Two Types Of UV Detectors Are Commonly Used Today

Two types of UV detectors are commonly used today:

  • Variable-wavelength (sometimes called "spectrophotometric" detectors )
  • Photodiode Array (sometimes simply called "diode array" detectors.)

Variable-wavelength detectors are less expensive; they are the standard detector type for quantitative analysis and routine assays. Photodiode array detectors are more versatile, because they allow simultaneous acquisition of both chromatographic and spectral information; they are frequently used in method development.

The detector wavelength is an important characteristic of an HPLC separation. As a general rule, the wavelength is set to the absorbance maximum of the analyte. Using the wrong wavelength may result in decreased peak sizes, or even no peaks at all!

Because different compounds can have different absorbance spectra, a direct quantitative comparison of different peaks in the same chromatogram can be misleading. A small quantity of a compound which absorbs strongly at the detector wavelength can give a bigger peak than a large quantity of a weak absorber. For reliable quantitation, a calibration must be carried out with a known quantity of the exact compound to be analyzed.

The Variable Wavelength UV Detector uses a monochromator (slits and a grating) to select one wavelength of light to pass through the sample cell.

The Photodiode Array Detector passes all wavelengths of light through the sample cell, then focuses each wavelength on a single sensor element.