Analysis sequential

The principle of sequential analysis consists of the fact that, when comparing two different populations A and B with pre-set probabilities of risks of error, a and /3, just as many items (individual samples) are examined as necessary for decision making. Thus the sample size n itself becomes a random variable. 

Sequential investigations may be used for both attribute testing and quantitative measurements (variable testing). The fact that it is enough to perform only as many tests or measurements as are absolutely necessary, is of great advantage in such cases if individual samples are either difficult to obtain or expensive, or if the same is true for the measurement. 

Based on the actual result of every individual measurement, it has to be checked whether a decision may now be taken or whether studies have to be continued. According to the final aim of sequential analysis, one can differentiate between closed sequential test plans that always come to a decision A B or A B (possibly with a large test expenditure) and open sequential test plans, which also allow - after a certain test expenditure -the statement A = B. 

Data evaluation can be done by calculation or graphically. An example of graphical sequential analysis is given in Fig. 4.12 for attribute testing. 

In the case of attribute testing, limit curves for acceptance and rejection are normally straight lines. In case of variable testing, they are mostly nonlinear functions (Graf et al. [1987]). 

---

Flow injection analysis (FIA) was developed in the mid-1970s as a highly efficient technique for the automated analyses of samples. °> Unlike the centrifugal analyzer described earlier in this chapter, in which samples are simultaneously analyzed in batches of limited size, FIA allows for the rapid, sequential analysis of an unlimited number of samples. FIA is one member of a class of techniques called continuous-flow analyzers, in which samples are introduced sequentially at regular intervals into a liquid carrier stream that transports the samples to the detector. ... 

E. E. Johnson, R. Gloor and R. E. Majors, Coupled column chromatography employing exclusion and a reversed phase. A potential general approach to sequential analysis , J. Chromatogr. 149 571-585 (1978). 

Figure 12.11 Coupled SEC-RPLC separation of compound Chemigum mbber stock (a) SEC ti ace (b) RPLC trace of fraction 1, dibutylphthalate (c) RPLC trace of fraction 2, elemental sulfur. Coupled SEC conditions MicroPak TSK 3000H (50 cm) X 2000H (50 cm) X 1000 H (80 cm) columns (8 mm i.d.) eluent, THE at a flow rate of 1 mL/min UV detection at 215 nm (1.0 a.u.f.s.) injection volume, 200 p-L. RPLC conditions MicroPak MCH (25 cm X 2.2 mm i.d.) column flow rate, 0.5 mL/min injection volume, lOpL gradient, acetonitrile-water (20 80 v/v) to 100% acetonitrile at 3% acetonitrile/min UV detection at 254 nm (0.05 a.u.f.s.). Reprinted from Journal of Chromatography, 149, E. L. Jolmson et al., Coupled column cliromatography employing exclusion and a reversed phase. A potential general approach to sequential analysis , pp. 571-585, copyright 1978, with permission from Elsevier Science.

In passing we remark that there are well-known statistical methods of hypothesis testing and parameter estimation used in decisionmaking. Sequential analysis is a method of sampling used to decide whether to accept or reject a lot with defective items, or whether to continue sampling. Also, there are various statistical methods used in quality control of a manufacturing process, to decide on how much the quality should be improved to be acceptable. 

A sequential analysis protocol includes three steps (1) extraction in water or other appropriate solvent for the colorant, (2) purification or concentration of the colorant, and (3) separation coupled with detection of the target molecule. Different methods of extracting synthetic colorants from foods have been developed using organic solvents followed by SPE protocols using as adsorption support RP-C18, amino materials, or Amberlite XAD-2. Eor qualitative evaluations, the easiest option for separating colorant molecules from unwanted ingredients found in an extract is SPE on polyamide or wool. 

Exclusion chromatography is also useful in the separation of small molecules from interfering matrices of larger molecules, for example in foods or other samples of biological origin. It can be used as the first step in the sequential analysis of complex unknown organic mixtures, which are first separated on a size basis by exclusion, then the collected fractions can be further separated by normal or reverse phase chromatography, where the separation is based on chemical differences. 

Fig. 4.12. Graphical evaluation of sequential analysis gaccept(n) acceptance function, grejea(n) rejection function...

Tong, H. and C. M. Crowe. Detecting Persistent Gross Errors by Sequential Analysis of Principal Components. AIChE J 43(5) 1242-1249 (1997). 

A sequential procedure was further developed by Tong and Crowe (1996) by applying sequential analysis of the principal component test using the sequential probability ratio test (SPRT). Dunia et al. (1996) also used PCA for sensor fault identification via reconstruction. In that paper it was assumed that one sensor had failed and the remaining sensors are used for reconstruction. Furthermore, the transient behavior of a number of sensor faults in various types of residuals is analyzed, and a sensor validity index is suggested, determining the status of each sensor. 

Tong, H., and Crowe, C. M. (1996). Detecting persistent gross errors by sequential analysis of principal components. Comput. Chem. Eng. 20, S733-S738. 

Ho JSY. 1989. A sequential analysis for volatile organics in water by purge-and-trap capillary column gas chromatography with photoionization and electrical conductivity detectors in series. J Chromatogr Sci 27 91-98. 

The chromatographic or electrophoretic behavior of a specific astatocompound must be considered similar, but not necessarily the same, as that of its analogous iodo and bromo derivative. This procedure has been developed and termed sequential analysis 99,102) in order to avoid a coincidental fitting of chromatographic data, several solvent systems should be used. 

Nymphaea caerulea, for seven natural anthocyanins stabilizing a DNA triplex, etc. Sequential analysis of the oligosaccharide structures of the flavonol tamarixetin-7-O-rutino-side has been performed by ID multistep-relayed COSY-ROESY experiments. Selective excitation was performed by Gaussian-shaped soft pulses. 

Schroeder, H. and Haslinger, E., Sequential analysis of oligosaccharide structures by selective NMR techniques. Part II. ID multistep-relayed C0SY-R0ESY, Liebigs Ann. Chem., 1, 751, 1993. 

We have been looking at reactions which degrade these molecules by splitting phosphate bonds. This problem is important for sequential analysis since agents are required that split phosphate bonds attached to one nucleotide base preferentially to phosphate bonds attached to other bases. It appears that the cleavage by zinc (II) is indeed such a specific reaction. 

Braunitzer, G., Chen, R., Schrank, B, and Stangl, A. 1972. Automatic sequential analysis of a protein (/3-lactoglobulin AB). Hoppe-Seyler s Z. Physiol. Chem. 353, 832-834 (German). 

Sequential analysis of amino acids in purified peptides and proteins is best initiated by analysis of the terminal amino acids. A peptide has one amino acid with a free a-amino group (NH2-terminus) and one amino acid with a free a-carboxyl group (COOH-terminus). Many chemical methods have been developed to selectively tag and identify these terminal amino acids. 

Even more versatile than the dansyl method is the Edman method (Figure E2.4). The NH2-terminal amino acid is removed as its phenylthiohydan-toin (PTH) derivative under anhydrous acid conditions, while all other amide bonds in the peptide remain intact. The derivatized amino acid is then extracted from the reaction mixture and identified by paper, thin-layer, gas, or high-performance liquid chromatography. The intact peptide (minus the original NH2-terminal amino acid) may be isolated and recycled by reaction with phenylisothiocyanate. Since this method is nondestructive to the remaining peptide (aqueous acid hydrolysis is not required) and results in good yield, it can be used for stepwise sequential analysis of peptides. The method is now automated. 

SEQUENTIAL ANALYSIS. The analysis of material derived by a sequential method of sampling, that is to say, it is tile data, not tile analysis, which are sequential. 

The introduction of commercial instrumentation in this automated area has been too slow and too disappointing to meet the need for routine analysis of numerous samples. The options have been the extraction of one sample at a time or individual samples in parallel. Either of these options make the repetitive analysis of the same sample or the sequential analysis of different samples exceptionally time consuming. Parallel analysis, proposed by one manufacturer, is susceptible to cross-contamination and across the board sample loss with clogging of one extraction vessel. In order to move supercritical fluid extraction into the realm of routine operations for residue analysis, rapid analysis of multiple samples needed to be addressed. 

---