Why RID in HPLC is ideal for the quantitative estimation of sugars ? why not PDA ?
If by RID you mean refractive index, then it is because most sugars do not absorb UV except below 200nm and so are very difficult to detect in UV. RI, on the other hand, detects refractive index and so could easily detect sugars.
the problem is that RIDs are not very sensitive, tend to be susceptible to environmental factors and can only be used with isocratic methods.
You can use other detectors, such as ELSD, CAD, or MS. A PDA of FLR can be used if you derivatize. If you use an MS you would normally derivatize as well, for sensitivity.
A good intro to the detection of carbohydrates is http://www.shimadzu.com/an/hplc/support/lib/lctalk/50/50intro.html
If by RID you mean refractive index, then it is because most sugars do not absorb UV except below 200nm and so are very difficult to detect in UV. RI, on the other hand, detects refractive index and so could easily detect sugars.
the problem is that RIDs are not very sensitive, tend to be susceptible to environmental factors and can only be used with isocratic methods.
You can use other detectors, such as ELSD, CAD, or MS. A PDA of FLR can be used if you derivatize. If you use an MS you would normally derivatize as well, for sensitivity.
A good intro to the detection of carbohydrates is http://www.shimadzu.com/an/hplc/support/lib/lctalk/50/50intro.html
Photo Diode Array detector of HPLC may be used for detection of polyphenols it seems. However, for sugars RID is the best one for polymers since it is a universal detector.
As the others have said, RI is used if you don't have a very tricky separation that requires a gradient. I successfully used ELSD to separate carbohydrates in the past, but you need to carefully optimize the mobile phase to avoid the baseline rising too quickly at the end of the run. The question is: which sugars are you trying to separate?
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