Optimization and evaluation of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity.
ABSTRACT A fast method of analysis for 20 representative pesticides was developed using low-pressure gas chromatography-mass spectrometry (LP-GC-MS). No special techniques for injection or detection with a common quadrupole GC-MS instrument were required to use this approach. The LP-GC-MS approach used an analytical column of 10 m x 0.53 mm I.D., 1 microm film thickness coupled with a 3 m x 0.15 mm I.D. restriction capillary at the inlet end. Thus, the conditions at the injector were similar to conventional GC methods, but sub-atmospheric pressure conditions occurred throughout the analytical column (MS provided the vacuum source). Optimal LP-GC-MS conditions were determined which achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC-MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injection volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labile analytes, such as carbamates; and (v) due to larger sample loadability lower detection limits for compounds not limited by matrix interferences. The optimized LP-GC-MS conditions were evaluated in ruggedness testing experiments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared with the conventional GC-MS approach. The matrix interferences for the quantitation ions were worse for a few pesticides (acephate, methiocarb, dimethoate, and thiabendazole) in LP-GC-MS, but similar or better results were achieved for the 16 other analytes, and sample throughput was more than doubled with the approach.
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ABSTRACT: The application of vacuum GC has several advantages over pressurized GC. One of the key characteristics is that the optimal gas velocity is very high. Combined with short capillary columns of wide internal diameter, this results in short analysis times using standard GC-MS equipment. To make vacuum GC possible using a GC-MS system, a restriction must be positioned at the injection side of the column. This restriction is usually made of deactivated 0.1 mm i.d. fused-silica tubing which is coupled to the analytical column. Such restrictions will work, but practical challenges are found in coupling, reducing dead volume and robustness. A new way of making restrictions is by incorporating the restriction into the injection port. Using well-defined short pieces of fused silica with internal diameter of 0.025 mm, one can make a restriction using a Press-Tight type connector, and position this inside the injection port. By doing this, the restriction is very short and at high temperature all the time. Activity plays a minimal role, and also leaks will not be an issue as the coupling is in 100% inert gas. Data obtained using this concept is promising as vacuum GC becomes easier and more robust.Journal of Separation Science 07/2009; 32(11):1849-57. · 2.59 Impact Factor
Chapter: Gas chromatography in food analysis01/2008: pages 119–144; , ISBN: 9781420045666
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ABSTRACT: The applicability of non-protected room temperature phosphorescence (NP-RTP) in real samples was demonstrated in the present work. In this methodology, only two reagents, potassium iodide and sodium sulfite, were used to obtain phosphorescent signals. Overlapping of the phosphorescence spectra was resolved by using first-derivative synchronous phosphorimetry. The synchronous first-derivative spectra of carbaryl and 1-naphthol in the mixture were completely separated by changing the synchronous wavelength interval; with 240 nm the first-derivative spectra of carbaryl were recorded, while with 200 nm those of 1-naphthol appeared. The intensities in the spectra were proportional to the concentration of carbaryl and 1-naphthol. The calibration graphs were linear up to at least 1.1 x 10(-5) mol L(-1) for carbaryl and 1.3 x 10(-5) mol L(-1) for 1-naphthol, and the correlation coefficients were 0.9971 and 0.9932, respectively. Carbaryl and 1-naphthol were successfully determined by the proposed method in a hydrolyzed sample of a commercial formulation.Analytical Sciences 06/2009; 25(5):623-6. · 1.57 Impact Factor
EASTERN REGIONAL RESEARCH CENTER
AGRICULTURAL RESEARCH SERVICE
UNITED STATES DEPARTMENT OF AGRICULTURE
600 E. MERMAID LANE
WYNDMOOR, PA 19038
Optimization and Evaluation of Low-Pressure Gas Chromatography-Mass
Spectrometry for the Fast Analysis of Multiple Pesticide Residues in a Food
Author(s): K. Mastovska, S.J. Lehotay and J. Hajslova
Journal of Chromatography A (2001) 926: 291-308
This article was written and prepared by U.S. Government employees on official time, and is
therefore in the public domain.
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