【正文】 NTRODUCTION In order to measure the progress of an enzymatic reaction and to measure the total change in the concentration of the reactant/substrate, various techniques [1] such as spectrophotometric, polarometric, amperometric, electrochemical, coulometric, polarography, radiochemical, and fluorescence are available. Instrument developed works on the principle of absorbance transmittance photometry. It is a highperformance,microcontrollerbased, photometric biochemical analyser to measure various blood biochemical parameters such as blood glucose, urea, protein, bilirubin, and so forth, and also to measure and observe enzyme growth occurred while performing the other biochemical tests such as ALT (alkaline amino transferase), amylase, AST (aspartate amino transferase), and so forth. The biochemical tests are very important as they are associated with various disorders and diseases such as diabetes, renal diseases, liver malfunctions,and other metabolic derangements. The quantisation of these parameters helphful in classifying such diseases,and under appropriate circumstances, results are used for diagnostic recent years, automation in clinical chemistry has progressed with a change from rigid to very flexible instruments. Automation of clinical instruments has brought about a revolution in the field of medical instrumentation. It has reduced 12 the load on clinical laboratories to a great extent by reducing the time taken in the test and minimizing the involvement of laboratory staff. Instrument developed is classified as semiautomated analyser [2] and has advantages of precision and accuracy. These systems are used in hospitals to test various blood biochemical parameters. All primary health centres, munity health centres, and district hospitals are the potential users of this machine. 2. MATERIALS AND METHODS . The instrument (i) Design principle The instrument is designed using the principle of absorbance transmittance photometry. According to Lambert and Beer’ Figure 1: Schematic of Lambert and Beer’s law. Figure 2: Relation between percent transmission and concentration. law [3], when monochromatic light is passed through coloured solution, the intensity of the transmitted light decreases exponentially with the increase in concentration of the absorbing substance. The value of absorption of light energy is dependent on the number of molecules present in absorbing material and the thickness of the medium. Thus,intensity of light energy leaving the absorbing substance is used as an indication of concentration of that particular shown in Figures 1 and 2, if I0 is the intensity of incident light in coloured solution and It is the transmitted light, then according to this law It = I0e kct (1) and transmission T = It/ I0 = e kct (2) log e T= kct (3) log e(1/ T) = kct (4) 13 where c is the concentration of absorbing material, t thickness of the light path, and k absorption constant. The quantity (logT) or log(1/T) is termed as extinction E/OD or the absorbance: A=log(1/T)=log100/(%transmission) (5) A = 2 log(%transmission). Therefore A = kct. If t is constant, then Aα C. In this system, the basic requirement is to measure optical density/absorbance and then concentration of the test parameter under run accurately. (ii)Microcontrollerbased hardware Figure 3 represents the basic modules of the system。C, 30176。C by initial rates using fixed time, end point, and kiic methods. System allows selecting any required temperature and maintains the temperature of flow cell at that selected temperature because enzymes are relatively fragile substances which have a tendency to undergo inactivation or denaturation [1]. So to get the proper enzymatic rate and for increasing the stability they must be properly handled while conducting the test and must be kept at required temperatures. Temperature sensor LM355 14 Figure 3: Block diagram of clinical chemistry analyser. Figure 4: Microcontrollerbased hardware design of clinical chemistry analyser. and peltier device are used to provide and maintain the required temperature for the samples in flow cell. Peltier works in both directions for cooling and heating. This effect is used to control the temperature of the sample. (iv) Peristaltic pump/aspiration system Port1 of 8031 microcontroller is interfaced with a stepper motor through a driver hardware that drives the roller type of