An evaluation of the Beckman Astra 8 analyser

Introduction The Astra-8 is a floor-standing seven-channel, automatic, discrete analyser for use in the clinical chemistry laboratory. A:t present it will analyse serum for urea, sodium, potassium, chloride, total carbon dioxide, glucose, and creatinine. It calculates the anion gap and osmolality, and also the ratio of blood urea.nitrogen to creatinine when these are expressed as mg/dl. Urine may be analysed for sodium, potassium, chloride, glucose and creatinine. Provision is made for the addition of two further analytical modules when these become available. The sample tray holds up to 38 specimens and two calibrating solutions, and requests for up to 76 specimens may be entered into the machine at one time. Any combination of available tests may be requested for each specimen or group of specimens, but sodium and. potassium are always measured together. The machine may be instructed to analyse an emergency specimen at any time, after which it will return to the original sequence of specimens. The analyser is controlled by a computer to which the operator communicates by means of a keyboard and a visual-display unit (VDU). The operator can select individual tests for each specimen, enter identification numbers, enter or alter reference ranges, initiate priming of reaction vessels and automatic calibration on all or any channels, request duplicate assays, and to return to a control specimen at any desired frequency. Special procedures for routine maintenance or diagnosis of faults can be initiated frorn the keyboard. In addition the computer monitors the functioning of the instrument, detects the presence of a sample in the cup, converts the outputs from the analytical modules to analytical results, expressed either as mass (eg mg/dl) or molar (eg mmol/1) concentrations. Results are displayed on the VDU and printed on a high-speed thermal printer in a form which could be used as the report. This includes the date and time of the analysis, patient identification number, the analytical results, the reference ranges, and an indication if the result is outside that range. The analyser may also be connected to external data-processing equipment via a multipin socket. Reagents provided by the manufacturer are stored on top of the machine. They are pumped to the reaction Vessels by peristaltic pumps via preheating elements, and excess is removed via an overflow. Although the principle components of each reagent are listed on the bottle, insufficient detail is given to enable the user to prepare them. Sodium’ and potassium are measured by means of ionselective elects:odes (lithium aluminium silicate glass and valinomycin respectively). The reference electrode is a second sodium electrode in contact with a sodium solution of constant concentration. The electrodes are equilibrated prior to measurement, and 50/1 of serum or urine are required. Chloride is measured by coulometric titration with silver ions released from a silver anode. It requires 8pl of serum or 6/.tl of urine. Glucose is estimated by measuring the rate of consumption of oxygen in the presence of glucose oxidase by means of an oxygen electrode. It requires 10gl of serum or urine.