AB SCIEX LC-MS/MS Analysis of Water using the Eksigent ekspert ...

ExperimentalLiquid Chromatography:All experimental data was acquired with the Eksigent ekspertmicroLC 200 system equipped with a HTC-xt Dynamic Load andWash (DLW) autosampler. The ekspert microLC 200 system’ssolvent delivery system is based on binary gradient pumps thatuse patented Microfluidic Flow Control (MFC) pumptechnologyThe column used was an Eksigent ChromXP Halo Fused-Core2.7 µm, Phenyl Hexyl 0.5 x 150 mm. The column temperaturewas maintained at 30°C for all experiments. The mobile phaseswere ammonium formate in water and methanol. The flow ratewas set at 15 µL/min with a 4 µL injection volume.For the conventional HPLC experiments a Kinetex Fused-Corecolumn was used with a flow rate of 600 µL/min and a 4 µLinjection volume. The following gradient profile was used for bothmicro flow and conventional flow (Table 1).Results and DiscussionThe aim of this work was to determine the quantitativeperformance using low volume injections with micro flow rates.To establish the performance a number of pesticides werespiked into water and serially diluted down to the limits ofdetection. The dilutions were analyzed at both flow rates;Figure 1 shows a comparison for Desphenyl-chloridazon at1ng/mL.Desphenyl-chloridazonMicro flow LCDesphenyl-chloridazonConventional flow LCTable 1. Analytical gradient profile used at both flow ratesTime (min) A (%) B (%)Figure 1. Desphenyl-chloridazon analyzed using micro vs. conventionalflow LC-MS/MS (1 ng/mL)0.0 95 50.5 95 55.0 25 757.0 5 958.5 5 95At 1 ng/mL when comparing the peak areas at both flow ratesthe micro flow showed a 6.5 fold increase in peak area and a 10fold increase in signal to noise. The parent Chloridazon was alsoanalyzed and the comparison is shown in Figure 2.8.75 95 515.0 95 5Mass Spectrometry:The AB SCIEX QTRAP ® 4500 system was used for all dataacquisition. Analyses were performed using multiple reactionmonitoring (MRM) with simultaneous positive/negative switchingelectrospray ionization. The Eksigent hybrid 25 µm IDelectrospray electrode was used for all micro flow analyses. Thishybrid electrode is designed to minimize post column peakdispersion to maintain excellent peak shapes. 2 The sourcesettings were setup for micro flow rates with the curtain,nebulizer and heater gas set to 20 psi with a temperature of350°C. For the conventional flow rates the source conditionswere scaled to the appropriate values.ChloridazonMicro flow LCChloridazonConventional flow LCFigure 2. Chloridazon analyzed using micro vs. conventional flow LC-MS/MS (1 ng/mL)p 2