| Mercapto compounds are a class of compounds containing the function group-SH in a molecule. Because of the important role in radical scavenging, heavy metal detoxification,taking part in metabolic pathways, antagonism of ionizing radiation, and so on, such compounds are commonly used in pharmaceutical, food, cosmetic and clinical disease. So it has practical significance to quantity this kind of compound. However, the lack of a chromophore leads to the smaller molar absorption coefficient in the UV-Vis region. This is bad for the detection of UV-Vis optical analysis. According to Beer-Lambert Law(A=Kbc, A is the absorbance, K is the molar absorption coefficient, b is the optical path, c is the concentration of analyte), three ways can be adopted to make the mercapto compounds suitable for the detection of UV-Vis analysis. The first way is to increase molar absorption coefficient. It can be achieved by derivation reaction or a selective optical system. The second way is to improve the optical path of the optical detector. This means need to transform the instruments but the effect is limited. The third way is to take the pre-column or on-column enrichment techonolgy.The stacking or enrichment can be obtained by the physical and chemical properties of the analyte. In this paper, three new methods was established to determine mercapto compounds,which were based on the chemical properties of the thiol group: One is a relative selective optical method that was based on the optical property of gold nanoparticles and the chemical property of thiol group; The others are capillary electrophoresis methods which were based on the pre-column derivatization of the thiol group and on-column stacking technologies. In this article, two thiol compounds, cysteine and thioglycolic acid were studied as models. This paper was divided into 4 chapters and the contents are as follows:Chapter 1: First, the mercapto compounds which were commonly used in pharmaceutical,food, cosmetics and clinical studies of common disease were introduced briefly and shown the corresponding molecular structure. It can be found that those low molecular weight thiols compounds lacks chromophore by the structure. In order to make the thiol compounds suitable for UV-Vis detection, the related research was established by the chemical propertiesof the thiol group. According to the chemical properties of the thiol group, the determination methods of the thiol compounds were classified. Based on the classification of thiol property,the principles of the current determination methods were described in detail and cited some relevant research corresponding spectroscopy, high perform liquid chromatography, capillary electrophoresis and electrochemical analysis methods. Finally, the purpose, content and significance of this paper were introduced respectively.Chapter 2: Gold nonoparticles have a highger molar extinction coefficient; the non-ionic surfactant-modified gold nanoparticles can't be gathered by electrostatic interaction; the non-ionic surfactant-modified gold nanoparticles can be gathered by forming Au-S with visible color change. Based on these properties, a new optical analytical method of determination cysteine has been developed by using the non-ionic surfactant-modified gold nanoparticles as a probe.Under the optimized conditions of salinity, temperature and time, by using suitable nonionic surfactant and dosage, the content of cysteine was measured. The linear range of Probe 1 was between 6.1 mg/L and 30.3 mg/L, with a correlation coefficient(R2) of 0.999. The linear range of probe 2 between 3.6 mg/L and 18.2 mg/L, with a correlation coefficient(R2) of 0.989. LODs of the two porbes were 0.1, 0.5 mg/L respectively. The recoveries of spiked samples were between 92.2% and 106.3%. The method was simple, rapid and suitable for the routine analysis of cysteine determination.Chapter 3: Based on the relevant literature, A new method was developed for the determination of mercapto compounds by pre-column derivatization combined with acid-induced transient isotachophoretic stacking capillary electrophoresis. Mercapto compounds were derivatized with 2-chloro-1-hylpyridinium iodide(CMPI) in Tris-HCl buffer at pH 8.15 at room temperature. The derivatized mercapto compounds were introduced into the capillary filled up with 40 mmol/L formatic buffer(pH=3.96), followed by injection of diluted sulfuric acid. Upon application of voltage at normal polarity, the derivatized mercapto compounds were preconcentrated due to transient isotachophoresis stacking electrophoresis with H+ as the leading ion and Tris+ as the terminating ion. The detection wavelength was set at 312 nm. Cysteine and sodium thioglycolate were chosen as the models of mercaptocompounds to be detected. Various experimental factors influencing transient isotachophoresis stacking were investigated. Under the optimal conditions, the linear relation between peak area and concentration was obtained in the range from 10.0 mg/L to100.0 mg/L for cysteine, and from 4.0 mg/L to 100.0 mg/L for sodium thioglycolate. The LODs were 0.2mg/L and 0.4 mg/L for cysteine and sodium thioglycolate, respectively. The developed method was successfully applied to the determination of thioglycolate in depilatory cream samples.Chapter 4: Based on the optimized derivative conditions of cysteine in Chapter 3, the determination method of cysteine was developed, which was based on pH-mediated stacking and pre-column derivation. Acidified by H2SO4, the derivatizative cations were determinated by the capillary electrophoresis pH-mediated stacking technology. The pH-mediated stacking process can be divided into two steps: the first step is the stacking process of the derivatizative product, the second step is that the derivatizative product is separated from the mixture by the capillary zone electrophoresis. The pH-mediated on-column stacking conditions were optimized carefully. The measurement of Cys conformed well with linear law between 1.2 mg/L and 60.0 mg/L, with a correlation coefficient(R2) of 0.999. The recoveries of spiked samples were between 95.7% and 106.0%. The present method was suitable for the determination of these compounds containing thiol group and amino group. |
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