The rate a t which electrochemical transformation takes place is obtained by differentiating the Faraday law equation [Q representing coulombs).
E
6’
=
96,490 dQ -
dE - = - - - - -dt - - - ---dt
96,490
I 96,490
(7)
The method is carried out in a manner to ensure strict equality between the electrolysis rate and the substance influx rate. Hence Equations 5 and, 7 can be equated to give the basic relationship
Because the two rates are kept identical, the present technique takes advantage of the precise electrical stoichiometry inherent in Faraday’s law, which is a virtue of batch methods
( 2 ) Allen, J. il., Suture 175, 83 (1955). (3) Eckfeldt, E. L., ANAL. CHEM. 31, 1453 (1959). (4) Eckfeldt, E. L., unpublished field experience from April 1949 to August 1953 with continuous coulometric analyzer, in which sample temperature varied widely [Eckfeldt, E. L., U. S. Patent 2,758,079 (Aug. 7, 1956)]. (5) Hodgman, C. I)., editor-in-chief, “Handbook of Chemistry and Physics,” 40th ed., pp. 1706-7, Chem. Rubber Pub. Co., Cleveland, Ohio, 1958. ( 6 ) Livingston, J., Morgan, R., Pyne, H. R., J . Phys. Chem. 34, 1818 (1930). ( 7 ) Livingston, J., Morgan, R., Richardson, A. H., Zbid., 34, 2356 (1930). (8) Stone, H. W., Eichelberger, R. L., AXAL.CHEY.23, 868 (1951). ( 9 ) Truesdale, G. A., Downing, A. L., Sature 173, 1236 (1954). (10) Truesdale, G. A., Gameson, A. L. H., J . Conseil, Conseil Perin. Intern. Exploration M e r 22, 163 (1957).
of coulometric analysis. The expression derivative coulometry retains this desirable connotation, yet clearly implies that current is measured. The derivative of coulombs ( d Q / d t ) is the current flow in amperes, I , as appears in Equation 7 . The term derivative coulometry applies equally well to the present technique, in which the measured substance reacts directly a t a working electrode, and to the continuous technique in which the substance reacts quantitatively with an electrolytically generated intermediary. ACKNOWLEDGMENT
Acknowledgment goes to our colleague, C. W. ROSS,for the equation used with the volumetric dilution apparatus.
RECEIVEDfor review March 17, 1964. Accepted June 22, 1964. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., 1964.
LITERATURE CITED
(1) A.B.C.11.-S.A.C. Committee, Analyst 82, 683 (1957).
Microdetermination of Selenium with 3,3’-Diaminobenzidine by the Ring Oven Technique and Its Application to Air Pollution Studies PHILIP W. WEST and CH. CIMERMAN Coatas Chemical laboratories, louisiana State University, Baton Rouge, l a ,
b A method for the identification and quantitative estimation of air borne selenium particulate!; is proposed, based on the use of ring oven techniques for the separation, concentration, and quantitative estimation. The average relative error for the method is 5% when applied to the range of 0.1 to 0.5 pg. of selenium. The method is readily applicable to air pollution studies and may also find use in other fields.
S
is increasing in significance as an air pollutant because of increasing possibilities of exposure. The present work describes a sensitive, reliable, and simple method for detecting and estimating air borne selenium particulates. The combination of the ring oven technique for separating and concentrating minute amounts of material coupled with the sensirivity, reliability, and selectivity of spot tests, provides an attractive means for studying air borne particulates. Test procedures based on such techniques require sensitive and selective reagents for final identification and estimation of the desired constituents. The reaction products should ELENIUM
be intensely ‘colored and insoluble, if possible. I n the case of selenium reagents, 3,3’-diaminobenzidine held promise for possible ube in conjunction with the ring oven method. This reagent, which was introduced by Hoste (4) in 1948 and later studied by Hoste and Gillis ( 5 ) provides a sensitive and remarkably selective means for the identification and colorimetric estimation of selenium. The analytical applications of 3,3’-diaminobenzidine have been summarized by Broad and Barnard ( I ) . Although this reagent has already been used for the colorimetric estimation of selenium in air ( 7 , 8 ) ,the present work describes the special applications of the reagent for air pollution studies when applied in conjunction with the ring oven method ( 9 ) . The reagent, 3,3’-diaminobenzidine, reacts with selenium to form an intense yellow piazselenol, H*N
\-
or possibly, 3,4-diaminophenylpiazselenol as thought by Parker and Harvey (6). The reaction has been studied in detail by Cheng ( 2 ) . The adaptation of the reaction to the ring oven technique and its application to air pollution and similar studies are now described. EXPERIMENTAL
Reagents and Standard Solutions.
STANDARD STOCKSELENIUM SOLUTION. A solution containing 0.50 mg. of selenium per milliliter was prepared by dissolving 50 mg. of pure selenium metal in a few d r o p (minimum necessary) of concentrated nitric acid, boiling gently to expel brown fumes, and making up to 100 ml. with distilled water. The standard stock solution was diluted as necessary for preparing standard working solutions. Formic acid, 2.551. Sodium oxalate, 1%. Buffer solution, p H 3. X buffer
XH2
-/
+
H , X - ~ - ~ - N H ~ 2 SeOz
-
Se=N
N=Se ‘I
k--t>--&S
+ 4 H20
VOL. 36, NO. 10, SEPTEMBER 1964
2013
prepared from potassium acid phthalate and tartaric acid is satisfactory. Sodium sulfide, 1%. 3,3'-Diaminobenzidine hydrochloride, 0.1%. Prepare fresh daily and store in a refrigerator when not' in use. All reagents and chemicals used in the present study were analytical reagent grade. Apparatus Used. Keisz ring oven. Yational Appliance Co., Portland, Ore. hIimarve1 hair dryer, model HD 1. Sperti Faraday, Hoboken, K. J. Powerstat. Superior Electric Co., Brist'ol, Conn., Type 116. Pandux surface temperat'ure thermometer, range +20° to +lSOO C. Pacific Transducer Corp., Los hngeles 64! Calif. Auxiliary accessories ( 2 2 ) for the ring oven. (a) aluminum retainer ring and (b) washing ring. Recommended Procedure. Specially purified filter paper (S and S 595) 55 mm. in diameter is placed on the ring oven maintained a t 90" to 95" C. T h e paper is fixed in position by means of the retainer ring with its plane surface on the paper, and the following operat,ions are performed in order. The usual precautions of allowing sufficient time between the addition of each solution to permit normal diffusion through the pores of the paper and to avoid flooding of t,he ring are assumed. First, add two 15-p1. portions of sodium oxalate, followed by from 1 to 10 standard drops of sample solution, sufficient to provide 0.1 to 0.5 pg. of selenium. Six 5-p1. portions of sodium oxalate, 5 pl, of formic acid, and 5 p1. of buffer solution are added next. Develop the test color by adding two 1O-pl. portions of reagent, five 5-pl. portions of buffer, and, finally, fifteen 5-pl. drops of dist,illed water. After the test ring develops and begins to separate from the wet spot, remove the filter paper by means of a forceps, and dry it in a current of cool air. The dried paper is then placed between two sheets of paper and rubbed with the fingers to create a uniform surface. Finally, place the washing ring on the hot ring oven, place the test paper on the washing ring, center it carefully, and fix its position with the retainer ring (plane surface up). The test ring is now washed with eight 15-p1. drops of distilled water, insuring that the wash water diffuses well past t'he colored ring. The filter paper is then dried in a current of cool air, and its surface is rendered uniform as indicated above. The citron yeliow ring of a positive selenium reaction is then matched against standard rings. For quantitative estimations, the color intensity of t,he test should be compared a t least 30 minutes after preparation by direct matching with a set of standard rings containing known quantities of selenium. Three rings of the unknown solution Phoiild be prepared (10) containing different, but known, amounts of the unknown mlution--.e.g. 5 : 15, 25 pl. The range of selenium contained in the three rings should he from 0.1-0.5 p g . If the solution of unknown is more dilute 2014
ANALYTICAL CHEMISTRY
than the standard, larger volumes may be taken. With more concentrated solutions of the unknown, dilute as required. Each of the three rings of the unknown must fall within the ra.nge of the standard scale. The best results are obtained when the concentration of the unknown is approximately the same as that of the standard solution. In preparing the standard scale, it is generally convenient to dilute the stock selenium solution to make a standard having 0.020 mg. of Se 'ml. By using 5$ 10, 15, 20, and 25 pl. of the standard solution, rinvs containing 0.1, 0.2, 0.3, 0.4, and Or5 p g . of Se are obtained. Final estimation is accomplished by determining where each of the sample rings falls in the series of standards. The sum of the number of microliter drops of matched standard divided by the sum of the number of drops of the three test rings equals the ratio of the two solutions. Multiplying this quotient by the known concentration of the standard solution yields the concentration of the unknown from which the total amount of selenium can in turn be calculated. Purification of Paper. A study made t,o determine the most suitable filter paper for t'he ring oven operation disclosed t h a t of the 22 variet'ies tested, all were found to have substantial amounts of selenium impurities. Schleicher and Schull S o . 595 made in the U.S.A. was selected as the best ail-purpose paper for these particular studies. I t was necessary, however, to purify this paper prior to use. Purification of the paper is accomplished by treatment with sodium sulfide which forms soluble selenosulfide complexes with either selenium salts or elemental selenium as shown by t'he following equations (3):
-
+ 2S+ + 3H20 Se" + 2s" + 6 0 H Se" + S-2-, [Se . . . SI-*
Se03-*
(1)
(2)
The selenium complex is washed from the paper using distilled water, the most efficient method being to use the ring oven itself for all of the purification steps. For this work the washing ring is placed on the ring oren and warmed to 95' C. A circle of the filter paper to be purified is positioned on the washing ring and fixed in place by means of the retainer ring with its plane surface up. Sodium sulfide solution ( I 5 i d . ) are added to the center of the paper by means of a capillary pipet. The sodium sulfide spot is then washed to the periphery of the paper by additions of distilled water wing the c>apillary pipet for the introduction of each volunie of washing solution. The filter paper is finally dried in a current of hot air and placed betiveen two sheets of paper m d rubbed with the fingers so as to produce a uniform surface. This latter stell iq necessari- to obtain even diffusion of liquids through the pores of the paper and so
afford even distribution of solutes in the final rings produced in the test procedures. RESULTS A N D DISCUSSION
Support Paper. The kind of filter paper used and its purity are critical to the success of this method. The filter paper must have good strength when wet. must present a suitable speed of diffusion, and must be of regular texture so that uniform rings are obtained. The question of selenium impurities in the paper is critical, and all of the papers tested were found to contain significant amounts of contaminant. Some of the papers contained as high as 2 p g . of selenium in a spot 22 nim. in diameter. hlthough selenium impurities can be removed efficiently, there are advantages in starting with the purest paper possible. The Formation of Rings. I n the ring oven technique uniform diffusion of solutes to the ring area is necessary. The rings formed should be completely regular and the deposited solutes should be in the form of a sharply defined ring. The formation of good rings is sometimes difficult in papers which have been rolled in the course of their manufacture. Papers with oriented fibers tend to give eliptical diffusion and often show rings of poor definition. I t is difficult to obtain regular rings if the surface of the paper is undulated after washing or storage. Generally, the support paper can be treated so as to minimize the more common aberrations: (a) at the time of the addition of different reagents, care should be taken so that the capillary pipet touches the support paper as lightly as possible so as to avoid making a cayity. (b) .ifter the supporting paper is dried following purification, it should be rubbed between two sheets of paper so as to establish uniformity of texture. Such treatment prevents channeling in the flow of liquids to the ring area. (e) Special care must be taken to prevent flooding of the ring. Each addition of solution should be followed by sufficient elapse of time to permit normal diffusion of the liquid through the pores of the paper through attraction of simple capillary forces. Thus, the solutions approach the heated ring area a t a rate sufficiently dow that evaporation of solvent occurs smoothly, and the deposited solutions are retained in the form of a sharply defined ring. Hurrying such steps results in the overrunning of the heated ring area and the formation of diffuse and irregular deposits. Precautions. I n the selenium procedure, the ring. should be dried using a current of cool air from the dryer. Hot air tend; to cauqe oxidation of the reagent and the formation of spurious colors. Test rings should be com-
pared with the standards at least 30 minutes after their formation, but during the same d a y of their preparation. T h e standard rings and t h e rings of the unknown should be prepared the same day. T h e solution of 3,3'-diaminobenzidiine must be prepared fresh daily and is best kept in a refrigerator as much of the time as possible, because it tends to darken upon exposure to air. Previous investigators have found that the maximum rate of color development occurs in the pH range of 2 to 3. These findings have been confirmed in the present studies. The formic acid contributes to the development of the yellow color of the test reaction. I t functions in establishing the optimum p H and it is a mild reducing agent serving to eliminate a number of undesirable oxidants without simultaneously reducing Se (IF') to elemental Se. Interferences. A lbroad study of possible interferences was undertaken. One series of tests \vat3 made using 10 pl. of solutions containing 1 p g . / p l . of potential interfering substance. A second series of tests wits made using 20 pl. of solutions, each of which contained equal volumes of 1 pg.1 pl. of test ion and 0.01 p g . / p I . of selenium. The rings were developed according to the regular procedure described above. Noninterference was recorded for all cases in which the first test was identical with a blank using all of the reagents or was less intensely colored than 0.1 pg. of selenium. The ions established as noninterfering are: Li+, ?;a+, K+, Rb+, Cs+, Be+2, Mg+2, CatZ, S r f 2 , Ba+2, Zn+2 C d t 2 , Hg+', BOZ-, B,O,-', Ga+3, Cef3, TI+, c03--',Si03-2, Ti+4, Sn+*,Pb+2,T h + 4 ,YH4+,KO3-, HP04-', H.h03-2, H h ~ 0 ~ Sb+3, - ~ , Sb+5, Bi+3, S04-2, Mooc-, Te03-2, Te04-2JW04-2, COzf2,U04-2, F-, C1-, Mn+2,Br-, I-, Reo4-, Pdt2, CY-, CXS-, acetate, oxalate, malonate, succinate, phthalate, tartrate, citrate, and mannitol. ; i number of ions were found to interfere, either because of their own color or because of reactions with the reagent. These ions are: -\g+, .4u+3, GeO3-', F e t 2 , Fef3, C U + ~Cet4, , vas-, Cri3, Cr04-', c103-,l I n o 4 - , bo3-, Io3-,Coi-', Si+z, R u + ~Rht3, , Pt+4,Fe(CN)6-3, Fe(CN)8-4, and NO2-. Of these only the iron, copper, chromium, nickel, and cobalt are likely to be of significance in air pollution studies. Elimination of Interferences. Iron and, to a lesser extent, copper may be antiripated as common constituents of air borne particulates, and it was considered necessary t h a t means for obviating their interference be incorporated in the test procedure. Marking was experimentally the most attractive approach, particularly becauqe both of these metals are readily
Table 1.
Micro Determination of Selenium with 3,3'-Diaminobenzidine
Se
Fe
0.10 0.10 0.10 0.10 0.10 0.20 0.20 0.20 0.20 0.20 0.30 0.30 0.30 0.30 0.30 0.40 0.40 0.40 0.40 0.40 0.50 0.50 0.50 0.50 0.50
...
present
pg.
cu
Cr
...
..*
10
...
...
...
5 10
10 5 10
, . .
...
...
10
, . .
.
.
I
.
.
I
...
5 10
...
10 5 10
...
10
...
... 5 10
10 5 10
...
...
10
... 5 10 ...
10 , . .
5 10
I
.
.
10 5 10
... ... 10 5 10
, . .
5 5 .
.
... . . I
Ni
, . .
, . .
...
...
I
.
.
5 5
5 5
I
co
... ... ...
... 5 5 I
.
.
, . .
...
5
5
5
5
...
...
... ...
. . I
I
.
.
5 5
5 5
... ...
... ...
... ...
.
.
.
5
5
I
.
5 5 . . I
... ... 5 5
complexed. A wide variety of complexing ligands were tried singly and in various combinations, but the systematic study indicated that a 1% solution of sodium oxalate was best suited for use in this procedure. This masking agent was found to be entirely effective when properly mixed with the test sample. I n order to insure proper mixing, it was found that the masking agent should be added both before and after the addition of the sample drops so that efficient mixing could be accomplished before any other reagents came in contact with the sample. Masking with sodium oxalate served also to eliminate possible interferences of trace amounts of iron that are often present in filter paper. Interferences from colored ions, such as Cr+3, Cot2, and Nit2, were readily eliminated by washing them from the ring zone as a final step in the test procedure. Because such ions are readily soluble in water, they are easily washed beyond the ring zone where they can no longer interfere. The product of the test reaction is insoluble and stable in water and, consequently, such washing operations in no way invalidate the final test. Accuracy of the Proposed Method. In order to establish t h e average relative error of the proposed method, 50 rings were prepared containing known amounts of selenium in t h e range of 0.1 to 0.5 pg. The various rings were prepared both with and
.
I
5 5
...
.
I
5 5 , . .
... ...
...
5 5
5 5
I
.
.
Se, pg. Matched Difference 0.10 0.10 0.10 0.10 0.15 0.20 0.20 0.20 0.20 0.25 0.30 0.30 0.30 0.30 0.25 0.40 0.40 0.40 0.35 0.45 0.50 0.50 0.50 0.40 0.40
...
...
...
+0.05 , . . , . .
... ... +0.05
... , . .
...
... -0.05 ... , . .
, . .
-0.05 +0. 05
... , . .
, . .
-0.10 -0.10
without varying quantities of interfering ions such as Fe+3, C U + ~C, r + 3 C O + ~ and Nif2. The average relati& wro; was calculated to be 5%, Table I summarizes the results obtained in estimating selenium in the presence of various interfering substances. An average value for the ratio of the test solution to the standard *as computed by the method of Weisz (IO). Based on 5 values calculated from 3 rings, an 0.016 was average value of 0.310 obtained a t the 95oj, confidence level for solutions taken to have a 0.310 ratio. Studies of the effects of varying amounts of possible interfering ions indicate the maximum allowable limit to be 10 p g . for iron, copper, chromium, cobalt, and nickel when present as simple mixtures with selenium. With mixtures of iron and copper, 10 pg. each can be tolerated. With mixtures of chromium, cobalt, and nickel, 5 p g , each can be tolerated. Range of the Proposed Method. The lower limit for estimation of selenium by this method is 0.1 pg. The upper limit for accurate estimation was established to be 0.5 pg. of selenium, because amounts greater than this tend to give rings of such intense color that visual comparison is difficult.
*
LITERATURE CITED
(1) Broad, W. C., Barnard, A. J., ChemzstAnalyst 5 0 , 124 (1961). VOL. 36, NO. IO, SEPTEMBER 1964
2015
k2) Cheng, K. L., ANAL.CHEM.28, 1738
(1?56). (3) Eeigl, F., West, P. W., Ibzd., 19, 351 (1947). (4) Hoste, J., Anal. Chim. Acta 2, 402 11948). ( 5 i Hosie, J., Gillis, J., Ibid., 12, 158 (1955). (6) Parker, C. A . , Harvey, L. G., Analyst 86, 54 (1961).
(7) Strenge, K., Arch. Gewerbepathol. Gewerbehyg. 16, 588 (1958). (8) Suzuki, Y., Nishiyama, K., Matsuka, Y., Shikoku Iaaku Zasshi 11, 77 (1957). (9) Reisz, H.,- "Microanalysis by the Ring Oven Technique," Pergamon Press. ., London. 1961. ~. . (lo, keisz, H., Ibid., p. 74. (11) West, P. W., Llacer, A. J., Cimerman, Ch., Mikrochimica Acta 6 , 1165 (1962).
RECEIVEDfor review May 22, 1964. Accepted July 1, 1964. One of the authors (Ch. Cimerman) was on a sabbatical leave from the Technion Israel Institute of Technology, Haifa. Both authors wish to acknowledge the support of the Division of Air Pollution of the U. S. Public Health Service under Research Grant APOOl17.
Determination of Diethyl Sulfate, Ethyl Hydrogen Sulfate, and Sulfuric Acid in Mixtures D. K. BANERJEE, M. J. FULLER, and H. Y. CHEN' Research Division, U. S. Industrial Chemicals Co., Cincinnati, Ohio A method for the determination of diethyl sulfate, ethyl hydrogen sulfate, and sulfuric acid in mixtures is described, Ethyl hydrogen sulfate and sulfuric acid are determined by nonaqueous titration with tetrabutylammonium hydroxide using pyridine as a solvent, Diethyl sulfate is determined by hydrolysis at 130" C. and titration of the sulfuric acid formed with aqueous base. Evidence of an unusual reaction between neutral diethyl sulfate and pyridine leading to the formation of a titratable complex was also obtained. Precision and recovery data for synthetic mixtures and production samples of ethylene absorbate are presented.
S
is produced by the hydrolysis of ethylene absqrbate which is a nearly anhydrous mixture of diethyl sulfate, ethyl hydrogen sulfate, and sulfuric acid containing some tars and polymers. Sumerous method.; for the analysis of mixtures of (C2Hs)?SOcC2H5HS04and H2S0, have been described ( 1 . 6 , 8 ) and critically revieu ed by Harris and Himmelblau ( 5 ) . They concluded that most of these methods are complex, indirect, and not suitable for clearcut reproducible quantitative work. Since a rapid control procedure for these three components in ethylene absorbate ~ o u l d be very useful for material balance calculations, a new approach u h g rapid titration in aqueous and nonaqueous media was investigated. Titration of a mixture of the three components in pyridine with tetrabut>-lammoniumhydroxide gave a curve with three inflection points. The H2S04 and C2H5HS04content of samples was PKTHETIC ALCOHOL
Present address, Research Department, Goodyear Tire and Rubber Co., Akron, Ohio. 1
2016
ANALYTICAL CHEMISTRY
determined from the first two inflection points of this curve. The third inflection point was caused by an unusual reaction between neutral (C2Hj)2SOI and pyridine leading to the formation of a titratable complex. The nature of this reaction was clarified by infrared and nuclear magnetic resonance spectrometry. However, this reaction which is relatively slow could not be used for quantitative determination of the diethyl sulfate. The latter was determined by hyd'rolysis of the mixture a t 120" to 130' C. and titration of the sulfuric acid formed with aqueous base. Satisfactory precision and recoveries were obtained using these methods for synthetic mixtures and production samples of ethylene absorbate. EXPERIMENTAL
Apparatus. A constant-rate buret of 10-ml. capacity and a delivery rate of 1 ml. per minute (E. H. Sargent & Co., Model C ) was used with a Beckman Model 76 p H meter for the nonaqueous titrations with 0 . 1 s tetrabutylammonium hydqoxide. The barrel of the constant-rate buret was sealed with a special baffle-type Teflon seal to prevent attack by the reactive titrant. Other types of seals were not suitable for use with the tit,rant. The titration curves were automatically recorded with a Sargent SR recorder used a t 5 millivolts full scale and a chart speed of 2 inches per minute. A Beckman general purpose glass electrode and a sleeve t,ype calomel electrode modified to contain methanol saturated with KCl were used as the electrode pair. The reservoir containing the titrant was connected to the two way stopcock on the constantrat,e buret through an all glass line. The titrant was protected from moisture and carbon dioxide with a mixture of Drierite and Ascarite. The buret tip and 100-ml. titration vessel were protected from air with a nitrogen blanket and the solutions were stirred with a Teflon covered magnetic stirring bar.
Reagents. Practical grade Eastman diethyl sulfate was purified using the method described by Harris and Himmelblau ( 5 ) . Synthetic mixtures containing 30.82 (I), 62.04 (11) and 82.82% (111) by weight of diethyl sulfate were prepared by mixing the purified material and 98% sulfuric acid. The samples were purged uith nitrogen, stoppered, and heated a t 70" C. for tF\o hours. * h o t h e r synthetic mixture (IV) had the same composition as I1 but was not heated. The mixtures were then allowed to stand for a month a t about 25" C. before samples were withdraxn periodically for analysis. The 0.1S tetrabutylammonium hydroxide (TBAH) titrant in benzenemethanol was prepared as described by Cundiff and Markunas (3, 4) and standardized against J. T. Baker reagent grade benzoic acid dried a t 103" C. for 1 hour. The pyridine used as solvent was purified by allowing it to stand overnight over sodium hydroxide followed by flash distillation. A 5% heads cut was discarded and the remainder collected. The distilled pyridine was satisfactory if equal breaks aere obtained in the titration of sulfuric acid with TRAH using the purified pyridine as solvent for the acid. Procedure for H2SOa and C2H5HSO4. From a tared Grethen weighing bottle containing the sample, add 75 to 100 mg. of sample to 40 ml. of purified pyridine in a 100-ml. beaker. Titrate the solution immediately under a nitrogen blanket keeping the tip of the buret just above the surface of the liquid in the beaker. Stop the flow of titrant \$hen a curve with three inflection points has been recorded. Calculate the H2SOa and C?HsHSO, content of the sample as follons: Per cent H2S04
=
B X S X 20
Per cent CzHsHSOa= ( A - B ) X A' X E 10 x c
