By Anonymous on Tuesday, June 11, 2002 - 12:02 am:
Can anyone explain what is the significance of bandwidth parameter in the HPLC detector?
By lcguy1 on Tuesday, June 11, 2002 - 05:43 am:
The bandwidth of a detector is how many wavelengths the photodiode is actually "seeing" when you set a specific wavelength. For example, if the bandwidth is 8nm and you are interested in 254nm, you are actually getting the average absorbance of 250nm-258nm. The output from the detector is actually an average of all of these wavelengths.
By Anonymous on Tuesday, June 11, 2002 - 09:05 pm:
Thank you for your reply. How change in bandwidth will affect the final results?
By H W Mueller on Wednesday, June 12, 2002 - 03:24 am:
Some aspects of this have been discussed before.
Also: One can imagine that the sensitivity may change when changing bandwidth. The optical selectivity may go down with a widening band.
By Tom Mizukami on Wednesday, June 12, 2002 - 03:26 pm:
Bandwidth is a little tricky because it affects both the response and the noise. If you set the wavelength to the lambda max of the analyte then using a larger bandwidth will decrease the response but since the output from multiple diodes are being averaged the noise is being reduced by more than the signal and you will be improving the signal to noise.
To optimize the bandwidth start by collecting a spectra of your analyte(s) then set the bandwidth to the width of the specrta about half way between the wavelengths of minimum and maximum absorbance. Then you can go up and down from here monitoring the s/n.
If you are going to be transfering methods back an forth between DAD and VWD detectors you might want to consider trying to match the VWD performance instead of optimizing the DAD.
The bandwidth setting will probably have no effect if you are just trying to quantitate assay level. At impurity levels optimizing s/n could be important. Controlling the bandwidth parameter is critical if you are going to attempt to quantitate impurities based on response factors. Good luck.
By lizrobertson on Wednesday, July 3, 2002 - 01:39 pm:
The other little tit-bit about bandwidth that was not mentioned was its effect on linearity. In general, that is for a compound response measured at lambda max on a symmetrical UV spectrum widening bandwidth can improve signal to noise peformance. However, as you are now averaging more wavelengths and are deviating from Beer's law you take a hit in linear range.
Liz Robertson Waters Corp
By H W Mueller on Thursday, July 4, 2002 - 11:12 pm:
Liz, how does the averaging of wavelengths cause deviations from Beerīs.... law?
Hans
By N.V.V.S.S. RAMAN on Tuesday, May 11, 2004 - 03:02 am:
Hellow
We validated our Purity by HPLC method using DAD? But we got a querry that DAD is not suitable for quantitative work and we have to use only VWD. Is it true? Can any body respond?
By tom jupille on Tuesday, May 11, 2004 - 07:56 pm:
There was a thread on this topic about 3-4
weeks ago. Look for the heading:
"Diode Array Detector vs. Photodiode Array
Detector ".
The final answer was that a PDA (DAD) is
perfectly suitable for quantitative work, as
demonstrated by the fact that you validated
your method.