Evaluation of the ASTRA 4 new microprocessor-controlled electrolyte analyzer.

A new programmable microprocessor-controlled multichannel chemistry analyzer, the Bechman ASTRA 4, was evaluated in an electrolyte configuration including sodium, potassium, chloride, and CO2. Sodium and potassium are analyzed with ion-selective electrodes, CO2 by differential rate pH measurement, and chloride by proportional coulometric titration, Day-to-day reproducibility studies yielded coefficients of variation of 0.8% for Na+, 1.2% for K+, 0.9% for Cl-, and 5.9% for CO2. Linearity was 100-200 mmol/l for Na+, 1.0-10.0 mmol/l for K+, 50-150 mmol/l for Cl+, and 5-50 mmol/l for CO2. There was excellent correlation between the ASTRA 4 and the comparison laboratory methodologies consisting of flame photometry, coulometry, and Beckman Chlorie/CO2 titrator. Performance of the ASTRA 4 was judged acceptable relative to requirements of medical usefulness. The instrument can be used as a routine electrolyte analyzer with a throughput of 60 samples an hour or as a stat analyzer with results obtained within 8.5 minutes. Each sample can be programmed for any combination of tests, and reagent is only consumed on those tests selected. Sample size is approximately 130 microliter for all four tests or reduced accordingly if fewer tests are selected.