Discrete analyser

Instruments in which each test is performed in its own container or slide are known as discrete analysers, in contrast to flow analysers in which the samples follow each other through the same system of tubing. All discrete analysers have a common basic design incorporating a pipetting system, a photometric detector and a microprocessor. A development of the single test instrument is the parallel fast analyser, which analyses several samples simultaneously but for only one constituent. However, the change-over from one analytical procedure to another is quick and simple. 

Figure 6.5 Transparent analytical test pack (100 mm X 80 mm) for Du Pont aca analyser containing all the reagents for the assay of glucose. A wide range of test packs is available for use in the automated discrete analyser. Once the pack is loaded into the instrument, sample and diluents are automatically injected. The sealed reagent compartments are then broken open at various stages in the assay and the contents of the pouch are mixed and incubated. The transparent pouch then serves as a cuvette for absorbance measurements.

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

The discrete method has the advantage that samples can he processed at a high rate. For example, commercial colorimetric analysers are capable of yielding between 100 and 300 measurements per hour, whereas for continuous analysers a processing rate of 20— 80 samples per hour is normal. However, the high-throughput discrete analysers are appreciably more expensive than the continuous analysers. 

Continuous analysis requires flexible tubes which are not attacked by the materials under examination, and this places certain limitations on the scope of the method. Certain reactive and corrosive materials cannot he satisfactorily pumped, although advances have been made in the development of inert plastics and other synthetic materials. Displacement pumping with the aid of a liquid compatible with sample and reagents provides an alternative, though generally inconvenient, approach. No such limitations arise in discrete analysers because there is no restriction on the choice of materials for sample and reagent containment. 

Fig 2.3 The basic configuration of the Olympus AU5000 Series discrete analyser. 

TTie major disadvantage of the GeMSAEC is that although several analyses are run in parallel, the system is discontinuous and the rotor has to he stopped for reloading it is also difficult to carry out more than one type of assay in a rotor at any one time. This problem was overcome in the DACOS approach (Discrete Analyser with Continuous Optical Scanning) described by Snook et al. [17]. In this approach, reaction tubes are situated at the periphery of the rotor, which turns in discrete steps, a few degrees at a time, to enable... 

Fig. 2.8 Schematic diagram of discrete analyser with continuous optical scanning.

K3. Kamp, H. H., Luderer, T. K. J., Muller, H. J., and Sopjes-Kruk, A., Rapidimmunoturbidimetric assay of albumin and immunoglobuUn G in serum and cerebrospinal fluid with an automatic discrete analyser. Clin. Chirrr Acta 114,195-205 (1981). 

As the craze microstructure is intrinsically discrete rather than continuous, the connection between the variables in the cohesive surface model and molecular characteristics, such as molecular weight, entanglement density or, in more general terms, molecular mobility, is expected to emerge from discrete analyses like the spring network model in [52,53] or from molecular dynamics as in [49,50]. Such a connection is currently under development between the critical craze thickness and the characteristics of the fibril structure, and similar developments are expected for the description of the craze kinetics on the basis of molecular dynamics calculations. 

Discrete analyses for nitrate, nitrite, phosphate, and silicate were performed on samples drawn from the flow with a modified Hitachi autoanalyzer system the full-scale ranges for these measurements are 0-30, 0-10, 0-2.4, and 0-45 /xmol/L, respectively. The precision and accuracy of these measurements are 1 % of full-scale values. Both Sagami standard nutrient solutions and standard solutions prepared from preweighed standards were used to standardize the nutrient measurements. Beer s law curves were run throughout the experiment to establish the output response of the spectrophotometers. The response functions were linear for the concentrations measured. A complete description of the analytical methods used for nutrients is given in References 15 and 16. 

There are two types of analyser discrete and continuous (Figure 9.3). In discrete analysers, samples are taken at selected intervals, placed in individual containers and any required sample preparation steps are carried out. Samples are then analysed in batches, with the information being fed to the controller and operator in the usual way. Obviously... 

The simplest application of these multiplexing methods involves the so-called direct-reading spectrometer , which was used with some success for a short period in atomic spectroscopy [42]. This instrument consists of a dispersion system with an array of exit silts arranged at appropriate locations. Behind each silt Is a photodetector —usually a photomultiplier. These multiplexing methods have also been used In UV-vIsIble spectroscopy, although to a lesser extent they have been Implemented on automatic discrete analysers featuring an optical system of this type with 5-10 channels or wavelengths... 

The change in the absorbance at 340 nm, due to the disappearance of NADH, is directly proportional to the bicarbonate concentration. This method is used on several discrete analysers. 

Calcium can be estimated by its formation with cresol-phthalein complexone to form a coloured complex. 8-Hydroxyquinoline can be added to bind magnesium and prevent interference from this ion. Other complexing agents have been tried, e.g. methylthymol blue. This type of method is used in many continuous flow and discrete analysers. 

Examples of discrete analysers are the Vicker s M300, the Abbott Bichromatic Analyzer and the Hycel Mark X. 

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