A. Micro amounts
Table 11. Determination of Mercury in Organic Mercurials Mercury(I1) Compound Weight, mg Taken,O p g Found, fig PMB 3.50 156 151 3.68 4.91 4.07
B. Submicro amounts
PMB Thiomersal
2.75 3.03 2.15 2.46
5
164 82 109 54.5 90.5
163 80.3. 108 52.9 88.7
30.6 33.7 20.6 10.3 23.6 11.8
30.3 32.7 20.2 10.0 24.0 11.4
Recovery, 97 99 98 99 97 98 99 97 98 97 102 97
Aliquots taken after digestion with 1 :1 (v/v) HC104:HNOs
all these titrations, the end point occurs at a 1 Hg:l RSH ratio. These titrations were performed automatically ; the same results were also obtained by manual addition of the titrant. Calibration of the method was performed by titration of 5-150 pg of mercury(I1) with 8.3 X loe4 DTC. The results are summarized in Table I. Determination of mercury in organic compounds or proteins requires a preliminary step of combustion. Satisfactory results were obtained using 1 :1 (v/v) HC1O4:HNO3 as a combustion mixture. In Table IIA the results obtained for the determination of micro amounts of mercury in organic mercurials are presented. Samples of PMB containing 3-5 mg of PMB were weighed, and after combustion, aliquots containing 50-1 50 pg of mercury were titrated amperometrically. Table IIB presents the results obtained for determination of mercury in organic materials on a submicro scale. In this series 2-3 mg of PMB and thiomersal were weighed. Amperometric titrations were performed on aliquots containing 10-30 pg of mercury with yields of over 97 %. Since titrations of 10-30 pg mercury(I1) after combustion gave satisfactory results, we applied this method for the determination of mercury in proteins. In this case the percentage of mercury in the derivative is quite small (between 1 to 10%) whereas the percentage of mercury in organic mercurials is around 50 %. The amount of protein taken for analysis was between 1-3 mg. From these samples, aliquots were taken after digestion, adjusted to pH 9.0, and titrated amperometrically. (It is preferable to dilute the digested samples as much as possible, to reduce salt concentration.) Table I11 summarizes the results obtained for determination of mercury in proteins. The accuracy of mercury determination
Table 111. Determination of Mercury in Proteins Mercury(I1) Weight, Taken,a Found, Recovery, Protein mg Plg Pg [RNase. 1 Hg] 1.625 9.3 9.2 99 [Insulin.3 Hg] 1.488 28.0 25.0 90 Pap. 2 Hg 1.560 8.6 9.0 105 Aliquots after digestion with 1 :1 (v/v) HC1OI:HNOI.
z
(I
was better than 10%. Considering the low percentage of mercury in the mercury proteins and the fact that the results of the amperometric titrations were compared to those obtained from radioactive measurements, this error is acceptable. This method is thus applicable in the range where atomic flame spectrometry (11) and atomic absorption spectrophotometry (12) are used and is particularly useful for determination of mercury in proteins. ACKNOWLEDGMENT We thank Ephraim Katchalski for his interest in this work, and Izchak Z. Steinberg for helpful suggestions in the preparation of this manuscript. RECEIVED for review December 22, 1969. Accepted April 20, 1970. Work partially supported by Research Grant GM 13637, United States Public Health Service. (11) J. M. Mansfield, J. D. Winefordner, and C. Veillon, ANAL. CHEM., 37, 1049 (1965). (12) W. R. Hatch and W. L. Ott, ibid., 40, 2085 (1968).
Ultraviolet Spectrophotometric Determination of Sulfur Dioxide M. W. Scoggins Research and Development Division, Phiiiips Petroleum Company, Bartlesviiie, Okla. 74004
THEIMPORTANCE of air pollution control has focused attention on the determination of trace quantities of industrial contaminants in the atmosphere and surface waters. Sulfur dioxide is one of these contaminants and reliable methods for its determination are being sought. In addition, improved pro-
cedures are needed to analyze complex research samples and plant streams when conventional methods fail. The procedure described herein is based on the observation that sulfur dioxide in 1M sulfuric acid solution has an absorption band at 276 nm. While the procedure is not sensitive
ANALYTICAL CHEMISTRY, VOL. 42, NO. 9,AUGUST 1970
1091
Table I. Determination of SOz by Ultraviolet Spectrophotometry Sulfur dioxide, wt Sample Added" Foundb A 0.979 1 .oo
z
B
0.572 0.190 0.097 0.053 0.00975
C
D E
F Recovery = 98.2 Pooled std dev 0.0038 Sulfur dioxide added as Na2S03and NaHSOs. b Average of six determinations.
0.577 0.190 0.092 0.050 0.00918
zx
w
V
z
U
Q
0
m
