PRISMA method

Cimpoiu et al. [72] made a comparative study of the use of the Simplex and PRISMA methods for optimization of the mobile phase used for the separation of a group of drugs (1,4-benzodiazepines). They showed that the optimum mobile phase compositions by using the two methods were very similar, and in the case of polar compounds the composition of the mobile phase could be modified more precisely with the Simplex method than with the PRISMA. 

Pelander et al. [81] developed a computer program for optimization of the mobile phase composition in TLC. They used the desirability function technique combined with the PRISMA model to enhance the quahty of TLC separation. They apphed the statistical models for prediction of retardation and band broadening at different mobile phase compositions they obtained using the PRISMA method the optimum mobile phase mixtures and a good separation for cyanobacterial hepatotoxins on a normal phase TLC plate and for phenolic compound on reversed-phase layers. 

On the basis of Snyder s system for characterization of solvents the PRISMA method for mobile phase optimization has been developed. This system enables the optimization of solvent strength and mobile phase selectivity and also the transfer of the optimized mobile phase to different planar chromatographic techniques, in our case the PLC. 

Procedures used vary from trial-and-error methods to more sophisticated approaches including the window diagram, the simplex method, the PRISMA method, chemometric method, or computer-assisted methods. Many of these procedures were originally developed for HPLC and were apphed to TLC with appropriate changes in methodology. In the majority of the procedures, a set of solvents is selected as components of the mobile phase and one of the mentioned procedures is then used to optimize their relative proportions. Chemometric methods make possible to choose the minimum number of chromatographic systems needed to perform the best separation. 

The three methods described in the preceding paragraphs each offer distinct advantages and disadvantages. The first and most obvious difference between the methods is the distinction between the sequential methods (sequential simplex and prisma method) and the simultaneous method (mixture design). With the sequential method some experiments are performed, these are evaluated, and on the basis of this evaluation new design points are selected, these are evaluated etc. With the simultaneous... 

The important difference between the statistical mixture design and the PRISMA method is that the former yields a computer-assisted optimum solvent composition whereas the latter relies on structured trial and error. In TLC, the PRISMA method is a viable alternative because the time to prepare and evaluate each solvent composition is small and several different compositions can be evaluated simultaneously with several development systems. The PRISMA is also very powerful for the selection of mobile phase in over-pressured layer chromatography. 

Optimization, 81-99 general methods of, 81-92 mixture design statistical technique, 88-91 multifactor optimization system, 91-92 the PRISMA method, 86-88 simplex optimization, 83-86,87 window diagrams, 81-83 miscellaneous methods of, 92-97 stepwise gradient optimization, 95-96 two-dimension optimization, 92-95,96 unknown component optimization, 97 of the mobile phase, 23-25 Organochlorine (OC) insecticides color reactions of, 805... 

Morita et al. [69] optimized the mobile phase composition using the PRISMA model for rapid and economic determination of synthetic red pigments in cosmetics and medicines. The PRISMA model has been effective in combination with a super modihed simplex method for fadhtating optimization of the mobile phase in high performance thin layer chromatography (HPTLC). 

The PRISMA model was developed by Nyiredy for solvent optimization in TLC and HPLC [142,168-171]. The PRISMA model consists of three parts the selection of the chromatographic system, optimization of the selected mobile phases, and the selection of the development method. Since silica is the most widely used stationary phase in TLC, the optimization procedure always starts with this phase, although the method is equally applicable to all chemically bonded phases in the normal or reversed-phase mode. For the selection of suitable solvents the first experiments are carried out on TLC plates in unsaturated... 

The last requirement, i.e. if all (root)cause areas are included, was used to retrieve three pro-active methods indicating safety risks. All three methods address the entire socio-technical system (technical, human and organizational). These three methods are used to construct a new pro-active method of indicating safety risks, which includes the benefits and addresses the limitations of these three existing methods. The three methods evaluated are MORT, Johnson (Johnson, 1980), TRIPOD, Hudson (Hudson et al., 1991), and PRISMA, van der Schaaf (Schaaf van der, 1992). 

From this analysis it appears that a huge discrepancy exists between deviations prior to accidents, that can be found in normal operation and the pro-active safety indicators and methods in current use. The re-occurring indirect safety related deviations that are the dominant class of events causing accidents are therefore defined as the precursors for accidents, as stated in Chapter 1. Furthermore, from Table 5 it can be concluded that a clear link between risk reduction and the normal way of working is not explicitly present in one of the three methods. Finally, the feasibility of methods (except PRISMA) needs some attention additional expert knowledge is often necessary to apply the method. The focus of the method indicating safety risks developed in this thesis will lie especially on these three criteria. 

The PRISMA model274 and factorial experimental design were applied in the development of a one-dimensional overpressured layered chromatography separation method for the anti-neoplastic bis-indole alkaloids vincristine (102a), vinblastine (102b) and some derivatives275. 

The separation of synthetic red pigments has been optimized for HPTLC separation. The structures of the pigments are listed in Table 3.1. Separations were carried out on silica HPTLC plates in presaturated chambers. Three initial mobile-phase systems were applied for the optimization A = n-butanol-formic acid (100+1) B = ethyl acetate C = THF-water (9+1). The optimal ratios of mobile phases were 5.0 A, 5.0 B and 9.0 for the prisma model and 5.0 A, 7.2 B and 10.3 C for the simplex model. The parameters of equations describing the linear and nonlinear dependence of the retention on the composition of the mobile phase are compiled in Table 3.2. It was concluded from the results that both the prisma model and the simplex method are suitable for the optimization of the separation of these red pigments. Multivariate regression analysis indicated that the components of the mobile phase interact with each other [79],... 

K. Morita, S. Koike and T. Aishima, Optimization of the mobile phase by the prisma and simplex methods for the HPTLC of synthetic red pigments. J. Planar Chromatogr.-Mod. TEC, 11 (1998) 94-99. 

PRISMA Chemometric optimization method of IMGE (isoselective multisolvent gradient elution). 

In this strategy, the optimum experimental conditions are approached in a series of consecutive steps. The choice of any step results strictly from the outcome of all those accomplished previously. One example of a relevant algorithm is the simplex method [18] the PRISMA [19] geometrical method is a suitable example of the overall optimization approach. 

Two-dimensional TLC is performed by spotting the sample in one corner of a square thin-layer plate and developing in the usual manner with the first eluent. The chromatographic plate is then removed from the developing chamber and the solvent is allowed to evaporate from the layer. Then, the plate is placed in the second eluent so that development can take place in a second direction which is perpendicular to that of the first direction of development. In 2-D TLC, usually, the layer is of continuous composition, but two different eluents must be employed to obtain a better separation of a mixture. The success of the separation will depend on the ability to modify the selectivity of the second eluent compared to the selectivity of the first eluent. Fig. 1 shows the scheme of spot distribution on a 2-D TLC plate, following two developments for a theoretical case. In 2-D TLC, any spot can be identified by a pair of x, and y, coordinates or Rfn and Rfi2, respectively, where x, divided by Zf,i is equal to Rf n for the first eluent and yi/Z 2 is equal Z fi2 for the second eluent. The final position of the spot can be determined by the coordinates (xi,yi), in which Rn2-o can be expressed as (Rf,ii,Rf,i2)-A very good method for selection of the appropriate mobile phase for 2-D TLC separations is with the use of the Prisma system. 

The PRISMA model is a structured trial-and-error method that covers solvent combinations for the separation of compounds from low to high polarity. Initial experiments are done with neat solvents, covering the eight groups of the Snyder solvent classification triangle. 

Nyiredy, S. Planar chromatographic method development using the PRISMA optimization... 

Optimization of the solvent strength by varying the selectivity points is carried out until the required separation is obtained. If no adequate separation is obtained then a different layer or additional solvents must be selected and the new system optimized by the previous procedure. Nearly adequate separations can be improved in the third part of the Prisma model by selecting a different development mode. If an increase in efficiency is required to improve the overall separation then forced flow methods should be used. If the separation problem exists in the upper Rp range then anticircular development may be the best choice, if in the lower Rp range, then circular development is favored. 

CAMAG has proposed a practical scheme (Figure 4) for guidance during method development, which is derived from the PRISMA model but omits any... 

Nyiredy, Sz. Planar chromatographic method development using the Prisma optimization system and flow charts. J. Chromatogr. Sci. 2002, 40, 553-563. 

The separation characteristics of a considerable variety of other TLC supports were also tested using different dye mixtures (magnesia, polyamide, silylated silica, octadecyl-bonded silica, carboxymethyl cellulose, zeolite, etc.) however, these supports have not been frequently applied in practical TLC of this class of compounds. Optimization procedures such as the prisma and the simplex methods have also found application in the TLC analysis of synthetic dyes. It was established that six red synthetic dyes (C.I. 15580 C.I. 15585 C.I. 15630 C.I. 15800 C.I. 15880 C.I. 15865) can be fully separated on silica high-performance TLC (HPTLC) layers in a three-solvent system calculated by the optimization models. The theoretical plate number and the consequent separation capacity of traditional TLC can be considerably enhanced by using supports of lower particle size (about 5 fim) and a narrower particle size distribution. The application of these HPTLC layers for the analysis of basic and cationic synthetic dyes has also been reviewed. The advantages of overpressured (or forced flow) TLC include improved separation efficiency, lower detection limit, and lower solvent consumption, and they have also been exploited in the analysis of synthetic dyes. 

A very good method for selection of the appropriate mobile phase for 2-D TLC separations is with the use of the Prisma system. ... 

Spiegeleer et al., 1987 De Spiegeleer and De Moerloose, 1988), a graphical method (Matyska and Soczewinski, 1993), numerical taxonomy and Information content derived from Shannon s equation (Medic-Saric et al., 1996), and the PRISMA system (Nyiredy et al., 1988, 1989, 1991 Nyiredy and Fater, 1995 Dallenbach-Toelke et al., 1986) (see Section I.D). All of these optimization procedures involve the use of some form of statistical design to select a series of solvents for evaluation or to indicate the best system by comparing the results obtained from an arbitrarily selected group of solvents (Poole and Poole, 1991). 

The PRISMA system for mobile-phase optimization is a more elaborate, structured trial-and-error version of the normal-phase and reversed-phase procedures described above. The PRISMA system, which is the most widely used of the systematic optimization methods, involves selection of the stationary phase, individual solvents, and vapor phase optimal combination of the solvents by means of the PRISMA model and selection of the appropriate development mode. With silica gel, 10 mobile phases representing the Snyder (1978) selectiv-... 

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