Peak purity analysis

The specificity of the method was checked with a peak purity test of the assay preparation performed with a photodiode array detector. The peak purity values for metformin and glibenclamide were observed to be 995 and 999, respectively. The results of the peak purity analysis show that the peaks of the analytes were pure and that the formulation excipients did not interfere with the analyte peaks. 

Peak purity analysis is also a useful addition to routine quality control procedures, especially in the analysis of pharmaceuticals and food products, for which contamination and quality of results are critical. 

PEAK PURITY ANALYSIS WITH DIODE ARRAY DETECTOR... 

Before the quantitative information contained in a chromatographic peak can be used, the purity of the peak should be confirmed. Only after we are sure that no coeluting impurity was present, which could have contributed to the peak response, can we convert the peak s area or height into quantitative information based on the equivalent response of a pure standard. This peak purity analysis can be based on the comparison of the various spectra recorded during the elution of the peak. If the peak is pure, then, apart from concentration differences, the spectra taken at several points during a peak s elution should all be identical and the match scores obtained should be very close to the perfect match scores. If significant deviations are encountered, this can be seen as an indication of impurity. 

One of the most important aspects of peak purity analysis that is often overlooked is the fact that any peak purity algorithm can only confirm the presence of impurities, but can never unambiguously prove that a peak is pure. 

Peak purity analysis software allows users to sample spectra at equidistant points across an HPLC peak. In general, the poorer the resolution between potentially coeluting peaks is, the more desirable it is to use greater numbers of data points to detect the impurity. Traditionally, spectra have been sampled upslope, at the apex, and downslope of the eluted peak. This selection pattern may overlook the presence of impurities near the peak extremities. However, acquisition of many spectra may increase calculation and display time without adding significant information. 

Simple peak purity analysis is relatively accurate when the impurity is present at significant concentration levels but, as the level of impurity diminishes, its impact on the target analyte spectrum becomes subtler and may require more sophisticated techniques. For this, statistical software routines are available for automated spectral comparisons. In these cases, peak purity determination and analysis of spectral differences are achieved using vector analysis algorithms. The more similar the spectra are, the closer the value is to 0.0° the more spectrally different they are, the larger the value. All the spectral data points across the peak are analyzed the data are converted into vectors, compared, and graphically plotted so that the results can be visualized. These software routines provide both numerical results and graphical representations such as similarity and threshold curves. 

Peak purity software incorporating routines for data acquisition and reduction, extraction and comparison of spectra, and display of analytical results can be utilized in either an interactive or automated fashion. A desired sequence of operations can be recorded in a peak purity analysis method file and can run unattended after input parameters are selected. As the quality of the determination is highly dependent on the preanalysis data treatment, results should be inspected visually to verify that peaks are properly baseline-separated and correctly integrated. 

The evaluation of a peak purity analysis is assisted by a well-organized visual display of the output of various peak purity analysis techniques. 

Peak purity analysis is designed to detect the presence of an impurity that is coeluting with the analyte peak. A DAD, using the almost instantaneous acquisition of a considerable portion of the UVA is spectrum of eluted peak components, can give accurate information to determine peak purity. The spectral uniqueness of each compound is used to indicate when there are two or more components present in the peak, to identify peaks, and to assess purity. 

Peak purity analysis is very useful in chromatographic method development, to confirm that all components have been chromatographically separated, and in quality control, to warn the analyst that an unexpected coeluting impurity has appeared. 

Kohn, A. The application of peak purity analysis in liquid chromatography and capillary electrophoresis. LC-GC November 1994, 7 (11). 

Comparison of these values with the ones calculated from peaks eluting at similar retention times in the analysis of extracts could be a fast way to verify the identity and to check the peak purity. Analysis of the semipurified taxine mixture by gradient HPLC-DAD revealed the presence of seven taxanes with 10-deacetyl baccatin III (10-DAB III) among them. All the nine expected taxines were positively identified (Table 1). 

Using DAD or scanning detectors it is possible to determine the purity of a peak by spectral peak purity analysis. Peak homogeneity can be demonstrated by a variety of methods. However, the most commonly used technique normalises and compares UV spectra from various peak sections. 

One of the most important aspects of peak purity analysis that is often overlooked is the fact that any... 

Peak purity analysis software allows users to sample spectra at equidistant points across an HPLC peak. In... 

Simple peak purity analysis is relatively accurate when the impurity is present at significant concentration levels but, as the level of impurity diminishes, its impact on the target analyte spectrum becomes subtler and may require more sophisticated techniques. For this, statistical software routines are available for automated spectral comparisons. In these cases, peak purity determination and analysis of... 

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