Voltammetry sample preparation

Measurement of trace metals, including nickel in seawater can be completed using an in-line system with stripping voltammetry or chronopotentiometry (van den Berg and Achterberg 1994). These methods provide rapid analysis (1-15 minutes) with little sample preparation. The detection limit of these methods for nickel was not stated. Recommended EPA methods for soil sediment, sludge, and solid waste are Methods 7520 (AAS) and 6010 (ICP-AES). Before the widespread use of AAS, colorimetric methods were employed, and a mrmber of colorimetric reagents have been used (Stoeppler 1980). 

The combination of preconcentration by electrodeposition with stripping by voltammetry is probably the most sensitive electroanalytical method in common use today. Consequently, this popular technique is discussed in more detail in Chapter 24. Preconcentration of material by an electrode reaction has been used in sample preparation for atomic absorption, neutron activation, x-ray fluorescence, microprobe, and several other spectroscopic techniques. 

Detection techniques of high sensitivity, selectivity, and ease of coupling with sample preparation procedures are of special interest for measuring PGM content in biological and environmental samples. ICP MS, electrothermal atomic absorption spectrometry (ET AAS), adsorptive voltammetry (AV), and neutron activation analysis (NAA) have fotmd the widest applications, both for direct determination of the total metal content in the examined samples and for coupling with instrumental separation techniques. Mass spectrometry coupled with techniques such as electrospray ionization (ESI) and capillary electrophoresis (CE) (e.g., ESI MS", LC ESI MS", LC ICP MS, CE MS", and CE ICP MS) offer powerful potential for speciation analysis of metals. MS is widely used for examination of the distribution of the metals in various materials (elemental analysis) and for elucidation of the... 

The use of these labels for DNA detection typically requires covalent attachment because the probe molecules lack intrinsic DNA-binding capabilities. However, access to probes whose structural and electrochemical properties can be chosen for optimal efficiency amply justifies the added sample preparation time. In many of these cases, the electrochemical processes used for readout do not involve the DNA/electrode interface per se. Rather, the molecular-recognition properties of DNA are exploited to recruit the DNA-bound redox probes to the surface for analysis by more traditional electrochemical techniques, such as enzymatic catalysis or stripping voltammetry. 

Figure 3.9 Shell-cross-linked nanotubes of PFS48-h-PMVS300 block copolymers (a) TEM image for the sample prepared for THF solution (b) cyclic voltammetry in dichloromethane benzonitrile (2 1) with 0.1M [Bu4N][PFg] as supporting electrolyte. (From Wang and Manners.26 Reproduced with permission.)...

Based upon these results, a simple, rapid, reproducible and accurate voltammetric method was proposed for the determination of xanthine, theophylline, theobromine and caffeine in the micromolar concentration range [26], The analytical performance characteristics of the method are comparable to those reported for the determination of xanthines by the use of chemically modified electrodes, biosensing techniques and differential pulse voltammetry. The excellent results obtained for caffeine determination in commercially available products, with very simple sample preparation, involving only dilution in electrolyte, demonstrates the practical analytical utility of the method. 

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