Analysis of pesticide residues in mixed fruit and vegetable extracts by direct sample introduction/gas chromatography/tandem mass spectrometry

Direct sample introduction (DSI), or "dirty sample injection," was investigated in the determination of 22 diverse pesticide residues in mixed apple, green bean, and carrot extracts by benchtop gas chromatography/tandem mass spectrometry (DSI/GC/MS-MS). The targeted pesticides, some of which were incurred in the samples, included chlorpyrifos, azinphos-methyl, parathion-methyl, diazinon, terbufos, p,p'-DDE, endosulfan sulfate, carbofuran, carbaryl, propargite, bifenthrin, dacthal, trifluralin, metalaxyl, pendimethalin, atrazine, piperonyl butoxide, diphenylamine, vinclozolin, chlorothalonil, quintozene, and tetrahydrophthalimide (the breakdown product of captan). The analytical DSI method entailed the following steps: (1) blend 30 g sample with 60 mL acetonitrile for 1 min in a centrifuge bottle; (2) add 6 g NaCl and blend 30 s; (3) centrifuge for 1-2 min; (4) add 5 mL upper layer to 1 g anhydrous MgSO4 in a vial; and (5) analyze 11 microL extract, using DSI/GC/MS-MS. Sample cleanup is not needed because GCIMS-MS is exceptionally selective for the targeted analytes, and nonvolatile coextracted matrix components do not contaminate the injector or the GC/MS-MS system. Average recoveries of the pesticides were 103 +/- 7% with relative standard deviations of 14 +/- 5% on average, and limits of detection were <2 ng/g for nearly all pesticides studied. The DSI/GC/ MS-MS approach for targeted pesticides is quantitative, confirmatory, sensitive, selective, rugged, rapid, simple, and inexpensive.     

Europium-sensitized luminescence determination of oxytetracycline in catfish muscle

An europium-sensitized time-resolved luminescence (TRL) method was developed to determine oxytetracycline (OTC) in cultivated catfish muscle. Extraction of OTC from fish muscle was performed with pH 4.0 ethylenediaminetetraacetic acid (EDTA)-McIlvaine buffer and clean up with hydrophilic-lipophilic balanced copolymer solid phase extraction (SPE) cartridges. The eluate was used without further concentration for TRL measurement in pH 9.0 micellar tris(hydroxylmethyl)aminomethane (TRIS) buffer. Cetyltrimethylammonium chloride (CTACl) was used as surfactant and EDTA as a co-ligand. The excitation and emission wavelengths were set at 388 and 615 nm, respectively. The linear dynamic range was 0-1000 ng g⁻¹ (R²=0.9995). The recovery was 92-112% in the fortification range of 50-200 ng g⁻¹ and the limits of detection (LOD) ranged from 3 to 7 ng g⁻¹. Incurred catfish samples were used to demonstrate the performance of the method around 100 ng g⁻¹, the European Union maximum residue level.     

STUDIES OF ADHESION OF METAL PARTICLES TO SILICA PARTICLES BASED ON ZETA POTENTIAL MEASUREMENTS

The zeta-potentials of silica, copper, platinum and gold particles have been measured as a function of pH. The isoelectric points were found to be at pH 3.0, 5.8, 3.0 and 3.5, respectively. In the pH range 3.0 to 5.8 copper and silica particles are oppositely charged and accordingly the coating of silica with copper particles could be demonstrated. In the case of gold and platinum the sign of the charge is such that direct adhesion to silica particles cannot be expected and this was also demonstrated in the case of platinum.     

Application of umbelliferone molecularly imprinted polymer in analysis of plant samples

The molecularly imprinted polymers (MIPs) were synthesised and the influence of the type of porogen, the nature of sample solvent, and the binding capacity of material were tested by high-performance liquid chromatography (HPLC). Umbelliferone was used as the template for imprint formation. Methacrylic acid was used as the monomer and acetonitrile, ethanol, and chloroform as porogen. Non-imprinted polymers (NIPs) were prepared by the same procedure. The highest value of the specific binding capacity (269 μg of umbelliferone per 100 mg of polymer) was obtained for polymers prepared in chloroform as porogen and methanol/water (φ _r = 1: 1) as the sample solvent. The group-selective MIP was used as sorbent for the SPE pre-treatment of umbelliferone from plant extracts prior to HPLC analysis. Analysis of the spiked samples showed good recoveries (> 77 %). The limit of detection, limit of determination, and repeatability of the method were also calculated.     

Fast and easy multiresidue method employing acetonitrile extraction/partitioning and "dispersive solid-phase extraction" for the determination of pesticide residues in produce

A simple, fast, and inexpensive method for the determination of pesticide residues in fruits and vegetables is introduced. The procedure involves initial single-phase extraction of 10 g sample with 10 mL acetonitrile, followed by liquid-liquid partitioning formed by addition of 4 g anhydrous MgSO4 plus 1 g NaCl. Removal of residual water and cleanup are performed simultaneously by using a rapid procedure called dispersive solid-phase extraction (dispersive-SPE), in which 150 mg anhydrous MgSO4 and 25 mg primary secondary amine (PSA) sorbent are simply mixed with 1 mL acetonitrile extract. The dispersive-SPE with PSA effectively removes many polar matrix components, such as organic acids, certain polar pigments, and sugars, to some extent from the food extracts. Gas chromatography/mass spectrometry (GC/MS) is then used for quantitative and confirmatory analysis of GC-amenable pesticides. Recoveries between 85 and 101% (mostly > 95%) and repeatabilities typically < 5% have been achieved for a wide range of fortified pesticides, including very polar and basic compounds such as methamidophos, acephate, omethoate, imazalil, and thiabendazole. Using this method, a single chemist can prepare a batch of 6 previously chopped samples in < 30 min with approximately 1 dollar (U.S.) of materials per sample.     

Potential artifact formation of dioxins in ball clay during supercritical fluid extraction

Earlier surveys indicate that meat, fish and dairy products are the principal source of polychlorinated dibenzo-p-dioxin (PCDD) exposure in the diet. A recent finding by others of PCDDs in chickens that consumed a feed containing PCDD led to the finding of ball clay, an anti-caking agent, as the source. Supercritical fluid extraction (SFE) was studied as a means to isolate PCDDs from commercial ball clays using GC-electron capture detection (muECD) as a means to screen for these contaminants. The finding of ng/g amounts and recoveries >100% in several samples of ball clay containing octachlorodibenzo-p-dioxin (OCDD) suggested that PCDD may form artifactually as a result of analysis. Studies on pentachlorophenol (PCP) fortified ball clay were carried out by SFE and soxhlet extraction and the results compared. The values obtained by SFE were considered more problematic. The results obtained from ball clay suggest that precautions need to be exercised when using SFE to analyze for dioxins in solid samples containing chlorophenols.     

Kinetic study of the degradation of a potential local anesthetic drug in serum using the DNA-based electrochemical biosensor

DNA-drug association interaction at the DNA modified screen-printed electrode for 1-methyl-2-piperidinoethylester of 2-hexoxyphenylcarbamic acid was found leading to an accumulation of the drug within the DNA layer. A procedure for the determination of drug in blood serum matrix using the protein precipitation and voltammetric measurement of the electroactive drug with the DNA biosensor was obtained and an effort was done to apply it for an assay of the drug enzymatic degradation in human and rabbit sera at 37 degrees C.     

Rapid fluorescence screening assay for tetracyclines in chicken muscle

A simple, rapid fluorescence assay was developed for screening tetracyclines in chicken muscle at the U.S. tolerance level (2 mg/kg). The method requires only a homogenization of the tissue in acetonitrile-ammonium hydroxide, centrifugation, addition of Mg+2, and another centrifugation before fluorescence of the supernatant is measured at 505 nm (excitation at 385 nm). Comparison of the fluorescence of control chicken muscle extracts with extracts from muscle fortified with either 2 mg/kg tetracycline, oxytetracycline, or chlortetracycline showed no overlap. A threshold level set at the average fluorescence for a series of fortified 2 mg/kg samples minus 3sigma minimized false-negative responses to provide a successful screening method. The method was tested with blinded samples as controls or samples fortified with tetracycline, oxytetracycline, or chlortetracycline in order to demonstrate its utility. This approach can provide an alternative to microbial screening assays.