Determination of Arsenic in Biological Material W. T. OLIVER and H. S. FUNNELL Department of Phyziological Sciences, Ontario Veterinary College, Guelph, Canada
b A method i s described for the determination of arsenic in animal and plant tissue. The homogenized tissue was mixed with concentrated hydrochloric acid in a flask fitted with a cold finger condenser and heated on a water bath until the sample had liquefied. The arsenic was distilled from the solution as arsine and a b sorbed on mercuric iodide. The absorbed arsenic was eluted with iodine solution and the arsenic content determined b y development of the heteropoly blue of arsenic. The method has been tested in a range from 0 to 50 y of arsenic.
E
the deterniination of arsenic have used n-et osidation or ashing procedures. The present riirthod is more rapid than either of these :inti the tissue digestion and arsine e ~ o l u t l o nare carried out in a single w-v!. This procedure has been applied TIJ brain, liver, kidney, hair, skeletal muscle, and a commercial cattle f e d with good recoveries and reproducihlc rrsults. The absorption of arsine b\- other mercury 11,'1 I'd 1 es on paper or i n solution has been described ( 1 , 3, 4). Attempts to apply the method of Berkhout and Jongen (3) resulted in inconsistent recowrips of aisenic added to tissue as arsenic trioxide.
Table I. KO.
of
Trials
5 5
5 5 5
6
5 5
~ R L I L R~ncthocisfor
REAGENTS
Hydrochloric Acid, concentmtetl reagent grade. Potassium Iodide. Dissolve 3 gr:ms of potassium iodide and make up to 10 nil. with watrr. Prepare frrsh before use. St'annoiis Chloride. Dissolve 20 grams of stannous chloride in 16 nil. of concentrated hydrochloric acid and makr up to 50 nil. \vitli water. l\Iercuric Iodide, purified. Mix nierciiric iodide thoroughly n i t h ~n excess of 0.0015 iodine solution, filter, nnsh tliorouglily with cold distilled water, riiise viith alcohol anti rther, and air dry. Absorption powder. Dissolve 100 nig. of' purified mercuric iodide in IO nil. of acetone, niix n-c4l xi-ith 1 gram of ccllulosr powder. and evaporate the acetone iinclcr a current of wirm air stirring conbinuonsly. Lead acetate, 10% aqueous. Tween SO, 1 to 1000 solution. Octyl alcohol. Zinc metal, ZO-n~esh,arsenic-free.
Recovery of Arsenic
Figure 1. Flask fitted with cold finger condenser
Stock Iodine Solution, 0.025. Mix 2.54 grams of iodine and 8 grams of potassium iodide with a mininlunl amount of n ater and n hen dissolved make u p to 1 liter and store in a dark bottle. Prepare fresh every 2 n-eeks. Alginate (Dariloid, K . R., Chas. Tennant Co., Toronto, Ont.). Iodine Solution, 0.001N. Dissolve 10 mg. of alginate in 60 ml. of water by heating to 70" C. and cool to room temperature. Add 5 ml. of 0.02S iodine solution and make up to 100 nil. with water. Prepare fresh before use. Ammonium Molybdate Solution. Stir 14 ml. of concentrated sulfuric acid into 60 ml. of water and while still hot add 1 gram of powdered ammonium molybdate. Stir until dissolved, cool, and make up to 100 ml. nith water. Prepare fresh before use. Hydrazine Sulfate, 0.15% aqueous solution. Prepare fresh before use. METHOD
TTeight 1 gram of macerated sample into a 125-ml. extraction flask. Add I 5 ml. of concentrated hydrochloric acid, insert the condenser system, and heat the flask on a steam bath for 1 hour after the sample has liquefied. Rinse the cold finger condenser (Figure 1) with five 10-ml. portions of distilled water into the extraction flask. Remove the flask and cool to 25" C. in a constant temperature bath. Add 2 ml.
Added 0 1 5 10 20 30
0 0 0
0 0
40.0 50.0
Arsenic, y Recovered Std. h v . dev. Range 0 1 5 10 20
0 0 50-52 0 0 1 9 5-10 5 0 0 5 2 0 45 19 5-20 5 30 4 0 52 29 0-31 0 39.8 0.68 39.0-40.5
49.9 0.89 49.0-51.0
of potassium iodide qolution. 3 drops of stannous chloride solution, niiu thoroughly, and let stand for at least 15 minutes. Plug the base of the scrubbing tube A with cotton hatting and fill with fine silica sand. Moisten the sand with 10% lead acetate solution and remove excess nith light suction. Place a small plug of batting in the absorption tube B and by tapping the tube end, gently pack in 0.15 gram of absorption powder, follon-ed by 0.15 gram of mercuric iodide. Lubricate the joints liberally with stopcock grease and clamp with elastic bands. After 15 minutes, add 1 ml. of Tneen 80 solution and 7 to 8 drops of octyl alcohol to the flask; add 5 grams of zinc through a powder funnpl and insert the absorption system. Leave in a water bath a t 25" C. for 1 hour. Elution. Remove the absorption t u b e from t h e apparatus a n d insert i t into t h e neck of a IO-ml. volumetric flask. Elute t h e powder with four 2-ml. portions of 0 . 0 0 1 5 iodine solution, blowing t h e last few drops into t h e flask. Color DeveloDment. Add 1 nil. of molybdate reagknt and mix; add 0.4 ml. of hydrazine sulfate solution, mix, and insert t h e flask in boiling water for IO minutes with occasional shaking. Remove and cool rapidly under running water. M a k e u p t o volume n-ith water, stopper, and mix b y inversion. Read in a spectrophotometer at 720 nip or a Klett-Summerson colorimeter with a No. 69 filter, in eithei case using a reagent blank. I
RESULTS
Known amounts of a stock solution of arsenic were added to 1-gram samples of macerated tissue and treated as described, The results are given in Table
I. DISCUSSION
It has been reported that complete VOL. 31,
NO. 2, FEBRUARY 1959
259
oxidation is not necessary for the full recovery of arsenic from animal tissue (6). However, when hydrochloric acid digestion of animal tissue was carried out in an open vessel, the recovery of arsenic vias always low. The modified digestion apparatus (9) permits tissue solution while maintaining a n upper internal temperature below the volatilization point of arsenic trioxide ( 2 ) and arsenic trichloride (IO). Kingsley and Schaffert (6) found that when reflux was used during the tissue digestion, less than 50% of the added arsenic was recovered because of the retention of hydrogen sulfide and other mercapto (-SH) groups in tissue 1% hich combined n i t h arsenic and prevented its distillation. The concentration of mercapto groups in 1 gram of tissue is too low in relation to the amounts of arsenic detectable by this method to produce any significant loss of the metal. Following digestion, the arsenic is
evolved as arsine and collected on cellulose containing mercuric iodide overlayered with mercuric iodide. The arsenic is eluted with iodine solution from the resulting mercury-arsenic compound, probably as arsenic acid. Alginate is incorporated in the eluent to act as a stabilizer for the colloidal molybdenum blue which is ultimately developed; without it the concentration curve is discontinuous above 25 y. The reaction between arsenate, niolybdate, and hydrazine sulfate has been reported by several workers (5, 7 , 8). The color is stable for a t least 1 hour and obeys Beer’s law for the limits investigated in this work.
ACKNOWLEDGMENT
The authors acknowledge the technical assistance of Gerrie Smeenk and E. J. Dillistone.
LITERATURE CITED
(1) Assoc. Offic. Agr. Chemists, “Official Methods of Analysis,” 7th ed., p. 369,
1950.
( 2 ) Baster, G. P., Bezzenberger, F. K., Kilson, C. H., J . Ana. Chem. SOC.42,
1386 (1920). (3) Berkhout, H. K.,Jongen, G. H., Chenzst Analyst 43 (3)) 60 (1954). (4) Cassil, C. C., Wichmann, H. J., J. Sssoc. Ofic. Agr. Chemzsts 22,436 (1939). (5) Chaney, A. L., Magnuson, H. J., IVD. ESG. CHEJI., h x a ~ . ED 12, 691 (1940). (6) Kingsley, G. R., Schaffert, R. R., -4x.4~.CHEJL 23, 914 (1951). ( 7 ) Magnuson, H. J., Watson, E. B., IND. ENG. CHEM., ASAL. ED 16, 339 (1944). (8) llorris, H. J., Calvery, H. D., Ibid., 9, 447 (1937). (9) Oliver, W. T., Funnell, H. S., Am. J . Vet. Research, in press. (10) Taylor, F. S., “Inorganic and Theoretical Chemistry,” 3rd ed., p. 570, William Heinemann, London, 1935. RECEIVEDfor revien- Apiil i , 1958. Accepted September 8, 1958.
Determination of Carbonyl Compounds JAMES S. FRITZ, STANLEY S. YAMAMURA,I and EVELIN CARLSTON BRADFORD lnsfifute for Atomic Research and Department of Chemistry, Iowa State College, Ames, Iowa
b Some principles of quantitative oximation with hydroxylammonium salts are discussed, and a simple, accurate method is proposed for determining aldehydes and ketones. The carbonyl compound is oximated in methanol-2-propanol solution, and the excess hydroxylamine is titrated with standard perchloric acid. Unlike most oximation methods, the end point in this titration (determined either visually or potentiometrically) is very sharp. All reagents are stable on storage.
D
of aldehydes and ketones b y osimation is probably the most satisfactory general method. Early work by Walther (14), Bennett ( I ) , Bennett and Donovan (2), Stillman and Reed ( I @ , Schultes ( I I ) , Bryant and Smith (S), Montes and Grandolini (9), Trozzolo and Lieber ( I S ) , and Knight and Swern (7) is significant. The Bryant and Smith method has been widely used for many years, although Higuchi and Barnstein (6) have recently pointed out that the end point is very poor. Metcalfe and Schmitz (8) used a ETERMINATION
1 Present address, Atomic Energy Division, Phillip8 Petroleum Co , Idaho Falls, Idaho.
260
ANALYTICAL CHEMISTRY
hydroxylamine solution, prepared in situ by mixing approximately equal molar proportions of hydroxylammonium chloride and octadecenylamine, for the analysis of high molecular weight ketones. Fon ler, Kline, and Mtchell ( 4 ) determined vanillin in the presence of acetovanillone by controlling the reaction time. Higuchi and Barnstein ( 5 ) investigated hydroxylammonium acetate as a reagent for aldehydes and ketones. The oximation vias performed in glacial acetic acid and the excess reagent n as titrated potentiometrically with perchloric acid. Although a n excellent break a t the equivalence point was observed for samples of aromatic ketones or aldehj des, the potentiometric curves for the lower aliphatic carbonyl compounds were considerably poorer, owing to the basicity of the oximes. Pesez (IO) recently proposed the use of a methanolic solution of hydroxylammonium formate for quantitative oximation. The excess reagent is titrated to a thymol blue end point with perchloric acid in dioxane. The carbonyl procedure described is simple, convenient, and accurate, and eliminates or minimizes the difficulties of existing methods.
Dissolve approximately 22.5 grams of freshly distilled 2-dimethylaminoethanol (Eastman Chemical Products, Inc., white label or equivalent) in 2-propanol to make 1 liter of solution. Hydroxylammonium Chloride, 0.4M. Dissolve 27.8 grams of the pure salt in 300 ml. of absolute methanol and dilute to 1 liter with 2-propanol. ?-Propanol. Reagent grade. absolute. Martius Yellow. Diwolve 0.0667
REAGENTS
Figure 1. Titration of blank showing indicator transition ranges
2-dimethy laminoethanol ,
0.2531.
pC0
51
2’ I, zi
YPRTIUS
YELLOW
and
MET-YL
j
V’OLET
~
“E..OW’
ml
of 0 2 Y
red,
