Determination of oxalate and citrate in urine by capillary electrophoresis using solid-phase extraction and capacitively coupled contactless conductivity based on an improved mini-cell

A new method for the rapid determination of the metabolites oxalate and citrate in urine samples was based on capillary electrophoresis and capacitively coupled contactless conductivity detection coupled with solid-phase extraction. The detection cell for capacitively coupled contactless conductivity detection was improved with a smaller inner volume (1.5 nL), reduced noise (0.2 similar to 0.5 mV) and better reproducibility and durability. Under optimal conditions, oxalate and citrate can achieve baseline separation within 4 min and the detection limits (S/N = 3) for oxalate and citrate are about 44 and 244 ng/mL, respectively. The overall recovery is between 80.0 and 89.2%. This method offers a better choice for quantitative analysis of strong anions such as oxalate and citrate in diagnostic testing associated with human diseases.