Development of a push-pull microdialysis sampling technique for the quantitative determination of proteins

An on-line push-pull sampling technique has been developed for continuous a nalysis of proteins of molecular weight from 5.7 to 67 kDa. The characteris tics of the system include gradient elution with a total cycle time of 21 m in, membrane stability, unattended automatic operation, and adjustment of t he sampling mode and extraction fraction (the ratio of the concentration of analyte in the dialysate to that in the sample) by varying the effective d ialysis length. The push and pull flow rates were adjusted in a manner whic h enabled three different modes of operation. When push-pull microdialysis was compared with conventional microdialysis sampling, significantly higher extraction fractions were obtained for all five model proteins studied. Th e technique has been applied to the quantification of proteins in cell samp les. On-line fractionation enabled complementary MS identification of the p roteins present.