Operational options to reduce matrix effects in liquid chromatography–electrospray ionisation-mass spectrometry analysis of aqueous environmental samples

Matrix effects like signal enhancement or suppression can severely compromise quantitative analysis of environmental samples with liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS). Several operational options were studied to reduce such matrix effects in the determination of polar organic trace contaminants from water, like non-steroidal anti-inflammatory drugs, among them ibuprofen, diclofenac and naproxen, lipid regulators like bezafibrate and clofibric acid and industrial chemicals (2-substituted benzothiazoles). A step-wise removal of organic matrix from a wastewater sample by ultrafiltration showed that the majority of matrix effects in that sample was due to low molecular weight compounds <1 kDa. For such wastewaters samples size-exclusion, as in restricted access material (RAM), is not a useful clean-up strategy. Reducing the eluent flow entering the ESI interface by post-column splitting increased instrumental sensitivity and reduced matrix effects. The flow optimum was analyte-dependent and ranged from 20 to 100 μL/min. Sensitivity in the positive ion mode increased up to nine-fold upon flow-reduction for some analytes detected in the positive ion mode. At low flow rates matrix effects are reduced by 45–60% on average. If moderate matrix effects occurred, post-column splitting may allow obtaining reliable quantitative data even with external calibration.