High-sensitivity flow method for the determination of proteins with micro-flow plunger pumps

In order to determine micoamounts of proteins with low molecular diffusivity, a flow method was developed by both miniaturizing the common flow-injection apparatus and using the dye association method. A very precise double-plunger micropump, which was recently developed for this purpose, was used. The optimum conditions using bovine serum albumin (BSA) as standard and some ion-association dye reagents at very low flow-rates were examined. It was shown that a flow-rate of less than 50 μl min^-1 was acceptable when a short, small-bore reaction tube was used. Up to 15 samples H^-1 could be analysed with a relatively long residence time; linear calibration graphs were obtained with both 8-μl volume loop valve injection and no-injection methods. The detection limit and relative standard deviation of the injection method were 0.003 μg ml^-1 and 0.15%, respectively, for BSA.