QTestPaper - 139 Anal. Chem. 1991. 63. 139-146 t...

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Anal. Chem. 1991. 63. 139-146 139 tetradecanol) are separated and detected, quantitation is hindered by poor solubility and the formation of micelles. Applications. Since a prerequisite for PAD reactivity is adsorption of the analyte, the presence of other surface-ad- sorbable substances, as well as electroactive compounds, can act as interferences. Therefore, general selectivity is achieved via chromatographic separation prior to PAD. This conclusion does not preclude additional selectivity from control of de- tection parameters. The assay for alcohols was applied to several matrices to illustrate the analytical utility of the procedure. Separation on an ion-exclusion column with direct detection is illustrated in Figure 8 for various aliphatic alcohols and polyalcohols in toothpaste (A), liquid cold formula (B), brandy (C), and wine cooler (D). The selectivity for alcohols in acidic media at a Pt electrode contributes to decreased time for sample prep- aration and simplified chromatograms. The versatility of separations on mixed-mode ion-exchange columns with selective detection is illustrated in Figure 9 by the simultaneous detection of ionic and neutral species in a pharmaceutical preparation. This experiment utilizes a UV detector and PAD in series after a PCX-500 column. Under acidic conditions, the cephalosporin antibacterial consists of a cation (i.e., cefazolin) and neutral and anionic compounds (i.e., lB-hexanediol, 1,4-cyclohexanediol, and p-toluenesulfonic acid). The neutral and anionic compounds are separated by the reversed-phase character of the column, while the cationic compound is separated by a combination of cation exchange and reversed-phase mechanism. Figure 9 shows that the p-toluenesulfonic acid and the cefazolin are both detected by UV at 254 nm (A), and the two diols, which do not have a chromophore, are easily detected by PAD (B). In addition, the cefazolin has a PAD signal, which has a higher limit of detection than UV, but may be utilized for added selectivity. LITERATURE CITED Kisslnger, P. T. In Laboratory Techniques in Electroanalytical Chemis- try; Klssinger, P. T., Heineman, W. R., Eds.; Marcel Dekker: New York, 1984; pp 631-32. Adams, R. N. Electrochemistry at SolM Electrodes; Marcel Dekker: New York, 1969. Gllman, S. In E/ectroana/ytica/ Chemistry; Bard, A. J., Ed.; Marcel Dekker: New York, 1967; Vol. 2, pp 111-92. Fleet, B.; Little, C. J. J. Chromtogr. Sci. 1874, 72, 747. Van Rooljen, H. W.; Poppe. H. Anal. Chim. Acta 1881, 730, 9. Hughes, S.; Meschi, P. L.; Johnson, D. C. Anal. Chim. Acta 1881. 732, 1. Johnson, D. C.; Lacourse, W. R. Anal. Chem. 1890. 62, 589A. Nachtmann, F.; Budna. K. W. J. Chromtogr. 1977, 736, 279. Jupille, T. J. Chromatogr. Sci. 1978, 77, 160. Beden, B.; Cetin, I.; Kahyaoglu. D.; Takky, D.; Lamy, C. J. Catal. 1987, 704, 37. Ocon, P.; Alonso, C.; Celdran, R.; Gonzalez-Velasco, J. J. Electroanal. Chem. 1888, 206, 179. Slingsby, R. W.; Rey, M. J. Li9. Chromatogr. 1880, 73(1), 107. Lacourse, W. R.; Jackson, W.
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This note was uploaded on 01/06/2012 for the course UGS 303 taught by Professor Foster during the Fall '08 term at University of Texas at Austin.

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QTestPaper - 139 Anal. Chem. 1991. 63. 139-146 t...

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