Automated gas chromatographic analysis of pesticide residues in food samples by means of fused-silica capillary columns data processing

SummaryAn experiment was designed to study the long-term stability of analyses of pesticide residues in a complex food matrix using three different injection techniques. A spinach sample was spiked with five sulfur-containing pesticides of varying volatility and thermolability: arinphos-ethyl, dimethoate, methiocarb, ethiofencarb, and tri-allate. Tri-allate was selected as internal standard because of its thermal stability and its good chromatographic properties. Flame photometric detection resulted in chromatograms not subject to interference by peaks of compounds of the matrix. Starting with a clean and freshly, silanized injector an additional deactivation was found to occur on the first injection of a food sample resulting in an increased peak area for all pesticides in relation to tri-allate. Highest long-term stability was found with PTV injection. Best results for thermolabile carbamates were obtained using on-column injection. However, they were prone to faster deterioration. I IntroductionDue to its higher separation efficiency [I, 21 gas chromatography on capillary columns is far better suited for the detection of pesticide residues than techniques using packed columns. Ouantitation by capillary gas chromatography is affected by many factors [3,4]. When used for the analysis of real-life samples, cold on-column injection exhibits a number of disadvantages. Automated sampling is more complex. Even more important is the poor tolerance of deposits from matrix compounds. Therefore, multiresidue analysis is widely performed by hot splitless injection because of the ease of exchanging the injector inlet which retains the nonvolatile deposits from the food matrix [5, 61. This paper presents a systematic investigation of the long-term stability of gas chromatographic responses to pesticides in a food sample using three sampling techniques. Experimental InstrumentationA Sichromat 1 gas chromatograph (Siemens AG, Karlsruhe, FRG) was equipped with splitless injector and a flame photometric detector in the sulfur-mode. Additionally a programmed temperature vaporizer (Gerstel, Muhlheim, FRG), an on-column injector (Hewlett Packard, Palo Alto, CA, USA), and an autosampler (HP 7673) were also fitted. Gas ChromatographyA fused silica column 25 m x 0.32 mm i.d. SE 54 "bonded phase", df = 0.25 km (Nordion Analytica Espoo, Finland) was used with hydrogen as carrier gas adjusted to a flow rate of 60 cm/s. Temperature program: 1 min at 100 "C -10 "/min to 200 "C -2 min -stop. Injection TechniquesAll injections were performed by means of an autosampler using 10 p1 fixed needle syringes (Hamilton 80377) for hot-splitless and PTV injection and for on-column injection (Hamilton 80378). The injection volume in all experiments was 1 pl. The common hot-splitless injector was equipped with a glass insert of 260 p1 volume and filled with 10 mg of silanized glass wool. The filled glass insert was deactivated in a solution of 10 % dichloromethylsilane in toluene overnight. Immediately before mounting, the insert was rinsed with a s...

Pesticide residue analysis in food with CGC — study of long‐term stability by the use of different injection techniques

Müller¹,

Stan²

1990

Organochlorine residue analysis of commercial milks by capillary gas chromatography

Redondo

Picó

Server-Carrió

et al. 1991

SummaryThe determination of organochlorine pesticides and polychlorinated biphenyls in milks requires the use of efficient extraction methods. A rapid procedure has been developed, based on extraction of organochlorine residues from milk on to octadecylsilica solid phase extraction cartridges and elution with Shaking the sample with concentrated sulfuric acid has proven valuable as an additional clean-up step after removal of the lipids.The chemically very stable PCBs and OCPs are not attacked and remain in the organic solvent. Interfering matrix components, on the other hand, are extracted into the acid phase [7, 81. hexane. The addition of different organic solvents to the milk before solid phase extraction has been studied. The use of methanol to disrupt the fat globules enables almost complete recovery of the residues with minimum extraction of fatty substances.Recovery experiments were performed for eighteen compounds present at ppb levels in whole, two per cent, and skimmed milks.The average recoveries of the compounds from two per cent and skimmed milks were73-84 YO; valuesfor whole milk were lower.The residues were determined by gas chromatography using two kinds of capillary column (non-polar and semi-polar) and electron capture detection. The procedure shows low lipid carry over, and extraneous interferences are minimal.The method has been applied to the detection of organochlorine pesticides and nine individual polychlorinated biphenyls in commercial milks. The results obtained demonstrated the presence of very low levels of organochlorine residues in the commercial milks analyzed. I IntroductionAccurate and precise analysis for organochlorine pesticides (OCPs) and polychlorinated biphenyl (PCB) residues in milk is difficult and complex owing to three principal factors: the complexity of the matrix, the low levels of contamination, and the large number of individual compounds concerned. The analytical determination is generally made by capillary gas chromatography with electron capture detection.If the sample solution has been properly cleaned, the samples can be applied splitless or on-column [ l l , 121. Non-polar and semipolar stationary phases, such as methyl silicones, or silicones containing 5, 7, or 50 % phenyl, are suitable [13, 141. 25 and 50 m columns are employed to enable both the best possible separation and reliable identification the compounds present [15, 161. This paper describes a rapid procedure comprising addition of methanol to the milk and selective extraction of PCB and OCP residues on to an octadecylsilica microcolumn. The chromatography of PCBs and OCPs on BP-5 and DB-17 capillary columns following both classical splitless and on-column injection is also compared in order to select the optimum chromatographic conditions. Materials and Methods ReagentsOrganochlorine pesticides, purity 95-99 %, were purchased from Promochem and polychlorinated biphenyls, 99 % pure, from Riedel deHaen Preparative octadecylsilica (55-105 pm) was obtained from Waters-Millipore Dichloromethane,...

Automated screening of food and water samples for pesticide residues by means of capillary GC‐MSD using a library of pesticide spectra and macro programming

Klaffenbach

Stan

1991