cell PDA

<p>Hello, we are using a PDA detector at 280 nm from the last March, in this period we analyze more than 1000 of samples, now the intensity of the lamp is 6000, and the lamp is over the half use. We think that the cell could be dirty. We cllean it using formic acid, after that the ingensity increase to 30000, the expected value, but after 40 injection decrease again. We are using 20 mM amonium acetate and acetonitrile methanol as eluents. The injections are a culture media derivatizated with DEM  to see biogenic amines and amino acids. Someone known what is the problem?. Someone is injecting  culture bacteria media?. Thanks a lot.</p>


  • I think it's safe to say something is gunking up your cell.  I think there are two possibilities.  The most likely one is that something in your injection sample is clogging the cell.  At low wavelengths the lamp gets hotter and so some things may start to burn on the lamp (ie. sugars and amino acids).  The second possibility I can think of is that the salt you're using in your gradient is precipitating due to the ACN/MeOH.  What I imagine might happen is in the beginning of your run ammonium acetate flows through freely but as the concentration of ACN/MeOH increases the ammounium acetate may precipitate.  This is unlikely and so long as you flush with water from time to time would not lead to a buildup.