In-syringe electrokinetic protein removal from biological samples prior to electrospray ionization mass spectrometry

Here, an electrokinetic extraction (EkE) syringe is presented allowing for on‐line electrokinetic removal of serum proteins before ESI-MS. The proposed concept is demonstrated by the determination of pharmaceuticals from human serum within minutes, with sample preparation limited to a 5× dilution of the sample in the background electrolyte (BGE) and application of voltage, both of which can be performed in‐syringe. Signal enhancements of 3.6-32 fold relative to direct infusion of diluted serum and up to 10.8 fold enhancement, were obtained for basic and acidic pharmaceuticals, respectively. Linear correlations for the basic drugs by EkE‐ESI‐MS/MS were achieved, covering the necessary clinical range with LOQs of 5.3, 7.8, 6.1, and 17.8 ng mL^-1 for clomipramine, chlorphenamine, pindolol, and atenolol, respectively. For the acidic drugs, the EkE‐ESI‐MS LOQs were 3.1 μg mL^-1 and 2.9 μg mL^-1 for naproxen and paracetamol, respectively. The EkE‐ESI‐MS and EkE‐ESI‐MS/MS methods showed good accuracy (%found of 81 % to 120 %), precision (≤20 %), and linearity (r>0.997) for all the studied drugs in spiked serum samples.