Nonionic surfactants trace analysis

Cloud point extraction of metal ions. The use of cloud point extraction as a separation technique was first introduced by Watanabe for the extraction of metal ions forming sparingly water soluble complexes [109], Since then, the technique has been applied successfully to the extraction of metal chelates for spectrophotometric, atomic absorption, or flow injection analysis of trace metals in a variety of samples [105-107,110]. Other metal complexes such as AUCI4 or thiocyanato-metal complexes can be extracted directly using nonionic surfactants such as polyoxyethylene... 

Particle beam (PB) El MS is less sensitive than capillary GC-MS. This can be partly compensated for by the fact that much larger volumes of sample can be introduced in the LC-MS method [8]. The method can therefore be applied to the trace analysis of nonionic surfactants. Certain species, which due to their low volatility, high polarity or thermal instability cannot be detected by GC-MS, can be analysed by LC-PB-MS. Similarly, some highly volatile species are difficult to analyse by PB-MS, and the two techniques are therefore complementary. 

Because of the lack of specificity, polarographic techniques are only useful for analysis of real world samples if they are coupled with separation procedures. For example, one team has demonstrated that the BIAS procedure for trace analysis of nonionics can be improved by using an electrochemical procedure for surfactant determination after first precipitating and isolating the potassium iodobismuthate-nonionic complex from the sample (18,26). They prevent interference of hydrocarbons by washing the precipitate with isooctane (27). 

X-ray fluorescence can be used for trace analysis of nonionic surfactants. In this case, the analysis is performed according to the titrimetric method using tetraiodobismuth-ate reagent, but the final measurement of bismuth concentration in the precipitate is made not by potentiometric titration, but by XRF (109). 

If certain anionic fluorescent molecules are immobilized in a matrix such as cross-linked polyvinylalcohol or a modified glass surface, they show an increase in fluorescent intensity and a decrease in emission wavelength in the presence of a cationic surfactant. Although not suitable for trace analysis, this phenomenon is proportional to concentration over a range of about 30, and is insensitive to anionic and nonionic surfactants (126). 

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