Peak tailing, chromatographic

An analytical method vahdation study should include demonstration of the accuracy, precision, specificity, limits of detection and quantitation, linearity, range, and interferences. Additionally, peak resolution, peak tailing, and analyte recovery are important, especially in the case of chromatographic methods (37,38). 

The influence of various structural and physicochemical parameters of the stationary and mobile phases on the tailing of a cationic dye in reversed-phase chromatography has been studied in detail. Measurements were performed in a C8 reversed-phase column (80 X 4.6 mm). The isocratic mobile phase was ACN-0.01 M aqueous HC1 (90 10, v/v). Analyses were carried out at 20°C and the flow rate was 1-5 ml/min. The concentration of the cationic dye, l,l -didodecyl-3,3,3, 3 -tetramethylindocarbocyanine perchlorate (Dil) in the model solutions varied between 0.9-309 pM. The dependence of the chromatographic profile of the dye on the injected concentration is illustrated in Fig. 3.112. Calculations and mathematical modelling indicated that the peak tailing of the dye can be... 

Almost always, compounds of high polarity and low volatility tend to undergo adsorption on the chromatographic support or decomposition on contact with it. These phenomena usually result in peak tailing and the quantitative evaluation of the chromatograms is difficult or even impossible. A wellknown example is the GC analysis of cholesterol, which can be analysed as such or as the TMS derivative (Fig. 1.1). If the support is not modified, free cholesterol provides a wide, tailing peak which can be evaluated quantitatively only with difficulty, whereas the TMS ether provides a sharp, symmetric peak the retention time of which is, however, substantially shorter [1]. 

Lead has been determined chromatographically in the form of its chelates with different j3-diketones [642]. A column packed with 15% of Apiezon L at temperatures around 200°C appeared to be the most suitable, but even with its use adsorption and peak tailing of chelates occurred. In combination with MS and using integrated ion-current curves the detection limit was about 10 14 g of lead. 

A five-factor (buffer concentration, pH, IPR and organic solvent concentrations, and column temperature) two-level fractional factorial design with four center points was performed. The center points of the design were the midpoints of the range for each factor. The response from the design did not focus on bare retention but on resolution, and particularly on the separation of potential impurities around the main peak. Peak tailing, run time and backpressure were also considered chromatographic responses [76]. 

Bisphosphonates (bone resorption inhibitor drugs) were subject to many investigations. They can chelate to metal surfaces, producing chromatographic peak tailing. Different tetraalkylammonium salts, commonly selected as IPRs in separation of bisphosphonates [85], were replaced by volatile organic amines when ELSD was used [86]. 

As we discussed above, efficiency and selectivity are complementary descriptors dependent on the different sets of chromatographic parameters. Efficiency is more dependent on the quality of the column packing, particle size, flow rate, and instrumental optimization, while selectivity is more dependent on the stationary phase properties and the nature of the analytes themselves. However, efficiency is sometimes affected by nonideal interactions of the analyte with the stationary phase (i.e., peak tailing). 

Peak tailing is the most commonly observed effect of sample overloading. In essence, in most cases this effect is associated with nonlinear adsorption isotherms. In Chapter 2 the relationship of the retention volume and the derivative of the excess adsorption isotherm of the analyte on given stationary phase surface was derived. If the isotherm is linear within the injected concentration region, all components of the chromatographic zone are moving... 

For good quantitative results from analytical hplc (or gc, see below) you should aim to produce chromatographs with symmetrical peaks. Tailing of the peaks is usually caused by overloading and can thus be avoided by reducing the quantity of sample applied. If this does not solve the problem and the tail of a component is long and drawn out, there may be an incompatibility between the compoimd and the stationary phase, a problem which is less easy to rectify. 

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