Introduction
Microfluidic technology offers the capability to integrate several fluidic and instrumental components onto a single device. The process of microfluidic integration has several advantages for the micro-LC user. First, the micro-LC fittings either between the column and ESI source, or between the column and injection valve, must be precisely fitted. Even micrometers of difference between the transfer line and the column can equate to several μLs of void volume, and at μL/min flow rates can result in large deviations in retention time or peak width due to dispersion. The ability to micromachine and integrate the post-column connections on a planar microfluidic device offers the simplicity of never having to replace or change post-column lines or ESI tips. Secondly, the clamp-on microfluidic fittings make it easy to replace the microfluidic iKey in a matter of seconds. This allows for trouble-free system maintenance, but it can also facilitate the process of method development with different column chemistries. In addition, the integrated heating elements, memory, and ESI tips require minimal programming, providing control of LC-gradients and ESI spray in a customized environment.
Operating at the micro-LC scale provides a number of advantages for minimizing laboratory solvent consumption. For pesticide screening applications, the Waters® ionKey/MS System utilizes a scaled down flow rate of 2.3 μL/min. This substantially lower rate of solvent consumption and consequential reduction of hazardous waste removal can result in significant cost savings to laboratories. In addition to the reduction in solvent consumption, there are also significant improvements in sensitivity for many analytes. In this application note, a mixture of pesticides was spiked into food matrices of varying levels of complexity. Initial work was undertaken to compare the iKey Separation Device with a conventional 2.1 mm diameter ACQUITY UPLC Column. For the 50 pesticides individually assessed, the sensitivity was improved by an average of 8x over the 2.1 mm format. The ionKey/MS System was further tested for robustness and performance with a range of matrices.
Sample preparation
A standard QuEChERS AOAC (2007.01) extraction protocol was performed using the Waters DisQuE Dispersive solid phase extraction (d-SPE) product, first by homogenizing the commodity in a blender, followed by weighing 15 g of the commodity into a vial. Next, 15 mL of extraction buffer consisting of acetonitrile with 1% acetic acid was added to the commodity along with pouch 1 of the DisQuE salt mixture. Vials were shaken for approximately 1 min and centrifuged at 1500 rcf for 1 min. The supernatant was removed and filtered through a 0.2 μm PFTE filter prior to dry down and reconstitution in mobile phase. Standards with 200 pesticides were constituted in extracted food matrix at levels ranging from 1 ppt to 10 ppb with 11 intervals. Matrix blanks from the extracted food matrix were collected along with solvent blanks. These blanks were used to identify the existing presence of pesticides in the commodity.
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