PDA is essentially a UV/Vis detector with a variety of photodiodes, both of these detectors are simple to use and interpret. The major difference between the UV and PDA detector is that the PDA is superior to UV since it can scan the entire 190-800 nm range, whereas UV/Vis can only scan a single wavelength.
The different types of detectors such as UV/VIS, mass, fluorescence, refractive index, electrochemical, conductivity, light scattering, and IR detector are used in the HPLC analysis they are classified into two, namely solute and bulk property detectors. However each form of detector works on different working principle.
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What is a UV detector in HPLC?
A UV detector is an in-line device that detects the UV absorbance of the HPLC eluent and generates a continuous signal that can be used to calculate the amount of chromophoric substances separating from the HPLC column. The compound can be recognized by measuring the absorbance of a sample solution of light at different wavelengths. UV absorption varies depending on which wavelength is used. UV detectors are classified as fixed wavelength, variable wavelength, or photodiode array detectors.
What is a photodiode array detector (PDA) in HPLC?
The photodiode array (PDA), also known as the diode array detector (DAD), is capable of measuring the whole range of wavelength in real-time, which may have additional benefits. It is a common UV detector that uses a photodiode imaging sensor to monitor the complete UV/VIS spectrum of material (Analyte/mobile phase) moving through the flow cell.
Both absorbance and spectral data are produced by the detector, which can be used for quantification, identification, and peak purity analyses. Some manufacturers provide a DAD as a multiple wavelength detector without the spectral scanning function for a low-priced.
Overview of UV and PDA detector:
The UV, VIS, and PDA detectors are classified as absorbance detectors; they have a better sensitivity to the picogram (~ PG) levels and use them to detect compounds that have chromophore (light-absorbing compounds). UV is a widely used detector for ultraviolet spectroscopy as well as high-performance liquid chromatography.
The UV absorbance varies, depending on the mobile phase and the use of the wavelength. It is significant to select a suitable wavelength based on the type of analyte or component. A typical UV detector permits a selection of wavelengths between 190 nm and 400 nm. In contrast to a UV detector, a Visible (VIS) detector employs longer wavelengths, such as 400 nm to 800 nm. The detector that gives a broad wavelength selection, it's covering a range of UV-VIS (190-800 nm) called a UV/VIS detector.
Conversely, the PDA detector passes a wide range of light through the sample and after that, the light is isolated into individual wavelengths after going through the sample. The spectrum of light is directed to an array of photosensitive diodes. Every diode can quantify a diverse wavelength which considers the monitoring of numerous wavelengths at a time. Generally, just 1-2 wavelengths are used during the chromatographic run.
Difference between the UV and PDA detector in HPLC:
- The key difference between the UV and PDA detector in HPLC is that the photodiode array detector can measure the peak area and height of the specific peak of the sample or analyte on the different wavelengths in the range of 200 to 800 nm, while a UV detector can determine the peak area and height in just one or two separate wavelengths, but the wavelength must also be selected before injecting the sample solution in the HPLC injector.
- The UV/Vis detector can only detect a single wavelength at a time, whereas the DAD can scan a different wavelength (190-800 nm).
- In a traditional HPLC system with a UV/VIS detector, the wavelength of the compound needs to be manually added, however in an HPLC system with a PDA detector, does not need to manually add the wavelength because it auto-detects the entire range.
- High-performance liquid chromatography has capable of separating the degradant peaks from the drug substance. Due to the broad applications and advantages in pharmaceutical analysis, a photodiode array detector is more preferred over an ultraviolet detector to perform the forced deterioration, stress testing, and stability-indicating analytical methods.
- PDA is a better option if you wish to scan a wavelength range, whereas if you know the absorption wavelength, you can use a UV/VIS detector to detect that particular wavelength.
- The UV/Vis detector is time-consuming; whereas PDA provides rapid analysis hence it is a preferable choice for method development of sample analyte.
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