MICROTITER PLATE-FORMAT OPTODE

Microtiter plate-format optodes could be assembled by casting bulk-res ponse membranes into the standard 96-well polypropylene-based plate or by screen printing them on an optically transparent substrate with 96 -well pattern. The compositions of thick optode membranes, especially the ratios of poly(vinyl chloride) (PVC) to plasticizer [bis(2-ethylhe xyl) sebacate (DOS)], were carefully optimized to provide reproducible and rapid response. Adjusting the ratio of PVC to DOS by 1:6, bulk-re sponse membranes containing neutral carrier (4-tert-butyl calix[4]aren e tetraacetic acid tetraethyl ester for sodium-selective membrane or v alinomycin for potassium-selective membrane) and lipophilic pH indicat or (ETH 5294) could exhibit equilibrium response in 5 min. The practic al utility of microtiter plate-format optodes has been examined by det ermining clinically relevant electrolytes in serum samples. It was dem onstrated that microtiter plate-format optodes can provide high sample throughput (similar to 100 samples in less than 5 min), analytical pe rformance comparable to that of a potentiometric clinical analyzer, an d additional information on electrolytes using the same samples prepar ed for other colorimetric measurements.