Analyzers discrete

To re-examine a ccrpound in GC/MS, the entire sample must be reintroduced to the gas chromatograph. In MS/MS, the original ion is simply again selected by the first mass analyzer. Finally, the time evolution of a number of compounds can be followed directly with MS/MS, for example, as the sample is heated. In GC/MS this sinple experiment generates a number of sanples, each of which must be discretely analyzed. 

E224 Palmer, J.J., Spolsdoff, E., Avelino, E. and Borer, W.Z. (1985). A field evaluation of the Kodak Ektachem 700 discrete analyzer. Clin. Chem. 31, 918, Abstr. 80. 

Discrete analysis, in contrast with continuous-flow analysis, allows each specimen in a batch its own physical and chemical space, separate from every other specimen. Early discrete analyzers, such as the 1970 vintage robot chemist, mimicked the steps of manual human analysis. Subsequently, many discrete analyzers were developed and are still widely used in clinical laboratories. Centrifugal and random access analyzers are examples of instruments that use discrete processing. 

The method of specimen delivery within the analyzer is the major difference between continuous-flow and discrete systems. In continuous-flow systems, the specimen is aspirated through the sample probe into a continuous reagent stream, whereas in discrete analyzers, the specimen is aspirated into the sample probe and then delivered through the same orifice into a reaction cup or other container. 

Fig. 12a. Mecolab, discontinuous discrete analyzer (by courtesy of Joyce, Loebl Co. Ltd., Gateshead-on-Tyne, England).

Fig. 12b. Robot Chemist, continuous discrete analyzer (by courtesy of Warner-Chilcott Laboratories Instruments Division, Richmond, Calif.).

Aiach and co-workers have reported on the adoption of five different substrate assays onto an automated discrete analyzer (A2). They observed excellent within-run precision coefficient of variation (CV) values ranging from 1 to 3%, as well as satisfactory day-to-day precision. Ito and Statland similarly evaluated and compared the DuPont aca and Kabi/CentrifiChem automated method for measuring antithrombin III and plasminogen (13). 

A2. Aiach, M., Leon, M., Mlchau, A., and Capron, L., Adaption of synthetic peptide substrate-based assays on a discrete analyzer. Semin. Thromb. Hemostasis 9, 206-219... 

CFA is very often used in process control. In CFA, the sampling process consists of samples flowing sequentially and continuously in a tube, where each sequentially mixes with reagents in the same tube at the same point downstream and then flows sequentially into a detector. Another automated device type is the discrete analyzer where the analysis is made by taking a batch sample at selected intervals and subjecting it to analysis. The main advantage of CFA is the objectivity assured by operator elimination at the sample pickup and sampling steps. However, when the complexity of the sample that is to be analyzed increases, CFA does not offer reliable analytical information therefore, one should use discrete analyzers as an alternative. 

In discrete analyzers, a batch sample is taken at selected intervals and then analyzed, with the information being fed to the controller and operator in the usual fashion. Obviously, the samphng and analytical dead times are increased over continuous analyzers, and the manipulated variable is held at a fixed value between measurements. If a transient error occurs between measurements, it may not be detected and corrected for. On the other hand, a short transient error may be detected during the measurement interval and a correction for this applied during the entire interval between measurements. 

Process control—continuous and discrete analyzers, p. 661 Automatic instruments, p. 664 Flow injection analysis, p. 665 Dispersion coefficient (key equation 23.1), p. 667 Sample volume, Sy2 (key equation 23.3), p. 670 Sequential injection analysis, p. 673 Microprocessors and computers in analytical chemistry, p. 674... 

The drawbacks of discrete analyzers are their mechanical complexity and high cost of operation. Sample cups, disposable cuvettes, rotors, and prepacked reagents increase the cost of individual assays above the acceptable limit for the strained budgets of most clinical laboratories. In addition, these machines are seldom used outside the clinical laboratory, because they are designed to handle three dozen of the most frequently required clinical tests. The advantages of the discrete approach are the ability of some of these instruments to perform assays via random access—which allows sequential assay of diverse analytes at will—and the capability of stat operation, which yields the analytical readout within 5-10 min after the machine has been switched on and a sample has been inserted by a technician. 

We discuss in this chapter analysers that arc highly automated, such as flow injection and discrete analyzers. In addition, laboratory robotic systems that are becoming more and more commonplace for sample handling and preparation arc also described. The latest advances in automation involve the development of microlluidic systems, which are sometimes called lab-on-a-chip or micro total analysis systems. These recent developnienis are also described here. It is important to note that the same principles of automatic analysis discussed here also apply to process control systems, which analyze the current state of a process and then use feedback to alter experimental variables in such a way that the current state and the desired state are nearly identical,... 

Today, a wide variety of discrete analyzers are avail-ble for clinical laboratories. Some of these arc gen-ra purpose and capable of performing many dilTerent eterminations. often on a random access basis. Oih-rs arc of more limited use intended for one or a few pccific determinations. Many of the general-purpose naly/ers use a combination of traditional chemical jsts and immunoassays in which aniibody-antigen itcractions arc used in the determination. Several encral-purpose analyzers are capable of performing lore than 100 tests, including the determinations hown in Table. 33-1. 

Figure 24.10. Ute sampling controller. The sampling controller accepts a logic signal from a discrete analyzer the chromatograph) and applies corrective action for a control interval established by a timer. Courtesy of the Foxboro Company.

Multi-channel. These instruments analyze each sample for many different components—in parallel for a discrete analyzer, and sequentially for a continuous-flow analyzer. 

Alternatives for automation in a laboratory are discrete analyzers and flowing systems. By means of discrete analyzers, unit operations such as dilution, extraction and dialyses can be automated. Continuous flow analyzers or flow injection analyses serve similar objectives for automation, for example, for the determination of clinical parameters in blood serum. 

Discretionary analysis, as opposed to multianalyte panel screening developed from the realization that nonselective screening did not yield the expected health benefits. This approach was best addressed with discrete analyzers. 

These modern discrete analyzers (Figure 2), typically utilize wet-chemistry with photometry of selective electrodes for the cations sodium and potassium. Dry-film technology using similar measurement principles are a significant minority of clinical analyzers. Each test is delivered as an individual slide, which minimizes infection risks. Either type allows different mixtures of tests within a defined menu to be done on different samples during the same analytical run (discretionary). The protein problem is circumvented by sample dilution and the use of surfactants. 

Discrete analyzers can operate at up to 300 samples per hour, but may be dependent on the number... 

Today such analyzers are discrete analyzers operating at high throughput on a wider menu of tests than their large cousins. They are usually suited to more sophisticated chemistries, such as those used in specific protein analysis or enzyme-mediated immunoassays for drug analysis. 

The advantage of discrete analyzers is that sample crossover in the system itself is the lowest possible. Volumes of 75 pi of reagent and sample volumes as large as 100 pi are sufficient. In an automated system with a throughput of 200 determinations per hour in the same sample 6 to 10 components (such as ammonium, alkalinity, aluminum, boron, bromide, calcium, chloride, chromium(VI), cyanide, fluoride, iron, magnesium, nitrate, nitrite, phosphate, etc.) can be determined. In discrete analyzers normally conventional spectrophotometric methods are used. These methods are prone to interference of the matrix of the sample. As a good concept for interference studies still is not available, interferences are as yet not sufficiently studied systematically even for routine analyses. 

Nevertheless, no truly reliable implantable sensor has yet reached the market. In the meantime, bedside-type discrete analyzers seem to offer the most economic and reliable means for critical care. In addition, ex vivo on-line analysis based on microdialysis sampling seems to be helpful. 

Automatic analytical systems are of two general types discrete analyzers and continuous flow analyzers, occasionally, the two are combined. In a discrete instrument, individual samples are maintained as separate entities and kept in separate vessels throughout each... 

Clinical instruments have long been the focus for laboratory automation. Indeed, the Technicon AutoAna-lyzer, an air-segmented continuous flow system, was the first truly automated instrument for a clinical laboratory. In 1968 DuPont introduced the ACA (Automated Clinical Analyzer), the first totally automated discrete analyzer. The analyzer was based on prepack-... 

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