Peak purity

An algorithm for an assesment of chromatographic peak purity was proposed. In this study ethyl 8-methyl-4-oxo-4/7-pyrido[l, 2-u]pyrimidine-3-carboxylate was also used (97MI13). Ethyl 7-methyl-4-oxo-4//-pyrido[l,2-u]pyrimidine-3-carboxylate, among other compounds, was applied to show practical mathematical tools for the creation of several figures of merit of nth order instrumentation, namely selectivity, net analyte signal and sensitivity (96ANC1572). 

It is possible to carry out a chromatographic separation, collect all, or selected, fractions and then, after removal of the majority of the volatile solvent, transfer the analyte to the mass spectrometer by using the conventional inlet (probe) for solid analytes. The direct coupling of the two techniques is advantageous in many respects, including the speed of analysis, the convenience, particularly for the analysis of multi-component mixtures, the reduced possibility of sample loss, the ability to carry out accurate quantitation using isotopically labelled internal standards, and the ability to carry out certain tasks, such as the evaluation of peak purity, which would not otherwise be possible. 

In some cases a principal components analysis of a spectroscopic- chromatographic data-set detects only one significant PC. This indicates that only one chemical species is present and that the chromatographic peak is pure. However, by the presence of noise and artifacts, such as a drifting baseline or a nonlinear response, conclusions on peak purity may be wrong. Because the peak purity assessment is the first step in the detection and identification of an impurity by factor analysis, we give some attention to this subject in this chapter. 

Application of factor analysis for peak purity check in HPLC... 

In pharmaceutical analysis the detection of impurities under a chromatographic peak is a major issue. An important step forward in the assessment of peak purity was the introduction of hyphenated techniques. When selecting a method to perform a purity check, one has the choice between a global method which considers a whole peak cluster (from the start to the end of the peak), and evolutionary methods, which consider a window of the peak cluster, which is... 

H.R. Keller and D.L. Massart, Peak purity control in liquid-chromatography with photodiode array detection by fixed size moving window evolving factor analysis. Anal. Chim. Acta, 246 (1991) 379-390. 

F.C. Sanchez, J. Toft, B. van den Bogaert and D.L. Massart, Orthogonal projection approach applied to peak purity assessment. Anal. Chem., 68 (1996) 79-85. 

F. Cuesta Sanchez, M.S. Khots, D.L. Massart and J.O. De Beer, Algorithm for the assessment of peak purity in liquid chromatography with photodiode-array detection. Anal. Chem., 285 (1994) 181-192,... 

UV (DAD) High resolution Component identity Peak purity testing Robust Limited to UV absorbing analytes Wide variability in compound absorptivities [31,48]... 

Principles and Characteristics The main reasons for hyphenating MS to CE are the almost universal nature of the detector, its sensitivity and the structural information obtainable, including assessment of peak purity and identity. As CE is a liquid-phase separation technique, coupling to the mass spectrometer can be achieved by means of (modified) LC-MS interfaces. Because of the low flow-rates applied in CE, i.e. typically below lOOnLmin-1, a special coupling device is required to couple CE and the LC-MS interface. Three such devices have been developed, namely a... 

Fig. 2. Schematic of peak purity determination by using the upslope, top, and downslope methods.

I. N. Papadoyannis and H. G. Gika, Peak purity determination with a diode array detector, Encyclopedia of Chromatography, online, Marcel-Dekker, Inc., 2003, http //www.dekker.com. 

FIGURE 6.34 Comparison of primary peak area results for 24 samples analyzed using PLC and HPLC. The primary peak purity (%) obtained using conventional HPLC and PLC differed by an average of 2%. 

The location of the concentration windows is the distinctive result of the classical EFA plots, as in Figure 5-37. Apart from information on peak purity in chromatography, there is not much that is directly useful in the information about concentration windows. In this section, we develop methods that, based on these concentration windows, result in complete concentration profiles C and subsequently the corresponding species spectra A. 

Since IRMS is a single-parameter chromatographic detector incapable of speciation, GC-IRMS places severe demands on the chromatographic resolution to guarantee peak purity [631,632]. This is sometimes checked by splitting the effluent between the IRMS and a conventional El mass spectrometer [633]. 

A PDA detector provides UV spectra of eluting peaks in addition to monitoring the absorbance of the HPLC eluent like the UVA is absorbance detector. It is the preferred detector for testing impurities and for method development. PDA facilitates peak identification during methods development and peak purity evaluation during method validation. Detector sensitivity was an issue in earlier models but has improved significantly (more than ten-fold) in recent years. ... 

If reference materials are not available, the challenge study lives np to its name. Specificity may still be demonstrated by a comparison of test results containing the impurities of interest to a second, well-characterized procedure (e.g., USP method). If a secondary method is unavailable, peak purity evaluation may be used to further demonstrate specificity of the method. 

Peak purity tests are used to demonstrate that an observed chromatographic peak is attributable to a single component. Mass spectrometry is the most sensitive and accurate technique to use for peak purity evaluation because of the specific information derived from the analysis. However, a good number of HPLC methods use mobile phase conditions that are incompatible with mass spectrometry detection. In this case, PDA spectrophotometers using peak purity algorithms may be used to support the specificity of the method. Almost all commercially available diode array detectors are equipped with proprietary software that will perform these calculations. Although this technique is more universal in application to HPLC methods, the data provided is neither particularly... 

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