Sample Preparation Protocol for ESI Accurate Mass Service

Guidelines for sample preparation for the ESI Accurate Mass Service are found below, or can be downloaded as a pdf.

(yellow Excel spreadsheet with ESI numbers for submission)

Only novel samples that need accurate mass confirmation and have already been run on Open Access systems should be submitted for this service. Please also submit either a reference number of the open access report, or attach the report to the ESI submission form.

Please aim the concentration of analyte in the range 10 micrograms per mL. When analyte concentration cannot be estimated, we may not be able to run your samples.

Over concentrated samples lead to increased chemical noise, poor mass resolution, blockage in the sample delivery lines and contamination of the mass spectrometer vacuum part. You should be able to see through your sample vial even if the solution is coloured. Please also make sure that there are no hard particles in the solution or precipitation at the bottom of your sample vial, and that the solution is not jelly-like or cloudy.

Only standard 2 ml Mass Spec sample vials with a soft septum on the top of the lid should be used. The vials are available off-shelf from CRL stores. No taller vials or vials with hard lids can be used.

All open access instruments use electrospray ionisation which is only compatible with volatile organic solvents and water. Samples have to be cleaned of inorganic salts: high inorganic salt concentrations are not compatible with ESI. Please follow the protocol below for sample preparation.

The following approach is recommended for making up samples for the High Resolution ESI service:

  1. Dissolve the sample in any organic solvent (e.g., DCM, CHCl3, EtOAc, MeCN, MeOH) or H2O to a concentration of 1mg/mL. Please do not use low vapour pressure solvents, such as DMSO, or dilute them >20-fold in another solvent.
  2. Take 10uL of this solution and dilute it with 1mL of either methanol, acetonitrile or water (or any combination of these solvents).
  3. If there is any precipitate in the resulting solution it must be filtered before running the sample otherwise this is very likely to cause line blockages and delays with sample analysis for all users.
  4. Place the solution in a standard 2mL sample Mass Spec vial with a screw cap lid and soft septum on the top (available from stores).
  5. Do not use Trifluoroacetic acid (TFA) in your samples. If you need to acidify your samples use formic acid.
  6. Do not use Tetrabutyl ammonium (TBA) in your samples (also avoid other ion-pairing agents) these will contaminate all subsequent samples run on the system.