406
ANALYTICAL CHEMISTRY Table I.
Results for Various Standard Samples Sample Weight
Material
Grams
NBS standard sample of steel 15d (0.054’% Cu) NBS standard sample of steel 8g (0.019% C U I New Jersey Zinc Co. ZnS‘
FeS 5
+ Zn. 1: 350
Sulfur Found
Sulfur Found
Accepted Value
Mg.
%
%
2.0561 2.0668 3.4072
0.650 0.657 1.084
0.0316 0.033-0.034 0.0318 0.0318
2.1192 4.7387 0.00128 0.00260 0.00401 0.7029 0.7622 3.0091b
0.532 1.180 0.422 0.855 1.321 0.748 0.806 3.195
0.0251 0.025-0.026 0.0249 32.90 32.90 32.87 32.95 0.1063 0.106-0.107 0.1057 0.1062
Weighed on microbalance and mixed with 1 to 2 grams of zinc dust.
b 50 ml. of KOCl solution with 7 grams of
KOH.
reaction is primarily between undissociated acids, in another between the ions, and in intermediate ranges partly betn-een acids and partly between ions of varioue types. As stereochemical conditions probably are important for the choice of mechanism, the reaction path may be strongly affected by a slight change in pH. 4. Colloidal sulfur is more rapidly oxidized by hypochlorite in a strongly basic than in a neutral solution. The over-all yield of oxidation as shown in Figure 2 may be a result of a combination of the various factors mentioned above. A tentative explanation for the incomplete oxidation would then be initial formation of sulfoxylic acid or its ion, Tvhich may react further according t o the scheme outlined under point 2. The peak a t 20’ C. for pH 12 still represents an open question.
solution has t o be acidified before titration, a buffer may require unreasonable amounts of acid for acidification. The best results were obtained in the very basic range, and as standard basicity an addition of 3.5 grams (26pellets) of potassium hydroxide per 25 ml. of solution was used. This corresponds t o a 2.5 N potassium hydroxide solution, and a pH of about 14.4. Various sulfides of known sulfur content and two Bureau of Standards steel samples were tested. The results of these analyses are listed in Table I. It is apparent from the data given in Table I t h a t under the right conditions this is a sensitive and accurate method. Its limitation for steel analysis lies in the fact that sulfur in steel may be present as sulfides, which are not soluble in acids. For example, steel 15d, for which slightly too lox values were found, contained as much as 0.054% of copper. Steel 8g, on the other hand, contained only 0.019% copper and the analysis showed a perfect agreement with Bureau of Standards values. SUMMARY
The oyidation of hydrogen sulfide with potassium hypochlorite was studied as a function of temperature and pH of the hypochlorite solution. Nearly quantitative oxidation t o sulfate was obtained in the pH ranges from 8 t o 11 and from 14 t o 15. At intermediate pH values the oxidation was incomplete, and a t 0’ C. and pH around 12 the least oxidation was found, corresponding t o the average exchange of 4 electronsper atom of sulfur. The products of oxidation were, in this range, a mixture of sulfate and rolloidal sulfur. The most favorable solution for the analysis of microgram quantities of hydrogen sulfide was found t o be hypochlorite in a 2.5 X potassium hydroxide solution, corresponding to a pH of about 14.4.
ANALYTlCAL APPLICATIONS
ACKNOWLEDGMENT
The incomplete Oxidation and poor reproducibility which were experienced when a solution of commercial bleaching powder was used as oxidizing agent may now readily be understood. Such a solution has a pH near 12. For analytical work the ranges between pH 9 and 10 and between 14 and 15 seem t o give the best possibilities. Attempts to work out a useful method in the lower basicity range were not very successful. It is difficult t o adjust the pH of the solution t o be just right. Some sulfuric acid is formed by the reaction and some hydrochloric acid may come over from the evolution flask and cause a large change in the pH. It might be possible t o add an appropriate buffer t o maintain correct basicity, but since the
The authors are indebted t o S . H. Xachtrieb for valuable suggestions and criticism. LITERATURE CITED
(1) Kitchener, J. A., Bockris, J. O’hl., and Liberman, A,, Discussions Faradau SOC.,4, 57 (1948). (2) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” p. 538, New York, Macmillan Co., 1947. (3) Ibid., p. 634. (4) Latimer. W. M.. “Oxidation States of the Elements and Their Potentials in Aqueous Solutions,” pp. 64-74, New York, Pren-
tice-Hall, 1938. ( 5 ) Pepkowitz, L.. ANAL.CHEM.,20, 968 (1948). RECENEDJ u n e 15. 1951.
Spectrographic Determination of Beryllium in Urine and Air R. G. SMITH, Bureau of Industrial Hygiene, Detroit Department of Health, A. J. BOYLE, Wayne University,
W. G . FREDRICK, Bureau of Industrial Hygiene, Detroit D e p a r t m e n t of Health, AND BENNIE ZAK, Wayne University, Detroit, Mich.
T
HE recognition of beryllium as an extremely toxic metal when inhaled in minute quantities has stimulated analytical research directed a t the accurate estimation of submicro amounts of this metal in air and urine. Various spectrographic procedures have been described in recent years (1,3, 4 , 67, all of which employ the direct current arc. A fluorometric method using morin, which achieves the desired sensitivity by using large quantities of urine, has also been described ( 5 ) .
The present study was undertaken in an effort t o develop a somewhat more rapid method, of acceptable accuracy and sufficient sensitivity t o permit use of the relatively small samples of urine and air that might be collected routinely in beryllium-using industries. It was further desired to utilize an alternating current spark technique for solution analysis, on which research has been in progress for the past 2 years. This technique, which utilizes the -4pplied Research Laboratories rotating electrode assembly,
V O L U M E 2 4 , NO. 2, F E B R U A R Y 1 9 5 2
Beryllium has been demonstrated to be extremely toxic to man when inhaled in less than microgram amounts. This high order of toxicity hasnecessitated much more sensitive analytical methods than any previously in use, if tedious concentration procedures are to be avoided. In a rapid spectrographic method for determining hygienically significant amounts of beryllium in urine and air, suitably prepared solutions are analyzed directly by means of
has been described for the determination of various metallic constituents in human plasma and urine (2, 7 ) . REAGENTS
All reagents are analytical grade, except where otherwise indicated. Nitric-Perchloric Acid Mixture. Add 3 volumes of nitric acid to 1 volume of 72% double-distilled perchloric acid. Manganese Chloride Solution. Dissolve 1 gram of manganese chloride tetrahydrate in 100 ml. of distilled water. Aluminum Internal Standard Solution. As described by Barnes ( f ) , dissolve 0.750 gram of metallic aluminum in approximately 10 ml. of 1 to 1 hydrochloric acid and make up to 500 ml. with distilled water. 0.25" h
END SIDE Figure 1. Assembly
Standard Beryllium Solution. As described by Barnes ( I ) , dissolve a weighed amount of fused metallic beryllium in a emall amount of 1 to 1 hydrochloric acid and dilute to volume with 1% hydrochloric acid, using a microburet and volumetric flasks. Standard solutions containing 0.01 and 0.001 microgram of beryllium per ml. have been used. Ethylenediaminetetraacetic Acid Solution. The tetrmodium salt of this acid, available commercially as Versene liquid, 34% solution, Bersworth Chemical Co., has been found satisfactory. Analytical reagent grades of similar compounds are available.
407
a rotating electrode using an alternating current spark; errors average about 10% of the amount present. Several direct current arc spectrographic procedures of the necessary sensitivity are cited, but no alternating current spark procedures have been published. The reduced number of manipulations afforded by the solution technique, with the inherent accuracy of the alternating current spark, ensures accuracy, speed, and ease of determifiation.
fumes of perchloric acid, and continue heating until a moist white residue of salts remains. Remove the beaker from the hot plate and allow to cool. This ashing has been found completely satisfactory for all urine encountered to date, and is somewhat less troublesome and time-consuming than other methods of ashing which were tried. To the cooled beaker add about 25 ml. of distilled water, and warm till all salts are in solution. Transfer the solution and beaker rinsings t o a 50-ml. conical tipped rentrifuge tube, and add 2 drops of phenol red indicator. By means of a small dropper, add 25% sodium hydroxide solution until the first color change of the indicator is definite and formation of reci itate is imminent. Continue the neutralization with 1% so8um fiydroxide solution until 1 drop produces a permanent preci itate. It is not necessary nor desirable to recipitate all the pEosphates a t this point, for Barnes ( 1 ) has &own beryllium to be quantitatively precipitated when only a fraction of the total phosphate is precipitated with ammonia; the same has been found true with sodium hydroxide. If too much precipitate is formed, add 1 drop of hydrochloric acid, and repeat the neutralization with dilute sodium hydroxide. Centrifuge for 2 minutes a t 2000 to 2500 r.p.m. and decant the supernatant liquid. Dissolve the precipitate with 1drop of hydrochloric acid and 25 ml. of hot distilled water, and add 2 drops of henol red. Stir t o dissolve the precipitate completely and a d f 1 drop of 34% Versene solution. Seutralize to the first appearance of the alkaline red color of the indicator, using 1% sodium hydroxide solution. ?io precipitate should appear a t this point, but should one form, dissolve with a drop of hydrochloric acid, add a drop of Versene solution, and again neutralize as previously directed. Carefully add 1% manganese chloride solution from a buret or dropper, mixing thoroughly after each addition, until the first permanent precipitate persists, as evidenced by a faint turbidity of the solution. Beryllium is satisfactorily collected with the least amount of precipitate detectable, so large precipitates are unnecessary. Centrifuge for a t least 5 minutes a t 2000 t o 2500 r.p.m., or until the supernatant liquid is perfectly clear. Decant as completely as possible, using a filter paper to remove liquid clinging to the tube when inverted. Add 1 drop of hydrochloride acid and 2.0 ml. of aluminum internal standard solution, and swirl to dissolve the precipitate completely. Particles of silica which may be present do not interfere. The solution is now ready for sparking.
CHEMICAL PROCEDURE
Each series of urines should include a blank specimen, obtained from someone known not t o be exposed t o beryllium. Standard series are likewise prepared, with appropriate additions of standard beryllium solutions to normal urine. Air Samples. Air samples are most satisfactorily obtained with an electrostatic precipitator of the type made by the Mine Safety Appliances Co. At the usual sampling rate of 3 cubic feet per minute, a 10-minute sampling period is ample when hygienically significant amounts of beryllium are present in the air, and 20- or 30-minute samples are sufficient for detecting as little as 0.001 microgram of beryllium per cubic meter of air. Filter paper samples may be obtained if desired, but these must first be ashed, and in general offer no compensating advantages. Samples obtained with an electrostatic precipitator are treated as follows.
Urine Samples. Transfer 50 ml. of recently voided urine to a 250-ml. beaker and add 20 ml. of nitric-perchloric acid mixture. If urine has aged to any extent, acidify in the original container with hydrochloric acid until a clear solution is obtained. Make suitable volume correction for the acid thus added. Cover the beaker and place on a hot plate a t medium heat. After the water has evaporated and vapors of nitric oxide are being evolved, increase the temperature of the hot plate just sufficiently to form
Rinse the precipitator tube walls with 95% ethyl alcohol from a wash bottle, then scrub xith a rubber-tipped glass rod, and repeat this procedure with small rinses until all collected matter is removed, catching the washings in a 100-ml. beaker. Use about 50 ml. of alcohol. Evaporate this solution to dryness, add 5 ml. of 1 to 1 hydrochloric acid, and again evaporate to dryness. To the dry residue add 1 drop of hydrochloric acid and 4.0 ml. of aluminum internal standard, warm gently, and spark a 2.0-ml. aliquot,
SPECTROGRAPHIC EQUIPMENT
Applied Research Laboratories. 1.&meter grating spectrograph, rotating electrode assembly, 220-volt alternatinv current spark source, Universal arc-spark stand with cylindrkd lens, and densitometer.
ANALYTICAL CHEMISTRY
408 as directed under spectrographic procedure. Dilute the remaining 2.0 nil. with aluminum internal standard solution if the amount of beryllium present is too great for the usual working curve range.
Table I. Be Added,
Be Found, 7
0.004 0,005
0.006 0.007 0.007
0.010
0.010 0,007 0.011 0.021 0.034 0.034 0.025 0.035 0.040 0.065 0.047
Av.
0.020 0.030 0.040 0,050
SPECTROGRAPHIC PROCEDURE
+50 +40 +40 43 0 -30 10 + 5 +13 13 - 16 13
+ + -
-20 +30
-6
14
I n Air Samplesb 0,004 0.004 0,005
The upper electrode is a standard 0.25-inch (0.6-em.) spectrographic carbon of the Kational Carbon Co., tapered, and with rounded tip. The lower electrode is a graphite wheel 0.5 inch in diameter, 0.1 inch thick, vith a hole 0.125 inch in diameter drilled through its center. A graphite rod 0.125 inch in diameter is inserted in the hole until its end is flwh w-ith the face of the wheel. The other end of this shaft is inserted into the rotating holder, and adjustment is made to piare the wheel directly beneath the upper electrode. The gap is adjusted to 0.15 inch and the lower electrode rotated a t 5 r.p.m.
- 25 - 25
0.003
0.003 0,004
- 20 AV.
0.010
0.020 0.030
/
0.050
0.010 0.011 0.014 0,009 0.009 0.009 0.019 0.036 0.028 0.028 0.031 0.025 0,052
23
+ 100 $40
- 10 - 10 - 10
-5 +20
-7 -7
+3 16 +4 10 -4 -4 -6 10
-
+
0.055 0.048 0.048 0.047
Av.
Total volume of internal standard solution added was 2.0 ml. for all samples. b Total volume of solution sparked was 2.0 ml. for all ssmples. a
Be in AIR,
2.00 2*40
yo Error
Av.
The electrodes are arranged in the ARL rotating electrode assembly as follows.
t
Determination of Beryllium I n Urine0
The above procedure has been satisfactory for all samples which the authors have had occasion to run, but is obviously not satisfactory for the analysis of air samples containing beryllium compounds insoluble in hydrochloric acid. When it is known that such compounds are to be collected, a preliminary fusion or dig=tion should be performed which is capable of rendering the beryllium soluble, after which the sample may be treated 88 a urine in order to separate the salts thus acquired.
Working Curve
7
RESULTS
.20 I-
1
Table I summarizes the determination of beryllium in a number of standard urine and air samples which were prepared as described in the procedures; all values were included. It is apparent that greatest accuracy is achieved when the amount of beryllium in the solution being sparked is greater than 0.005 microgram per ml. As shown in Table I, the average error for a urinary analysis is 14% of the amount present on the range 0.005
o.40/
01 0
I I
I
2
I 3
I 4
I 5
I
x IO-' microgram ~ e / mi. 2 eol'n
Figure 2.
Working Curve
Figure 1 shows :t sketch of the assembly. The electrode dimensions have not been found to be critical, and satisfactory %%heels may be made by appropriately cutting and drilling 0.5-inch Sational Carbon Co. electrodes. Wheels thus made should be purified by treating for several days with hot hydrochloric acid, and rinsing thoroughly. The spark source i. set a t full inductance, and %-volt primary voltage. The electrodes are pres arked for 55 seconds. The sample solution is then transferre$ to a small glazed porcelain conibustion boat of about 2-ml. capacity, which is placed on the platform beneath the rotating electrode. The platform is raised until the wheel is immersed in the solution as far as possible. The solution is then presparked for 25 seconds, the electrode gap is readjusted, and the film is exposed for a 55-3econd sparking interval. Another exposure is usually made, although with smaller solution volumes; thi? can be omitted, if the working curves are made from single exposure ratios. The densities of Be 3130.4 -4. and AI 3059.9 A. are measured on the densitometer, and the ratios determined in the usual manner. Be 3131.2 A. may be used when the amount of beryllium in the qolution exceeds about 0.01 microgram, and is the preferred line due to the absence of any background line. Typical working curves are shown in Figure 2.
to 0.025 microgram of beryllium per ml. of solution sparked. Such concentrations correspond to 0.2 to 1.0 microgram of beryllium per liter of urine if a 50-ml. aliquot of urine is used, and thevolume of the solution sparked is 2.0 ml. Similarly, if 100 ml. of urine are originally taken, and the h a 1 volume of solution sparked is only 1.0 ml., the urinary concentrations would be 0.05 to 0.25 microgram of beryllium per liter. Lesser amounts of beryllium have been determined, down to as little as 0.002 microgram of beryllium per ml. of solution sparked, but such results may be in error by 40 to 50%, as shown. Greater accuracy is attainable with air samples, for the obvious reason that less manipulations are performed upon the sample. Thus, in the range 0.005 to 0.025 microgram of beryllium per ml. of solution sparked, an average error of 10% is obtained, while in the lower range-Le., down to 0.002 microgram of beryllium per ml.-the error is about 20% of the amount present. Lesser amounts may still be detected, but accuracy is erratic and uncertain. DISCUSSION
The isolation of beryllium from urine described by Barnes et a / . Many samples were run on the dissolved phosphate precipitate obtained by a single precipitation with ammonia. It was evident that tht. calcium and magnesium phosphate present restricted the lon-et (1) appeared to be the most satisfactory starting point.
V O L U M E 24, NO. 2, F E B R U A R Y 1 9 5 2 limit of detection to about 0.4microgram per liter, and means were therefore sought t o extend the sensitivity downward to t h a t attainable with pure beryllium standards. The preferential chelating ability of ethylenediaminetetraacetic acid on calcium and magnesium a t a neutral pH appeared promising. Previous work in these laboratories showed this compound to have virtually no chelating power toward beryllium under these conditions. Manganese was chosen to serve as a gathering agent, as it is only moderately complexed by ethylenediaminetetraacetic acid and a t the same time yields a gelatinous precipitate with alkali. It was found possible to precipitate a very minute quantity of manganese phosphate by this procedure, which on sparking proved to contain virtunlly all of the beryllium and yield intensities comparable to those attainable with pure beryllium solutions. Varying amounts of manganese phosphate precipitate do not depress beryllium line intensities. Of the several metals tried as internal standards, aluminum gave most satisfactory results. .4relatively week reference line of aluminum was chosen to avoid the pclssibility of error due to extreneous sources of this metal in uri le and reagents. S o interferences due to manganese or other variables were manifest in this line. What appears t o be a water bar d spectrum presents a faint line a t 3130.4A. This primarily acco ints for the failure of blank sample ratios to pass through zero. 'Phis background line is sufficiently constant to permit the estbnation of beryllium on the concentrations cited. For concentratj on greater than 0.005 micro-
409
gram of beryllium per ml., Be 3131.2 A. may be used instead of 3130.4 A. Other beryllium lines may be used for greater concentration than those described, the most useful of which has been found to be Be 2348 A. This line first appears a t a concentration of about 0.005 microgram of beryllium per ml. When it is desired to extend the lower limit of detection of beryllium in urine, 100-ml. samples of urine may be handled if larger centrifuge tubes are used, a6 difficulty may be experienced in keeping potassium perchlorate in solution. Limiting the final volume of solution sparked to 1 ml. further increases the sensitivity of the method. LITERATURE CITED
Barnes, E. C., Piros, W.E., Bryson, T. C., and Wiener, G. W., h . 4 ~ CHEM., . 21, 1281 (1949). Boyle, A. J., Whitehead, T., Bird, E. J., Batchelor, T. hf., Iseri, L. T., Jacobson, S.D., and Myers, G. B., J . Lab. Clin. Med., 34, 625 (1949). Cholak, J., and Hubbard, D. M., ANAL.CHEY.,20, 73 (1948). Ibid., p. 970. Klemperer, F. IT., and Martin, A. P., Ibid., 22, 828 (1950). Peterson, G. E., Welford, G. A., and Harley, J. H., Ibid., 22, 1197 (1950). Smith, R. G., Craig, P., Bird, E. J., Boyle, A. J., Iseri, L. T., Jacobson, S. D., and Myers, G. B., Ana. J . Clin. Path., 20, 263 (1950). RECEIVED July 19, 1961. Presented before the Division of Analytical Chemistry at the 119th Meeting of the AVERICANCHExrcAL SOCIETY,Boston, Mass.
Photometric: Determination of Microquantities of Arsenic CLARK E. BRICKER AND PHlLIP B. SWEETSER Princeton University, Princeton, N . 3.
Comparatively few applica .ions of the photometric method for detecting the t nd points in volumetric determinations have been recorded. No previous use of the ultraviolet regicn of the spectrum or of the Beckman spectrophbto neter has been found for the determination of photometric end points. Ceric ions show a strong absoiption band at 320 mp, whereas cerous, arsenious, and arsenic ions do not absorb at this wave lengti. With an inexpensive titration cell for use on tlie Beckman DU spectrophotometer, it is possible to detect the end point photometrically in the titrr tion of microgram quantities of arsenious acid with ceric sulfate. The ac-
N
UMEROUS applications of the photometric titration
principle have been cited in 1. review by Osburn, Elliot, and Martin ( 4 ) . Later work may be found in the bibliography of a paper by Goddu and Hume ( 1 ) . This work was almost exclusively done with a special oorimercial photometer. The adaptation of the Coleman Model 1i spectrophotometer for use in photometric titrations was desci ibed by Goddu and Hume ( 1 ).
Xo previous reference has been found to the use of the ultra-
violet region of the spectra for photometric titrations, where the molar extinction coefficients for many volumetric reagents have their maximum value. The application of the ultraviolet region t o photometric titrations should lead to a greatly increased sensitivity, better adherence to Beer's law, the use of more dilute
curacy of these determinations is 1 to 2 parts per thousand. The preparation and stability of very h') ceric sulfate solutions have been studdilute ied and a method for preparing a solution which is stable for at least 2 months is described. As the photometric determination of the end point in the determination of arsenic with a standard ceric solution eliminates the use of indicators and of indicator errors, and also obviates the necessity of titrating to the exact end point, this method is very accurate and rapid. Use of the ultraviolet region of the spectrum for photometric titrations suggests many more applications of this method.
volumetric reagents, and a greatly increased number of volumetric reagents which show no strong characteristic absorption in the visible region of the spectrum. The advantages of working in the ultraviolet region are verified in this paper, where a very dilute ceric(1V) sulfate solution is used for the determination of micro quantities of arsenic. APPARATUS
The Beckman Model DU spectrophotometer, being one of the most widely used spectrophotometers and having a useful wavelength range of 220 to 1000 mM, was chosen for this work. The adaptation of this instrument for use in photometric titrations was very simple and inexpensive. .4 titration cell was made along the lines described by Goddu and Hume ( I ) , except that a rrctangular tube (1 8 X 3.0 cm ) was
