Centrifugal analysers

Figure 6.1 Diagrammatic representation of a typical transfer disc for a centrifugal analyser.

Which of the following statements are true of centrifugal analysers ... 

Many automated instruments measure enzyme activity using fixed time colorimetric methods. Some, however, can be classed as reaction rate analysers, e.g. the centrifugal analysers, and these instruments determine the reaction rate from either the initial slope of the reaction curve or from repeat measurements at fixed intervals. In both methods the slope of the line is taken to represent the activity of the enzyme. 

Fig. 2.9 The Cobas Fara II robotic centrifugal analyser. Reproduced with permission of Roche Diagnostics.

Artuch R, Vilaseca MA, Farre C, Ramon F (1995) Determination of lactate, pyruvate, beta-hydroxybutyrate and acetoacetate with a centrifugal analyser. Eur J Clin Chem Clin Biochem 33 529-533... 

Li PK, Lee JT, Mac Gillivray MH, Schaefer PA, Siegel JH (1980) Direct, fixed-time kinetic assays for beta-hydroxybutyrate and acetoacetate with a centrifugal analyser or a computer-backed spectrophotometer. Clin Chem 26 1713-1717... 

White RM, Cross RE, Savory J. Enzyme coupled measurement of uric acid in serum with a centrifugal analyser. Chn Chem 1977 23 1538-40. 

Mount JN, Heduan E, Herd C, Jupp R, Kearney E, Marsh A. Adaptation of coenzyme stimulation assays for the nutritional assessment of vitamins Bl, B2 and B6 using the Cobas Bio centrifugal analyser. Ann Clin Biochem 1987 24 (Pt l) 41-6. 

Vuilleumier JP, Keck E. Flourimetric assay of vitamin C in biological materials, using a centrifugal analyser with fluorescence attachment. J Micronutr Anal 1989 5 25-34. 

Davidson W, Barbour HM. Determination of urine magnesium using the magon method on the Monarch centrifugal analyser. Ann Clin Biochem 1990 27 595-6. 

Centrifugal analysers, discussed In Chapter 4, are discrete In nature. Sample collection and reagent dispensation take place In an automated dosing module. However, the transfer disc containing the radially arranged samples and reagents Is transferred manually to the analyser module, where reaction, signal measurement and data acquisition and treatment, all completely automated,... 

Fig. 1.13 Seemingly complete automation of the analytical process (Type 9 analyser). Centrifugal analysers feature an Intermediate stage involving the manual transport of the transfer disc.

Automatic centrifugal analysers are also batch analysers with final transfer of the reaction mixture prior to measurement. They have become very popular in clinical laboratories in the last few years. The different manufacturers offer a wide a range of models the Centrifichem Models 400 and 600, manufactured by Union Carbide, are probably the best known and most widely used, so they will be described here as the most typical representatives. It should be noted, though, that there are no significant differences between... 

Centrifugal analysers consist of two separate instrumental units the dosing module, which dispenses samples and reagents, and the analyser module, where samples and reagents are mixed and the reaction mixture is measured, generally spectrophotometrically. The most advanced models feature a computer that controls the operation of the two units and allows the user to program the system for the determination of a given number of parameters and delivery of printed results. 

Fifl. 8.6 Scheme of automatic centrifugal analysers. Dosing module (a) sample turntable (b) radial transfer unit (c) location of the previous units on sample and reagent dosing. 

Fig. 8.7 Scheme of automatic centrifugal analyser. Analyser module (a) location of the transfer disc (b) the transfer of the reaction mixture takes place during centrifugation (c) optical detection system on a single, fixed point. 

It is significant that Technicon, the pioneering and virtually exclusive developers of continuous automatic analysers, have recently devoted their production efforts to batch models. Probably, their RA-1000 model was created to compete with the centrifugal analysers introduced by other firms and which were gradually displacing continuous-flow AutoAnaiyzers, widely used until a decade or so. 

The rapid growth of instruments with built-in microprocessors or computers has been the result of a number of reasons. First, the enormous growth of the number of clinical analyses required, which increased by 10-20% yearly between 1970 and 1980. Second, the need for better performance from analysers whose precision could not be improved or even preserved without computerization. Even the basic concept behind some analysers (e.g. centrifugal analysers) or enzymatic rate measurements with multi-detection are not feasible without recourse to computerization. 

These, In turn, can be classified Into centrifugal and non-centrifugal analysers. 

Procedure manually shake the sample bottle for 5 min to homogenize contents and take sample for analysis directly from the bottle. Operations should be carried out at 20 2°C. Weigh 10.00 g soil into a 250 mL polyethylene bottle add 100.0 mL of 0.01 mol L CaCl2 solution and extract on shaker for 3 h at 30 rpm decant about 60 mL into a centrifuge tube and centrifuge for 10 min at 3000 g measure and report the room temperature before and after the extraction and also the temperature of the extracting solution at the end of the extraction measure pH in the extract before centrifugation analyse immediately. 

Simplex optimization has been used with success in many areas of analytical chemistry, e.g. atomic-absorption spectrometry, gas chromatography, colorimetric methods of analysis, plasma spectrometry, and the use of centrifugal analysers in clinical chemistry. When an instrument is interfaced with a computer, the results of simplex optimization can be used to initiate automatic improvements in the instrument variables. 

A study of the kinetics of the Beckman Enzymatic Amylase Method, for determination of human serum and urinary amylase, by use of the centrifugal analyser showed that the rate of reaction is not linear. It showed a pronounced initial lag period of 10 min, after which the lag was diminished but never completely abolished. Furthermore, the function relating rate of reaction to enzyme activity was not linear but increased disproportionately with increase in enzyme activity. When glycogen was substituted for soluble starch in the Beckman reagent, the initial lag period was less than 3 minutes and subsequently the reaction became linear. When mixed soluble starch-glycogen substrate was used, the a-amylase activity of serum and urine specimens correlated well with the activity determined by the Phadebas method. A dialysable factor present in a urine specimen from a kidney transplant patient inhibited the Beckman assay but not the Phadebas assay. This inhibition was simulated by the addition of pyruvate and reversed by the addition of NADH. 

See also centrifugal analysers, continuous flow analysis, discrete analysis... 

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