By Thomas Gottfreund on Wednesday, February 19, 2003 - 04:24 am:
Does anybody know of the frequently use of indirect UV-detection in HPLC, except ion chromatography?
Are there applications for indirect detection concerning the determination of alkylamides, or other substances? I'm currently trying to measure erucamide and oleamdie with the HPLC and direct uv-absorption, but ... problem is the sensitivity and that I don't have a DAD :-|
So I came up with trying indirect UV.
It would be fine, if someone can help me.
Thanks
By Chris Pohl on Wednesday, February 19, 2003 - 11:50 am:
Thomas,
Actually, indirect detection isn't used all that much in Ion Chromatography anymore. It's certainly possible to use indirect detection in reversed phase work but it would take a fair amount of work to devise a system that worked well. In addition, the main problem with indirect detection is that it's not very sensitive and there are a lot of problems with drifting baselines, etc. Probably the best way to detect these surfactants would be refractive index (even though it's not that sensitive, either) but I assume you don't have access to a refractive index detector. If you're only option is UV detection, I would say you would be better off using direct detection at low wavelength and working with an acetonitrile based eluent system.
Also, I'm a bit puzzled by your DAD reference. As far as I know, the best you can say about the sensitivity comparison between standard monochromator based detectors and DAD is they are approximately equivalent with a slight edge going to standard monochromator based detectors.
By Anonymous on Wednesday, February 19, 2003 - 01:45 pm:
Thomas,
You might try putting about 0.2 - 0.3% acetone in your mobile phase and use a detector wavelength of 254 nanometers. Like Chris said there are some problems to overcome but if you are careful and look in a fairly narrow concentration range this might be a place to start. Also, wonder why you don't use GC for these compounds, I would think this to be the method fo choice, excellent sensitivity and wide linear range on an FID detector.
Regards,
Mark
By Thomas Gottfreund on Thursday, February 20, 2003 - 06:01 am:
Thank you for your replies.
Chris: The low sensitivity wasn't meant to occur through the DAD but because of the amides (as far as I know does amides have no significant absorption around 230nm and up and I'm not happy with measuring in the range 200nm and below). The lack of a DAD is a problem where I have to identify unknown substances, and this could happen.
Mark: Yep, I'm afraid there is no GC available for me to use, only the HPLC.
Have a nice day
Thomas