Articles by Limian Zhao - Chromatography Online
Articles by Limian Zhao

Limian Zhao


Articles
Agilent NA - Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis
October 11, 2013

Flow path inertness plays a critical role in pesticide analysis accuracy and precision, especially for active analytes such as organophosphate pesticides. The Agilent Inert Flow Path, including Ultra Inert columns and liners, Ultra Inert gold seals, and inert split/splitless inlet, provides excellent surface inertness through the entire flow path, prevents loss of analyte response and peak share distortion, and thus delivers reliable qualitative and quantitative analysis of pesticides. Other inert supplies, including UltiMetal Plus flexible metal ferrules and capillary flow technology devices, are also highly recommended for pesticide analysis in complicated matrices.

The Use of Hollow Fibers in Liquid-Phase Microextraction
August 1, 2010

In this installment, the subject of LPME is reviewed, with emphasis on the use of hollow fibers.

Determination of Quinolone Antibiotics in Bovine Liver Using Agilent SampliQ QuEChERS Kits by LC–MS–MS
March 2, 2010

The procedure involves a rapid and efficient pretreatment by SampliQ QuEChERS kits. The homogenized liver sample was initially extracted in a buffered aqueous, 5% formic acid acetonitrile system. An extraction and partitioning step was performed after the addition of salts. Clean-up was done using dispersive solid-phase extraction (dispersive-SPE). The final extracts allowed determination of all compounds in a single run using LC–ESI-MS–MS operating in positive ion multiple reaction monitoring (MRM) mode. Norfloxacin was selected as the internal standard. The accuracy of the method, expressed as recovery, was between 62 and 113%. The precision, expressed as RSD, was between 2.2 and 13.4%. The established limit of quantification (LOQ) was 5 ng/g and is significantly lower than the respective maximum residue limit (MRL) for quinolones in food producing animals.

Determination of Sulphonamide Antibiotics in Bovine Liver Using Agilent SampliQ QuEChERS EN Kits by LC–MS–MS
March 2, 2010

The procedure involves a rapid and efficient pretreatment with SampliQ QuEChERS kits. The homogenized liver sample was initially extracted in a buffered aqueous/1% acetic acid acetonitrile system with an extraction and partitioning step after the addition of salts. Finally, the sample was cleaned up using dispersive solid-phase extraction (dispersive-SPE). The final extracts were analysed by the sensitive and selective determination of all compounds in a single run using LC–ESI-MS–MS operating in positive ion multiple reaction monitoring (MRM) mode. Sulphapyridine was selected as the internal standard. The accuracy of the method, expressed as recovery, was between 53 and 93%. The precision, expressed as RSD, was between 2.1 and 16.8%. The established 5 ng/g limits of quantification (LOQ) were much lower than the respective maximum residue limit (MRL) for sulphonamide in animal food products (20–100 ng/g).

Determination of Sulfonamide Antibiotics in Bovine Liver Using Agilent SampliQ QuEChERS EN Kits by LC–MS-MS
February 1, 2010

The procedure involves a rapid and efficient pretreatment with SampliQ QuEChERS kits. The homogenized liver sample was initially extracted in a buffered aqueous/1% acetic acid acetonitrile system with an extraction and partitioning step after the addition of salts.

Determination of Quinolone Antibiotics in Bovine Liver Using Agilent SampliQ QuEChERS Kits by LC–MS-MS
February 1, 2010

The procedure involves a rapid and efficient pretreatment by SampliQ QuEChERS kits. The homogenized liver sample was initially extracted in a buffered aqueous, 5% formic acid acetonitrile system.

Analysis of 17-Pesticide Residues in Apple Using Agilent SampliQ QuEChERS EN Kits and Agilent J&W Ultra Inert columns by GC–MS
December 2, 2009

The QuEChERS method for pesticide analysis was first introduced by USDA scientists in 2003. The EN method 15662:2007 is a European variation to the QuEChERS method. The method uses acetonitrile extraction, followed by the salting out of water from the sample using anhydrous magnesium sulphate (MgSO4, NaCl and buffering citrate salts to induce liquid–liquid partitioning.

Analysis of 17-Pesticide Residues in Apple Using Agilent SampliQ QuEChERS EN Kits and Agilent J&W Ultra Inert columns by GC–MS
October 2, 2009

The QuEChERS method for pesticide analysis was first introduced by USDA scientists in 2003.1 The EN method 15662:2007 is a European variation to the QuEChERS method.2,3

Analysis of Pesticide Residues in Apples Using Agilent SampliQ QuEChERS AOAC Kit by LC–MS-MS Detection
June 1, 2009

Based on the QuEChERS AOAC Official Method 2007.01, sixteen pesticides were used for evaluating the performance of the Agilent's AOAC Buffered Extraction and SampliQ QuEChERS Dispersive SPE kits for General Fruits and Vegetables. Apple was selected as the fruit matrix. The pesticides are from the "representative pesticides" list (1). A method working well for these representative pesticides should work equally well for the other pesticides that are routinely monitored in multi-class, multi-residue methods. The compounds are from nine different pesticide classes: including acidic, basic, neutral, base-sensitive, and acid-labile pesticides. The selected pesticides are suitable for LC–MS-MS analysis. The MRLs of these pesticides have been set at 10 ng/g or higher (2–4).

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