A microfluidic system for introduction of nanolitre sample in inductively coupled plasma mass spectrometry using electrokinetic flow combined with hydrodynamic flow

Abstract

A microfluidic system for introducing nanolitre sample in inductively coupled plasma mass spectrometry using electrokinetic flow combined with hydrodynamic flow was developed, which consisted of a microfluidic chip, a syringe pump, a high voltage power supply, a homemade microflow nebulizer and a heated single pass spray chamber. In the microfluidic chip, the sample in the reservoir S automatically flew across the intersection P₁ to the reservoir SR under hydrodynamic pressure. Two porous polymer plugs C₁ and C₂ were created on the microchip to isolate electrokinetic flow from the pressure-driven flow. Once a high voltage between S and buffer reservoir B was applied , the sample was driven through the porous polymer plug C₁ into the metering channel by electrokinetic force. Simply changing the sampling time can freely optimize the sampling volume down to 0.18 nL, which was injected into the nebulizer by the pressure-driven makeup solution. The nanolitre sample introducing system has the advantages of low sample consumption, satisfactory precision, low sampling dead volume (0.38 nL) and low sampling dead time (0.42 s). The proposed system was successfully applied to determine platinum content in a serum sample of a cancer patient on cisplatin chemotherapy. The sample consumption of 1.8 nL was about 10⁵ times less than that with the conventional sampling system. The sample throughput up to 112 h⁻¹ could be achieved with the detection limit of 64 ng L⁻¹ for ¹⁹⁵Pt. The content of Pt in the sample was 8.4 ± 0.3 μg L⁻¹, agreeing well with that (8.5 ± 0.3 μg L⁻¹) determined by the conventional sampling system.