Continuous-flow assay with immobilized enzymes for determining of inorganic phosphate in serum.

An automated method for the determination of inorganic phosphate based on flow-injection analysis and on the use of immobilized enzymes is reported. The method features a linear range between 0.1 and 20 mumol/L with a CV < 2.1% and 3.4% for the within-run and between-run studies, respectively, and a sampling throughput of 40 h-1. The sensitivity of the method makes a 1:250 dilution of the serum samples feasible, thus making undetectable the interferences from analytes commonly present in serum. The method shows an excellent correlation with conventional automated analyzers based on the same enzymatic reaction (Hitachi, r = 0.988) but with the catalyst in solution, and with the Kodak Ektachem method (r = 0.974) based on the use of dry reagents and formation of the phosphomolybdo heteropolyacid.