A protein and peptide monitor with a hollow-cathode light source.

This communication describes an inexpensive system that will monitor protein and peptide concentration in chromatogram eluates by light absorbance at an adjustable wavelength.Proteins in chromatogram eluate streams are commonly metered for concentration by absorbance measurement at 280 nm. Besides a range of commercially manufactured monitors, there is the apparatus described by Bennett et al. (1) which uses a selectively modulated magnesium lamp. Measurements in the region of 280 nm are of no value, however, when the material does not contain aromatic amino acids. Monitoring then becomes necessary at 230 nm in the region of absorption due to the peptide bond. The common resort in such a case is the standard ultraviolet-visible spectrophotometer, which has the disadvantage of being both unnecessarily elaborate and expensive for the purpose required. The deuterium lamps in these instruments require frequent replacement because of the extended periods of operation, adding to the cost factor.We have investigated the use of a hollow-cathode lamp of the type manufactured for use in an atomic absorption spectrophotometer. These lamps have high stability and a long working life, due to the considerably lower level of power dissipation compared with deuterium lamps. Their emission spectra are discontinuous, but the lamp for the element iron provides adequately strong lines at both 229.5 and 279.2 nm, suitable for a protein monitor.