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Adsorptive stripping voltammetry (AdSV) is compared with capillary zone electrophoresis (CZE) for the detection and determination of trace concentrations of metal ions such as Co2+, Cuz+, Cd2+, Zn2+ and Pb2+ as their 2-(5'-bromo-2'-pyridylazo)-5-(diethylamino)phenol (PADAP) chelates. Limits of detection for Cd2+, Zn2+, Pb2+ and Co2+ were 9, 3, 6 and 0.3 ppb, respectively, using the AdSV method, with Cu2+ not giving a reproducible cathodic signal as the Cu2+-PADAP chelate. The technique would appear to be selective towards the determination of Co2+ in a mixture since its adsorbable chelate with PADAP was reduced at -670 mV, giving a voltammetric response not affected by the presence of equimolar concentrations (1 x lo-' rnol dm-3) of Cd2+, Pb2+ and Zn2+. CZE using PADAP at a concentration of 10-4 rnol dm-3 in the run buffer had higher limits of detection than AdSV but possessed greater selectivity in that, at pH 6, Coz+, Cd2+, Zn2+ and Cu2+ could be resolved as their chelates with PADAP, the Pb2+ chelate not giving a signal at all. Other selectivities could be observed at higher pH values. The CZE technique was also found particularly responsive to the Co3+-PADAP chelate in the presence of other trace metal ions. It is therefore being investigated as a trace analytical method for the determination of Co2+ in selected complex matrices.

The differential pulse polarographic (DPP) behavior of SK&F 95601 (I) has been studied in the pH range 0 to 14. At pH I 2 , (I) rapidly degrades into the sulfenamide (D:) and sulfide (DS), which are both reduced by 2e-processes, the former being subject to strong reactant adsorption. SK&F 95601 itself is reduced in a 4e process up to pH10, and either pK2 or pK, values, determined spectrophotometrically, are manifested polarographically at neutral pH A pK, value of 9.0 corresponding to the benzimidazole N-H group deprotonation is manifested polarographicallp with a pK5 value of ca. 11. SK&F 95601 and its degradation products D;, degraded D:, and DS can all be determined by adsorptive stripping voltammetry (AdSV) with limit of detections (LODs) of lo-' mol dm-3, except for the latter molecule with an LOD of lo--mol dm-3. These LODs are superior to those determined by DPP. Mixtures of these molecules can also be resolved with similar LODs. Cd" can be determined by ASV with a superior LOD in the presence of (I), i.e., 0.08 ppb as compared to 0.57 ppb in its absence, due to chelation phenomena. KEY WORDS: ATPase inhibitor, Stripping voltammetry, Pulse voltammetry lATRODUCTIONThe H+'/K+ ATPase inhibitor such as SK&F 95601 (I) is effective in stomach ulcer treatment due to its acid-catalyzed rearrangement to form the sulfenamide (D:), which then irreversibly inhibits the H+/K+ AWase enzyme, part of the "proton pump" located in the parietal cell of the stomach wall, by reaction with a thiol residue [ 1-31. Earlier articles in this series [4,5] have primarily shown the utilization of W spectrophotometry, high-performance liquid chromatography and differential pulse polarography to monitor the degradation of (I) and the structurally related omeprazole in acidic solutions pH2 and also the reactions of these benzimidazole sulfoxides with 2-mercaptoethanol in acidic solutions pH2 as a mimic of their believed reactions in vivo. This article concentrates on the differential pulse polarographic (DPP) and stripping voltammetric behavior of (I) and its degradation products such as D: and D: , which results in methods for their determination at nanomolar concentration levels. The interaction of heavy metal ions such as Cd2+ with (I) has also been investigated, which has resulted

The ASV and AdSV behavior of Zn" , Cd", Pb", Cu", Ni'+ and Sn4+ in the presence of selected complexing/chelating agents has been studied. The presence of 2,5-dimercapto-l,3,4-thiadiazole (I) lowers the limit of detection (LOD) for the ASV determination of Zn", CdZt and Pb2+ in 5 x lo-' moldm-' LiCl supporting electrolyte with a deposition time of 120s to 0.82, 0.17 and 0.34ppb, respectively, due to participation of the adsorbed complexing agent in the overall process. Similarly, Cd" can be determined in the presence of benzimidazole sulfoxides (11) and (111) by ASV in Britton-Robinson (BR) buffer p H 9 with 120s deposition with lower LODs of 0.12 and 0.06ppb. respectively. AdSV can also be used to determine Cd2+ with (II), (111) and ammonium pyrrolidine dithiocarbamate (IV) with LODs oF0.70, 0.64 and 0.20ppb, respectively and with Zn" having a n AdSV LOD of 1.09 ppb using adsorption of its chelate with (IV) at -900mV for 60 s in a supporting electrolyte of 5 x mol dm-3 LiCI. Participation of the adsorbed complexing agent in the ASV process is also observed for Sn4+ and Cu'+ in an oxalate/ammonium chloride/HCl buffer with lowered LODs of 0.5 I ppb and 0.76 ppb in the presence of p-methylene blue (V). The chelating agent 2-(5-bromo-2-pyridylazo)-5-diethyla1ninophenol (VII) can be used to determine Cd2+, Zn" and Pb2+ using the AdSV technique down to LODs of 9.3, 2.7 and 6.3 ppb, respectively. Several of these methods have been combined in the development of an automated method for the determination of trace Zn, Cd, P b and Cu in an artificial river water matrix. The accuracy and precision of this procedure is discussed. Determination of Ni, Sn and As by this automated method and in such a matrix proved to bc inaccurate.