Non-separation techniques

Ion-pairing, as discussed in Chapter 2, exerts dramatic effects on the chemical behaviour of analytes. Changes of charge status and hydrophobicity are the bases for the success of IPC separations as explained in Chapter 3. However, ion-pairing influences many other separative and non-separative techniques. In many papers dealing with theoretical facets of separative techniques, ion-pairing was claimed to profoundly affect separation. 

A different approach has been the coupling of microdialysis with biosensing techniques. These latter are non-separation techniques based on molecular recognition of the target analjde, which may form a complex with a bioreceptor, allowing its selective identification even in a complex mixture. 

Solvent extraction is probably the separation technique which is most widely used in conjunction with AAS. It often allows the extraction of a number of elements in one operation and, because of the specific nature of AAS, non-selective reagents such as the thiocarbamate derivatives (e.g. APDC) may be used for the liquid-liquid extraction (see Section 6.18). 

With the development of HPLC, a new dimension was added to the tools available for the study of natural products. HPLC is ideally suited to the analysis of non-volatile, sensitive compounds frequently found in biological systems. Unlike other available separation techniques such as TLC and electrophoresis, HPLC methods provide both qualitative and quantitative data and can be easily automated. The basis for the HPLC method for the PSP toxins was established in the late 1970 s when Buckley et al. (2) reported the post-column derivatization of the PSP toxins based on an alkaline oxidation reaction described by Bates and Rapoport (3). Based on this foundation, a series of investigations were conducted to develop a rapid, efficient HPLC method to detect the multiple toxins involved in PSP. Originally, a variety of silica-based, bonded stationary phases were utilized with a low-pressure post-column reaction system (PCRS) (4,5), Later, with improvements in toxin separation mechanisms and the utilization of a high efficiency PCRS, a... 

CHARACTERISTIC CONCOMITANT DEVELOPMENTS IN NON-SEPARATIONAL FLOW TECHNIQUES... 

In fact continuous titration belongs to this class, but has already been treated above on the basis of the use of the sensor merely as an end-point indicator of the titration reaction. For the remaining non-separational flow techniques, such a multiplicity of concomitant developments has occured since 1960 that in a survey we must confine ourselves to a more or less personal view based substantially on the information obtained from some important reviews and more specific papers presented at a few recent conferences78 82, or from leaflets offered by commercial instrument manufacturers. The developments are summarized in Table 5.1. 

In Table 5.1 we stressed characteristic concomitant developments in non-separational flow techniques, which does not mean that these would not play that role in separation techniques on the contrary, their influence may on the one hand be simplified by the previous separation of analyte compounds, but the detection requirements may on the other hand be increased as a consequence of the slight amounts and concentrations of components even passing through at high speed. Some specific remarks now follow on measurement aids, whilst additional field effects will be discussed separately later. 

The dependence of the lamellar thickness and the number of arms (n = 1, 2, 4 and 16) for symmetric PSn-arm-PIn miktoarm stars shows an increase in the spacing with n (Fig. 43). This indicates an additional chain stretching induced by the spatial confinements close to the junction point. However, the exactness of the results may be influenced by non-separable impurities. As these contamination species are resistant to detection via standard SEC and other separation techniques, it can be reasoned that previous results reported in the literature might suffer from the same shortcomings [121]. 

HPLC is a universal separation technique that is capable of separating both volatiles and non-volatiles without the need for derivatization. We are developing methods that employ both on-line photodiode array (PDA) detection and mass selective detection, HPLC/PDA/MS. This approach also utilizes an ion-trap mass... 

Selectivity The method you choose must be selective enough to measure the analyte of interest in what may be a complicated matrix. Frequently, not one method is selective enough, and a separation technique must be used before the determination step. Selectivity is a continuum from highly selective to completely non-specific for a given analyte. Different degrees of selectivity can be achieved in different ways (Table 21.7). 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

A partial resolution to some of the problems with the non-competitive technique is to carry out the reactions of the separated isotopomers at the same time, and under the same conditions, but in different containers (say in a common thermostat). In this fashion one can directly compare isotopic differences as the reactions progress. For example, if the concentration of product or substrate can be followed spectropho-tometrically, one might use a two-beam instrument with the two samples placed next to each other. The photometric signal, then, is proportional to the difference in the absorption, A, of light and heavy species, and therefore to the difference in their concentrations, (provided the experiment is carried out in a region where the Lambert-Beer law is valid, and the molar extension coefficients are equal for both isotopomers), see Fig. 7.1. 

Charpin, J. and P. Rigny. 1990. Inorganic membranes for separative techniques From uranium isotope separation to non-nuclear fields. Proc. 1st Inti Corf. Inorganic Membranes, 3-6 July, 1-16, Montpellier. 

Dedicated applications of capillary zone electrophoresis (CZE) coupled to MS are discussed, particularly in the field of drug analysis. Development of other capillary-based electrodriven separation techniques such as non-aqueous capillary electrophoresis (NACE), micellar electrokinetic chromatography (MEKC), and capillary electrochromatography (CEC) hyphenated with MS are also treated. The successful coupling of these electromigration schemes with MS detection provides an efficient and sensitive analytical tool for the separation, quantitation, and identification of numerous pharmaceutical, biological, therapeutic, and environmental compounds. 

Valcarcel, M. Luque de Castro, M. Non chromatographic Continuous Separation Techniques, Royal Society of Chemistry Cambridge, UK, 1990. Karlberg, B. Thelander, S. Anal. Chim. Acta., 1978, 98, 1. 

Separation technique in which separation mainly according to the hydrodynamic volume of the molecules or particles takes place in a porous non-adsorbing material with pores of approximately the same size as the effective dimensions in solution of the molecules to be separated. 

M. VALCARCEL and M.D. LUQUE DE CASTRO, "Non-Chromatographic Continuous Separation Techniques", Royal Society of Chemistry, Cambridge, 1991. 

---