Post-column continuous-flow analysis combined with reversed-phase liquid chromatography and computer-aided detection for the characterisation of peptides

Rapid determination of the ratios of three aromatic residues in peptides by reversed-phase high-performance liquid chromatography with a high-resolution photodiode-array detector

A method for the simultaneous determination of the ratios of three aromatic residues in peptides by derivative UV spectrophotometry on a spectrophotometer with a resolution of 0.1 nm can be used for the RP-HPLC analysis of peptides because of the recent development of high-resolution photodiode-array detectors (1.2 nm). The difference between the theoretical and experimental ratios of aromatic residues of peptides determined in real time is less than 5%. This method could become a powerful tool for the study of peptides and hydrolysates: A variety of possible applications are discussed.

Strategies for peak-purity assessment in liquid chromatography

One of the key requirements for the validation of chromatographic methods is to determine the purity of a chromatographic peak. Statistical modelling of the chromatographic process suggests that overlapping components are highly probable in a chromatogram. Hence extensive efforts have been directed at the development of sensitive, reliable and robust methods to assess peak purity. This is especially the case in the pharmaceutical industry, where liquid chromatography (LC) is widely utilized and the demands on method validation are justifiably high. On-line multiwavelength absorptiometric detection is often used to generate the additional data required to facilitate peak-purity assessment in LC. This approach, using photodiode-array technology, is directly compatible with the aqueous-based reversed-phase LC solvents used extensively in drug analysis. Consequently, this work highlights many of the peak-purity algorithms, which may be applied using LC with diode-array detection. The relative merits of the individual techniques are discussed, and a rationale is developed for their application.

A multiwavelength approach to the selection of absorbance ratios for the assessment of chromatographic peak purity

The routine use of diode-array detectors (DAD), based on the linear photodiode array device, has transformed the practice of UV-vis detection in liquid chromatography (LC). Multiwavelength detection is widely employed to generate absorbance ratios as a relatively non-specific method for characterizing peak purity in LC. If several wavelength pairs are selected the selectivity of the absorbance ratio method and its sensitivity to an interfering impurity can be increased, however, these attributes still depend on the selection of suitable pairs of wavelengths. This paper presents a novel approach to the selection of absorbance ratios for the assessment of peak purity in LC, utilizing a matrix derived from all the spectral data collected. As with single absorbance ratios, the absorbance ratio matrix (ARM) generated (containing all possible finite absorbance ratios) is characteristic for the analyte and independent of the analyte concentration. Moreover, the ARM technique eliminates the need to select "appropriate wavelength pairs", for sensitive discrimination of small spectral differences, when used for peak purity assessment. The ARM is found to give comparably high sensitivity to the presence of co-eluting species, as compared with the use of the wavelength pair selected on the basis of the conventional optimization criteria.