of Bangladesh where tube-wells, drilled in the 1960s to provide a source of potable water, were found in the 1990s to be contaminated with arsenic. This case represents the largest mass poisoning in history affecting over 50 million people who were chronically exposed to arsenic at levels over 10 ppb. Moreover, it was discovered that about 1.4 of 4.7 million tube-wells contained arsenic at levels greater than 50 ppb affecting more than 20 million people (123). Deeper tube-wells (more than 150 m in depth) have been found to be safer while shallow wells between 20 and 100 m contain the most toxic water (124).

152 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

Table 1. MCL and MCLG Data for Hg, As, and Se Mercury μg/L

Arsenic μg/L

Selenium μg/L

1942: U.S. Public Health Service (129) Limit

NA

50

50

1946: Public Health Service (130) Limit

NA

50

50


1962: Public Health Service (131) MCL

NA

10

10

1974: Safe Water Drinking Act (SWDA) MCL

0.002

10

50

SWDA: July 30, 1992 (132) MCL

0.002

50

50

MCLG

0.002

0

50

SWDA: January 23, 2006 (133) MCL

0.002

10

50

MCLG

0.002

0

50

The EPA and Safe Water Drinking Act: History Cases like some of the foregoing instances of mass poisonings caused by natural and anthropogenic sources, led to a Paracelsian paradigm shift regarding public approaches to protecting human health as implemented by WHO (125), and in the U.S., by the establishment of the EPA on December 2, 1970 (126). Moreover, in the U.S., the Safe Water Drinking Act (SWDA) of 1974 was enacted to protect the quality of drinking water from toxins such as mercury, arsenic, and selenium (127). To carry out this mission, the EPA devised and set: (a) a maximum containment level (MCL) and (b) a maximum containment level goal (MCLG) for toxic elements and compounds (128). The MCL is an enforceable standard regulating the maximum level of a contaminant allowed in drinking water, while the MCLG is established to provide a level below which no health risk is expected, but it is not enforceable. The SWDA directs the EPA to set the MCL as close to the MCLG as is technically feasible, requiring public water systems to detect and remove contaminants using suitable treatment technologies that are feasible and affordable. When health benefits are great, methods are cost-effective, and when technology is readily available, MCLs are set close to MCLGs. Currently there are fewer than 100 chemicals for which an MCL has been established. Legal limits, 153


as well as MCL and MCLG values for arsenic, mercury, and selenium are listed below in Table 1 in chronological order according to how they were changed by the Public Health Service (129–131) and the Safe Water Drinking Act (132, 133).

History of EPA Mercury Cold Vapor and Hydride Methods


Mercury Boyle’s visionary acumen in establishing the field of chemical analysis is today recognized through the Robert Boyle Prize for Analytical Science (134) as awarded annually by The Royal Society of Chemistry. The value of analytical environmental chemistry is also exemplified in the work done by often neglected analysts whose work in normal science enables the implementation of safety regulations protecting populations from the many health hazards associated with arsenic, mercury, and selenium. EPA approved methods for the determination of arsenic, selenium and mercury can be placed into five groups: graphite furnace atomic absorption (GFAA), inductively coupled atomic plasma (ICP), cold vapor atomic absorption spectrometry (CVAAS), AA-hydride and spectrophotometric. Although graphite furnace (135) has been used to analyze for arsenic and selenium at low detection limits, it has never been a viable choice for mercury, due to its high vapor pressure at room temperature. On the other hand, while inductively coupled atomic plasma (136) analyzes for all three elements, required detection limits for drinking waters cannot be met using it. Spectrophotometric methods have not been used for mercury due to its volatility. Of these five methods, only the classes of cold vapor and hydride methodology can analyze for all three elements at detection limits mandated for drinking waters. In the following sections, the term cold vapor applies to mercury analyses whereas gaseous hydride refers to analyses for arsenic and selenium. The history of cold vapor analytical methods as used by the EPA to analyze mercury in drinking waters will be covered first. In 1963 Poluektov et al. (137) suggested a new analytical method, dubbed cold vapor, as a tool for mercury analysis, but it was Hach and Ott (138) in 1968, who first reported its successful use, analyzing geological samples, both rocks and soils, for mercury to a level of 1 ppb. A schematic of instrumentation typically used is shown in Figure 1. Sample preparation takes place in a BOD bottle where a mixture of various acids and potassium permanganate break down the sample matrix, converting bound mercury to Hg2+. To determine the concentration of mercury using cold vapor atomic absorption (CVAA), mercury ion in the sample is first reduced to its elemental form with stannous chloride:



Figure 1. Mercury cold vapor instrument schematic.

A stream of inert gas is then pumped into the sample bottle to carry mercury vapor into and through a 10 cm quartz absorption cell that is placed in the optical path of an AA instrument containing a mercury hollow cathode lamp that emits radiation at 253.7 nm. A uv detector measures the intensity output which is a linear function of the mercury concentration in the sample. The original technique had a detection limit of about 0.2 micrograms/liter, which hasn’t changed over the years. While Hatch and Ott provided the initial breakthrough instrumental method in 1972, Kopp, Longbottom and Lobring (139) published a historic paper, titled “Cold Vapor” Method for Determining Mercury in the Journal of the American Water Works Association that greatly influenced the development of published EPA methods relating to mercury cold vapor. Their method determined total mercury in drinking, surface, ground, sea, brackish waters, and industrial and domestic wastewaters and soils. The paper’s major strength was its systematic approach that solved several critical problems relating to mercury analysis, and laid a framework for EPA’s future step by step analytical methods. For example, it demonstrated that potassium permanganate was ineffective in releasing mercury from organic compounds such as phenyl mercuric benzoate, and showed that potassium persulfate (K2S2O8) was necessary in the digestion of organic samples, on the one hand to release bound mercury, and on the other hand to remove organics whose broad uv absorption bands overlap the 253.7 nm mercury line. It also provided in depth data demonstrating that copper, tellurium, and other heavy metals did not interfere with the analysis, except at very high concentrations, possibly over 10 mg/L. Moreover, it showed that hydrogen sulfide, present in sewage samples, was eliminated by potassium permanganate. The paper also pinned down air flow rates, how to eliminate water vapor interferences, calibration, and provided statistical data to validate the method through reproducibility and spiked sample recovery. One of the authors of the just mentioned 1972 landmark paper, Larry B. Lobring, worked in the Inorganic Chemistry Branch of the Chemistry Research Division Environmental Monitoring System Laboratory located in Cincinnati, Ohio. He coauthored numerous EPA methods and manuals on the determination of metals, including mercury in environmental samples. One of his most 155



substantial contributions in the realm of mercury analysis, was based on his previous work, and resulted in the enduring Method 245.1, Determination of Mercury in Water by Cold Vapor Atomic Absorption Spectrometry (140). This method was specific for drinking waters, and could be applied to analyze for mercury in a wide variety of forms, such as phenyl mercuric acetate (cosmetics), and methyl mercury (fat tissue in sea food). Sample preparation involved converting bound mercury to divalent mercury ion through a two hour digestion in a glass BOD (biological oxygen demand) bottle with a persulfate- permanganate mixture under heating. Subsequent research focused on lowering the detection limit, on removing, circumventing or avoiding matrix interferences, increasing speed through automation, implementing digestion cell modifications to remove interferences and, instrumental modifications. Following development of method 245.1, an automated method, 245.2. was issued in 1974 (141). In 1984, Varian Instruments, later acquired by Agilent, marketed its VGA-76 assembly (142) that allowed for an automated and rapid determination of many samples using EPA approved methods. Method 245.1 went through several revisions. However, all calibration procedures and detection limits (0.2 ppb) remained essentially the same. One of the most striking differences between revisions was that revision 3 offered three options for apparatus design whereas only one is offered through revision 2.3. Revision 2.3 and 3 also introduced large sections devoted to quality control (QC) whereas the original paper did not address the issue. Revision 3 also contained an extensive section on sample collection, preservation and storage whereas minimal information is provided in revision 2.3, and nothing in the original version. As far as the wet digestion procedure goes, the original paper gave a two-step procedure that is expanded to eight steps in revision 2.3, and expanded to more steps in revision 3. As far as water quality, the original papers through revision 2.3 did not contain any information about water purity, but revision 3 required ASTM Type II water. Also, in revision 3, it is stated that the analyst must be vigilant regarding environmental contamination and background interferences arising from unusual sample matrices. This procedure also warned that when doing low level work, the analyst must physically separate both Kjeldahl nitrogen and chemical oxygen demand (COD) determinations from mercury determinations because they contained the reagent mercury(II) sulfate. These interferences were described: sulfide, copper, chlorides, tellurium, chlorine and other volatiles whereas the original interferences specified only: sulfide, copper, chlorides, and volatile organics. In addition, the first published method did not contain a safety section but revision 2.3 contained an expanded safety section, including: (a) notes on mercury toxicity, (b) indications that a fume hood should be used, (c) directions that workers be immunized when human waste is analyzed, and (d) to watch for the evolution of sulfide and cyanide. In 1998, EPA released Method 1631 (143) titled: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence to meet the lower mercury water quality criteria (WQC) published through section 304(h) of the Clean Water Act, the clean water programs of 1999 in the National Toxics Rule (144), and in the Final Water Quality Guidance for the Great Lakes System. Bloom (145) and Fitzgerald (146) played major roles in developing the method. 156



Method 1631 established formal procedures to quantitate low level mercury in water at detection levels of 1 parts per-trillion (ppt), although the fluorescence method allows determination of mercury to 0.5 ppt. The only interferents listed are gold and iodide. It utilizes a class-100 clean room. In 1999, after public comments were made, revision B was released, addressing correction of test sample results for reagent blanks. In 2001, revision C added requirements for the reporting and use of field blank results. It also clarified that field blank results must be reported separately, and that a field blank correction must be performed if requested or required by a regulatory authority or in a permit. In 2002, revision E corrected many minor clarifications, technical errors and inconsistencies. Regarding sample preparation, according to Method 1631, samples are digested using bromine monochloride (BrCl) to oxidize bound mercury to Hg2+(aq) which then undergoes sequential reduction with ammonium hydroxide and stannous chloride to convert Hg(II) to volatile Hg(0). Finally Hg(0) is purged from water and preconcentrated onto a gold-coated sand trap, followed by thermal desorption from the trap, and detection by cold-vapor atomic fluorescence spectrometry. Although the major advantage of CVAFS techniques is a low detection limit, there are several disadvantages including: (a) the periodic replacement of gold traps, and (b) that some sample matrices pose challenges, especially those with high volatile organic concentrations. Comparing CVAFS methods, Method 1631 is at least 500 times more sensitive than Method 245.1. Furthermore, Method 1631 is also faster than Method 245.1 because it avoids a lengthy permanganate digestion. Although the last revision of Method 245.1 was completed in 1994, the method is still in use today. Nevertheless, Method 245.1 has generally been supplanted by EPA Method 1631, cold-vapor atomic fluorescence spectrometry. In 2005, EPA also approved a second CVAFS procedure, Method 245.7, that is very similar to 1631, and quantifies mercury in filtered and unfiltered water, and is applicable to drinking water, surface and ground waters, marine water, and industrial and municipal wastewater. Although both methods require use of a CVAFS detector to measure low levels of mercury, Method 1631 uses oxidation, a purge and gold trap isolation, and desorption followed by CVAFS, while Method 245.7 uses liquid-gas separation and a dryer tube for isolating mercury analyte. Method 245.7 suffers from gold, silver and iodide interferences. Since both methods 1631 and 245.7 meet a detection limit of about 1 ppt, they are normally carried out in a “clean room” environment to prevent contamination of samples, and moreover, sampling procedures required must also implement special cleanliness procedures. One advantage of Method 245.7 is that it is faster and simpler than Method 1631 because it avoids a heating step, so that digestion blocks are not required. In August 1998, EPA released Method 1630 (147) for the determination of methyl mercury (CH3Hg) in water by distillation, aqueous ethylation, purge and trap by CVAFS; its range was 0.02 to 5 ng/L. Table 2 lists EPA approved mercury cold vapor methods for water in chronological order, along with their most important advancements. In Table 2 below are summarized the major published revisions in methods 245.1 (148–151), 245.7 (152–154), and 1631 (155–161) in chronological order. 157


Table 2. Timeline of EPA Mercury Cold Vapor Methods 245.1: Mercury in water by CVAAS. (Detection Limit = 0.2 μg/L). Revision

Critical Changes


1.0 in 1972 (148) 2.0 in 1979 (149)

1. Quality control addressed. 2. Includes interlaboratory precision data.

2.3 in 1991 (150)

Emphasizes and improves quality control

3.0 in 1995 (151)

1. Incudes three options for the apparatus. 2. Interferences from COD and Kjeldhal nitrogen analyses. 3. Quality control greatly expanded.

245.7: Mercury in water by CVAFS. (MDL = 1.8 ng/L). Revision

Critical Changes

1.1 in 1996 (152) Draft in 2001 (153)

The draft is based on collaborative work between EPA’s Environmental Monitoring Systems Laboratory, EPA-Region 4, and Technology Applications, Inc. and on peer-reviewed publications.

2.0 in 2005 (154)

1. Addresses matrix spikes and precison. 2. This method is performance based.

1631: Mercury in water by CVAFS. (MDL = 0.2 ng/L). Revision

Critical Changes

Proposal/Draft in 1991/1995 (155, 156)

Result of the Clean Water Act requiring lower Hg detection levels.

Validation in 1996 (157)

Provided guidance for quality control, interferences, technical difficulties, and general use of the method.

CFR in 1998 (158)

Published as law in the federal register.

B in 1999 (156)

Released after public comments.

C in 2001 (160)

New requirements were made regarding field blank results.

E in 2002 (161)

Clarifications and corrections were made for technical errors and inconsistencies.

Today’s analytical challenge is to determine the concentrations and distribution of various mercury species in the hydrosphere. The future of mercury cold vapor method may rely on new instrumental methods in which cold vapor is combined with ICP-MS (162), GC-AFS (163), and IC-ICP-MS (164) that allow determinations of individual mercury species to (10-15) ppq levels. 158 Benvenuto and Williamson; Elements Old and New: Discoveries, Developments, Challenges, and Environmental Implications ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

Arsenic and Selenium


Analytical methods centering on hydride generation for the determination of arsenic and selenium are described in this section. The Gutzeit method for arsenic analysis was first published as a qualitative test in 1879 (165), that improved on Marsh’s arsenic mirror. In 1907, Sanger and Black (166) modified it into a reliable quantitative measure of arsenic via a hydride method. In their determination, arsenic in the sample is first reduced to As(III) as arsenious acid (H3AsO4) using for example, a reducing agent such as potassium iodide. Hydrogen gas, generated through the reaction of granulated zinc with hydrochloric acid in a second apparatus, is then passed into the arsenious acid solution producing arsine gas:

Arsine then reacts with paper impregnated with mercuric chloride to produce a yellow stain (AsHg3Cl3) whose color intensity is indicative of the quantity of arsenic in the sample. In 1942, Jacobs and Nagler (167) published a paper that reviewed seven existing methods for determining arsenic at low levels, with the object of finding a better quantitative method. The authors then recommended a new method that combined the Gutzeit and molybdenum blue methods. In this modified method, arsine gas is generated using the Gutzeit procedure, and is trapped in a sodium hypobromite solution. The sample is then transferred to a Nessler tube, and ammonium molybdate is added. After 30 minutes, the developed blue color is compared to a standard for a visual determination of arsenic that is quantitative with a detection limit of 0.038 μg/L. Its range was reported as 1.5 to 50 μg. However, both phosphorus and silicon were found to interfere with the determination because they also form blue molybdenum complexes. Following the successful development of the Jacobs-Nagler colorimetric method, in 1942, the U.S. the Public Health Service mandated that it be required for analyzing arsenic. The Public Health Service also established an As and Se drinking water standard at 50 μg/L. In 1952, Vasak and Sedivek (168) reported the silver diethyldithiocarbamate (SDDC) method for quantitatively determining arsenic in water samples. The SDDC colorimetric method for arsenic involved reducing inorganic arsenic to arsine gas using a reducing agent and hydrogen generated from the zinc/acid reaction. The AsH3 hydride generated was then scrubbed though glass wool infused with lead acetate, and then absorbed in SDDC-pyridine solution. Arsine then formed a red complex with SDDC, whose absorbance was easily measured at 535 nm using spectrophotometry. In 1962, three papers were published that established SDDC as a new quantitative method for trace arsenic analysis. Stratton et al. (169) discussed the strengths and weaknesses of the SDDC method established by Vasak and Sedivek. Ballinger et al. (170) reported that the SDDC method for arsenic was superior to alternate methods such as the (a) heteropoly blue method, and (b) the Gutzeit-heteropoly blue methods. Advantages included improved time of analysis, ease of analysis, precision, and accuracy. Also in 1962, Clarke et al. 159



(171) reported that the detection limit for arsenic by the SDDC method was 0.03 mg/L. In 1962, the Public Health Service lowered the arsenic drinking water standard to 0.010 mg/L for which the SDDC colorimetric methods became the approved method. In 1971, based on the previously described work, the EPA issued Method 206.4 (172) to determine arsenic (total, dissolved, suspended) by SDDC to a limit of 10 μg/L. In 1978, Sandhu (173) published a modification of the As-SDDC Method addressing these metal ion interferences: antimony, cobalt, copper, chromium, mercury, and molybdenum. He also studied arsenic recovery in the presence of the afore-mentioned interferents. In 1974, Method 206.3, the atomic absorption gaseous hydride method (174) for determining inorganic arsenic at a detection limit of 2 μg/L was published by the EPA, and was designed to be applicable to drinking waters. Interferences arise when sample matrices contain high concentrations of chromium, cobalt, copper, mercury, molybdenum, nickel or silver. For sample preparation, arsenic is first reduced to As3+ using SnCl2, and then converted to arsine, AsH3, using zinc metal and HCl. The gaseous hydride is then swept into an argon-hydrogen flame of an atomic absorption (AA) spectrophotometer and analyzed at 193.7 nm. The working range of the method is 2 -20 μg /L. In February, 2002, Method 206.3 was removed from EPA’s list of analytical methods because other technologies with lower detection limits became available and were more useful (175). In April 1995 was published the first draft of Method 1632, Determination of Inorganic Arsenic in Water by Hydride Generation Flame Atomic Absorption Absorption, which was developed under the direction of William A. Telliard of the U.S. EPA. (176). This method determines dissolved and total arsenic in the 10 - 200 ng/L concentration range. The analysis involves treating an aqueous sample with 6 M HCl and 4% NaBH4 to form various hydrides such as arsine, AsH3(g). The gas is purged and collected in a liquid nitrogen gas trap packed with 15% OV-3 Chromasorb. Upon desorption, the various hydrides are swept into a flame AA instrument where absorbance is measured at 193.7 nm. The method is based on the work of Braman (177) and Andreae (178). In January, 2001, revision A (179) was published that allowed determination of dissolved, total and arsenic species through hydride generation quartz furnace AA. The following species may be analyzed: total inorganic arsenic (As), arsenite (As3+), arsenate (As5+), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). Dissolved and total arsenic can be determined in the 10 to 200 μg/L range. Having released Method 1632, the colorimetric-SDDC methods for arsenic were both removed and did not appear in the Feb. 19, 2015 EPA proposed rules. In the 1996 amendments to the SDWA, Congress directed the EPA to consider a new arsenic regulation. Later, in 2006, arsenic was set at 10 ng/L and Se raised to 50 ng/L. Although GFAA is the preferred method for determining As and Se in drinking water, since the theme of this paper focuses on methods common to Hg, As and Se, furnace methods won’t be discussed further. Analytical methods for the analysis of selenium follow the pattern set by arsenic. In 1958, Danzuka and Ueno (180) published a colorimetric method to determine trace levels of selenium(IV) using 3,3’-diaminobenzidine. This 160



colorimetric method measures selenium at 420 nm in the pH range 6-7, but does not employ a hydride. Method 270.3 (181) was issued in 1974 to determine inorganic selenium in drinking water by the gaseous AA hydride method. It covers inorganic selenium in water (drinking, fresh, saline). In the analysis, selenium is reduced from the +6 oxidation state to the +4 oxidation state using of SnCl2. Zinc is then added to the acidified sample, producing hydrogen gas which reacts with selenium to produce the hydride, SeH3, which is carried into an argon-hydrogen flame of an AA spectrophotometer and analyzed at 196.0 nm. The method determines Se to a 2 ng/L level. Interferences may occur in the presence of high concentrations of chromium, cobalt, copper, mercury, molybdenum, nickel and silver. Table 3 shows approved and retired EPA methods for arsenic and selenium analyses. A compendium of EPA analytical methods is available (182, 183).

Table 3. EPA Methods for Inorganic As and Se Water Instrumentation

Date Issued

Range ng/L

λ nm

LOD ng/L

206.2

As: AA-Furnace

1978

5-100

193.7

1

206.3 retired

As: Ar/H2 AA-GaseousHydride

1974

2-20

193.7

2

206.4 retired

As: Spectophotometric-SDDC in pyridine

1971

535

10

1632

As: 4% NaBH4 Hydride Quartz Furnace AA

1998

0.01-50

193.7

0.003

270.2

Se: AA-Furnace

1978

5-100

196

2

270.3 retired

Se: Ar/H2 AA-Gaseous Hydride

1974

2-20

196

2

Conclusion and Summary Analyzing a historical perspective on arsenic, mercury and selenium demonstrates that Jabir, Paracelsus, Boyle, and the EPA respectively launched scientific revolutions in alchemy, medicine, chemistry, and environmental safety. Hence studying the history of these elements can help educators see the big picture of how these three elements impacted society and influenced scientific thought through the ages. In the age of alchemy, mercury was viewed as a paradigm in itself, but in modern times, both mercury (and arsenic compounds) were finally recognized as rather blunt instruments for treating disease when more precise and effective tools were needed. Before the Safe Water Drinking Act of 1974, few methods existed for the analyses of mercury, arsenic, and selenium. However, after its inception, the need to reduce exposure to arsenic, mercury, and selenium in drinking waters spurred the EPA to invent new methods for their detection. Mercury detection limits were 161


first regulated in 1974 at 2 ng/L (ppb) as determined by cold vapor. In 1991, CVAFS techniques allowed a much lower the detection limit to 0.001 ng/L (1ppt) to be met. Arsenic and selenium were first regulated in 1942. In 2006, the MCL for arsenic was set to zero because no level was considered safe. In 1974, qualitative methods were replaced by spectrophptometric methods when Flame AA-hydride methods were advanced. In 1988 AA hydride quartz furnace allowed arsenic to be determined at 0.01 μg/L. However GFAA is still a superior method allowing As and Se determinations to 1 ng/L.


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170. Ballinger, D.; Lishka, R. J.; Gales, M. E. Application of Silver Diethyldithiocarbamate Method to Determination of Arsenic. J. Am. Water Works Assoc. 1962, 54, 1424–1428. 171. Clarke, N. A; Weeks, J. D. Analytical Procedures for Measuring Chemicals in the Public Health Service Drinking Water Standards. J. Am. Water Works Assoc. 1962, 62, 172–176. 172. EPA Method 206.4: Arsenic (Spectrophotometric-SDDC) Methods for the Chemical Analysis of Water and Wastes (MCAWW). Environmental Monitoring Systems Laboratory Office of Research and Development; U.S. Environmental Protection Agency: Cincinnati, OH, 1971. 173. Sandhu, S. S. Arsenic Determination by the Silver Diethyldithiocarbamate Method and the Elimination of Metal Ion Interference. EPA-600/4-78-03; Environmental Monitoring and Support Laboratory: Cincinnati, OH, 1978. 174. EPA Method 206.3: Arsenic (AA, Gaseous-Hydride). Methods for the Chemical Analysis of Water and Wastes (MCAWW). Environmental Monitoring Systems Laboratory Office of Research and Development; U.S. Environmental Protection Agency: Cincinnati, OH, 1974. 175. Federal Register. Clean Water Act Methods Update Rule for the Analysis of Effluent. https://www.federalregister.gov/documents/2015/02/19/201502841/clean-water-act-methods-update-rule-for-the-analysis-of-effluent (accessed February 4, 2017). 176. EPA Method 1632: Determination of Inorganic Arsenic in Water by Hydride Generation Furnace Atomic Absorption. Environmental Monitoring Systems Laboratory Office of Research and Development; U.S. Environmental Protection Agency: Cincinnati, OH, 1996. 177. Braman, R. S.; Foreback, C. C. Applications of arsine evolution methods to environmental analyses. Science 1973, 182, 1247–1249. 178. Andreae, M. O. Determination of Arsenic Species in Natural Waters. Anal. Chem. 1977, 49, 820. 179. EPA Method 1632: Chemical Speciation of Arsenic in Water and Tissue by Hydride Generation Quartz Furnace Atomic Absorption Spectrometry. Revision A. Environmental Monitoring Systems Laboratory Office of Research and Development; U.S. Environmental Protection Agency: Cincinnati, OH, 1998. 180. Danzuka, T.; Ueno, K. Determination of Trace Amounts of Selenium in Sulfuric Acid. Colorimetric Method Using 3,3′-Diaminobenzidine. Anal. Chem. 1958, 30, 1370–1371. 181. EPA Method 270.3: Selenium (AA, Gaseous Hydride) Analysis of Water and Wastes (MCAWW). Environmental Monitoring Systems Laboratory Office of Research and Development; U.S. Environmental Protection Agency: Cincinnati, OH, 1974. 182. Sources of EPA Test Methods. Environmental Health and Safety online. http:/ /www.ehso.com/testmethodsdl.php (accessed February 7, 2017). 183. National Service Center for Environmental Publications (NSCEP). https:// www.epa.gov/nscep (accessed February 10, 2017).


Analytical Methodologies for Arsenic, Selenium ... - ACS Publications

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