1410
ANALYTICAL CHEMISTRY
Table 111. Determination of Polyvinylpyrrolidone in Serum PVP Added,
P\’P Found,
Recovery,
0 0155
0 0233 0 W33
0 0152 0 0240 0 0233
98 1 103 0 100.0
Sormal rabbit serum
0 0155 0 0233 0 0233
0 0159 0 0239 0 0235
102 6 102.8 100 9
Reconstituted normal human plasma
0 0155 0 0233
0 0164 0 0230
105.9
%
Type
Xorrnal dog serum
Table IV. Time, Nin. 1
5 15
R
%
98.7
Polyvinylpyrrolidone Concentration in Rabbit Serum (% PVP)
Level 1 1 . 1 9 , 0 . 9 4 , 0.90 1.08, 0 . 8 8 , 0 . 9 1 o 81, 0 . 6 3 , 0 . 7 3
Level 2
Level 3
0.46, 0.32, 0.36 0 . 4 5 , 0 . 3 4 . o 36 0.46, 0.34, 0.38
0.29, 0.34, 0.27 o 76, , . . , 0 . 2 7 0 . 2 5 , . . . , 0.26
0 65, 0.57, 0.35, 0.36, 0.24,
0.32, 0.22, 0.23 0.24, 0.24, 0.24 0 . 1 8 , 0.16, 0 . 1 5 0 13, 0 . 1 2 , 0.11 0.11,0.11, 0 . 0 9
0.19, 0.14, 0.10, 0.08,
Houn 1
4 24 48 72
0.47, 0.51 0 42, 0 . 4 6 0.30, 0.35 0.24. 0.29 0.20, 0.27
0.24, 0 19, O,l5, 0.10, 0.05,0 09,
0.16 0.12 0.08 0.00 0.04
values represent lower physiological ranges and the precision approaches that obtained in water. To illustrate the technique in animal work, results of polyvinylpyrrolidone determination in rabbit serum are included in Table IV. Kine animals received one infusion each of polyvinylpyrrolidone plasma extender. The animals were in three groups of graded dosage levels in the range of usual human dosage, with the highest level at 440 mg. per kg. This experiment was carried out over a 72-hour period, by which time the serum level was in the range of 500 p.p.m. in some animals. The method is suitable for the analysis of body fluids, despite the fact that these are known to take up iodine. The spectral absorption of the polyvinylpyrrolidone-iodine complex is identical with that of the potassium triiodide solution, except for intensity. Horvever, when the complex is formed, some iodine is removed from the solution, so that its own absorption is somen-hat decreased; for this reason no true “blank” is available. The solvent (water) is used instead, and the calibration curve corrects for the reagent blank. While the body fluids do not interfere with the formation of the color complex, they too may consume
some iodine. The method is designed to minimize this effect and to enhance the intensity of the color complex. The small residual reduction of intensity of color of the reagent due to the body fluids appears to be approximately balanced by their color, In unusual instances, where there is an abnormal iodine uptake, faulty results are not likely to be obtained, because this uptake is gradual and the “bleaching” will warn the operator. The main disadvantage of the technique described is the variation of absorbance with the molecular weight of polyvinylpyrrolidone. This defect is common to some degree to the other methods cited. This effect should not be ignored, but its importance is minimized by the fact that commercial polyvinylpyrrolidone plasma extenders have similar characteristics. It is known that the frartions of lower molecular weight (lower K value) are excreted first and the fractions of higher molecular weight are excreted only gradually. For most exacting work this should be taken into account and the polyvinylpyrrolidone content read off the calibration curve corresponding to the K value of the sample. If this is not done, the result may be in error by 10 t o 25%. The sensitivity of the method is high: 5 to 30 p.p.In. of polyvinj~lpyrroliJonein the final dilution, which is adlquate for all practical purposes. Moreover, by using 5-em. cuvettes and the iodine reagent as a blank, this range was mtended down to 1 p.p.m. of pol\~in~lpyrrolidone. ACKNOWLEDGIIEYT
The clinical samplce of human urine were supplied by J. E. Rhoads, University Hospital, Philadelphia, Pa., and the other test samples by J. Y. P. Chen Pharmacology Division, Schenley Laboratories. The authors wish t,o acknowledge their kind cooperation, and to thank Bruno Puetzer and Kurt Ladenburg for encouragement’ and discussions and Srhenky Laboratories, Inc., for permission to puhli~hthip paper. LITERATURE CITED
Chinard, F. P., J . Lab. C‘lin. M e d , 39, 666 (1952). (2) Frijtag Drahhe, C. -1.J. yon. and Reinhold, J., Ibid., 40, 616 (1)
(1952).
(3) Haden, R. L., .l.B i d . Chem., 56, 469 (1923). 24, (4) Levy, G. B., Caldas, I., Jr., and Fergus, D., ANAL.CHEM., 1799 (1952).
( 5 ) Thrower, W.R., and Caniyhell, H., Lamxt, 1951, 1096. (6) Zipf, K., ICZin. Ff’ochachr., 23, 340 (1944). RECEIVED for review Soreinher 14, 1952.
Accepted 118y 8, 1953.
Determination of Acrylonitrile in Colored Solutions G. J. JANZ AND N. E. DLNC4N Department of Chemistry, Rensselaer Polytechnic Institute, Troy, Y. Y .
the quantitative determination of acryloliitrile in A -coloredforsolutions arose in the course of studies in progress ~ E E D
in this laboratory concerning the reactions of nitriles and dienes a t high temperatures. The standard analytical procedure for acrylonitrile (1, 2 ) is based on the cyanoethylation of dodecanethiol (dodecyl mercaptan) in the presence of a basic catalyst.
RSH
+ CH-CH-CX
catalyst +
RSCH,-CH?-CN
The excess mercaptan is determined iodometrically, the conipletion of reaction being noted by the appearance of the charncteristic faint color of iodine (yellow). Starch cannot be used to detect this end point, as the characteristic blue complex does not form readily in nonaqueous solutions. To adapt this method
for use with colored solutions in which the above end point is not detectable, a potentiometric titration of the excess mercaptan with silver nitrate was cho-en.
RSH
+ .\g-
-
RS.lg J,
+ H+
For this purpose, the calomel electrode is replaced by a silver electrode in order to determine the end point. The method is thus based on the precipitation of mercaptans with silver nitrate ( 3 ) . The results for precipitation of silver dodecyl sulfide are shown in Figure 1. The curve has the typical steep vertical change and point of inflection a t the end point. The e.m.f. scale in this figure is relative only. Two further changes are necessary in the procedure of the standard method. In place of the bromate-iodide reagent for the iodometric titration, silver nitiate in isopropyl alcohol is re-
V O L U M E 2 5 , NO. 9, S E P T E M B E R 1 9 5 3
141 1
Table I.
Potentiometric Titration of Acrylonitrile
Analysis Sample, Gram Blank
-4gSOa (0.1001 N),M1. 35.40 4.80 12.44 10.12 16.72 14.00
0.1630 0.1220 0 1348 0 0992 0 1141
45
42 A ~ N O ~ (IOON O
1
Acrylonitrile Fyund, Purity, emm %
....
0.1622 0.1216 0.1340 0.0990 0 1134
99: 5 99.7 99.4 99.8 99 4
was found than an acid stop solution containing 10 ml. of glacial acetic acid per liter of isopropyl alcohol caused no interference and served satisfactorily. A4comparison of the standard iodometrir and the potentiometric methods is of interest. A sample of acrylonitrile, carefully purified by dijing and distillation, was found to be 99.5% pure by the standard iodometric method of analysis. The results for a series of potentiometric analyses on this same sample are summarized in Table I. The data in the third column compared nith the actual weight of sample taken give the acrylonitrile purity as determined by the potentiometric titration. The potentiometric titration, using a silver electrode, is capable of the same precision and accuracy as the standard iodometric (visual) method. JTith the potentiometric procedure the quantitative determination of acrylonitrile in colored solutions can be readily achieved.
48
MILLILITERS
Figure 1. Potentiometric Titration of Dodecanethiol with Silver Nitrate in Isopropyl Alcohol
quired. It was found in practice that a 0.100 N silver nitrate folution giving satisfactory behavior can be readily prepared using a combination of isopropyl alcohol and ethyl alcohol in equal amounts as the solvent medium. Secondly, an acid stop solution other than the recommended hydrochloric acid stop solutioii must be used. The latter cannot be used, since silver chloride is less soluble than silver dodecyl sulfide. In the present ~ o r kit
LITERATURE CITED
(1) A m e r i c a n C y a n a m i d Co., New Tork, “Acrylonitrile,” 1951 (2) Bcesing, D. W., Tyler, W. P., Kurtz, D. AT., and H a r r i s o n , S.-4.. A W ~ ICHEM., .. 21, 1073 (1949). (3) Tnmele, 11.W., a n d R y l a n d , L. B., I n .ENG.CHEM.,ANAL.ED,8, 161 (1936). R E C E I \ E for D reiiem .4prll 25, 1953.
Accepted June 15, 1953
Absorptiometric Determination of Nickel with Beta-Mercaptopropionic Acid JAMES B. LEAR WITH M. G. MELLON Purdue University, Lafayette, Znd. ago (4)an e\tensive study \\as made in this laboratory on the use of mercaptoacetic acid as a color-forming reagent for iron. This compound is of particular interest, inaemuch as it contains two carbons and two functional groups, -SH and -COOH. Recently Uhlig and Freiser ( 6 ) attiihuted the color-forining reactivity of p-isothioureidopropionicacid to a hydrolytic product, @-mercaptopropionicacid. It seemed of interest, therefore, to return to the earlier work with mercaptoacetic acid and to study the use of the three-carbon mercapto compound in directions not fully covered by Uhlig and Freiser. In doing this, some of their work was checked. The present work includes the newultraviolet region of the spectrum. In contxast to mercaptoacetic acid, \+hich is an e\cellcnt reagent for iron, the color given by mercaptopropionic acid with this metal is too instable for use. With nickel, however, the color is reasonably satisfactoi y. Consequently, the study centered on this metal. OUI: 3 ears
S
T H E COLOR SYSTEM
In general, the absorptive data checked those of Uhlig and Freiser. Maximum absorbance was found a t 330 mp, with a minor band a t 410 mp. The optimum acidity for the colorforming reaction is close to pH 9. -
~
~
~~~~
Table I.
Ion
C.P.
nickel chloride and standardizing by electrodeposition and weighing the nickel ( 2 ) . .4 1% solution of p-mercaptopropionic acid (Eastman) was prepared. No decomposition was noted over a &week period. All other chemicals were reagent grade, no further purification being made.
~~
~
~
~~~
__
~.
~~
Effect of Interfering Diverse Ions
( a l l solutions contained 10 p.p.rn. of nickel and 10 ml. of reagent, at pH 9.0 =t0.5. XIeasurements were taken a t 330 and 410 mp a t band widths of 6.0 and 0.90 m#, respectively, in I-cm. glass cells) Diwrae
REAGEYTS AND APPARATUS
.4 standard solutioii of nickel was prepared by dissolving
tlbsorbance measurements lwre niadc with a Beckman spectrophotometer, Model B. The slit widths used gave a nominal band width of 6.0 mp a t 330 mp and 0.9 mp a t 410 mp. The 1cm. cells were matched for thickness. A Becknirtn pH meter, calibrated with a buffer solution (pH 7.00), served for pH measurements.
Cll cot+ re+-+ PbTT YInOgCzO4 - CsHiOi -- +
.iddd as
CdSO, Co (NOa) 2 FPCll Ph SOa)r
KIInOl
KaKsOa
SaiCsHsOi
Conrn., P.P.II.
89 > 50 50 ( l f n )
10 20
Error,
%
1
100
PPt. 0 1 5 100 100
Max. Concn. for 2% Error,
P.P.M. 80 0 0 50 50 0
0
