Direct analysis of formate in human plasma, serum and whole blood by in-line coupling of microdialysis to capillary electrophoresis for rapid diagnosis of methanol poisoning.

A simple method using direct injection of human blood samples and quantitative analysis of formate was developed for rapid diagnosis of methanol poisoning. A sample pretreatment device including a 500Da molecular weight cut-off dialysis membrane was in-line coupled to capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D). 50μL of 1:9 diluted blood samples and 50μL of DI water were filled into the donor and the acceptor chamber, respectively, and small ionic species in blood samples were electrokinetically injected across the dialysis membrane directly into the separation capillary. Matrix components, such as red blood cells, proteins, lipids and other high molecular weight compounds, were retained by the dialysis membrane and did not interfere with subsequent CE separation. Formate was separated from other small anions in an optimized background electrolyte solution consisting of 20mM l-histidine and 25mM l-glutamic acid at pH 4.8. The method showed excellent analytical parameters in terms of repeatability and linearity; RSD values for migration times and peak areas at a formate concentration typical for methanol poisoning were below 0.3% and 7.4%, respectively, and linear calibration curves with correlation coefficients better than 0.999 were obtained. Limit of detection and limit of quantification were 15 and 50μM formate in original (undiluted) blood samples, respectively. The method was applied to determination of formate in serum samples of a patient diagnosed with acute methanol poisoning.