Electrokinetic injection across supported liquid membranes: new sample pretreatment technique for online coupling to capillary electrophoresis. Direct analysis of perchlorate in biological samples.

A simple and sensitive method for quantifying perchlorate in biological samples using CE and capacitively coupled contactless conductivity detection was developed. An online combination of a supported liquid membrane, an inert polypropylene membrane impregnated with 1-hexanol, and electrokinetic injection of perchlorate across the supported liquid membrane directly into the separation capillary reduced the need for laborious sample pretreatment procedures, resulting in a cheap and rapid method with low LODs capability. Baseline separation of perchlorate and other anions in biological samples was achieved in background electrolyte solution consisting of 15 mM nicotinic acid and 1 mM 3-(N,N-dimethylmyristylammonio)propanesulfonate at pH 3.3. The analytical method showed excellent parameters in terms of reproducibility; RSD values for peak areas and corrected migration times at a spiked concentration of 100 μg/L of perchlorate were below 10 and 0.4%, respectively. Linear calibration curves were obtained for perchlorate in the concentration range 10-1000 μg/L (r(2) >0.999) with LODs between 2 and 5 μg/L for human urine, breast milk, serum, cow's milk, and red wine. Recoveries at 25 μg/L of perchlorate were between 97 and 106% for all biological samples. The low LODs rivaling those of presently used analytical methods support the use of this method for quantification of perchlorate in biological samples in the future.