Table 11. Sulfate Determinations for Various Waters Samp!e SO., meqbter Std dev Municipal water 0.755,0.748,0.725 0.037 Supply, Bahia Blanca 0.730,O.725,O.730, 0.730 Colorado River 3.82,4.06,4.Oo,3.89, 0.089 3.82,3.90,3.90
for 1 hour. Filter about 25 ml of the suspension through a good quality filter paper which retains fine particles. Add 5 drops of the phosphate buffer, mix, and measure the absorbance at 530 mp. Determine the sulfate concentration with a calibration curve prepared by carrying aliquots of the standard KzS04solution and a distilled water blank through the entire procedure. Because of the nature of the equilibrium, the amount of chloranilate in solution due to the solubility of barium chloranilate decreases as the initial sulfate in solution increases. As a result, the calibration curve is not linear. Therefore, the absorbance of the blank should not be subtracted from the absorbance of the standards or samples. The total absorbance of the standards should be plotted against sulfate concentration, and the sulfate concentration of the unknowns should be determined by comparing their total absorbance with the calibration curve.
these waters and the recovery of sulfate is presented in Table I. In all cases the recovery of sulfate was within 3 of the added amount. The reproducibility of the method was tested by carrying aliquots of two water samples through the procedure seven times. Each determination was made on a different day. One sample was taken from the municipal water supply of the city of Bahia Blanca and the other was taken from the Colorado River near its mouth in the southern tip of the Province of Buenos Aires. The individual determinations and their standard deviations are presented in Table 11. The procedure presented in this work improves the sensitivity of the original procedure of Bertolacini and Barney without the necessity of access to an ultraviolet spectrophotometer. It should prove of value for the determination of sulfate in water samples and similar aqueous solutions.
R.M. CARLSON' R. A. ROSELL W. VALLEJOS
Instituto de Edafologia e Hidrologia Universidad Nacional del Sur Ave. Alem 925 Bahia Blanca, Argentina 1 Present address, Department of Pomology, University of California, Davis.
DISCUSSION
This procedure was tested on four water samples of known sulfate concentrations which had been prepared by dissolving reagent grade salts in distilled water. The composition of
RECEIVED for review November 14,1966. Accepted February 24, 1967.
Correction Applications of Signal-to-Noise Theory in Molecular Luminescence Spectrometry In this article by P. A. St. John, W. J. McCarthy, and J. D. Winefordner [ANAL.CHEM. 38, 1828 (1966)] the following corrections should be made: 1. On page 1829, Equation 5 should read as below
Pe,
=
P.&s
=
P.b*QhW' __-4rAAX'
3. On page 1832, Equation 22 should read as below
6%
*
ANALYTICAL CHEMISTRY
4. The constant Ks* defined under Equation 23 should be
I"k&.f&~
2. On page 1830, Equation 7 should read as below
.
w,=
5. It should be noted thatf3 is equal to& X fs in Appendix 11. 6. The source intensities, I", used to calculate the values of Cminin Table I were calculated from blackbody theory by assuming that the xenon arc plasma had a temperature of 6OOO" K and an emissivity of 0.06.
