Apichai Santalad

Mixed micelle-cloud point extraction for the analysis of penicillin residues in bovine milk by high performance liquid chromatography

A mixed micelle-cloud point extraction (MM-CPE) has been developed for the analysis of penicillin antibiotics (ampicillin, penicillin G, oxacillin, and cloxacillin) in milk samples using Triton X-114 (TX-114) and cethyl trimethylammonium bromide (CTAB) as the mixed micellar extractant. The parameters affecting the MM-CPE that were investigated including solution pH, CTAB concentration, TX-114 concentration, electrolyte salt, equilibration temperature and incubation time. The optimum MM-CPE conditions were: 10 mmol L(-1) phosphate buffer pH 8, 0.06% (w/v) CTAB, 1.5% (w/v) TX-114, and 7% (w/v) Na(2)SO(4), and 5 min equilibration at 40 degrees C. The separation of penicillins was achieved within 8 min under the HPLC conditions: a Vydac C(18) column, isocratic elution of 5 mmol L(-1) phosphate buffer (pH 6.6) and methanol (55:45, v/v), and a flow rate of 1 mL min(-1), with photodiode array detection at 215 and 244 nm. Under the selected condition, the proposed method gave linear calibrations in the range 0.002-10 microg mL(-1) with correlation coefficients greater than 0.999. Limits of detection (LOD) were 2-3 ng mL(-1), and 15-40-fold enhancement compared to that without preconcentration. Good reproducibility was achieved with relative standard deviation <5% for peak area and <3% for retention time. High accuracy, with recoveries higher than 80%, was obtained. The proposed mixed micelle-CPE-HPLC method has shown to be of high potential for the analysis of penicillin residues in milk with LOD comparable to the established maximum residue limits (4-30 ng mL(-1)).

Micellar electrokinetic chromatography with amperometric detection and off-line solid-phase extraction for analysis of carbamate insecticides.

Six selected primary carbamate insecticides, methomyl, carbaryl, carbofuran, propoxur, isoprocarb, and promecarb, were hydrolyzed in alkaline solution, resulting in electroactive derivatives detectable at a platinum (Pt) electrode poised at +0.8 V vs Ag/AgCl (3 M NaCl). The Pt electrode was inserted into a small electrochemical cell and positioned close to the capillary outlet as an end-column detector to detect the carbamate derivatives after electrophoretic separation. Based on their predicted pK(a) values and aqueous solubilities, micellar electrokinetic chromatography (MEKC) was optimized for baseline separation of the derivatives using 20 mM borate, pH 10.2 containing 20 mM sodium dodecyl sulfate as a running buffer. When combined with solid-phase extraction (SPE) on octadecyl silica, a preconcentration factor of 100-fold achieved detection to 0.5 microM methomyl and to 0.01 microM for the remaining five pesticides, significantly below the level regulated by government agencies of most countries. The SPE-MEKC method when applied to the separation and analysis of spiked river water and soil samples, yielded results with excellent reproducibility, recovery and selectivity.

Role of Different Salts on Cloud-Point Extraction of Isoprocarb and Promecarb Insecticides Followed by High-Performance Liquid Chromatography

The influence of salt additive on cloud point extraction (CPE) of isoprocarb and promecarb insecticides is described. Types of salt (Na(2)CO(3), CaCl(2), MgSO(4), Na(2)SO(4), NaHCO(3) and NaCl) and concentrations were studied. The extracted target compounds were analyzed using reversed phase high-performance liquid chromatography. Among the salts studied, Na(2)CO(3) was found to be the most effective salt for salting out of both insecticides, resulting in high extraction efficiency (>95%) and high enrichment factor of up to 18 compared to extraction without preconcentration. The optimum CPE conditions were 1.5% (w/v) Triton X-114, 3.0% (w/v) Na(2)CO(3), and 20-min equilibration at 45°C. Under the selected conditions, the linear range of 0.05 to 3.0 mg/L was found for both analytes. The limits of detection for isoprocarb and promecarb were 10 and 20 µg/L, respectively. High intra-day (n = 9) and inter-day (n = 3 × 4 days) precisions with relative standard deviations <1% and <8% were obtained for retention time and peak area, respectively. The proposed method was successfully applied for the residue analysis of target compounds in beverages (i.e., fruit juice, vegetable juice and wine samples), which provided high recoveries (>80%, on average) for spiked samples at three levels (0.05, 0.10 and 0.50 mg/L).