A simple and sensitive cloud point extraction high-performance liquid chromatography method is proposed for the determination of isoniazid in blood. The procedure is based on the product of the reaction of isoniazid with benzaldehyde. It can be validated that there is a linear relationship between the signal of isonicotinyl hydrazone and the concentration of isoniazid. A cloud point extraction system of nonionic surfactant Triton X-100 is applied for preconcentration of isonicotinyl hydrazone. Then the analytes in surfactant-rich phase are detected with HPLC-UV system. calibration graph was obtained in the range of 2.0 × 10(-3)-0.5 mg/L, the detection limit was 5.0 × 10(-4) mg/L. Method validation is performed on serum samples spiked at two levels, the recoveries ranging from 82.17-83.81%, with relative standard deviations from 2.45% to 3.89%.

A new method for the determination of nine organophosphorus pesticides (OPPs): Dichlorvos, methamidophos, acephate, diazinon, dimethoate, chlorpyrifos, parathion-methyl, malathion and parathion-ethyl in concentrated fruit juice was developed using the cloud point extraction coupled with ultrasonic-assisted back-extraction prior to gas chromatography with flame photometric detection (GC-FPD) analysis. The parameters and variables that affect the extraction were investigated. Under optimum conditions: a solution containing 6% (W/V) polyethylene glycol 6000 (PEG 6000) and 20% (W/V) Na(2)SO(4) for the extraction of the OPPs. The coacervation phase obtained was back extracted with ethyl acetate. The upper ethyl acetate solution was centrifugated simply for further cleanup for the sake of automatic injection. A preconcentration factor of 50 was obtained for these nine pesticides. Using this method, the limits of detection (LOD) and limits of quantification (LOQ) were in the range of 0.5-3.0 and 1.5-9.0μgkg(-1) in concentrated fruit juice, respectively; the relative standard deviations (RSD) were <9%.

Melamine shows a polarographic wave at-0.34 V(vs.SCE) in a solution of KOH-Na2SO3,and the second derivative peak current of the wave is linearly proportional to the melamine concentration in the range from 1.0×10-2 to 10.0 mg/L(r=0.9992).Melamine in milk samples can not be directly determined by the polarographic method because of the interference of colloidal protein in milk.In this paper,many methods were studied for dispelling the interference.When the concentration of NaCl in milk was 150 g/L and the solution was kept at 100 ℃ for 10 min,the interference of colloidal protein could be avoided.In the case,the linear sweep polarographic method could be used for the determination of melamine in milk.The peak current was linearly proportional to the melamine concentration in the range of 0.4～10.0 mg/L with the detection limit of 0.1 mg/L.The recoveries were between 78.2% and 92.5%.The whole determination procedure could be completed in 20 min.

A highly sensitive method for the determination of arprocarb (AC), carbofuran (CF), isoprocarb (IC), and fenobucarb (FC) is proposed. The method is based on alkaline hydrolysis of the four carbamate pesticides, and the resultant hydrolysis products are reacted with 4-aminoantipyrene (AP) to give four red color products. The colored compounds are enriched and separated by cloud point extraction (CPE) method, and the coacervate phase containing the compounds is determined with a high-performance liquid chromatography (HPLC) system in the visible region. AC, CF, IC, and FC were determined on the basis of a linear correlation between the signals of the colored compounds and the concentrations of the pesticides. The method is applied to determine the four pesticides in corn samples; the limits of detection are 2.0 x 10(-4) mg L(-1) for AC, CF, and IC and 5.0 x 10(-4) mg L(-1) for FC, with recoveries ranging between 84.8 and 93.0%, at spiking levels of 5 x 10(-3), 2 x 10(-2), and 0.2 mg kg(-1), respectively.

Isoniazid (IN) can not be sufficiently extracted by the cloud point extraction (CPE) of polylethyleneglycol (PEG) 6000, and reacts with para-chlorobenzaldehyde to form a derivative (para-chlorobenzaldehydeisonicotiny-hydrazone, CIH). It was proven that there was linear relationship between the signal of CIH and the concentration of IN. A cloud point extraction system of polylethyleneglycol 6000 (NH4)(2)SO4 coupled with high performance liquid chromatography was developed for the separation and the simultaneous determination of isoniazid (IN), pyrazinamide (PZ) and rifampicin (RF). Under the optimum conditions, the analytes were eluted with a gradient mode and detected with a UV-detector at 310 nm, the retention time of isoniazid, pyrazinamide and rifampicin was 14.5, 34.4 and 38.1 min, respectively, the linear calibration curves in the range of 0.01 - 10 mg/L for isoniazid and 0.05 - 20 mg/L for pyrazinamide and 0.08 - 25 mg/L for rifampicin, respectively (r > 0.99). Average recoveries of three drugs ranged from 91.5% to 98.6% with relative standard deviations from 0.2% to 1.5%. The limits of detection of IN, PZ and RF was 4 x 10(-3), 2 x 10(-2) and 3 x 10(-2) mg/L, respectively. The CPE-HPLC-UV method had been applied to the determination of IN, PZ and RF in pharmaceuticals and in urine samples.

Carbofuran can be hydrolysed to from 2,3-dihydro-2,2-dimethyl-7-benzofuranol (BF). BF is coupled with 4-aminoantipyrene (AP) in presence of potassium ferricyanide (K3Fe(CN)6) to generate red coloured derivative(BFAP)having λmax 530nm. Cloud point extraction (CPE) methodology and using surfactant Triton X-100 as extractant was applied as a preconcentration step prior to HPLC, the surfactant-rich phase containing BFAP was then analysed by HPLC in visible region. The high back ground absorbance of Triton X-100 in UV region was completely avoided. A new visible detection method with high-performance liquid chromatography (HPLC) has been developed for the determination of carbofuran. Using this method, we found that carbofuran residues could be determined with recoveries ranging from 80.4% to 84.5%, relative standard deviations in the range of 2.51–3.26% for three fortified rice levels, and the limit of detection as 5.0×10−4cJ/cK.

Isoniazid (INH) reacted with p-dimethylaminobenzaldehyde (DABD) in the presence of trichloroacetic acid to give isonicotinylhydrazone (INZ) having λmax 365nm. Cloud point extraction (CPE) is carried out to extract INH and IHZ in aqueous solutions using surfactant poly(ethylene glycol) 4000 (PEG4000), respectively. Langmuir model is used to study the adsorption behaviors of the two solutes on micelles of PEG4000. A linear correlation is found between variation of PEG4000 concentration required for feed concentration of the two solutes and used to predict PEG4000 concentration required for extracting INH and IHZ in CPE procedure. The results calculated show that, for a desired recovery level of 90%, only can IHZ be sufficiently extracted by PEG4000. In this experiment, the feed concentration of PEG4000 is defined by above-mentioned correlation, and the effects of other operating parameters, e.g., concentration of salt, pH and centrifugation time on extraction of PEG4000-IHZ system have also been studied in detail. The proposed CPE method coupled with HPLC-UV system is successfully used for the determination of INH in urine sample.

Sample of elementary silicon was dissolved in conc.HF and the matrix silicon was expelled by volalitalization as SiF4↑. The residue was taken up with HNO3 and HCl and evaporated to near dryness by fuming with HClO4.After dissolving the residue with HCl(1+1),an aliquot of the solution was taken and extracted with Tween-20,PAR and(NH4)2SO4 in a total volume of 10 mL at pH 4.5 buffered with hexamine,to remove all of the co-existing Fe(Ⅲ),Cu(Ⅱ),Cr(Ⅲ) and Ni(Ⅱ),part of Co(Ⅱ) and Pb(Ⅱ),while Al(Ⅲ) remained quantitatively in the lower aqueous phase together with Ca(Ⅱ),Mg(Ⅱ) and Na(Ⅰ).Aluminum(Ⅲ) in the lower phase was determined spectrophotometrically with chrome azurol S at pH 4.5 in the presence of CPC.Linear relationship between the absorbance measured at 642 nm and the concentration of Al(Ⅲ) was obtained in the range of 0.02-0.50 mg·L-1,with detection limit of 0.01 mg·L-1.Recovery was tested by the standard addition method,the results obtained were in the range from 96% to 101%.Values of RSD′s(n=5) found were less than 3.5%.