QuestionableWord Usage in Analytical Chemistry M. G. Mellon Purdue University, W. Lafayene, IN 47907 Whether one refers to usage of various terms by writers as nomenclature, terminologv, or definitions. there is need for clear understanding of what each term means. Also there should be consistency among different specific kinds of terms. Someone has stated that the great enemy of understanding is imprecise language. The general concern here is the definition or meaning of terms, used either alone or in combination with other terms. Attention is directed to two asDects of claritv. The first involves the use of imprecise, uninformative, inappropriate, or even wrone terms. The second involves lack of claritv in imprecise or &informative names for methods of chemical analysis. he overall objective is the improvement of entries in printed indexes and in chemical data bases. Such improvement should facilitate manual searching of printed sources and computer searching of data bases. A searcher not knowing the right word finds nothing in either case. Oral and written communication about methods is involved. Deflnltions A definition is an explanation of the signification of a word or term. C. W. Mason ( I ) has written, "A definition must both include and exclude." The anest for certaintv of expression is an endless task, however, as noted by Stuart Chase (2) in his hook, The Tyranny of Words. Elimination of redundant and conflicting definitions of terms is a prohlem in organizations, such as the American Association for Testing a i d Materials (3). Use of imprecise, inappropriate, or wrong terms in textbooks is particularly unfortunate because authors are therehy conditioning students to use such expressions. Two goals of effective technical writing are clarity and accuracy. Along with these two should he consistency. With these requirements in mind, attention is directed to questionable usage of a number of common terms. The comments assume that, for consistency, process (chemical) terms should end in -tion and that operation (physical or instrumental) terms should end in -meter. metrv. or -metric. Acid. When the analyst uses this kord, &'it clear whether the term means an A-acid (Arrhenius). a B-acid (Brdnsted). ., . , or an L-acid (Lewis)? A-acids are ass&ed here. Acidimetry. This term illustrates a lone-time confusion in naming subdivisions of titrimetry. ~ h u s , m a n yhave used it to designate titration of bases with an acid. Others have used it to designate the titration of acids with a base. The practice of the with adherents is followed here for all titrants. This agrees with the IUPAC definition of acidimetry (4) and the author's usage in his textbook (5b). Alkalimetry. This term means the titration of acids with a base. Amperometric.This term is an exampleof naming a kind of method of measurement in terms of the unit of measurement, rather than the ~ r o o e r t vmeasured. The same comment applies to cou~omktricand voltammetric. Examples of nonexistent coordinate terms would be eramimetric and literometric. Analysis us. Determination. Failure to distinguish hetween these two words persists. Quoting from the Spectroscopic Nomenclature of Applied Spectroscopy, "Analysis is the ascertainment of the identity and/or the concentration
of the constituent(s) of a sample, and determination is the ascertainment of the quantity or concentration of a specific substance. Only samples can be analyzed and constituents determined." This distinction represents the usage of the American Society for Testing and Materials (6). For example, its ASTM Designation E 39-85, "Chemical Analysis of Nickel", includes procedures for determining C , Co, Cu, Fe, Mn, Si, and S i n the metal. Advertised "analyzers" in general do not analyze the element designated. One for oxygen, for example, does not determine the minor constituents in oxygen, but, rather, oxygen in some other substance. A recent advertisement is for pH analyzers. How can one chemically analyze pH values? Anyway, why not use meter? One equipment firm designates such equipment as determinators. The process term, analyzation, is used infrequently. G . E. F. Lundell (7) thought that the word, "determination", should aoolv onlv to measurement. and the word. "analysis", to thechemifal processes used prior to measure: ment. Based on his long exoerience and broad knowledee of applied inorganic anal&,-lundell always argued, in meetings of the Advisory Board of Analytical Chemistry. that determining the density of spectral lines or the specif;cgravity of antifreeze solutions, for examole, is not chemical analysis. Following the usage advocated herein, the ending, -tion in determination, should indicate a process term. However, general usage has a broader connotation. Thus, a method for thc. determination of nickel in steel romprises whatever chemiitr\,nnd or physics may be employed in the procedure. .Anal)ticul (.'lzrmrctry. I h e s thiserpressi~~n meanqualitatire and or quantitative chemical analysis'? In contrait tc, Robert Boylc's concise definition of rhcmiral analysis as the determination of thr composition of substances, ones for annlvtiral chemistrvare varied and less than definite. A new proposal follows: he branch of applied chemistry comprising the inorganic and/or organic chemical orocesses and/or the phy~icaio~erations used in making chemical analyses. Aquametry. Does a book bearing this title deal with measurement of or with water? The ending, -metry, implies only determination. Chromatography. As stated by Walton and Reyes (S), this is a separation term, which, as a process, should end in -tion. What is the process? One suggestion is redistribution (9). Also, the prefix, chroma-, implies color, but there is color in the separated entities in only a small percentage of the systems. Classical and Conventional. Some instrumentalists compare their "instrumental" method to classical or conventional methods. Do they mean gravimetry, titrimetry, densitometry, refractometry, polarimetry, or some other -metry? Why not he specific in the comparison? Color. As defined by the Committee on Colorimetry of the Optical Society of America, color consists of the characteristics of light other than spatial and temporal inhomogeneities (10, Chapter 9). T o name a color adequately, one needs more than simple words, like flesh and rose. There are three attributes to consider: hue, saturation, and luminance. Chemists are likely to designate only hue (with an occasional limiting term, such as Navy blue or Indiana red). The three attriVolume 64
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butes can be sensed with color solids, such as those of Munsell or Ostwald. "The ISCC Method of Designating Colors" (11; also 10, Chapter 9) provides systematic modifying words for use with the usual hue name to indicate, as far as words suffice, the attributes of colorimetric purity and lightness. Based on preliminary reports of the Committee on Colorimetrv. one text (12) used these svstematic names for the colored solutions and precipitates."~oreprecise specification is obtainable with a stimulimeter or soectroohotometer. Colorimetry. T o a physicist this'term means determination of color, with no information about the nature or amount of the colorant, as with a tristimuls colorimeter. Long usage by chemists (13) has involved cornoarison measureken& that is, matching the color (intensity) of the unknown with that of a standard, such as a solution or colored glasses. The instrument is a comparimeter, such as that of Duboscq. Dry and Wet. According to the Britannica (141, "The methods of chemical analvsis mav be classified as drv. consisting d t h e examination of the &tance in the dr; state, and U ~ inI whirh a sulution of the iuhitanre is treated with other substances of known character, termed reagents, to produce change or reaction whereby a new compound of distinctive properties is produced." The term wet is open to considerable criticism. These two words dry and wet seem unnecessary and rather absurd when used to designate a method of measurement. What orooertv is measurable? There mav be wet and drv analysis, but n o such methods of chemical analysis. 0n"e chemical firm did advertise for a "wet" analvtical chemist. Electrograuimetry. What is implied here is weighing something separated by electrodeposition, such as copper. Electrolytically deposited copper, for example, need not he weighed. The deposit may be dissolved and measured titrimetrically with thiosulfate solution. Might not electrogravimetry he interpreted as the use of an electronically controlled halance? Fluorimetry. This spelling is consistent with iodimetry, but the intended meaning is;ery different. As the properiy measured is fluorescence, why not use fluorescimetry? Likewise, phosphorescimetry would replace phosphorimetry. Gasometric. This term implies nothing about the property measured in analvzine eases. It relates onlv to the nhvsical state of the material. Fcere are no coordinate terms:li&idimetric and solidimetric for liauids and solids.. resoectivelv. . Gravimetry. Gravimetry is determination by mass (5), with no implication of how the substance weighed is obtained. As mass (not gravity) is the property measured, massimetry would seem to be the consistent term (not to he confused with the German Massanalyse). A nonchemical meaning is measurement of gravity. Many writers, no doubt unintentionally, have implied that gravimetric methods of measurement are somehow connected to precipitates. Many such methods do involve weighing precipitates, but there are many others in which the substance weighed is not obtained by precipitation. Also, not all precipitates have to be weighed. For example, calcium, precipitated as the oxalate, CaC20a.Hz0,may be ignited to CaC03 or CaO for weighing; dissolved in sulfuric acid and the oxalate ions titrated with oermaneanate solution: or determined spectrophotometrically by ;dissolving the precipitate in sulfuric acid, addine excess standard oermanean&e solution, and determiningihe decrease in abkrbanceof the unreacted permanganate. Did the ancient Biblical writer (Lev. 19:35) anticipate gravimetry in his commandment, "Just balances and just weights shall ye have"? Was there no need in those times to include "just" weighers? lodimetry. This subdivision of oxidimetry covers the use of iodine dissolved in a solution of potassium iodide. One titrates with the triiodide ions in the solution. 736
Journal of Chemical Education
The word "iodometry" was coined for situations in which the triiodide ions are liberated from a solution of potassium iodide by reaction with something, such as copper. The triiodide is then titrated with thiosulfate solution. This orocess exemplifies an of titration, with thiosulfate being the litrant. The Hallett renort . (151 . . recommended the term "thiosulfatimetry". If one were a consistent of adherent, other titrimetric, -ometry terms would he acidometry, alkalometry, oxidometry, reductometry, precipitometry, and complexometry. None of these seem to be in use, so why retain iodometry? Instrumental. This o o ~ u l a term, r when used for a kind of method of measurement, is both misleading and unnecessary. I t implies existence of noninstrumental methods of measurement. What are they? Generally its use seems intended to distinguish between instrumental and chemical methods. Presumably the latter are gravimetric and titrimetric, but both of these are instrumental. With gravimetry one weiebs with a balance. and with titrimetrv usuallv one " measures volume, mass, or electric current. Thus, instrumental is not a differentiating term. Some writers use physical instead of instrumental (16).The same criticism applies. Instrument us. Aooaratus. There mav not be much disagreement here. I t seems reasonable to iimit instrument to measuring devices, such as meters, and apparatus to nonmeasuring devices, such as Soxhlet extractors. Light. Light is the aspect of radiant energy of which a normal human observer is aware through visual sensations arising from stimulation of the retina of the eye (10,Chapter 4). Certainly this is the sense implied in Genesis 1:3, for the Biblical writer hardly meant to include X-ray, ultraviolet, and infrared light, terms used by some analytical writers. Ultraviolet, or "black" light is most misused. I%lorogroph?. This is another term for measurement not having the operationid ending, -merry. Was the word, coulopotentiographic, coined for this method of measurement? If so, the ending could have been -metric. I t would still be a hvbrid, combinine the unit of measurement and the oroner. r). measured. \vould current-potrntiometric serve (Y,? Radrotirrn. I.ike . orecioitatinn and extraction. for examole. . this is a process term, ending in -tion (10, Chapter 5). ~ o r ' t h d electromagnetic spectrum, the entity radiated is radiant energy. Spectral Slit Width. A spectrum does not have a slit; therefore, i t cannot have a slit width. The portion of the spectrum isolated by a particular instrumental adjustment is the spectral bandwidth. Spectrochemical. For decades this term bas been used by ASTM Committee E-2 to refer to methods of analysis of metals, such as aluminum. Coordinate terms, such as grauichemical and titrichemical, are not used. Occasionally the terms electrochemical and thermochemical are found, hut generally in nonanalytical writing. The ending, -chemical, generally is not used for analytical methods, so why retain i t for one area? The ex~ression.atomic emission soectrometrv. .. is murh preferable t(;spe(:tro~hemical,with indication ofthe mean-. oiexcitation, if des:red. Rarrls one finds soerrrorhemica1 used instead of molecular absorption spectrometry. A new periodical, Journal of Analytical Atomic Soectrometry, presumably covers both emission and ahsorption methods. Spectrum. The Newtonian sense of spectrum is being polluted by some writers. Thus, one sees advertisements for a spectrum of analytical balances, reads of bringing a spectrum of excellence to analytical programs, or is solicited about a spectrum of insurance protection. Do not simple words, such as range, variety, series, or line, convey the intended meaning? True Value. o i l y counting numbers have true values (56). Measuring numbers have, at best. onlv most vrobable values, an expression long &ed by t h e - ~ a t i o n a lBureau of
.
Standards for its standard reference materials. The table of relative atomic masses of the chemical elements may be the best example of measured values used by analysts, but they are not true values. A striking examole of chanee occurred whvn the vnlur for buron was decreased from 1 1.0 to 10.82 hy the lnternat~onalCnmmitrw on Atumir \\'eiehts. Volumetric. This term, widely used in titrimetry, is inapplicable if the titrant solution is weighed in order to avoid possible errors arising from non-uniform drainage of the volumetric measuring vessels, or from change in volume of the titrating solution and measuring vessel with change of temperature. There are uses for the term, as in some methods of analyzing gases. Volumes of solids, such as precipitates, have had little use. A century ago Mohr's "Titriermethode" (17) was correctly entitled. Why did authors in the United States not follow his example? Namlng Methods of Chemical Analysls As Ihde (18) has stated, "Only through chemical analysis can matter, in its variety of forms, he dealt with intelligently." In many cases it is important to know the nature of the methods used in making the chemical analvses. Effective communication about the methods would seem to indicate the need for a svstematic scheme to designate them. A personal ekperience illustrates thisneed. T o ascertain the use of the spectrophotometric determination of nickel, a search was made of t h e subject indexes of Chemical Abstracts for a 10-year period. Under the heading "nickel, detn." there were 160 entries; and under the subheadings "in steel" and "in ironand steel" there were, respectively, 90 and 10 entries. In summarv. the subiect headines for the 260 entries showed nothingon the kind of metiod used. The titles of the abstracts were adeauate for 170 Daners. . . . and the abstracts for 234. Thus, for 26 papers i t was necessary to consult the original publications. A hit of analytical history relating to nomenclature of methods seems relevant. In 1941 R. H. Miiller (19) published a noteworthy review article entitled, Instrumental Methods of Chemical Analysis. Filling the entire October issue of Industrial and Engineering Chemistry, Analytical Edition, it contained 191 figures and 313 references. The material was divided into 25 sections, with the following headings: Density; Ultracentrifuge; Thermal; Gas Analysis; Raman Spectra; X-Rays; Dielectric Constant; Infrared; and Electron Diffraction. In addition, there were eight terms ending in -metric: three in -tic or -oic: . , two in -metrv:., two in -eraohic. - . . and one on -graphy. Criticism of this inconsistent nomenclature led H. E. Howe, then editor of the journal, to appoint a six-member Committee on Naming Analytical Methods. A progress report of the committee (20) noted a t least a dozen ways then beina used to designate kinds of analvtical ~rocedures.An appeal was made for a systematic, functionai nomenclature of methods. In 1949 a personal general outline was proposed for classifying methods in terms of measuring static or dynamic properties. Consistent names were used, all ending in m e t r y (21). In 1950 a different personal, and more detailed, classification took into account items such as mechanical handline" of samples, biological testing and activity, and purely mechanical tests. Manv terms were used endine" in -tion. -metric. and -metry (22). The Committee on Namine Analvtical Methods became a responsibility of the ACS ~i;ision bf Analytical Chemistry. L. T. Hallett. then associate editor of Analvtical Chemistrv, agreed to assume chairmanship of the committee when the author was appointed the analytical representative on the ACS Committee on Nomenclature. In 1952 the Hallett committee issued a report (9) which recommended definitions for some 30 terms, including "thiosulfatimetry". Several
common terms were not recommended. The overall problem of namiue" analvtical methods remained unresolved. In the meantime several specialized reports dealt with relatively narrow areas hut did not contirbute to the broad problem of naming methods systematically. Two examples were the Huehes - reDort (231 on nomenclature in aDDlied .. spectroscopy, and the author's suggestions for naming spectroscooic methods (241. In i973 the author resigned frvm the ACS Commit~eeon c i2.51 contained a list of quesNomenclature. A ~ a r t i n rppurt tionable terms relating analytical methods, gleaned largely from proofreading galleys for Chemical Abstracts. The following enlarged selection displays inconsistent and/or unclear writing: attestation, azotometry, bomb washing, catalometric, chemometric, chroma distillation, chelatopotentiometric, chromatometric, coaminometric, coulopotentiographic, derivatographic, digimetry, ellipsometry, evaporometric, float, frequentometric, headspace, impedimetrv. oscimhometric, per" . oncometer. oscillo~olaroeraohic. .. . rnitt~\.ity,pharmaceutical, polarustr~r~~omrtric, quantometric, mreometric.. rintozronhic. Iliintrenometric, Srhonincer . - . flask, stalagometric, tempometry, tensammetry, thermocentrifugometric, thermogravimetric, thermoponderometric, vacuum fusion, and frustrated internal reflection. A reader may be frustrated by such usage, hut can a beam of radiant energy he so affected? What do these words mean? Would a searcher, of printed indexes or of chemical data bases. be likelv to think of them? Even less informative than these words is the use of names of individuals who orieinated methods of analvsis, or devised particular reactions or reagents. Perhaps the best known analytical method, named for its originator, was proposed by J. G. C .T. Kjeldahl for determining nitrogen in organic compounds. Any such name honors the originator, but it reveals nothing about any preparative and/or separative chemical processes involved, or the method of measurement. Much more informative would be the Kjeldahl distillationtitrimetric method for nitrogen. Almost as uninformative as an author's name are various other usages for designating kinds of methods of analysis, such as Bureau of Mines method, the A.O.A.C. method, the micro method, the Parr bomb method, the nitron method, and the fusion method. The A.O.A.C. method is named for the Association of Official Analytical Chemists, which approved the procedure. As such, there is no information on the nature of the method. Comoarahle methods are the A.P.H.A., the U.S.P.. and the A.S.T.M. procedures. Then in 1978 the Comuendium of Analvtical Nomenclature appeared (4). This Eompilatioi comprises the "Definitive Rules 1977" of the Analvtical Division of the International Union of Pure and plied Chemistry. The large collection of terms, symbols, definitions, and other information fills 222 pages, with some 1700 index entries. Manv common terms are missing, such as analysis, chronometric, color, colorimetric, determination, gravimetric, radiation, spectrum, and wet. Examples of indexed terms, considered questionable here, are amperomtery, chromatography, iodometry, instrumental, spectrochemical, and voltammetric. What improvements have been made in more than four decades? There have been no organizational or editorial general recommendations for use as guidelines for a consistent, functional nomenclature for analytical methods. Striking examples of the continuing use of questionable terms and nomenclature are the table of contents of recent editions of "instrumental" works, including three texts and one reference treatise (16.26-28). Omitting the chapters containing the -meter, -metry, and -metric terms, thefollowing examples of inconsistent headings are included: Analysis of gases, electrodeposition, and scattering of radiation. In addition, VOl~me64
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Table 2.
Terms Used In Analytical Chemistry Relatlng to Measurement
Table 1.
Separation Propetty measured
Terms Kind of method
instrument
Chemical reaction Color Density Electric current El~ctrical potential Energy absorption Energy emission FiuorescenCe Mass Optical interference Optical refraction Optical rotation Pressure Spectrum Temperature Time Volume
Adjective
Titrimeter
Titrimetry
Titrimetric
Coiorimeter Densitometer Cmiometer (Currentimeter) Potentiometer
Colorimetry Colorimetric Densitometry Densitometric Couiometry Coulametric (Currentimetry) (Curentimetric) Potentiometric
Absorptimeter
Absorptimetry
Emissimetric
Fiuorescimeter Balance (Massimeter) interferometer
Fiuorescmatric Gravimetric (Massimetric) interoferometric
.
Poiarimeter Manometer Spectrometer Thermometer Chronometer Voiumimeter (Buret: pipet;
Manometry Spectrometry Thermometry Chronometry Voiumimetry
Manometric Spectrometric Thermometric Chronometric Volumetric
738
~
~
Anaiyte
Absorption Centrifugation Dissoiution Distillation Electrodeposition Extraction Precipitation
Volumetric Volumetric Gmvimetric Titrimetric Gravimetric Gravimetric Gravimetric
Oxygen Fat Sand Nitrogen Capper Fat Nickel
Precipitation
Titrimetric
Calcium
Volatilization
Titrimetric
Carbon
Volatilization
Spectrometric
Fluorine
Material
Chemistry
Air Milk Sucrose Fertilizer Ore Milk Steel
Pyragailoi Sulfuric acid Water Sulfuric acid Nitric acid Diemyi emer Dimethylglyoxime Limestone Potassium psrmanganate Steel Barium hydroxide Organiccpds. Heteropaiy com-
Refractmeter
various headings are for -al, -ance, -escence, -ography, -oscopy, -tion, and X-ray measurements or methods. Who is responsible? Authors, reviewers, and editors are most involved. Authors should try to use informative terms in titles and elsewhere in publications. Competent reviewers of manuscripts should recommend improvement where needed. Editors are in a unique position to insist upon good usage. As an example of noteworthy editorial involvement, the work of R. S. Cahn, long editor of the Journal of the Chemical Society, has contributed to the improvement of organic nomenclature (29).Teachers have the responsibility of guiding their students. In many documents, of course, named methods are not the center of interest. Two examples of such titles are, "Errors in Analvsis of Wastewater", and "Studies of Precision in FTIR ~~ec&oscopy". Additional examples of generally uninformative titles follow: "Analyzing Chemical Substnaces"; "Acid Fog"; "Linear Repression"; "Separation Agent"; and "Remote Measure. ment". Much more informative titles follow: "~xrractionS p e c tronhott~metricDeterminntim of Roron with Benlilic Acid" an4 "Spectrometric Determination of Micro Amounts of Hvdroeen Sulfide in Pronvlene Carbonate by the Molybde.. n;m ~ i u Method". e Efforts to achieve informability may encounter editorial suggestions for brevity, hut the follo&ng title survived inspection: "Rapid Extraction of Barium from Strontium with Nitrohenzene Solution of Polypropylene Glycol, Having a Mean Molecular Weight 400, and Tetrasodium Salt of Trans-cyclohexanediamine-N,N,N,N-Tetraacetic Acid". Note that this long title deals only with a separation. What items should be included to render a named method sufficiently informative for indexing and searching purnoses. along" with more understandable oral and written communication? Suggested items to consider follow: method of senaration (if anv): method of measurement (if quantitative);constitu&s)"identified or measured; materid ana~~~~
Measurement
Absorptimetric
Emissimeter
Gravimetry (Massimetty) interferometry
Examples ot Naming Analytlcal Methods
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~
~
Journal of C h e m i c a l Education
~
.
~
lyzed; micro- or macro-amounts of sample or constituent(s); any special chemistry (such as a chromogenic reagent). A variety of chemical process terms indicate the means employed to make analytical separations (30). Common examples are absorption, adsorption, centrifugation, chromatoeranhv, dialvsis. " . diffusion. dissolution. distillation. electrodeposition, evaporation, ektraction, ion exchange, precipitation, sublimation. and volatilization. s o m i of the commonly measured properties are listed in Table 1, along- with the corresvondine - measurement terms (-meter, -metry, -metric). Under lodimetry, (in the Definitions section) objection was noted for -ometry terms as subdivisions of titrimetry. In Table 1the instrumental terms have some inconsistent endings: -imeter, -ometer, and -iometer. Editors might try to agree on uniform usage of the "i", "o", and "io" terms. The generally used term, volumetric, is inconsistent with volumimetry in Table 1. Table 2 contains examoles of sueeested named methods .... used in determining wmmon constitue~ni. The first line of the table. for examvle, would read,"The Absorption-Volumetric Determination of Oxygen in Air with Pyrogallol". Use of Abbreviations and Acronyms. There is a rapidly expanding use of initials or acronyms to designate a t least part of the name for a method of chemical analysis. The objective is to conserve space and time. Thus, to speak or write, "The FIR Method" is shorter than, "The Frustrated Internal Reflection Method". Two general examples, one for seoarations and one for measurements. indicate the trend. Chromatography is a widely used process for separating substances in eases and liouids. The followine abbreviations are examplesUof those frkquently encountered: GC (gas); GPC (gel permeation); HPLC (high performance liquid); IC (ion); LC (liquid); SFC (super fluid); and TLC (thin layer). T o indicate the means used to measure the separated entities, une finds nl~l~re\.iations such as thr following for liquid p r ~ ~ r c s sLCffTIR; e~: 1.C NMH;I.C/MS; and LC MS/ \IS. As an example of measurement, spectrometry is used extensively, and a variety of techniques have been developed. The following abbreviations are well known: AA (atomic absorption); AE (atomic emission); AES (Auger electron spectroscopy); ESCA (electronic spectroscopy for chemical analvsis): (furnace atomic ahsor~tion):IR (infrared): ~,~ ,FAA , FTIR (Fourier t'ransform); MA (mole&ar ahsor&ion); MS (mass): NMR (nuclear maenetic resonance): UV (ultravioiet); VIS (visible); and XR$ (X-ray fluores&ce). In addition to such group abbreviations, many single examples are common, such as E C (electron capture); FIA
rflo\e injrrrion a n n l y i i ~ rF ; F F \iield flow fracrionarion~;ISE
i, Fdrn,,,,. ,\, ,,,I", MI. 1942 I:,. M ~ i l m ?M. . C. Oililrirndr.v/,,i rhemirts. 1;. F. Smith Chemical: Columbu%OH. 1945: A n a l Chem 1962.24.924-917. I 4 Ellis. R. A , Ed. Escycioprdia Hrifnnniro. Eneyelo~ediaRritannica: New York. 1929, 6.999. 15. ~ n l l e l lr.T. ~ . And. Chrm. 1952.24.1848-1849. I 6 Bert, W. G.,Ed. P h y s i c n l M ~ t h n d r i nChcrniraiAnaivsia:4uols.. Academic: NewYork, 1968-61; Kuwana, T., Ed. Physicnl Mcihndr i n Modern Chemical Anol,v$ia:3uoIs. Academic: New YIr k , 1978-1980. 17. Muhr.P. L e h d u u h dr , Chemir .
,
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