Adsorption stripping methods

Method 2 -An adsorptive stripping method also involving pulse voltammetry, which yielded a peak current that was proportional to the concentration of chlorpromazine in the range of 83 to 2000 nM. 

Adsorption stripping methods are quite similar to the anodic and cathodic stripping methods we have just considered. Here, a small electrode, most commonly a hanging mercury drop electrode, is immersed in a stirred solution of the analyte for several minutes. Deposition of the analyte then occurs by physical adsorption on the electrode surface rather than by electrolytic deposition. After sufficient analyte has accumulated, the stirring is discontinued, and the deposited material is determined by linear-scan or pulsed voltammetric measurements. Quantitative information is based on calibration with standard solutions that are treated in the same way as samples. 

Electrode reactions are heterogeneous reactions taking place at the surface of the electrode. Sensitivity in detection of some compounds has been increased by several orders of magnitude by taking advantage of the adsorption phenomena at the electrode surface. In adsorptive stripping methods accumulation of compounds can be improved by proper selection of the electrode potential. 

Distinguish between (a) voltammetry and amperometry, (b) linear-scan voltammetry and pulse voltammetry, (c) differential-pulse voltammetry and square-wave voltammetry, (d) an RDE and a ring-disk electrode, (e) faradaic impedance and double-layer capacitance, (f) a limiting current and a diffusion current, (g) laminar flow and turbulent flow, (h) the standard electrode potential and the half-wave potential for a reversible reaction at a working electrode, (i) normal stripping methods and adsorptive stripping methods. 

A novel sensitive and seleetive adsorptive stripping proeedure for simultaneous determination of eopper, bismuth and lead is presented. The method is based on the adsorptive aeeumulation of thymolphetalexone (TPN) eomplexes of these elements onto a hanging mereury drop eleetrode, followed by reduetion of adsorbed speeies by voltammetrie sean using differential pulse modulation. The optimum analytieal eonditions were found to be TPN eoneentration of 4.0 p.M, pH of 9.0, and aeeumulation potential at -800 mV vs. Ag/AgCl with an aeeumulation time of 80 seeonds. The peak eurrents ai e proportional to the eoneentration of eopper, bismuth and lead over the 0.4-300, 1-200 and 1-100 ng mL ranges with deteetion limits of 0.4, 0.8 and 0.7 ng mL respeetively. The proeedure was applied to the simultaneous determination of eopper, bismuth and lead in real and synthetie samples with satisfaetory results. 

Alternatively, cetrimide (197c) and cetylpyridinium chloride were determined in industrial and consumer products, by indirect adsorptive stripping voltametry on a dropping mercury electrode425. A rapid method for benzalkonium chloride (197b) in pharmaceutical preparations was based on LLE of the picrate into chloroform in an F1A system and determination of the anion426. 

The adsorption behavior of the psychotropic drug flunitrazepam (256) at the hanging mercury drop electrode was studied by staircase voltammetry and by adsorptive stripping differential pulse voltammetry. 256 can be determined down to nanomolar levels by using adsorptive preconcentration prior to the differential pulse voltammetry scan. The method was applied to determination of 256 in human urine530. 

For the analysis of surface-active, electroactive organic compounds, the adsorptive stripping SWV was used. The method was applied to numerous analytes. Several of them are listed in Table 3.2. Some examples of metal complexes which were used for the quantitative analysis of metal ions by adsorptive... 

Barek et al. have reported on the determination of AT-nitroso compounds, azo compounds, heterocychcs, aromatic nitro compounds, heterocychc amines and even benzyl chloride using electrochemical methods such as voltammetry and polarog-raphy. The nitro and AT-nitroso compounds work particularly well in reductive mode [47, 48]. For appropriate analytes, adsorptive stripping voltammetry and anodic stripping voltammetry can give orders of magnitude lower detection hmits than are available from HPLC with electrochemical detection [48]. 

Song et al. have reported the determination of chlorpromazine by adsorptive stripping voltammetry [169]. Phosphate buffer saline solution (pH 7.4), consisting of 0.2 g KH2PO4,1.15 g Na2HP04,0.2 g KCl, 8 g NaCl, and 0.047 g MgCl2, was used as the supporting electrolyte. Two methods were reported for the determination of chlorpromazine ... 

Safavi et al. [68] have described an indirect method for the determination of CN ions and HCN. The method utilized the effect of cyanide on cathodic adsorptive stripping peak height of Cu-adenine. 

Electrode mechanism and analytical determination of cocaine and its metaboKtes, such as benzoylecgonine, ecgonine, and ecgonine methyl ester have been studied [192] at HMDE. These compounds were adsorbed at the electrode. Adsorption of benzoylecgonine was stronger than that of cocaine. Consequently, adsorptive stripping voltammetric method for the determination of cocaine was based on reduction of benzoylecgonine. 

Stripping voltammetry has also been applied to the quantitation of the drug in formulations. A sensitive and precise method using square-wave adsorptive stripping voltammetry has been developed for the determination of sulpha-quinoxaline in veterinary formulations [157]. The differential pulse adsorptive stripping voltammetric determination of midazolam in injectable formulations as a method for quality control has been demonstrated [158]. 

Schwartz, J., Henze, H. and Thomas, F.G. (1995) Voltammetric speciation of butyltin compounds. 1. An adsorptive cathodic stripping method. Fresenius J. Anal. Chem., 352, 474 178. 

Riso, R.D., B. Pemet-Coudrier, M. Waeles, and P. Le Corre. 2007. Dissolved iron analysis in estuarine and coastal waters by using a modified adsorptive stripping chronopotentiometric (SCP) method. Anal. Chim. Acta 598 235-241. 

The dissociation constant and solubilities of rufloxacin HC1 (21 HC1) were measured (89MI4). An adsorptive stripping voltametric method with a hanging Hg drop electrode was developed for the determination of 21 in tablets and biological fluids (95MI20). 

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