Anal. Chem. 1983, 55, 1175-1176
Table 11. Comparison of Results of Alkalinity Tests by Titration, IKL, and TAAa sample no. 1103 1111
1112 1113
1114 1116 1118
1119 1120 av
titration, IKL, mg/L TAA, mg/L mg/L __-mean std dev mean std dev mean std dev 26.1 44.6 14.9 13.4 20.3 56.6 147 104 266
0.9 0.3 0.7 0.7 0.7 0.3 0.3 0.3 1.6
26.5 44.1 15.2 13.8 19.6 57.3 144 102 259
0.6
0.5 0.5 0.9 1.3
0.6 0.3 2.5 3.6 2.4 1.4
25.4 44.3 13.9 13.4 18.7 57.8 141 104 264
0.2 0.1
1.2 2.3 1.5 0.9 1.4 2.9 1.2 1.3
a Based on five measurements for each determination of mean or standand deviation.
Table 111. Appa.rent Result of Successive Samples with a Concentration of 8 0 mg/L Which Immediately Followed Samples with a Concentration of 550 mg/LQ apparent result as a % of equilibrium value sample no. condition 1 condition 2 1
119
2 3 4 5
106 102 100
167 118
105 103 100
See text for case description. low alkalinity follows one of high alkalinity (Table 111, case 1). Successive samples with a concentration of 550 mg/L were analyzed with the TAA until equal results were obtained. They were immediately followed by samples with a concentration of 80 mg/L. When preceded by a sample containing 550 mg/L, an 80 mg/L sample was overestimated by approximately 19%. The error on the TAA results from intersample mixing between any sample and the adjacent sample in the segmented flow trystem. The problem of intersample mixing on the TAA is worse where the tubing is dirty. The experiment described was conducted with a short length of slightly dirty tubing following the sample probe. In this case, the first 80 mg/L sample that followed the 550 mg/L sample was 67% high. Succeeding samples were also higher (Table 111, case 2). Another problem with the TAA is a slight drift of the bass line. A typical drift for bicarbonate over a span of 50 samples is 2 mg/L. This amount of drift is enough to account for all the deviation shown in Table 11.
1175
When the IKL was used to measure samples with an 80 mg/L concentration that followed samples with a 550 mg/L concentration, the alkalinity measured in the first 80 mg/L sample was slightly higher than the actual concentration. The largest error observed was 10%. Intersample mixing cannot occur on the IKL since samples are kept in separate cups. Any error in the IKL system results from carryover from one sample to the following on the sample probe, stirring paddle, or colorimeter tubing. The stirring paddle and sample probe are made of a nonwetting material to minimize any carryover.
CONCLUSIONS The primary objective of this study was to develop reagents that can be used to measure low concentrations of alkalinity in water samples using the TAA. The reagents in Table I allow accurate determinations of alkalinity in the 10 to 700 mg/L range. The IKI, and TAA were about equally accurate provided one watched for the possibility of intersample mixing on the TAA. If the approximate alkalinity of the samples is known, one can immediately choose the appropriate reagent for the sample. If the approximate alkalinity is not known, it is recommended that one start with the reagent useful for the highest concentrations (reagent C for the TAA, reagent E for the IKL). Accurate results will be obtained for samples within the usable range of this reagent (Table I). Approximate results will be obtained for samples with a concentration below this range. Such samples should be separated from the remainder and rerun by using the reagent with the usable range appropriate for these samples. This procedure also eliminates the problem of intersample carryover (Table 111). Registry No. Water, 7732-18-5. LITERATURE CITED (1) McKay, D. K.; et al. Clin. Chim. Acta 1965, 12, 75-79. (2) Larson, T. E.; Henley, L. Anal. Chem. 1955, 27, 851. (3) Thomas, J. F. J.; Lynch, J. J. J . Am. Water Works Assoc. 1960, 52, 259-268. (4) American Public Health Assoclation; American Water Works Associatlon; Water Pollution Control Federation "Standard Methods for the Examlnation of Water and Wastewater", 15th ed.; Amerlcan Publlc Health Association: Washington, DC, 1980; p 253. (5) Rechnitz, G. A. Report 238490/7 GA; U.S. National Technical Information Service, 1974, Chem. Abstr. 1975, 83, 152043. (6) Small, H.; et al. Anal. Chem. 1976, 47, 1801. (7) Deguchi, T.; et 81. J. Chromatogr. 1977, 133, 173. (6) United States Environmental Protection Agency, EPA-600/4-79-020, 1979; p 310.2.
RECEIVED for review October 13,1982. Accepted January 24, 1983. The use of trade, firm, or corporation names in this paper is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the U.S. Department of Agriculture or the Forest Service of any product or service to the exclusion of others that may be suitable.
Glass-Sample-Tube Breaker Wllllam E. Caldwell and Jerome D. Odom" Department of Chemistty, 1Jniversity of South
