Chromatography Forum

Having a problem with a method originally developd using a HP1050 UV-Vis detector. Sensisitivity was satisfactory at 229 nm with a range setting of 0.02. Now I am using a Perkin Elmer series 200 UV-Vis as part of a PE Series 200 system (pump and autosampler) all controlled by Total Chrom. There is no equvailent "range" setting" on PE UV-Vis so all I am seeing is "raw" signal from detector to data system. There is no way to incease sensitivity or attenauate signal. Sensitivity is much less than what I was seeing earlier with HP 1050 detecor. Any suggestions?

Normally, there is no "range" setting adjustment needed today as everything should be 1:1. You did not say which HP 1050 detector you used, but all of them have analog outputs which can be changed to provide a different scale for your data system (if it uses some odd multiplier that is). This can be done fron the front panel menu's as well as through the ChemStation software. Determine what output range you used before and what output range the new detector and CDS is expecting. Set accordingly. *This sounds like something related to your new CDS only. Look over the software functions carefully to find out what range of data it is looking for so you can match it with your detector. Usually 1 mv = 1 mAU, but some systems use other ratios.

What data system were you using with the HP 1050 ?

Bear in mind that what we think of as sensitivity (which really is "detectability") is tied to signal/noise ratio, and that should be approximately independent of the range setting you use (changing the range affects both the signal and the noise).

Hi,
I had to change all my methods from 1050 to 200 Series.
Is this the first method you have transferred?
Unfortunately there will be differences in tubing, dead volume, gradients etc.
It takes a bit of work but I find good features in the 200 Series especially
the autosampler.
Regards
WK

Thanks for replies. No other changes were made to system. Am using same TotalChrom data system. Only removed HP 1050 UV-Vis and replaced it with PE Series 200 UV-Vis. HP 1050 had "functioning" range settings (i.e. set range lower - saw large peaks). For example with HP 1050 range setting 0.02 I saw 800mV response when injecting 50uL of 4 ppm std. Now, with all else being exactly the same, I only see a 350mV response when injecting the same volume of a std of 40ppm (10x greater).

Hi,

What about precision? S/N ratio? Linearity?
Having just smaller numbers in arbitaty units is not a problem. Check the noise. I presume it is much smaller on the PE.

Alex

Have you check the PE flow cell? is it clean?

I second Alex's question: without knowing the noise level on the two systems, there is not enough information.