Perkin elmer DAD and tetracyline

[oscarBAL]

Hello all!!
I am tring to analyze tetracycline residues for that I am using a C8 column and a DAD perkin elmer series 200.
when I inject my std, i get very poor sencivity, I think the reason could be that wave of lenght is 360 nm. this is the wave of length that usually comes by default as reference so I chance the reference to 420mn and my "wavelenght" to 360 nm, but I get very poor senciviti!!!
I do not want to think that this could due to the lamp....
I know my peak is tetracyclin because I can Confirm it with the UV spectra, but I have another problem....

I think I have something wrong in my brain!!!! (a synapsis problem or something like taht) because I never been able to understand the trubochrom software, and less the setting of this link-detector, and that is why i Think my sencivity problem is really a setting problem.

Thanks in advance.

Oscar

[rnelson]

Take a look at your UV spectra. Are you setting your analytical wavelength to your absorbance max value from your spectra? Also, the reference wavelength should be a wavelength where you are seeing no absorbance at all, which you could also see from your absorbance spectra. Not knowing much about tetracycline, you may be trying to select a reference wavelength too close to your analytical wavelength.

You should double check your bandwidth setting also. I think the default is 20nm, which should be OK to give sufficient sensitivity.

It's not a bad idea to check your lamp though, there should be a mercury indicator on the lamp wire that tells you how many hours your lamp has on it. Anything over 1000 hours for these lamps, then it's probably time to replace it.

[Alex Buske]

Hi,

do you have any historical data on the sensitivity of YOUR detector, that you could check now? Sensitivity changes and the mecury indicator at the lamp is just a very rougth guess on the actual intensity.
Deep in the system is a reference wavelength to set (or not to set). If that had been set to something close to 360 nm, the S/N ratio would be terrible. In TC C/S it is under Methods / Instrument control / Detectors and for our system qualification method it is actually set at 360 nm. So there is a good chance that this is the default value. Try to enter 0, that migth switch off the wavelength reference thing.

Alex