Chromatography Forum

Hi there ,

I read a lot by googling about detector but i am sure i will find here distinction answer .Now i use one detector called ( UV-VIS ) and my friend and others use the same ( UV-VIS ) but each one use it from different company . The question is :

when I rum my standard the ( peak in height and Area ) are different one are small and other is big etc .
which factor control this and make detector different from each other ?

I am really need this information so please be " good lover " and help me

Best Regards

New

If you're going to be doing HPLC, it would be worthwhile investing a some good books. Two that I can recommend:
Modern HPLC for Practicing Scientists by Mike Dong (Dong: http://tinyurl.com/4cx8flw)
Introduction to Modern Liquid Chromatography by Snyder, Kirkland, and Dolan (http://tinyurl.com/48tu3b7)

With that out of the way, some of the factors that will affect signal intensity (peak height).
- Lamp energy (for single-beam systems)
- Photodetector response (for single-beam systems)
- Instrument design (single vs. double beam)
- Flow cell path length
- Monochromator bandpass (or slit width on some systems)
- A/D convertor output voltage

An additional factor that will affect peak area (but usually not height):
- sampling rate

The bottom line is that it would be very unusual for two detectors of different models (much less from different manufacturers!) to give exactly the same response. That's why we run calibrations on the same instrument (and on the same day) that we run the samples.


Add

Can I ask a follow-up question? Why should lamp energy affect the output of a detector? Most of the detectors I've come across give an output in absorbance units, and since these are defined in terms of the proportion of light that's absorbed (1 unit = 10% transmission) the instrument is lying if its value varies as the bulb ages. 10% transmission is still 10% whatever the absolute photon flux corresponding to the 100% that went into the flow cell. The only consequences of decreasing lamp energy should be decreasing S/N as the overall light it's detecting decreases... or am I misunderstanding?

Why should lamp energy affect the output of a detector?

It shouldn't. I sit corrected.

lmh, that´s the reason for old lamps to become a problem due to loss of light output, the S/N , that can be severe, that is, one detector may function as it should the other one doesn´t because of a bad lamp. The Beer-Lambert Law doesn´t know whether an operator doesn´t know what he is doing . . . .
One shouldn´t forget that knowing the absorption coefficient of a substance one should get the right concentration of a (ideal) solution with any photometer (if the instrument works).

Thanks both! Not having much of an analytical background, and not working in an environment full of experts, I much appreciate the chance to learn here.

Thanxxx