should be given to chelation in the presence of diverse ions to minimize interference, Tables 111 and IV show the results of this study. The dibenzyl derivative was found to react most favorably in the presence of diverse ions. Effect of Reagent Concentration. Observations on the dibenzyl derivative showed that extraction is complete as long as the derivative is present in a molar excess of 250 or greater. Simultaneous Extraction of Platinum and Palladium, Table V shows t h a t t h e dibenzj-1 derivative can be used successfully to extract simultaneously platinum a n d palladium. Simultaneous Separation in the Presence of Diverse Ions. Table V I
reports the results of‘ a simultaneous separation of platinurn and palladium, with dibenzyl D C h in the presence of selected diverse ions. T h e extreme interference of rhodium in t h e
simultaneous analysis may be a t tributed to the fact t h a t a reduced form of Rh(II1) is reacting with the derivative in a manner analogous to t h a t of platinum and palladium. Copper reacts in both the univalent and bivalent states with the derivative. Synthetic samples were prepared which contained several diverse ions along with varying amounts of platinum and palladium. The results of these analyses are found in Table V I I . LITERATURE CITED
(1) Bode, H., 2. Anal. Chem. 142, 414 I 1 9.54 ).
(2jCallan, T., Henderson, J. A. R., Analyst 54, 650 (1929). (3) DelBpine, M.,Compt. Rend. 146, 981 (1908): (4) DelBpine, M., Bull. SOC.Chem. 3-4, 652 (1908). (5) Gleu, K., Schwab, R., Angew. Chem. 6 2 , 320 (1950).
(6) Jacobs, W. D., ANAL. CHEM. 33, 1279 (1961). ( 7 ) Kanner, L. J., Salesin, E. D., Gordon, L., Talanta 7 , 288 (1961). ( 8 ) Malissa. H., Miller, F. F.. Mikrochim. (9) Martens, R. I.)’Githens, R. E , Sr., A N A L . C H E M . 24, 991 (1952). (10) Pollard, W. B., Analyst 6 7 , 184 (1942). (11) Pyle, J. T., Jacobs, W. D., Talanta 9, 761 (1962). (12) Sandell, E. D., “Colorimetric Determination of Traces of Metal,” 3rd ed., p. 193, Interscience, Sew York, 1959. (13) Welcher, F. J., “Organic Analytical Reagents,” Vol. 4, pp. 77-91, Van Nostrand, Sew York, 1048. (14) Yoe, J. H., Kirkland, J. J., ANAL. CHEM.26, 1335 (1964). RECEIVED for review February 28, 1964. Accepted May 1, 1964. Southeastern Regional Meeting of the American Chemical Society, Charlotte, hT. C., November 14-16, 1963. During part of this study one of the authors ( J T P ) held a Xationa Science Foundation Summer Fellowship.
Indirect Spectrophotometric Determination of Ammonia J. H. HOWELL’ and DI.
F.
BOLTZ
Department o f Chemistry, Wayne State University, Detroit,
b A rapid spectrophotometric method for the determination of ammonia is proposed and the results of an investigation of the experimental variables are presented. Ammonia is oxidized to nitrogen by hypobromite and the differential absorbance at 330 mk of the sample relative to that of a reference standard is proportional to the ammonia concentration. The differential technique minimizes errors due to ammonia contamination of reagents and distilled water as well as the effects of reagent decomposition. Conformity to Beer’s law was observed for 1 to 42 p . p m of ammonia, the optimum concentration range being from 3 to 23 p.p.m. The absorptivity for ammonia was found to b e 0.030 cm.-’ p.p.m.-’ Concentration of ammonia in the range of 0.1 to 1.0 p.p.m. may b e (determined using 5.0-cm. silica or borosilicate absorption cells with either a hydrogen or tungsten lamp source.
T
spectrophotometric method for the determination of ammonia involves the use of Sessler’s reagent, which generally requires rigid control of reaction conditions and reagent stability l o prevent solution turbidity ( 2 ) . A sensitive method based H E MOST EXTENSIIELY USED
Mich.
on the use of a pyridine-pyrazolone reagent and the extraction of the resulting purple system with carbon tetrachloride has excellent sensitivity and specificity ( 5 ) . However, the control of p H is rather critical, the reagent is relatively unstable, the colored system does not show strict conformity to Beer’s law, and the extraction process is time-consuming. The reaction of ammonia with a phenol and hypochlorite reagent to give indophenol has also been utilized, but control of hypochlorite concentration, as well as pH, is very critical ( 1 ) . Ammonia in water has been determined recently by a colorimetric method based on the conversion of ammonia to trichloramine by treatment with hypochlorite, destruction of excess hypochlorite with nitrite, and the development of a blue color as the trichloramine reacts with a cadmium iodide-linear starch reagent (6). The high sensitivity of this method, its specificity, and its freedom from interferences are distinct advantages, but again the controi of p H is critical in order to avoid either the osidation of iodide by the nitrite under too acidic conditions or the incomplete conversion to trichloramine under more basic conditions. During a spectrophotometric study of chlorine dioxide and related species the effect of pH on the ultraviolet
spectra of hypochlorite and hypobromite solutions was investigated. On the basis of this study, hypochlorite and hypobromite have been used to oyidize ammonia, with the excess oyidant being determined by ultraviolet absorbance measurements. Because of a lack of stoichiometry and reproducibility, in spite of rigidly controlled reaction conditions, the hypochlorite oxidations were found to be inferior to those obtained with hypobromite. The osidation of ammonia by hypobromite proved to be reproducible and nearly stoichiometric. This paper reports the results of the investigation of the effect of experimental variables on the proposed method. EXPERIMENTAL
Apparatus. Absorbance measurements were made with a Cary Model 14 spectrophot~ometer and 1.000-em. silica cells, unless ot,herwise indicated. Reagents. .kmmonia-free distilled water was prepared by redistillation of distilled water from a n acidic permanganate solution in a n all-glass distillation apparatus. Reagent grade reagents were used unless otherwise specified.
Present address, Department of Chemistry. Western Michigan I-niversity, Kalamazoo, Mich. VOL. 36, NO. 9, A U G U S T 1964
1799
and hypochlorite occurs according to the following reaction: Br-
+ C10-
-+
Br0-
+ 3Br0-
Figure 1 . Ultraviolet absorption spectra for hypobromite solutions Approx. 270 p.p.m. N a B r O
SOLUTION.-1. Prepare a 0.025 to 0.3051 sodium hypochlorite solution by taking 23 to 28 ml. of a 5.25% commercial bleach-e.g., Roman cleanser bleach-adjust the pH between 11.2 and 11.4 with sodium hydroxide, and dilute to 1 liter with distilled water. SOLUTIONB. Prepare a solution which is 2% potassium bromide and lOyo dipotassium hydrogen phosphate by dissolving 20 grams of KBr and 100 grams of K z H P 0 4in distilled water and diluting to 1 liter. SOLUTIONC. Prepare this reagent shortly before it is needed, by thoroughly mixing solutions .I and I3 in a ratio of approximately 2 t,o 1 by volume and wait'ing 3 minutes for the completion of the reaction. SOLUTIOND. Prepare a 10% tripotassium phosphate hydrate solution by dissolving 100 grams of K 3 P 0 4 . z H 2 0 in distilled water and dilute to 1 liter. General Procedure. Transfer an aliquot of ammonia solution containing from 0.05 to 3.0 mg. of ammonia to a 100-ml. volumetric flask. Pipet 15.00 ml. of solution C into the flask containing the ammonia solution and 15.00 ml. int,o a volumetric flask containing a volume of ammonia-free distilled water equivalent to the volume of the ammonia solution taken. Shake thoroughly from time to time and aft'er 3 minutes add approximately 10 ml. of solution D to each flask, mix, and dilute to volume. Measure t'he absorbance a t 330 mp using the reference standard containing the ammonia-free distilled water in the sample cell and the sample in the reference cell. Read the concentrat'ion from a linear calibration graph, or compute from the I3ouguer-Beer relationship using 0.030 cm.-' p.p.m.-1 as t,he absorptivity. Fundamental Reactions. The formation of hypobromite from bromide 1800
ANALYTICAL CHEMISTRY
0.8W
+
+ 3Br- + 3 H 2 0
0.7 -
2 a
0.6-
0
0.3-
U J
m
a Xz
WAVELENGTH, m p
0.9-
+ C1-
The reaction is rapid in solutions of pH 9 0 or less. In solutions of pH 9 5 and above, a marked decrease in reaction rate was observed. The oxidation of ammonia with hypobromite proceeds according to the equation : 2xH3
1.01
0.5 0.4
0.1
RESULTS
'"7
Absorption Spectra. Hypobromite exhibits a broad band with a maximum absorbance a t 330 mp, (Figure 1). The masimum absorbance for hypobromite was found to occur in solutions of p H 11.3 to 11.1, while deviations of 0.1 p H unit beyond this range showed only slight changes in absorbance. Solutions of p H above 11.5 decreased slowly in absorbance on standing, presumably because of decomposition of the hypobromite t'o form bromate ( 3 ) . When the pH was lowered below 11.1 a relatively rapid change in absorbance on standing was found, again due to decomposition of the hypobromite. As the p H was continually lowered, the change in absorbance due to decomposition was found to be less, as evidenced by relatively stable absorbance readings with time. However, the decrease of absorbance with respect to p H cont,inues as bromine formation becomes more significant when excess bromide is present a t lower p H values. This was evidenced by the fact that another absorption peak a t approximately 260 mp begins to appear a t a pH of about 8.6, while the peak a t 330 mp has been decreased significantly. When the p H of the solution is approximately i . 7 a very clearly defined absorbance maximum is obtained a t 266 mp with the only remnant of the hypobromite band appearing as a shoulder in the region of 300 to 330 mp. The absorbance masimum of hypobromite solutions of pH 6.8 is completely masked by the absorbance maximum of bromine a t 266 mp. Further reduction of the pH of hypobromite solutions tended only to characterize the spectra of bromine. Concentration of Reagent. Hypobromite concentrations in excess of that required for approsimately 50 p.11.m. of ammonia became optically dense, rendering direct measurement of &A impossible with the spectrophotometer being used. M'hen measuring very dilute concentrations of ammonia it was found advisable, although not always necessary, to reduce the amount of excess hypobromite proportionately
1
0.2
The reaction is rapid and quantitative when the p H is approximately 8 0 (4).
1
8
9
IO
II
12
13
PH
Figure 2. Effect of pH on absorbance of hypobromite solutions 324 p.p.rn. NaBrO, 330 rnp
in order to take advantage of the narrower slit widths afforded by the spectrophotomet,er. The stoichiometry of the ammonia osidation reaction appeared to be unaffected by the amount of excess hypobromite. Therefore, sufficient hypobromite is needed to ensure osidation of ammonia in the sample. Ammonia Concentration. Conformity to Beer's law was observed for 1 to 42 11.p.m. of ammonia. A Ringbom plot of the data indicates the optimum concentration range to be 3 to 23 p.p.m. A slight deviation from linearity in the region of 0.5 to 0 p.p.m. of the Beer's law plot is a t least in part attributable to the wide slit settings and stray radiant energy. Both sources of error could be further minimized by reducing the amount of escess hypobromite added to both the sample and reference standard. Ammonia in concentrations less than 1 p.p.m. was determined with 5.0-cm. absorption cells. Beer's law was obeyed under these conditions. pH. .Ilthough the adjustment of p H was not found to be critical, control of this variable was necessary. The broad plateau in Figure 2 estending from approximately p H 11.2 to 12.5 would seem to indicate the existence of a relatively wide range in which to adjust the p H before absorbance measurement's. h s previously mentioned, hypobromite decomposition occurs in solutions when the p H exceeds 11.5 and tends to give high results for ammonia. Temperature. Varying the temperature did not apparently affect the osidation of ammonia over a temperature range from 35' to 15' C. The reaction times were kept constant a t the prescribed 3 minutes for all temperatures with no observable effect on the reaction rates.
Stability. T h e stabilities of hypobromite and hypochlorite solutions were studied a t various pH values by following the decomposition spectrophotometrically for a1)proximately one month. Hypobromite solutions stored at room temperature in air-tight, lightproof bottles showed the decomposition to be less than 107, :after 18 days for solutions buffered between pH 11.2 and 11.7. Solutions buffered a t lower pH values tended to decompose almost completely within several days. Hypochlorite solutions seemed to exhibit essentially the same behavior, except that the decomposiiion rates were somewhat larger than those for hypobromite. I n all cases refrigeration enhanced stability significantly. I n spite of the relative stability of properly buffered hypobromite solutions, it seems advisable to prepare the reagent as needed rather than )use a stored reagent. If stored reagent is to be used, the p H would naturally be adjusted with a buffer a t its masimiim biiffer capacity in order to pr’event pH changes and subsequent decomposition during storage. However, this would introduce some problem in adjustment of the pH of the ammonia oxidation reaction mixture. A more serious objection is the introduction of foreign. materials due to alkali action upon rhe glass storage bottle. The stability of several solutions for the determination of ammonia was investigated under the conditions which might be encountered during the routine determination : AA(5.40 p.p.m. of NH,) 29 2.711.2 1.1 hr. days Initial min. hr. 0.164 0.164 0.164 0.160 0.160 There was no significant change in A A upon standing in borosilicate flasks under normal room conditions after 25 hours. Significant decomposition was observed visually after 4 hours; however, A A values remained essentially constant up to 32 hours, a t which time the deviation from the initial reading was only 0.010 absorbance unit. Diverse Ions. The effect of diverse ions was studied in the determination of 8.95 p.p.m. of ammonia (Table I). A11 cations which form either insolutile hydroxides or phosphate salts exhibited a significant interference. I n the case of some of the a,inphoteric species, such as zinc and aluniinum, appreciably larger amounts could be tolerated when an excess of tripotassium 1)hosphate was added. An increase in the buffer capacity of the phosphate system provided additional hydroxyl ions to form aluminate and zincate ions. hlost of the observed interferences can be removed by a Kjeldahl distillation.
Table I.
Effect of Diverse Ions
(Determination of 8.95 p.p.m. of ammonia)
Substance
Type of interference (over permissible amount) Kone Kone Kegative Negative Negative Negative Xegative Negative Yegative Xegative Negative Negative Postive Sone Sone None Positive Positive None Negative None None Positive Segative Sone Kone Positive None None Kone Positive Positive Positive Positive Positive None
Permissible amount, p.p.m. 12000 1300a
Added as
Ka + K+
0 0
“g+?
Ca Mn+a
0
0 0 0
Fe +a c o+2
Ni c u +% Zn + 2 Cd +%
0 100 1 0
Fe + 3 A1 + 3
F-
c1-
100 1000 1000 260On
KC1 KBr KI NaCN NaC~H302 NaC102 KClOi
BrT-
1 0
1000 50 1000 1000 i_. n
50 1000 1000 1
1000 11ooa 1000 10 0
AsO4-3
Citrate Aniline Hydroxylamine Methylamine ITrea Pyridine a
0
1
0
980
Concentration exceeds nor.mal amount added. Table II.
Statistical Study of Hypobromite Method for the Determination of Ammonia
Detn. No.
No. of detns.
P.p.m. S H 3 added
Av. p.p.m. XH3 found
1 2 3 4 5 6
10 10 10 10 20 10 5 5 5 5 5 5 7
1.70 1.40 5.10 8.50 17.00 25.24 0.17 0.42 0.42 22.42 15.96 8.42 17.38
1,72 3.35 5.04 8.46 16.97 25.28 0.20 0.40 0.41 22.36 15.90 8.42 17.38
7a 80 96 10 11 12
13
Error
Rel. std. dev
+o
02 -0 05 -0 (16 -0 04 -0 03
$0 04
+0 -0 -0 -0 -0
03 02 01 OB 06
-0 04 0 00
1.7 1.5 1.0 0.6 0.3 0.1 8.8 3.1 3.2 0.8 0.0 0.6 0.3
5.0-cm. silica cells and hydrogen lamp source employed. All others employed 1.0cm. silica cells and hydrogen lamp source. 5 0-cm. borosilicate cells and tungsten lamp source employed.
Precision. Determinations 1 through 6 of Table I1 were carried out 15 ith conventional 1 .O-cm. d i c a cell. uqing a hydrogen lamp source, n herea. 7 through 9 repre-ent determination. a t lower ammonia concentration. employing 5.0-cm. cell.. The data for determinationq 7 and 8 \+ereobtained with silica cells and a hjdrogen lamp
source, while for determination 9 borosilicate cells and a tungsten light source were used. Determinations 11 through 13 of Table I1 represent .simples of Detroit tap water, having 0.0 l).i).rn, of ammonia, to which the indicated amount of ammonia was added, distilled, and subsequently analyzed. Determination 13 employed an 8yc IiotasVOL. 36, NO. 9, AUGUST 1964
1801
sium dihydrogen phosphate fixing solution to illustrate its applicability as an ammonia fixing agent, while the other distillations employed a 1000p.p.m. boric acid fixing solution. The per cent relative standard deviation decreases as the concentratioll of am-
mania increases and indicates factory reproducibility.
LITERATURE CITED
( 1 ) Bolleter, W. T., Bushman, C. J., Tidwell, P. W., A N ~ LCHEM. . 33, 592 (1961). ( 2 ) Boltz, D. F., “Colorimetric Determination of Nonmetals)’’ -“Chemical Analysis,” V O l . 8, PP. 86-77 Interscience, New York, 1959. ( 3 ) Chapin, R. M., J . Am. Chem. SOC.56, 2211 (1934).
( 4 ) Kolthoff, I. M., Stenger, V. A,, IKD. ESG.CHEW,ANAL.ED.7, 79 (1935). ( 5 ) Kruse, J. M.1 Mel1on, M. G., CHEM.25, 1188 (1953). ( 6 ) Zitomer, F., Lambert, H. L., Zbzd., 34, 1738 (1962). RECEIVEDfor review March 20, 1964. Accepted April 30, 1964. Pittsburgh
Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 3, 1964.
Ultraviolet Spectrometric Determination of Mixtures of Arylsulfonic Acids J. M. ARENDS, HANS CERFONTAIN, 1. S. HERSCHBERG,’ A. J. PRINSEN, and A. C. M. WANDERS Laboratory for Organic Chemistry, University of Amsterdam, The Netherlands
b Mixtures of arylsulfonic acids in water or aqueous sulfuric acid can b e determined quantitatively by spectrophotometric analysis, based on observation of the ultraviolet absorption of the mixture and of its constituting sulfonic acids. The absorbances of the unknown mixture and of its constituents, measured a t a large number of wavelengths, are subjected to a least squares treatment by an electronic computer. This method seems of general applicability; it is illustrated for mixtures of benzenesulfonic acid and the three isomeric toluenesulfonic acids, for mixtures of benzenesulfonic acid and p- and m-tert-butylbenzenesulfonic acids, and for the system consisting of o-xylene-3- and o-xylene-4sulfonic acids with 0 - and p-toluenesulfonic acids. For all these mixtures very satisfactory analyses were obtained.
T
quantitative analysis of mixtures of arylsulfonic acids in sulfuric acid solution is not very attractive. The difficulties commonly encountered in such analyses have been discussed ( 3 ) . The excellent results obtained in the ultraviolet spectrophotometric determination of the three isomeric toluenesulfonic acids in excess aqueous sulfuric acid ( 3 ) encouraged us to study the applicability of this method to other mixtures of arylsulfonic acids. The principles of the multicomponent analysis have been adequately described (6, 9 ) . The analysis is based on a linear least squares resolution of the absorption spectrum of the mixture to be analyzed in terms of the spectra of the pure components. HE
1 Present address, Mining Research Establishment, Dutch State Jlines, Hoenshroek. The Netherlands.
1802
ANALYTICAL CHEMISTRY
To obtain a high precision in the analysis, it is necessary to determine the absorbances of the mixture and the components a t a number of wavelengths which is large relative to the number of components. The observed absorbances then define an overdetermined system to which, for the evaluation of the unknown concentrations, a least squares treatment by an electronic computer is applied. The applicability of the method depends on the differences in shape of the absorption spectra of the components. The infrared spectrophotometric multicomponent analysis of mixtures of four mononitrofluoroanthenes was recently reported (10). The particular constituents of the arylsulfonic acid test mixtures, as well as their composition, were chosen because of their expected relevance to sulfonation studies planned for the near future. EXPERIMENTAL
Materials. T h e preparation and purification of the three toluenesulfonic acids (11) and benzenesulfonic acid ( 2 ) have been described. The preparation of m- and p-tert-butylbenzenesulfonic acids and of o-xylene-3and o-xylene-4-sulfonic acids will be described in a separate paper (1). Apparatus. The optical measurements were made manually with a Zeiss PMQ I1 spectrophotometer. As a special device, this instrument was equipped with either a sliding or a rotating cell holder. These cell holders, both designed in our laboratory, can accommodate eight and 24 quartz absorption cells of 1-cm. path length, respectively. Procedure. Test mixtures were made bj- mixing appropriate amounts of standard solutions of the pure arylsulfonic acids. The concentrations of the standard solutions, and consequently those of the constituents in
the mixtures, were chosen so as to have maximum absorbances between 1.0 and 1.6 in the wavelength region employed. Absorbances of the test mixtures and of the reference solutions were measured at some 25 to 40 equidistant points in the wavelength region 240 to 300 mh, as nearly simultaneously as possible for any given wavelengthe.g., within 3 minutes for eight cells. CALCULATIONS
The X1 computer (8)was programmed to express the observed spectrum of the mixture as a linear combination of the simultaneously observed spectra of the reference solutions. The linear combination sought is best in the least squares sense; its coefficients represent the relative concentrations of the several components of the mixture when the known absolute concentrations of the references represent unity. Moreover, the calculations yield a mean square residual, 8 , which is a measure of the unexplained variance of the residuals-Le., that part of the absorbance of the mixture that cannot be accounted for as a linear combination of the reference absorbances. 8 is calculated as:
where n is the number of coefficients sought and r, are the residuals; the summation extends over all k wavelengths of observation. I n view of the assumption of a constant background absorbance, A A , n is one greater than the number of components analyzed. The mean square residual, 8, is of twofold interest. In the first place, it may serve to calculate l,the mean square estimated error per observation of absorbance. The relation between t* and 8 is:
