V O L U M E 26, N O . 8, A U G U S T 1 9 5 4 Effect of Reagent Concentration on Error. Absorption curves for complexes obtained with dilute and concentrated reagents are shown in Figure 2. For curves 1, 2, and 3 dilute (81 volume %) sulfuric acid was used in the reagent. Curves 1, 2, and 3, respectively, are typical for pentose alone (150 y anthronated arabinose), hexose alone (75 y anthronated glucose), and the mixture of arabinose and glucose (the same concentrations as for curves 1 and 2 ) mixed before anthronation. They indicate some mild interaction, for the total absorption of the mixture is greater than can be accounted for with the absorption contribution from the individual components (curves 1 and 2). The wave length of maximum absorption, hoir ever, remains unchanged a t 625 mp. For curves 4 and 5 concentrated (96.4 volume yo)sulfuric acid was used in the reagent. Curve 4, typical for a mixture of pentoses and hexoses, was obtained from independently anthronatcd solutions of arabinose (300 y ) and glucose (150 y ) , mixed to same concentration as curve 5, just before the measurement. Curve 5 was obtained when arabinose (150 y ) and glucose (75 y ) were mixed before anthronation. The effect of the concentrated acid on interaction betM-een pentose and hexose is drastic. Deviation of curve 5 from curve $ indicates a change in maximum absorption by some 50 mp and also a great increase in absorbance of the solution. I n each case and for all curves, final concentration of anthronated sugars was 150 y of arabinose and/or 75 -i of glucose in 12 ml. of solution. The measurements of actual interference by pentoses are shown in Table 111. These results indicate that the error was increased rapidly as the strength of the acid in the reagent was increased; also, the percentage error vias less with weak sugar solutions than with strong ones for any given concentration of acid. Keaker solutions also have the advantage that the 625 mp tiansmittance filter works more effectively than with stronger solutions. Thus an error of approximately 50yo with a high sugar and a high acid concentration can be reduced t o less than
1333 10% using sugars in the same ratio, but a t only one quarter of the concentration, and acid of 81 volume % instead of 96.4 volume %. These data show that it is desirable t o use a considerably less concentrated acid than that used in hexose determination when hexoses are being estimated in a hexose-pentose mixture, and also, that there is an advantage in using weaker sugar solutions. As the concentration of acid is decreased, increased time is requircd for good color development and this too may increase the pentose interference. I n practice, 81 volume % ' acid with a slight increase in both time and temperature gives satisfactory results. For plant material, semiquantitative chromatographic determination of pentose offers a simple means of assessing error; this approach has been used extensively and was found expedient. ACKNOWLEDGMENT
The author wishes to express thanks to Charles \Vilson, DiviPion of Plant Industry, C.S.I.R.O., Canberra, for construction of the spinning disk, and Irene Verners of the same address, for laboratory assistance. LITERATURE CITED
(1) Barnett, A. J. G., and Miller, T. B., J . Sci. Food Agr., 1, 337 (1950). (2) Black, H. C., Jr., ANAL.CHEY.,23, 1792 (1951). (3) Bridges, R. R., Ibad., 24, 2004 (1952). (4) Dreywood, R., IND. ENG.CHEX.,A s i L . ED., 18, 499 (1946). (5) Durham, W. F., Bloom, W. L., Lewis, G. T . , and Mandel, E. E., Publzc Health Repts. ( C . S.), 65, 670 (1950). (6) Fairbairn, S . J., Chemistry and Industry, 4, 86 (1953). (7) Johanson, R., h'ature, 171, 176 (1953). (8) Koehler, L. H., .4N4L. CHEM.,24, 1576 (1952). (9) Morris, D. L., Science, 107, 254 (1948). (10) Rlorse, E. E., IND. ENG.CHEM.,ANAL. ED., 19, 1012 (1947). CHEY., 23, 1795 (11) Samsel, E. P., and DeLap, R . d.,.IN*L. (1951). (12) Viles, F. J., Jr., and Silverman, L., Ibad., 21, 950 (1949). R E C E I ~ Efor D review July 8, 1953. Accepted March 23, 1954,
of Determination of Diphenylmercury Alone orgnL,Presence vm T Phenylmercuric Compounds Application to Ethyl Analogs V. L. MILLER
and
DOROTHY POLLEY
W e s t e r n Washington Experiment Station, Puyallup, W a s h .
In an investigation of phenylmercuric fungicides, it became desirable to determine why some formulations appeared to give better results than others. One possible explanation was that diphenylmercury, a relatively inactive material against the fungus under investigation, might be formed. The described procedures make possible the analysis of diphenylmercury alone or in the presence of phenylmercuric compounds. A procedure is aIso given for the estimation of diethylrnercury alone or in the presence of ethylmercuric compounds.
T
H E diphenylthiocarbazone reaction has been used for the determination of phenylmercuric compounds by Gran ( 2 ) and both the ethyl and phenyl compounds by the authors ( 3 ) . Webb et d.( 5 ) reported that, in macro amounts, diphenylmercury reacts slowly with diphenylthiocarbazone (dithizone) in benzene to form phenylmercuric dithizonate a t room tempera-
ture. However, the authors found that in micro amounts diphenylmercury does not react 15 ith dithizone in chloroform at room temperature in the presence of 0 . 3 S acetic acid. K h e n it became desirable to separate diphenylmercury and phenylmercuric compounds, the diphenylmercury interfered in the published procedure. The 3 5 hydrochloric acid used caused a partial decomposition of the diphenylmercury with the formation of phenylmercuric chloride according to the equation:
cI> H g 0+ H C l + 0HgCl + 0
(6)
(1)
When a chloroform solution of diphenylmercury is shaken with 9.V hydrochloric acid, this reaction becomes quantitative. This permits diphenylmercury to be determined as a phenylmercury compound. In chloroform solution, phenylmercuric salts may be separated from diphenylmercury by extraction into the aqueous phase with acidified thiosulfate solution in a manner similar to t h a t used by Cholak and Hubbard for mercury ( 1 ) . This permits direct determination of diphenylmercury by the dithizone reaction.
1334
ANALYTICAL CHEMISTRY
A 0.05S hydrochloric acid solution, 1s in sodium chloride, does not decompose a chloroform solution of diphenylmercury. By use of this reagent the analysis of phenylmercuric salts with dithizone in the presence of diphenylniercury is possible. An alternative procedure for the determination of diphenylmercury is based on the reaction with mercuric chloride:
The det,ermination of mercury using this reaction will be the subject of a separate paper. The analysis of ethylmercuric salts and diethylmercury is conducted in a way .similar t o that outlined in the separation of diphenylmercury and phenylmercuric compounds, except that it is necessary t o use 12X hydrochloric acid for the reaction in Equation 1. Under the conditions described, the reaction in Equation 2 does not occur with dipthylmercury. REAGENTS
Reagent 1. Fifty milliliters of 1S hydrochloric acid containing 2.5 ml. of 2007, hydroxylamine hydrochloride is added to 200 ml. of 5.1- sodium chloride and 750 ml. of redistilled water. The stock solutions of hydroxylamine hydrochloride and sodium chloride are dithizone extracted. The pH of the reagent is about 1.15. Reagent 2. Glacial acetic acid is diluted a t the rate of 40 ml. per liter of water. Reagent 3. Sodium thiosulfate: a 12% solution prepared in water daily. Reagent 4. Hydrochloric acid, 9.\-. Reagent 5. Hydrochloric acid, 3.\-. Reagent 6. Ethanolic mercuric chloride, 600 y per ml. Reagent 7. Acetic acid, approximately 35 ml. per 2 liters of solution. Reagent 8. Eastman Kodak nhite label diphenylthiocarbazone dissolved in chloroform a t the rat,e of 1 mg. per ml. This stock fiolution is diluted in chloroform as needed. Jt-hen 1 to 30 -!of organic mercury compound is to be determined, the diluted dithizone should contain approximately 3.3 mg. per 100 ml. In case of larger amounts (90 to 120 7 ) ) a solution of 10 mg. per 100 nil. is necessary. The standard materials used were Eastman white label diphenyl and diethylmercury and phenylmercuric chloride. The diethylmercury contained an appreciable amount of contaminant that reacted with dithizone but could be extracted with acidified thiosulfate. Similarly, the phenylmercuric chloride contained a small amount of mercury that was removed by extraction with 31Y hydrochloric acid. The ethylmercuric chloride came from E. I. du Pont de Nemours & Co. and Bios Laboratories. Both were recrystallized from methanol and melted a t 191" to 192" C. ( 4 ) . 'The phenylmercuric acetate vas Berk's C.P. product. PROCEDURE
Diphenylmercury in Absence of Phenylmercuric Compounds. A chloroform solution of the sample not exceeding 10 ml. in volume is transferred to a small separatory funnel. The amount of organic mercury compound is such that a mixed color is formed with the dithizone in the end r e a d o n . Sufficient chloroform is added to make a total of 10 ml. in the separator. Ten milliliters of 9N hydrochloric acid is added and the funnel immediately shaken for 30 seconds. The chloroform phase is transferred to a second separator containing 50 ml. of reagent 7 . Exactly 1 ml. of the diluted standard dithizone solution is added and the separator shaken again for 30 seconds. The chloroform phase is now transferred to a suitable volumetric flask (10 to 15 ml.), and diluted to volume and the percentage transmittance is determined a t approximately 620 mp. Diethylmercury may be determined by the same procedure, except that 1 2 5 hydrochloric acid is used in place of 9N for the hydrolysis step. Alternative Procedure for Diphenylmercury. As the amount of phenylmercuric chloride formed in the alternative procedure is twice that formed in the preceding one, the amount of sample should be estimated accordingly. Half a milliliter of reagent 6 is added to the separator containing the chloroform solution of the sample diluted to approximately 10 ml. with chloroform. The solutions are swirled to mix. Twenty milliliters of reagent 5 is added and the mixture shaken for 30 seconds to extract the excess mercury into the aqueous phase. The chloroform phase is then transferred to another separat,or which contains 50 ml. of reagent 7 . Exactly 1 ml. of the diluted dithizone reagent is added, and the mixture is shaken for 30 seconds. The percentage transmittance is determined as above.
Phenylmercury in the Presence of Diphenylmercury, or Ethylmercury in the Presence of Diethylmercury. The chloroform solution of the ethyl- or phenylmercuric compound, which may contain the diphenyl- or diethylmercury as contaminant, is placed in a small separator. The quantitv of organic mercury compound is adjusted so that a mixed dithizone color is formed. Sufficient chloroform is added to make a total of 10 ml. Twenty milliIiters of reagent 1 is added and the mixture is shaken for 1 minute. The chIoroform phase is then transferred to a second separator containing 50 ml. of reagent 7, and 1 ml. of diluted standard dithizone solution is added. The funnel is then shaken for 30 seconds. The resultant chloroform phase is d.luted to a convenient volume and the percentage transmittance determined a t 620 mp. Only the phenyl- or ethylmercuric compound reacts in this portion of the procedure. Diphenyl- or Diethylmercury in the Presence of Phenyl- or Ethylmercuric Salts. Because the ethyl- or phenylmercury salts react with dithizone, they must be removed from the mixture. The sample in chloroform solution is added to a sufficient volume of chloroform in a small separator to total 10 ml. One milliliter of reagent 3 is added, followed by 50 ml. of reagent 2. The separator is immediately shaken for 1 minute. This step removes the phenyl- or ethylmercury. The estimation of the diphenyl- or diethylmercury is done by the procedure given for these compounds alone. The concentration of the dithizone is regulated so that a mixed color is formed. Standard curves are prepared from known amounts of the pure materials. The calibration curves follow Beer's law. The procedures seem to work equally well with small (1 to 30 y ) and larger amounts (90 to 120 y ) . Khen the ratio of the compounds to one another is lsrge, it is advantageous to use two concentrations of dithizone. The amount of phenylmercuric acetate present in the determination of diphenylmercury did not exceed 2000 y . I n the reverse determination, the diphenylmercury d d not exceed 4000 y .
Table I. Approximate Solubilities of Several Organic Mercury Compounds a t Room Temperature In
C6HsHgOAc CaHsHgCl (CGHL)?H~ C3HsHgC1
water 4,300 2-1 6
Soliihilitv ( v / A I l . ) In
chloroforni 105,000
975 (1 4 ) a
0
(C2Hn)zHg 101 Calculated from literature d a t a .
5,450
433,000 62,800 (38,000)" Cornlilete
In
reagent 1 23 19 0
862
20
DISCUSSION
The separation described depends on the quantitative extraction of the phenylmercuric compound from chloroform solution into the acidified thiosulfate. The original solutions of the compounds must be in chloroform. rllcoholic solutions cannot be used. The solubility of the diethyl- or diphenylmercury in chloroform is so much greater than in water that the extraction loss is negligible. Table I s h o w data on solubilities. Water solubilities of phenylmercuric acetate and chloride agree fairly well with accepted values. The solubility of ethylmercuric chloride in water and chloroform is much higher than previously reported (4). The solubilities were repeatedly determined by machine shaking of the compound in the solvent for over 20 hours during at least 2 days. The solutions rvere filtered through sintered glass. The organic mercury compounds were determined as described in this paper. Also in some cases the chloride from the water saturated solution of ethylmercuric chloride R as determined gravimetrically by precipitation with silver. If the same dithizone solution was used to prepare standard curves of diphenylmercury and phenylmercuric acetate, it was found that by calculating to equivalent phenylmercury (CsHsHg), the standard curves would superimpose. The same u-as true with ethylmercuric chloride and diethylmercury. Typical data are shown in Table 11. Cholak and Hubbard ( 1 ) used a dilute sulfuric acid-sodium thiosulfate reagent to extract mercury from the chloroform to
V O L U M E 26, NO.
e,
AUGUST 1954
1335
Table 11. Comparison of the Absorbance of Equivalent ,ilkylmercuric Dithizonate from Aryl or Alkylmercuric Chloride IIaterial,
Procedure ('sHsHgOAc, direct
t C s H ~ ) * I l g113 , drolysis CZHsHgCl, direct
CzfI~)sHg, hydrolysis
Equiralent t o ,
Y
7
CsHsHgO.kC 6.1 18.2 30 (CeHs)zHg 3.2 9.6 16.0 6.4 19.2 31.9 C z H s H g C1 5.8 17.3 28.8
('sRsHg
(CzHdzHg 5 6 16.9 28 2
.iti-orbance
5 15
25
0 606 0.432 0 2,:s
and diethylmercury is a volatile, toxic mat'erial. The data in Table 111 give the results obtained when mixtures of diphenylmercury and phenylmercuric compounds were analyzed by t,he described procedure. The results were considered satisfactory for this type of work. Based on these and other results, the analysis will not be in error greater t,han 2 y or 5%, whichever value is the greater. -
Table 111.
.inalysis of 3lixtures
_Calcrilated _C8HsIIgOAc, _ _ y Fo: ~1nJ~ - ___________ ~ -ICeHs)rFTe, y Calciilatrd 6 1
192 640
C2HiHg D
15
25
1
15
25
6 4 6 4 l!l2
wn
6.4 n.4 6 4 6.4 6.4 40
0 634 0 15'1 0 280 0.G29 0.456 0.280
6.0 6 8 1 !I0 fi3R 1 28i 1 ,!iR7
6-40
1.283 I ,920 42
Found 6.7
960 40
041 42
ACKSOWLEDGJI ENT
the aqueous phase. Honever, a dilute acetic solution \vas to \I? preferred in the extraction of phenyl- or ethylmercuric compounds from the chloroform to the aqueous phase because of less clec-omposition of the thiosulfate. I n this step, the addition of the thiosulfate to the separatory funnel should be followed immediately by the acetic acid and the separator promptly shaken, as standing even for a minute had a deleterious effect on the beparation. Only thiosulfate of the highest purity should bp uQed. The presence of 10 y of added sulfide (which may be an impurity) seriously interfere i with the separation. Good separation of diphenylmercury from phenylmercuric acetate was obtained when the ratio of diphenylmercury to phenylmercury was 1 to 150, or conversely, when the ratio was 1 t o 300. Similar separations of diethylmercury from ethylmercuric chloride were obtained. The investigation was mainly concerned with the phenyl compounds because they are cheaper,
,\clino\vledgment is made to C. 11. Brenster of the State College of \Yashingt,on for aid in the literature review. One sample of ethylmercuric chloride \viis a gift from E. I. du I'ont de Semours & Co., Inc. LITERQTURE
crrm
(1) Cholak, J., and Hubbard. D. 11..IS.LI.. CHEM..18, 148 (1046). ( 2 ) Gran, Gunnar, S w i s k Paprrsfid?i.. 53, 234 (1950). (3) Miller, V. L.. Polley, Dorothy, and Gould, C. J., . b i . ~ r . . CHEM., 23, 1280 (1050). (1) ~, Slotta. K. H.. and Jacohi. li. H.. J . i ~ r n k i (. ' h r m . . 120. 249 (1929). (5) Webb, J. L. .1.,Bhatia, I. S.,C o r w i i i . A. €I., and Sharp. .I.G., .I.-4~7. C h e m . SOC..72, 91 (1950). (6) Whitmore. F. C., "Organic Coiiipoundn of llercury," S e w York, Chemical Catalog Co., 1921. I
\
,
RECEIVED for review January 4 . IU54. Accepted M a y 2 2 , 1964. Presented before Korthwest Regional Meeting of t h e . ~ M E R I C A S CHEMICALSOCIETY, Richland, Wash., June 1954. Bcientifir Paper KO.1279, Washington Agricultural Experiment Station, Pullinan Project S o . 724.
Separation of Platinum and Palladium and Their Subsequent Colorimetric Determination with p-Nitrosodimethylaniline JOHN
H. YOE
and
J. J. KIRKLAND'
f r a t t Trace Analysis Laboratory, Department o f Chemistry, University o f Virginia, Char/ottesvi//e, V a .
The wide variation i n the rate of reaction of platinum and palladium with p-nitrosodimethylaniline to give highly colored products has been utilized to develop a sensitive additive absorbance colorimetric procedure for these metals. Palladium and platinum can be determined individually w-ith average relative errors of 1.0 and 1.5yo,respectively, when in the concentration range of optimum photometric measurement. Samples containing palladium to platinum ratios of 10 to 1 to ratios of 60 to 1 platinum to palladium may be analyzed by this method with good accuracy. Larger proportions of palladium may be determined by utilizing a differential measurement technique. Relatively large amounts of palladium may be quantitatively separated by extraction of the palladium-p-nitrosodimethylaniline complexes in chloroform. .4 method is proposed for the simultaneous separation of platinum and palladium from other platinum metals interfering with their colorimetric determination; these metals are extracted as their diethyldithiocarbamate salts into
chloroform, the solvent is evaporated, and the residues are ashed with concentrated nitric acid and peroxide. Final determination of the metals is easily made by means of the additive absorbance method.
T
HE color reactions between p-nitrosodimethylaniline and palladium and platinum have been individually proposed as means of determining small amounts of these metals ( 4 , 5 ) . As is .the case with the other existing colorimetric methods for platinum, this reaction is also interfered lvith by relatively small amounts of palladium and to varying extents by other platinum metals. In this paper p-nitrosodimethylaniline is recommended as a colorimet,ric reagent for the determination of both platinum and palladium in trace concentrations. -1 method for selectively separat,ing these metals from commonly associated elements interfering with their colorimetric determination is also proposed. During the course of the experimental work embodied in this re1 Present address, Experimental Station, E. I . du P o n t de Nemours & Co., I n r . , Wilmington, Del.
