Automation in multiresidue analysis of pesticides using on-line solid-phase extraction and liquid chromatography

Abstract

Solid-phase ex t raction simplifies the sample pre t re atment step , but there is still some evap o ration and transfer of the extract. The on-line SPE-LC-UV diode array detection (UV-DAD) system is being used routinely in many laboratories and an increasing number of applications is currently described using on-line SPE-LC coupled to various interfaces and MS detection [1]. Important advantages in coupling on-line the pretreatment and the LC separation and detection are a decrease of the risk of contamination of the sample and sample extract, the removal of analyte losses by evaporation and finally the transfer and the analysis of the totality of the extracted species. In contrast to off-line SPE, where only an aliquot of the extract is injected into the chromatograph, the analysis of the complete sample allows the sample volume to be dramatically reduced to less than 5 -10 mL when SPE is coupled to GC or to 100 -150 mL when it is coupled to LC. It was surprising to see that GC has been the preferred method of environmental chemists for a long time, but that on-line systems using LC became the first robust on-line techniques. This is explained by the good compatibility of the LC aqueous mobile phases with the SPE of the samples. On-line coupling of SPE with GC is more delicate because of the inherent incompatibility between the aqueous part of the SPE step and the dry part of the GC system. Although not reported here, much work has been done in this area and automated devices have re c e n t ly become available. On-line set-up and precolumn designThe on-line set-up coupling SPE to LC is particularly easy to perform in any laboratory, and has been described extensively in general reviews [1][2][3][4][5][6][7][8][9]. The apparatus is represented in figure 1 [10]. The trace-enrichment is carried out on a small precolumn, generally made of stainless steel in order to be pressure-resistant, which is placed at the sample-loop position of a six-port liquid switching valve. A solvent delive ry unit (SDU) provides the solvents necessary to purge, wash, and activate the precolumn. After conditioning, sample application, and eventual clean-up via the pump of the SPE part, the precolumn is placed in front of an analytical column by switching the valve into the "inject" position. The trapped compounds are then eluted directly from the precolumn into the analytical column by a suitable mobile phase allowing the ch ro m at ographic sep a ration of the extracted analytes. Quantitative results of good accuracy can be expected as there is no sample manipulation between the preconcentration and the analysis. The LC system is often run in the reve rsed-phase mode, using C 1 8 a n a ly t i c a l columns because the mobile phase is a partly aqueous solvent mixture. Th e re fo re, residual water in the pre c o l u m n after the preconcentration of aqueous samples does not have to be removed before the desorption. The addition of a second sw i t ching va l ve allows both direct injection onto the analytical column and preconcentratio...

Automated On-Line Column-Switching HPLC-MS/MS Method with Peak Focusing for the Determination of Nine Environmental Phenols in Urine

“…For improved analytical separation, we used peak focusing (i.e., diluting the SPE eluate before HPLC). An analogous on-line SPE-HPLC operation can be achieved by using commercial (but often costly) systems with multiple switching valves and special software. ,, In the present report, we demonstrate that these on-line SPE functionalities can be achieved by in-house-built systems using common HPLC modules and only one 10-port switching valve. The method has sensitivity and selectivity comparable to off-line SPE-derivatization-GC/MS methods for measuring urinary phenol derivatives. − , Furthermore, the method allows for the analytical separation and quantification of dichlorophenol and trichlorophenol isomers.…”

“…Specifically, off-line 12,22-25 and on-line SPE , have been used to measure phenolic compounds in urine. On-line SPE has also been used for the analysis of a variety of environmental phenols in water. − …”

HPLC-MS/MS method for analysis of isoproturon in difficult matrix: poppy seeds

“…This extraction mixture was selected for further experiments. Nevertheless, the amount of matrix components was rather higher than acetonitrile and/or methanol, they could be removed easily in the following clean-up step realised by SPE that is widely used for sample preparation prior to HPLC analysis of various pesticides (Hennion 1998(Hennion , 1999Rossi & Zhang 2000). The results of SPE clean up optimisation Relative absorbance Time (min) experiments are summarised in Table 2.…”