i noticed that there are some significant differences among PDA detectors from vendors.
for example, the same peak is broader on one brand PDA while on another brand PDA, the peak is sharper, narrower with higher intensity. the injection amount, column and the gradient are all the same. can anyone tell me what is the exact reason behind this?
the wavelength resoultion and steps for spectral scan are also similar.

Cell Volume & Cell Geometry are the primary factors.

Bandwith is a very good possibility.

Bandwidth won't change sharpness. Rise-times (time constants) will, if it's a sharp peak.

to the last post:
do you mean that if the rise time long enough the peak will be sharper? or the other way?

Other way - If the rise time of the detector is too long (or time constant is too slow), the peak will be artificially broadened and will appear to elute later than it actually did.

thanks,
but i also noticed that the noise level from the broadened detetctor is higher than the sharper one, which is supposed to be nosier because of short rise time?

there may be other differences besides the rise time.

The key factor is the diode array itself. A PDA's efficiency, like other UV detectors, is a function of its optics and its detection system.

Most PDA vendors claim bandwidth resolutions of 1 nm or better - such bandwidths aren't obtained in real life. A PDA with, say, 1024 diodes and a wavelength range of 180 to 800 nm is presumed to yield a resolution of 0.8 nm. This is merely a theoretical calculation - or the PDA's so-called "electronic" resolution.

The PDA's true resolution however, is decided by the efficiency of its grating - NOT necessarily by the number of diodes it has. This is the optical resolution of the PDA.

Different PDA manufacturers use different gratings. This is why PDA's with similar specs yield differing results on the same sample.

So check out the grating efficiency for your PDA. I've seen PDA's with 512 diodes give better results than PDA's with 1024 diodes.

C'est la vie.

S.K. Srinivas

SK Srinivas just described the difference between the PDA-detectors from Waters (512 diodes) and Agilent (1024 diodes) and the arguments which come from both marketing departments, when discussing THEIR instrument.

Oui, c'est vraiment la vie.

Good thing I have a fast scanning UV detector. SK Srinivas, what do you men with "better results"? More SPECTRAL resolution, higher chrom intensity....?
One would presume that more diodes will give better spectral resolution if the grating is efficient enough, but that less diodes and a low resolution, low scattering grating would give higher intensity? (This would agree with anonymous who pointed out that bandwidth does not relate to chrom peak width.)