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52 Modern Analytical Chemistry

8. Ibrahim and co-workers developed a new method for the 9. A sample was analyzed for the concentration of two analytes,
quantitative analysis of hypoxanthine, a natural compound of C and D, under two sets of conditions. Under condition 1 the
14
some nucleic acids. As part of their study they evaluated the calibration sensitivities are
method’s selectivity for hypoxanthine in the presence of k C,1 = 23 ppm –1 k D,1 = 415 ppm –1
several possible interferents, including ascorbic acid.
a. When analyzing a solution of 1.12 ´10 M hypoxanthine, and for condition 2
–6
the authors obtained a signal of 7.45 ´10 amperes (A). k C,2 = 115 ppm –1 k D,2 = 45 ppm –1
–5
What is the sensitivity for hypoxanthine? You may
assume that the signal has been corrected for the method The signals under the two sets of conditions are
blank. S meas,1 = 78.6 S meas,2 = 47.9
b. When a solution containing 1.12 ´10 M hypoxanthine
–6
and 6.5 ´10 M ascorbic acid was analyzed a signal of Determine the concentration of C and D. You may assume
–5
–5
4.04 ´10 A was obtained. What is the selectivity that S reag is zero under both conditions.
coefficient for this method? 10. Examine a procedure from Standard Methods for the Analysis
c. Is the method more selective for hypoxanthine or for of Waters and Wastewaters (or another manual of standard
ascorbic acid? analytical methods), and identify the steps taken to
d. What is the largest concentration of ascorbic acid that may compensate for interferences, to calibrate equipment and
be present if a concentration of 1.12 ´10 M instruments, to standardize the method, and to acquire a
–6
hypoxanthine is to be determined within ±1%? representative sample.

3 K SUGGESTED READINGS

The following papers provide alternative schemes for classifying Several texts provide numerous examples of analytical procedures
analytical methods for specific analytes in well-defined matrices.
Booksh, K. S.; Kowalski, B. R. “Theory of Analytical Chemistry,” Basset, J.; Denney, R. C.; Jeffery, G. H.; et al. Vogel’s Textbook of
Anal. Chem. 1994, 66, 782A–791A. Quantitative Inorganic Analysis, 4th ed. Longman: London, 1981.
Phillips, J. B. “Classification of Analytical Methods,” Anal. Chem. Csuros, M. Environmental Sampling and Analysis for Technicians,
1981, 53, 1463A–1470A. Lewis: Boca Raton, 1994.
Valcárcel, M.; Luque de Castro, M. D. “A Hierarchical Approach to Keith, L. H., ed. Compilation of EPA’s Sampling and Analysis
Analytical Chemistry,” Trends Anal. Chem., 1995, 14, 242–250. Methods, Lewis: Boca Raton, 1996.
Further details on evaluating analytical methods may be found in Rump, H. H.; Krist, H. Laboratory Methods for the Examination of
Wilson, A. L. “The Performance-Characteristics of Analytical Water, Wastewater and Soil. VCH Publishers: New York, 1988.
Methods,” Part I-Talanta, 1970, 17, 21–29; Part II-Talanta, Standard Methods for the Analysis of Waters and Wastewaters,
1970, 17, 31–44; Part III-Talanta, 1973, 20, 725–732; Part IV- 19th ed. American Public Health Association: Washington,
Talanta, 1974, 21, 1109–1121. DC, 1995.

3L REFERENCES

1. Taylor, J. K. Anal. Chem. 1983, 55, 600A–608A. Chapter 1, pp. 3–6; (b) Potts, L. W. Quantitative Analysis—Theory and
2. Fitch, A.; Wang, Y.; Mellican, S.; et al. Anal. Chem. 1996, 68, Practice. Harper and Row: New York, 1987, p. 12.
727A–731A. 8. Valcárcel, M.; Ríos, A. Anal. Chem. 1993, 65, 781A–787A.
3. Basset, J.; Denney, R. C.; Jeffery, G. H.; et al. Vogel’s Textbook of 9. Valcárcel, M.; Ríos, A. Analyst, 1995, 120, 2291–2297.
Quantitative Inorganic Analysis, 4th ed. Longman: London, 10. (a) Amore, F. Anal. Chem. 1979, 51, 1105A–1110A; (b) Taylor, J. K.
1981, p. 8. Anal. Chem. 1981, 53, 1588A–1593A.
4. Ingle, J. D.; Crouch, S. R. Spectrochemical Analysis. Prentice-Hall: 11. D’Elia, C. F.; Sanders, J. G.; Capone, D. G. Environ. Sci. Technol. 1989,
Englewood, NJ, 1988, pp. 171–172. 23, 768–774.
5. Barnett, N. W.; Bowser, T. A.; Gerardi, R. D.; et al. Anal. Chim. Acta 12. Jiménez-Prieto, R.; Velasco, A.; Silva, M.; et al. Anal. Chim. Acta 1992,
1996, 318, 309–317. 269, 273–279.
6. Rogers, L. B. J. Chem. Ed. 1986, 63, 3–6. 13. Oungpipat, W.; Alexander, P. W. Anal. Chim. Acta 1994, 295, 36–46.
7. (a) Sandell, E. B.; Elving, P. J. In Kolthoff, I. M.; Elving, P. J., eds. 14. Ibrahim, M. S.; Ahmad, M. E.; Temerk, Y. M.; et al. Anal. Chim. Acta
Treatise on Analytical Chemistry, Interscience: New York; Part 1, Vol. 1, 1996, 328, 47–52.