Discrete analyzers sequential

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. 

Discrete sampling instruments. In discrete sampling, each sample undergoes reaction (and usually measurement) in a separate cuvet or chamber. These samples may be analyzed sequentially or in parallel (see below). 

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. 

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

Having a closer look at the pyramid algorithm in Fig. 40.43, we observe that it sequentially analyses the approximation coefficients. When we do analyze the detail coefficients in the same way as the approximations, a second branch of decompositions is opened. This generalization of the discrete wavelet transform is called the wavelet packet transform (WPT). Further explanation of the wavelet packet transform and its comparison with the DWT can be found in [19] and [21]. The final results of the DWT applied on the 16 data points are presented in Fig. 40.44. The difference with the FT is very well demonstrated in Fig. 40.45 where we see that wavelet describes the locally fast fluctuations in the signal and wavelet a the slow fluctuations. An obvious application of WT is to denoise spectra. By replacing specific WT coefficients by zero, we can selectively remove... 

Discrete or batch analyzers In these, each sample preserves its integrity in a vessel transported mechanically to various zones of the analyzer, where the different analytical stages are carried out in a sequential manner. Each sample finally arrives at the detector where the relevant signals are recorded. 

Figure 1.3. A random-access continuous-flow analyzer (Chem 1-Technicon, USA), which aspirates sample (S) and necessary reagents (Rl, R2) sequentially from a two carousels (not shown). The resulting stream is air segmented and oil encapsulated (oil is shown as solid lines on top of liquids in the cups and on the walls of tubing to minimize the carryover. Detection is by a series of optical detector stations that discretely record gradual development of color during the flow transport. (P is a peristaltic pump.)...

Since soil-adsorbed plutonium contamination exists as discrete particles of various sizes, analysis of larger soil volumes (25 to 100 grams) is recommended (Bernhardt 1976). Commonly, soil samples with high amounts of carbonate are difficult to analyze. More rapid, efficient, and economical procedures are being developed to sequentially analyze a number of radioactive actinides (Flindman 1986). 

There are two basic instrumental concepts for MS/MS. The first is tandem mass spectrometry in space (or tandem-in-space MS). In order to perform two consecutive mass-analyzing steps, two mass analyzers may be mounted in tandem. Thus, tandem-in-space refers to MS/MS instrumentation where product ion spectra are recorded using spatially separated m/z analyzers. Speedfic m/z separation is performed so that in one section of the instrument ions are selected, then dissociated in an intermediate region, and the products thereof are finally transmitted to a second analyzer for mass analysis (Fig. 9.1). All beam transmitting devices, e.g., multiple sector, ReTOF, TOF/TOF, QqQ, and QqTOF instruments follow this route to tandem MS (Fig. 9.2) [4]. The second approach, tandem mass spectrometry in time (or tandem-in-time MS), enploys a single m/z analyzer (QIT, LIT, FT-ICR) that may be operated by executing the discrete steps of ion selection, activation, and product ion analysis in the very same place but sequentially in time [4]. 

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