The solubility and stability of calcium arsenates at 25 • C was determined by both precipitation and dissolution experiments. Ca 3 (AsO 4 ) 2 ·3H 2 O(c), Ca 3 (AsO 4 ) 2 ·2 1 / 4 H 2 O(c), Ca 5 (AsO 4 ) 3 (OH)(c) and Ca 4 (OH) 2 (AsO 4 ) 2 ·4H 2 O(c) were identified in our experiment over a wide range of pH and for Ca/As molar ratios between 1.25 and 4.0. The solids precipitated at pH = 3 ∼ 7 and Ca/As = 1.5 were phase-pure and well-crystallized Ca 3 (AsO 4 ) 2 ·xH 2 O(c) and had relatively larger grain size than those formed at pH > 7. Based on the analytical results and using the computer program PHREEQC, the solubility products for Ca 3 (AsO 4 ) 2 ·3H 2 O(c), Ca 3 (AsO 4 ) 2 ·2 1 / 4 H 2 O(c), Ca 5 (AsO 4 ) 3 (OH)(c) and Ca 4 (OH) 2 (AsO 4 ) 2 ·4H 2 O(c) were calculated as K sp of 10 −), respectively. Correspondingly, the free energies of forming ( G o f ) of these calcium arsenates were calculated to be −3787.87 kJ/mol, −3611.50 kJ/mol, −5096.47 kJ/mol and −4928.86 kJ/mol.

Although manganese (Mn) is an essential element, exposure to excessive levels of Mn and its accumulation in the brain can cause neurotoxicity and extrapyramidal syndrome. We have investigated the differences in the accumulated levels of Mn, the degree of lipid peroxidation, and its effects on the levels of trace elements (Fe, Cu, and Zn) in various regions in the brain of rats having undergone acute Mn exposure. The rats in the dose-effect group were injected intraperitoneally (ip) with MnCl2 (25, 50, or 100 mg MnCl2/kg ) once a day for 24 h. The Mn significantly accumulated (p<0.05) in the frontal cortex, corpus callosum, hippocampus, striatum, hypothalamus, medulla, cerebellum, and spinal cord in each case. The rats in the time-course group were ip injected with MnCl2 (50 mg MnCl2/kg) and then monitored 12, 24, 48, and 72 h after exposure. The Mn accumulated in the frontal cortex, corpus callosum, hippocampus, striatum hypothalamus, medulla, cerebellum, and spinal cord after these periods of time, In both the dose-effect and time-course studies, we observed that the concentration of malondialdehyde, an end product of lipid peroxidation, increased significantly in the frontal cortex, hippocampus, striatum, hypothalamus, medulla, and cerebellum. However, no relationship between the concentrations of Mn in the brain and the extent of lipid peroxidation was observed. In addition, we found that there was a significant increase (p<0.05) in the level of Fe in the hippocampus, striatum, hypothalamus, medulla, and cerebellum, but the Cu and Zn levels had not changed significantly. These findings indicated that Mn induces an increase in the iron level, which provides direct evidence for Fe-mediated lipid peroxidation in the rats' brains; these phenomena might play important roles in the mechanisms of Mn-induced neurotoxicology.

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This work presents a review of the microdialysis (MD) sampling technique for on-line coupling with high-performance liquid chromatography (HPLC) for biomedical analysis. MD-HPLC was first used in the field of brain metabolism to study neurotransmission, and this remains its common application in the biomedical field. On-line MD-HPLC hyphenated methods provide advantages over those with off-line MD-based techniques, including simplified sample preparation, automated analyses, avoidance of contamination introduced during the analytical process, and in situ analysis of the extracellular fluid of living organisms. This review outlines the effectiveness of the continuous monitoring of unbound chemicals from tissues, organs, and body fluids by on-line MD-HPLC methods. In addition, a discussion is presented on the application of in vivo on-line MD-HPLC toward obtaining biochemical event information in the extracellular fluid of various tissues and in biological fluids for pharmacokinetic, pharmacodynamic, toxicological, and bioprocess monitoring.