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Open Access Sample Prep

SAMPLE PREPARATION

Three instruments are available for Open Access use:

  • Agilent 6210 Time-of-Flight LC/MS
  • Waters Micro Mx MALDI-TOF 
  • Agilent 1200 HPLC with DAD

Open Access (OA) provides a "Do It Yourself" mechanism for users to acquire mass spectra. Sample information is entered into a login Interface by the user. For LC-MS, samples are prepared in auto injector vials and placed in the instrument's auto injector rack as instructed by the login system. Data are printed out after each sample has been analyzed. You can also log in a batch of samples.  Samples must be in solution and in a volatile solvent for ESI or MALDI ionization.  The solvent system used on the open access HPLC is water and acetonitrile.  If your analyte does not stay in solution under these conditins, please consult with us.

No more than tens of picomoles of sample should enter the instrument. It should be ensured that there is absolutely no particulate/undissolved matter in the sample, so as not to clog the autosampler and other tubing, including the ESI spray needle. Please make sure that your concentration is not too high.  This will produce a number of problems including producing poor signal and poor mass accuracy.  On the ESI-TOF, for example, concentration higher than about 10 μM will start saturating the detector producing a broad peak and poor mass accuracy.  In addition, you will form non-covalent dimers and trimers if the concentration is high, instead of the typical molecular ion.  These are all reasons to stay within the recommended concentration range.

  • You may contaminate the ion source of the instrument.  To discourage overloading, a service charge will be applied to your account if the instrument needs to be cleaned because of high concentration used in your sample.  Signal in mass spectrometry is concentration dependent, and thus depends on the molecular weight (g/mole) of your analyte. However, as a rule of thumb, please keep your concentration around 10-20 μM.  This corresponds to 0.01 mg/ml for a molecule of 500 g/mole molecular weight.
  • Please make sure that there are no particles or precipitate in your sample.  This can clog the system and cause excessive down-time. You can remove particles in most cases by centrifuging at 14000g for 5-10 minutes. Submission of undissolved samples which cause damage to the instrument will result in a service charge.
  • For protein samples (yes we run accurate mass on proteins  beteen 8 kDa-67 kDa!), please have the protein in solution and at a concentration of approximately 10-20 μM.
  • Make sure that there are no non-ionic detergents in the samples such as TWEEN, Thesit, Triton-X etc.  These contain polyethylene glycol which causes strong interference through the abundant formation of ions for all the polymeric ions.
  • If your samples are in an organic solvent like chloroform, methanol or acetonitrile, be sure to avoid the use of plastics since these contain plasticizers which also cause high background problems.