Basics of HPLC
Diode-array UV detector
The diode-array UV detector is a spectrometer that measures the absorbance of the sample at wavelengths generally between 190 and 400 nm (Ultra-Violet).
This absorption is achieved by groups of chromophores that have the capacity to absorb the energy of ultraviolet radiation.
Drawer: “Using a spectrometer”
Basic functioning principle
Unlike a conventional detector whose receptor is capable of analyzing only one wavelength at a time, the diode-array UV detector, consisting of a multitude of miniature light-sensitive diodes, is capable of analyzing a wide range of wavelengths simultaneously often from 190 to 400 nm.
The radiation emitted by a lamp is composed of a multitude of wavelengths (polychromatic). With the help of a monochromator, the radiation is decomposed and each diode of the array will receive radiation of a very specific wavelength.
The luminous radiation is split in two: one part will pass through the sample and will be subjected to the absorption of certain wavelengths whereas the second part will not undergo any modification. In this way, the evaluation of the absorption of the sample is done by subtracting the signal intensity detected on diode-array 1 from that of diode-array 2.
The diode-array detector has 3 major advantages:
- It offers the possibility to detect molecules on a continuum of wavelengths (in the given range set by the detector).
- For each chromatographic peak, the corresponding spectrum can be obtained, which provides information about the structure and/or the purity of the chromatographic peak
- It allows you to obtain 3D chromatograms which are made up of time on the x-axis, wavelength on the y-axis and signal intensity in color on the z-axis.
