FISHER AWARD SYMPOSIUM
A group of papers honoring John E. Yoe, presented before Division of Analytical Chemistry a t the 131st Meeting of the American Chemical Society, Miami, Fla., April 1957
fisher Award Address
Colorimetric Analysis with Organic Reagents JOHN H. YOE Praft Trace Analysis laboratory, Department of Chemisfry, University o f Virginia, Charloffesville, V a .
T
for making quantitative chemical measurements is as old as the science of chemistry itself. More than 2000 years ago Pliny developed a test for iron in vinegar (8). The reagent was simply a piece of papyrus soaked in an aqueous extract of gallnut tannins; when dipped in vinegar, it turns dark blue or black if iron is present. This seems t o be the first chemical reagent on record, and although now more than 20 centuries old, it still may be used for the detection of iron in vinegar and other liquids, though filter papers, rags, or wood shavings have replaced the ancient papyrus. Thus, the oldest recorded test for a chemical element is a colorimetric one; indeed, it is an organic reagent (gallnut tannins) supported by an organic substance (papyrus). The ancient Greeks and Romans detected the presence of alkalies in natural water by their decoloration of red wine. Keates is said to have been the first t o determine copper colorimetrically; this \I-asdone in 1830, 127 years ago. During the past 30 years, especiaIly the past 20, many new colorimetric reagents have bcen discovered, and new and highly sensitive methods have been developed, bo that now most of the more common elements, a number of the less common ones, and many organic compounds may be detected and quantitatively determined by color reactions. Modern colorimetric analysis may be said t o date back only about a quarter of a century. It is true that during the past century many color reactions have been discovered and used in qualitative and quantitative work, but few of these were developed into reliable and sensitive colorimetric methods. There are a t least three or four reasons for this slow development. One is the failure to HE USE OF COLOR
1246
ANALYTICAL CHEMISTRY
recognize the often very important role the hydrogen ion concentration plays in color reactions. Of course, we have had acid-base indicators in use for many years, but it was not generally realized that many of the analytical color reactions are in fact often profoundly influenced by the hydrogen ion concentration. HYDROGEN ION CONCENTRATION
This situation may be said to date back to about 1920. At about that time we had available on the market a group of indicators and indicator papers for the colorimetric measurement of hydrogen ion concentration over a wide pH range, making it possible to determine easily whether or not a change in pH affected a given colored species and if so, t o adjust quickly to the optimum pH for the particular color reaction. Moreover, we had by that time buffer systems that had been well studied, so that buffer solutions could be purchased or prepared for use in the control of pH for a given colorimetric reaction. Of course, the hydrogen ion concentration could have been measured potentiometrically, but this was before the day of the relatively inexpensive pH meters which became available towards the end of the 1920’s. So from then on-the past quarter of a century-it has been possible to study accurately and easily the effect of pH on a particular color system and adjust to its optimum when such was found to be necessary. Back in these days, the early 1920’s, all colorimetric analyses were made visually in Nessler tubes or in visual colorimeters, such as the Dubosq type and others. The slightest difference in the tint of a color made it difficult, if not impossible, to make an accurate color match-that is, to match the intensity
of the colored sample solution with that of the standard. PHOTOELECTRIC CELLS
The second advance in colorimetric analysis occurred in the late 1920’s, when inexpensive photoelectric cells became available. It was then possible to substitute for the human eye a photoelectric cell. Hence, exact match in tint was not so important as in visual matching of color intensity, as the photoelectric cell measures the total transmitted light or radiant energy that strikes its surface-strictly speaking, the energy to which the particular cell is sensitive. Then, another advancement came in the availability of inexpensive color filters, so that instead of transmitting through a solution the entire visual range-that is, 400 to 750 mg-it was possible to select a filter that would transmit a broad band of radiant energy to which the colored species was the most sensitive-Le., a t the maximum absorbance. Such filters transmit an energy band of 40 to 70 mp. Still more recently interference filters have been introduced; these transmit bands of radiant energy of the order of only 10 to 15 mp. Hence, the advent of the photoelectric colorimeter, equipped with color filters, may be said to mark a second advance in the development of modern colorimetric analysis. SPECTROPHOTOMETERS
A third important advancement came in the middle or late 1930’s with the introduction of the spectrophotometer in colorimetric analysis, making it possible to transmit a selected narrow band of radiant energy, 1 mp or less. Moreover, these instruments are not limited to the visual spectral range, but with
appropriate photoelectric cells they permit making absorbance measurements far down in the ultraviolet and up into the infrared spectrum, thereby extending the practical range of colorimetry, or, more precisely, absorptiometry. I n a sense, modern colorimetric analysis may be said to date back t o the introduction and general arailability of the spectrophotometer-about 20 years ago, when TI e had available for the first time such instruments as the Reckman and the Colcman, to mention only two well-known spectrophotometers. Often the sensitivity and adaptability of a given method may be improved by the use of a photoelectric colorimeter or a photoelectric spectrophotometer. The use of such instruments makes it possible for an analyst who is color blind, or who has a dulled or imperfect susceptibility to color, to perform colorimetric analyses entirely satisfactorily. They also eliminate errors due to fatigue and eyestrain. Moreover. with the aid of these instruments it is sometimes possible to determine two or more elements with the same reagent, simply by transmitting through the sample solution an appropriate wave length of radiant energy for a given colored species. Furthermore, it is now often possible to eliminate or greatly reduce interference due to excess of the reagent and/or foreign colored species, thus making a preliminary separation unnecessary-Le., simply transmit through the sample solution a nearly monochromatic beam of radiant energy which is absorbed only, or chiefly, by the colored species being determined. WATER-IMMISCIBLE ORGANIC LIQUIDS A N D ION EXCHANGE RESINS
There are two other recent advancesstrictly speaking, analytical aids. First, the availability of a large number and variety of vvater-immiscible organic liquids, nliich often permit the separation and/or determination of the colored species in the organic liquid phase, thereby eliminating interfering substances and sometimes even increasing the color intensity of the substance being determined-that is, increasing the sensitivity of the colorimetric method. The introduction of ion exchange resins marks a second advancement in aids to colorimetric analysis. Tf’ith the aid of these resins (both cation and &,ion) it is possible to concentrate an ion that is to be determined and/or frce it from other ions that cause interference. RADIOACTIVE ISOTOPES
Summing up, then, we may say that modern colorimetric analysis has developed for the following principal reasons: First, the realization of the importance of the hydrogen ion concentration in color rmwtions and simple means of
John H. Yoe, born in Oxford, Ala., in 1892,received his B. S. and M.S. degrees from Vanderbilt University. I n 1917 he received his M.A. degree from Princeton University, but further graduate study was interrupted by United States entry into the first World W a r and his resultant service in the Chemical Warfare Research branch of the U. S. Army. Not long after being discharged from the army, Yoe married Francoise Cheely in Nashville and then started his teaching career at the University of Virginia in 1919 a s an assistant professor of chemistry. Rising rapidly, h e had become professor of chemistry by 1927,in the meantime earning his Ph.D. degree from Princeton University in 1923. Since 1953 he has served a s chairman of the Department of Chemistry at the University of Virginia. Yoe is also director of the Pratt Trace Analysis Laboratory, organized at Virginia with a grant-in-aid established by J. L. Pratt in recognition of his work. Yoe is author or coauthor of 330 scientific articles, books, and reports. His ‘LOrganicAnalytical Reagents,” done with L. A. Sarver, and his treatise on colorimetry and nephelometry have become foremost reference works. At present, Yoe is engaged in editing papers presented in the Symposium on Trace Analysis at New York in 1955,of which h e was chairman.
measuring pH; secondly, the introduction of the photoelectric colorimeter and abridged spectrophotometer-that is, colorimeters with a series of color filters; thirdly, the introduction of the spectrophotometer; and fourthly, the availability of ion exchange resins and a wide variety of water-immiscible organic liquids. Finally, the most recent aid in developing and applying a neIT colorimetric method to trace analysis is the availability of radioactive isotopes. K i t h the use of these it is now possible to check each step in a procedure and t o determine accurately and easily the percentage recovery of certain elements in trace amounts and in trace concentrations. Radioactive isotopes offer the analyst a powerful and convenient tool in his development of highly sensitive and accurate methods of analysis. CHELATES
Among the new organic reagents for the colorimetric determination of metallic constituents, the most interesting and most promising are those that form a ring containing a metal, the product being called a chelate compound or inner-complex salt. The chelates were so named by Morgan (?) because of the imagined structural resemblance to the great c l a w of the lobster and other crustaceans. The name is derived from the Greek Ford meaning claw. I n the majority of cases the metal is united to the rest of the compound by two arms, or bonds, but for a complete consideration of these substances they must be classified into unidentate, bidentate. terdentate, and quadridentate compounds. respectively, according t o the number of points of union involved. These metallo-organic compounds. or
chelates, are often highly colored, and hence give promise of being developed into useful colorimetric procedures. ACIDIC GROUPS
The great majority of salt-forming or salinogenic reagents (32) are acidic in nature, but fortunately we are not limited to the more conventional types of organic acids, because the carboxy acids have yielded only a few salts of analytical value and few indeed that are suitable in colorimetry. Of far greater interest than the carboxy group are other groups that are capable of splitting off hydrogen ions in solution. with subsequent replacement by metallic ions. Frequently organic compounds that are not ordinarily considered to be acids. yield small concentrations of hydrogen ions due to keto-enol isomerism, when the equilibria are disturbed by the presence of certain metallic ions that are capable of forming highly stable complexes. The most common acidic radical in organic compounds is the hydroxyl or OH group; it seldom splits off hydrogen ions t o any great degree, but it frequently does so sufficiently to yield stable complexes. Other acidic groups are : the sulfhydryl (SH), amino (NH2), oxime or enolic form of the nitroso group (KOH), nitroxyl or enolic form of the nitro group (NO.OH), sulfinic acid (S02H), sulfonic acid (SOSH), arsenic acid [As(OH),], and arsonic acid [AsO(OH),]. Phosphorus gives rise to phosphonic [PO(OH),], phosphinic (PO. OH), and phosphinous (POH) acids, but these hare not been extensively investigated for use as analytical reagents. Antimony and bismuth are too basic in nature to yield acidic substances and VOL. 2 9 , NO. 9, SEPTEMBER 1957
1247
in such examples as are known the hydroxyl group splits off as a unit in aqueous solution. K h e n a new color reaction between a metallic ion and an organic compound is discovered, it is then necessary to make an extensive investigation in order to establish its value and use as a colorimetric reagent. A complete study would include (1) a determination of the mole ratio of metal ion to organic ligand; ( 2 ) the sensitivity, accuracy, and precision of the reaction under the experimentally determined optimum conditions, such as pH, rate of reaction, stability of color, effect of temperature. and order of adding reagents; (3) concentration range; (4) interference of various ions; and finally ( 5 ) a procedure for its application to the analysis of a variety of standard samples. Table I is a suggested outline for a comprehensive study of a new color reaction and its development into a colorimetric procedure. Khile the order need not be followed step by step as listed in the table, nevertheless it is a practical one, which should serve as a helpful and convenient guide in developing a new color reaction into a satisfactory colorimetric method Exactly 20 years ago this month a little article in the Journal of Chemical Education (18) outlined a microtechnique for the search of new organic color reactions with inorganic ions. Since that time we have investigated about 6000 compounds with some 7 5 to 80 metallic ions, each reaction being carried out in acid, neutral, and alkaline media wherever the reacting system permitted the use of all three conditions. This was a fairly long-range cooperative program, but unfortunately it had to be interrupted in the early days of Korld War I1 after about 5 years of work. Although the cooperative program was not resumed after the war, the major objective had been acconiplishednamely, a systematic spot plate or micro-glass cell (0.5 m1.)-study of some 5000 organic compounds, representing a wide variety of structure types. About half of these were tested in the laboratories of nine cooperating institutions and the others a t the University of Virginia. where an additional thousand have been studied since the war. -4s a result of these cooperative studies and those made by us after the war and by many other independent workers in this field, especially Fritz Feigl, internationally known pioneer in spot-test analysis, we are now in a better position to select organic compounds that offer promise of being of interest in colorimetric analysis based upon their molecular structures; at least we feel that a more intelligent guess is possible. It was not expected that a large per cent of the 6000 compounds tested would prove t o be analytically useful; 1248
0
ANALYTICAL CHEMISTRY
Table I. Investigation of a New Organic Colorimetric Reagent
A . The Reagent 1. Suitable solvent 2. Solubility
3. Stability (in solution)-i.e.,
resistance to hydroiysig, light, oxygen, carbon dioxide, etc. B. The Color Reaction 1. Effect of pH 2. Stability of colored complex to light 3. Order of adding ieagents 4. Rate of color formation 5 . Tature of color reaction (mole ratio of metallic ion to organic ligand) 6. Conformity to Beer's law 7 . Sensitivitv of color reaction 8. Optimum concentration range 9. Effect of temperature on color reaction over the range 15' to 35" c. 10. Effect of foreign ions upon colored complex 11. Best conditions for analytical use of color reaction 12. Application of reagent to analysis of a variety of standard samples however, a number of nen and highly sensitive colorimetric reagents have been discovered and their reactions have been developed into satisfactory procedures for certain inorganic ions. Some of these are briefly described here and citation to the original literature is given. ORGANIC COLORIMETRIC REAGENTS
Reagents for Palladium(l1) and Platinum(I1). -4 large number of aromatic amines n-ere studied and it was revealed t h a t those containing t h e p-nitrosophenylamino group, p-XOC6H4N-namely, p-nitrosoaniline, p-nitrosodimethylaniline, pnitrosodiethylaniline, and p-nitrosodiphenylamine-form similar highly colored complexes with divalent palladium (9, 30). It was predicted that divalent platinum would give similar complexes, but it was necessary to develop a means of reducing platinum(I5') quantitatively to platinum(II), as the former does not form colored complexes 11ith the p-nitrophenylaniino type of compound. This was accomplished some years later and the reaction n-as developed into a colorimetric method for platinum. Thus it is n o x possible to determine both palladium and platinum with the same reagent (4, 28). Obviously, these reagents will differentiate between divalent and quadrivalent platinum. The substitution of tv;o methyl groups for the hydrogen and phenyl in p-nitrosodiphenylamine gives a more favorable reagent-i.e., very little absorption by the compound near the maximum for its palladium complex-thus largely eliminating the ef-
fect of' excess reagent. Substitution of two ethyl groups gives similar results, so that either the dimethyl or diethyl derivative may be used with equal success (Table 11). Reagent for Iron(III), Titanium (IV), and Molybdate. DISODII-LI-~,~DIHTDROSYBEKZESE-3,~-DIS~LFOS.4TE
(Tiron) yields intensely colored complexes with iron (111), titanium( IV), and molybdate (Jlo04--) suitable for t,heir spectrophotometric determination. The trivial name Tiron was given t o the compound because it may he used to deterniinp both titanium and iron in the same sample solution, simply by adjusting the p H to 4.7, measuring the absorbance a t 560 nip (for Fe). then reducing the iron (in the spectrophotometric cell) by the addition of a little sodium dithionite, and measuring the absorbance a t 400 or 410 mp (for titanium). Before molj-bdenuni can be determined with Tiron, both iron and titanium must be removed; a number of other elements also interfere. Instead of separation of the interfering ions from molybdenum. niolybdenum is separated from almost all other elements by precipitating it from dilute hydrochloric acid solution in the cold ( 5 " to 10" C.) with a-benzoinoxime. The molybdenumbenzoinosime is filtered off on paper with gentle suction and then washed with a cold dilute solution of the reagent acidified with a little hydrochloric acid. The precipit'ate is dissolved directly on the filter paper with hot dilute ammonium hydroxide and finally with enough acetone to dissolve the reagent residue and prevent' precipitation of the reagent in the filtmte. The dissolved precipitate is allon-ed to pass through the filter paper into a volumetric flask of convenient8size and the solution is diluted to the mark and mixed. The molybdenum is determined by adding Tiron to a suitable aliquot adjusted to p H 7 i 0.5 and measuring t'he absorbance at 390 mp. References to the literature and analyt'ical data on the deterniination of iron(III), titaniuni(IV), and molybdenum are given in Table 11. I f E R C A P T O A C E T l C ACID (thiOglycO1ic acid) may be used for the spectrophotometric deterniination of both molybdenum (MoO4--) and iron(II1) in the same solution. The method is simple and accurate and is useful for determination of mhlybdenuni in steels. molybdates. and other materials. especially those containing large amounts of iron. For molybdenuin, the solution is adjusted to p H 4.0 & 0.5, a iittle potassium perchlorate is added. then the solution diluted to the mark in a volumetric flask and mixed, and the absorbance is measured a t 365 nip. For iron. an aliquot is transferred to a volumetric flask that will yield a n iron concentration of 3 to 10 p.p.m. in the final solution. After the p H has been adjusted to 8 to
Table II.
Organic Colorimetric Reagents
Analytical Wave Length, Determination ;iluniinum
Reagent
PH
hurintricarhoxilic acid ( S H , salt) Tetrahromochrysaein Diaminoc hrysazin Dinitrochr ysazin Dicyanoquinizarin Diaminoanthrarufin Dinitroanthrarufin Tribromoanthrarufin 5-Benearnido-A‘-chloro- 1,l‘his( anthraquinony1)amine 5-p-Toluidino-1,l’his( anthraquinonyl) amine
M p
Cell Thickness, Cm.
Concn. Rangc, -,
P.P.1I.
Rrferenccs
0 04
(16, 26)
0 02 0 02 0 067
(23) (2)
Sensitivity,
111.
Nes.qler tubes, 22 540 525 490 545 605 505 625 635
1 00 1.00 1.00 1.00 1.00 1 .OO 1.00 1 00
0 23-0, 85
720
1.00
0.1-0.5
550 425 450 fif Ni is present)
1.OO 1.00
0.1-1 (7 0 , 0 2 5 best
0 005 0.02
(sol
5.6-6.5
5.0-9.5
600
1 00
fl.5-2 0
0.011
(11)
0
625
1 00
u .l-60
ca. 0 . 1
(H)
2-3
Visual
Nessler tubes, 21
0 1
(l?)
9-10
Visual
Nessler tubes, 21
7.5-50 1-2 (opt.) 0.05-2
3.5-4.5
Visual
Nessler tubes, 21
0 4-16
4-Hvdroxgbiphenyl-3carboxylic acid
3 2 . 5 (if T i is present)
Visual
Xessler tubes. 21
u. 2-1
Sodium l-azoS-droxy-3(2,4-dimethylcarboxaniliodonaphthalene-l’-(2hydroxvbenzene-5-sulf onate)
“11-12” in 95y0 ethanol
510
1 00
tI .04-0.
Disodium- 1,2-dihydroxybenxene-3,5-disulfonate (Tiron) Mercaptoacetic acid
6.6-7,5
390
1.00
:i- 10
0 1
3,5-4.5
365
1.00
4-15
0 15
Sickel
Diethyldi thiocarbamate Potassiuni dithiooxalate
9.5
325 Visual
1.00 Nessler tubes, 21
0.24-1.4 10
0 01 0 008
Omiium
l-Saphthylaniln~-2,5,7trisulfonic acid For 27 other similar reagent?
1.5
560
1 00
I 5-5 . 5
0 067
2
Nessler tubes, 22 Nessler tubes, 22 Nessler tubes, 22
0.1-0.25 0.1-0.25 0.1-0 25
0 005 0 005 0 005 0 015
Boron
Cobalt
Copppr
Iron
2-Sitroso-1-naphthol o-Sitrosorrsorcinol
2-Carhoxy-2 ’-hvdroxy-5Isulfof ormazylbenzene (Zincon) Triethanolamine 8-Quinolinol-7-iodo-5sulfonic arid (ferron) Disodiun~-l,2-dih\~droxvbenzcne-:3,5-disulfonic acid (Tiron)
0 1-0 5
0 1-0. 5 0 1-0 5 0.1-0 5 0 1--0.5 0.1-0.5 0.1-0.5
4
(9)
(24) 0 005 ($7) (red complex) 0 033 (blue comolesi 0 033-
0 02
(12)
I’allatliiim
p-Sitrosodiphcnylaniine p-Xitrosodimethglamine p-Sitrosodiethylamine
4-5 4-5
1-isual Visual Visual
Plat inmn
p-Sitrosodimethylamine
2.0-2.4
525
1 00
I). 7-2.4
Silver
2-Thio-5-keto-4-carbrthosy1,:~-dih!-tfropyriniidine
ca. 7
Visual
Sessler tubes, 22
0 16-0.24
Titaniiim
I~isodiiini-l,2-dih~droxyi,c,iizcnc-3,5-disiilfonate (Tiron)
4.7
T’isual
Sessler tubes, 22
4.7
400
1.00
6.5-8.5
305
1.00
2.54
8.5-9.5
620 600 (if Cu is present )
1.00
Spot plate
I’raniuni
(UO?+-) Zinc
P-Carhoxv-2’-hvdroxy-5 ’.sulfoformazylbenzene (Zincon)
Zirconium
5-C horohromainine
d
Ii
01-0.8
0 01 0 01 (visual) 0 005 (spectrophot.) 0 0043
(.1;3)
0.5-2.0
0 014
(11 I
0 . 5 .‘0.(751111I.
0.002
(30)
VOL. 2 9 , NO. 9, SEPTEMBER 1957
1249
11 with ammonium hydroxide, the absorbance is measured a t 535 mp (Table IT),
to 400 mesh) [(5) reagent (I), (6) (11); for analytical data, see Table IT]. Reagents for Boron. During the past 3 years we have discoyered nine Reagent for Zinc and Copper. 2new and highly sensitive reagents for CARBOXY-2'-HYDROXY-5'-SULFOFORhIboron and the spectrophotometric A Z I L B E N Z E N E (Zincon) forins stable characteristics of their color reactions blue complexes with zinc and copperwith boron (in concentrated sulfuric (11) ions. T h e zinc complex is stable acid) have been studied. Seven of these at pH 8.5 to 9.5, while the copper comare derivatives of the dihydroxyanthraplcv is stable over the p H range 5.0 t o quinones, anthrarufin, chrysazin, and 9.5 Both complexes obey Beer's law quinizarin, with amino, nitro, cyano, or over the range 0.1 t o 2.4 p.p.m. a t the halogen substituents; two of the rean a~ e length of maximum absorbance, gents are substituted bisanthraquin620 n~Mfor zinc and GOO mp for copper olylamines. The spectral absorption (Table IJ), Reagent for Uranium. DIBEA-ZOYL- characteristics of these compounds and their borate complexes are much more METHAN reacts with the uranyl ion favorable for the spectrophotometric (GOz++)to form a stable yellow comdetermination of boron than is the case plex having a maximum absorbance at with quinalizarin, which is commonly 395 mp, Uranium is separated from used for this purpose. With the exinterfering ions by ether extraction of ception of one of the nine reagents, all uranyl nitrate. The method is u s e are more sensitive than quinalizarin: ful for the determination of small one is almost ten times as sensitive as amounts of uranium, especially trace quinalizarin, another is about six times quantities. The ratio of U02 to reaas sensitive, and two are approvimately gent is 2 to l as established by the three times as sensitive. method of continuous variations. BeApparatus and procedures have been cause dibenzoylmethane is known to exdeveloped for rapidly decomposing the ist in the enolic form, C6H5COCH= sample and subsequently separating the COC8H5, the following structure of the boron as trimethyl borate (Table 11). colored complex is suggested: Reagents for Osmium. Sulfonic acid derivatives of naphthylamine and substituted naphthylamines vield stable and intensely colored compiexes with osmate ions. T h e spectral abI sorption characteristics of 28 of these H compounds and their osmate comTable I1 gives analytical data and plexes have been studied. The reagents literature references. give violet or purple colors with hexavalent osmium but not with octal-alent Reagents for Magnesium. Reosmium. A rapid and simple method cently two new spectrophotometric for reducing osmium(VI1T) to osmiummethods have been developed for the (VJ) has been developed, thus making it determination of trace concentrations possible to identify and determine these of magnesium based upon the formaoxidation states of osmium. A protion of stable colored complexes with cedure for the determination of trace sodium l-azo-2-hydroxy-3-(2,4-dimeth- quantities of osmium has been devised. ylcarboxani1ido)-naphthalene-1'- (2-hyThe new method is more simple, precise, droxybenzene-5-sulfonate) (I) and 1and highly sensitive than those deazo - 2-hydroxy-3 - (2,4 - diniethylcarboxscribed in the literature. Moreover. anilido) -naphthalene - I' - (2 - hydroxythe color reaction is carried out in benzene) (11). weakly acidic medium (adjusted to p H 1.5) in contrast to a strongIy acid one A 5-ml. aliquot of reagent (TI) solurequired for the thiourra method. for tion is transferred to a 25-ml. volumetric flask; to this is added an aliquot conexample (Table IT). taining 1 to 10 y of magnesium in 2 to 15 ml. of solution which has been adCONCLUSION justed so as to be just acid to phenolphthalein. Then 0.5 ml. of 0.08X borax There still remains much experiniensolution is added and the solution is tal work to be done to establish a better made up to the mark with 95% ethyl alcohol, and mixed. The absorbance knowledge of the relation between the is measured at 505 mp, using a distilled molecular structure of organic comwater blank. The weight or concentrapounds and their color reactions with intion of magnesium in the unknown is organic ions. With such knowledge we determined from a working curve prewould be in a better position to prepared by this procedure using known dict whether or not a given type of oramounts of magnesium. ganic compound would be likely t o Interference by diverse ions may be yield a color reaction with one or more eliminated by extraction n-ith 8-quinometallic ions. As there are to be found linol in chloroform and by ion exchange in the literature hundreds of qualitative fractionation using Dowex 50-X12 (200 color reactions with organic compounds,
1250
ANALYTICAL CHEMISTRY
a systematic and critical examination of them should give some insight into the nature of their reactions. Indeed, it 1:' likely that some of the known qualitative reactions mould prove to be suitablr for quantitative work, provided propc.1 conditions are established. K h e n ,I given color reaction is selected for stud) or a new one discovered, it is then necessary to make a thorough investigation to determine its characteristics: find a suitable solvent; establish optimum conditions for its use; determine its sensitivity, precision, and accuracy: study the interference of various ions and devise a way to separate or mask those that interfere; and, finally, apply the reaction to the analysis of a variety of materials. The standard samples supplied by the National Bureau of Standards have been most helpful in many of our studies. The vast number and great variety of organic compounds offer a promising field for new and better reagents for colorimetric analysis, both inorganic and organic, and amply justify further research. ACKNOWLEDGMENT
Although acknowledgment has been made in several previous publications we wish to take this opportunity again to thank the cooperating laboratories Hampden-Sydney College, Mary Baldwin College, Randolph-Macon College (Ashland), Kashington and Lee Vniversity, College of William and Mary Tulane University, University of Sorth Carolina, Virginia Military Institute and Virginia Polytechnic Institutc. LITERATURE CITED
(1) Cluett, M. L., Yoe, J. H., unpuii-
lished.
(2) Co bill, E. C., Yoe, J. H., A m i . $him. Acla 12,455 (1955). Ihid., 14,253 (3) Grob, R. L., Yoe, J. H., f 19.56). K&kiand, J. J., Yoe, J. H., A X I L . CHEW26, 1340 (1954). Mann, C. K., Yoe, J. H., Ibid., 28, 202 (1956). Mann, C. K., Toe, J. H., Anal. Chirn. Acta 16, 155 (1957).
Morgan, G. T., Drew, H. D. I< J . Chem. SOC.117, 1456 (1920) Xierenstein, M., Anulyst 68, 212 (1943). Interesting historical note on Pliny's gallnut test for iron and 24 references to the literature on its early development. ( 9 ) Overholser, L. G., Yoe, J. H., I s n . ESG. CHEM.,ANAL. ED. 15, 310 ~
(1943).
Overholser L. G., Yoe, J. H., J. L 4 ~ r i , Chem. Soc. 63, 3224 (1941).
Rush, R. M., Yoe, J. H., ANAL. CHEW26, 1345 (1954).
Steele, E. L., Yoe, J. H., unpublishrd. TT'ill, F. 111, Yoe, J. H., h A L . CHEJI. 25, 1363 (1953).
Will, F. 111, Yoe, J. H., Anal. Chin!. Acta 8, 546 (1953).
Wingfield, H. C., Yoe, J. H., Ihid., 14, 446 (1956).
Yoe, J. H., J. Am. Chem. SOC. 54, 1022 (1932).
(17) Zbid., p. 4139. (18) Yoe, J. H., J. Chem. Educ. 14, 170 (1937). (19) Yoe, J. H., Armstrong, +4.R., IND. Esa. CHEM.,ANAL. ED. 19, 100 (1947). (20) Yoe, J. H., Barton, C. J., I b i d . , 12, 405 (1940). (21) Ibid., p. 456. (22) Yoe, J. H., Boyd, G. R., Jr., J . A m . Chem. SOC.64, 1511 (1942). 123 J Toe, J. H., Grob, R. L., ANAL.CHEM. 26, 1465 (1954).
(24) Yoe, J. H., Hall, R. T., J . Am. Chern. SOC.59, 872 (1937). (25) Yoe, J. H., Harvey, A. E., Jr., Zbid., 70, 648 (1948). (26) Yoe, J. H., Hill, W,I,., Ibid., 49,2395 (1927). (27) Yoe, J. H., Jones, A. L., IND.ESG. CHE?d., AN.4L. ED. 16, 111 (1944). (28) Yoe, J. H., Kirkland, J. J., ANAL. CHEM.26, 1335 (1954). (29) Yoe, J. H., Overholser, L. G., IND. ESG. CHEM..A s . 4 ~ .ED. 14, 148 (1942).
Zbid., 15, 73 (1943). Yoe, J. H., Overholser, L. G., J . A m . Chem. SOC.61, 2058 (1939). Y_ o e.. J. H.. Sarver. L. A.. “Oreanic Aklyticftl Reagents,”’ p. -112, Wiley, New York, 1941. (33) Yoe, J. H., Will, F. 111,Black, R. A., ANAL.CHEM.25, 1200 (1953). (34) Yoe. J. H.. Wirsina F. H., J . A m . Chem. Soc. 54, lg66 (1932).
RECEIVED for review April 25, 1957. .ICcepted ?\lay29, 1957.
Spectrophotometric Determination of Boron with Diaminochrysazin, Diaminoanthrarufin, and Tribromoanthrarufin Determination in Plant Tissue with Diarninochrysazin EVERETT C. COGBILL’ and JOHN H. YOE
P raft Trace Analysis laboratory, Department o f Chemistry, University o f Virginia, Charloftesville, Va.
b Diaminochrysazin, diaminoanthrarufin, and tribromoanthrarufin give sensitive color reactions with borate in concentrated sulfuric acid solution. These color reactions and the variables that are important to their analytical use were studied, in order to apply them to the determination o f trace amounts of boron. The spectrophotometric sensitivities o f the three reagents in 95.4% sulfuric acid are, respectively: 0.0022, 0.0025, and 0.0009 y of boron per sq. cm. Boron in the range 2 to 7 y may b e determined with a precision within 1%. Titanium is the only common metallic ion likely to interfere; oxidizing anions and fluoride must b e absent. A procedure for the spectrophotometric determination of boron in plant tissue employs wet digestion and separation of the boron b y methyl borate distillation. Using diaminochrysazin, 6 to 12 y o f boron in a 0.1- to 0.3-gram sample of plant tissue may b e determined with a precision within 4%.
T
spectral absorption characteristics of six new organic reagents which give sensitive color reactions with borate ion in concentrated sulfuric acid medium have been described ( 2 ) . These reagents are derivatives of the tlihydroxyanthraquinones: anthrarufin, chrysazin, and quinizarin, having amino, nitro, cyano, or halogen substituents in the molecule. HE
Present address, Research Laboratory, .4merican Tobacco Co., Richmond, Va.
Anthrarufin, chrysazin, and quinizarin are the common names for the isomeric dihydroxyanthraquinones with the hydroxyl groups in the lJ5-, I,%, and 1,4-positionsJ respectively. The six derivatives of these substances investigated as colorimetric reagents for boron were : diaminoanthrarufin (1,5diamino-4,s- dihydroxyanthraquinone), diaminochrysazin (1,8 - diamino - 4,5dihydroxyanthraquinone), dinitroanthrarufin (1,5 dinitro - 4,8 dihydroxyanthraquinone), dinitrochrysazin (1,8dinitro - 4,5 - dihydroxyanthraquinone), tribromoanthrarufin [1,5(?)-tribromo4,8-dihydroxyanthraquinone], and dicyanoquinizarin (2,3 - dicyano - 1,4dihydroxyanthraquinone) . Further examination showed three of these to be the most promising of the group as colorimetric reagents for boron-dinminochrysazin, diaminoanthrarufin, and tribromoanthrarufin-and more detailed investigation was confined t o these. The present paper describes a study of these three compounds as reagents for the determination of trace amounts of boron. It shows the effect on their color reactions of the variables which are important to their analytical use and details a procedure by JThich they may be applied to the determination of boron in plant tissue. From an overall consideration of the characteristics of the three reagents, diaminochrysazin !vas judged to be somewhat superior to the other two, and was used in the analyses of plant material reported. The two anthrarufin derivatives can be substituted for it, with only minor changes in the procedure.
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APPARATUS
Spectrophotometer. Transmittance measurements were made with a Beckman Model DU quartz spectrophotometer, using matched 1-cm. Corex or silica cells. Glassware. Glassware employed for the storage and ordinary handling of cold acid solutions was either of the “soft-glass” type or made of Corning alkali-resistant (“boron-free”) glass No. 7280. Pipets and volumetric flasks were of Kimble Brand glass. The No. 7280 glassware was employed exclusively for operations requiring heating or evaporation of solutions, and for the storage of alkaline solutions. Distillation Apparatus. The apparatus used for the separation of boron by distillation as methyl borate was similar in design t o t h a t described by Yoe and Grob (6, I S ) . The exit tube of the receiver flask mas an Nshaped tube with funnel top on its outlet arm. A few drops of water placed in the lower loop of this guard tube during the distillation serve as a trap for any escaping vapors of methanol or borate ester. REAGENTS
Sulfuric Acid, 960j0. Except where otherwise indicated, the reagent grade concentrated sulfuric acid of commerce (assay 95 t o 96%) was used, and all solutions were made u p in this medium. Care should be taken t o select a n acid which is water-white and has a low boron blank. B and A Brand reagent grade sulfuric acid, manufactured by General Chemical Division, New York, N. Y., is satisfactory. The lot of acid used for the work reported was analyzed 95.4% sulfuric acid, by alkimetric titration. VOL. 29, NO. 9, SEPTEMBER 1957
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