Purity is the key to successful mass spectrometry of your sample. Salts, detergents, plasicizers, polymers, and other small-molecule contamination can significantly impact the ability to successfully ionize and analyze your sample. It is easy to inadvertently contaminate your sample.
The following are general guidelines for sample preparation and submission:
- Use HPLC to purify and collect samples whenever possible. Be sure that there is no contamination from previous samples or background contamination from the HPLC system before collecting fractions of your samples. Collect fractions in clean microcentrifuge tubes (see below).
- Always use “cleaned” or new glassware for preparations of solutions and reagents. Rinse common-lab glassware copiously with organic solvents and nanopure water before use; glassware may have traces of detergents or polymers adsorbed in the surface of the glass. Glassware that has been washed at one time with detergents will be contaminated. It’s a good idea to dedicate new glassware to certain solutions only, so that solutions don’t become inadvertently contaminated.
- All polypropylene tubes and vials should be rinsed with acetonitrile, methanol, and nanopure water before making up solutions, storing, or collecting samples (including microcentrifuge tubes).
- Use clean (rinsed with methanol and nanopure water) microcentrifuge tubes to submit samples, unless the solvent your sample is in is not compatible with polypropylene (e.g. acetone). (NalgeneTM has published tables of compatibility of polypropylene with different solvents).
- Do not wrap sample vials with parafilm. Parafilm will contaminate samples that are in organic solvents in the microcentrifuge tubes.
- Desalt samples prior to sample submission (e.g. HPLC, C18 sep-pack, C18 Ziptip, dialyses). Salts will have a significant impact on ionization, both for ESI or Maldi ionization. If needed, we can also desalt with Ziptip purification at the MS Facility.
- Certain buffers (non-volatile buffers, such as HEPES) and purification methods, such as sephadex, will actually contaminate your sample. Polymers from certain types of sephadex preparations can inhibit or completely suppress ionization.
- Always use HPLC-grade quality solvents and only nanopure water for sample preparations.
- Do not prepare your samples in DI water or tap water (these are heavily contaminated); use only nanopure water.
- Do not concentrate (e.g. lyophilization or speed-vac) your sample from large volumes of solvent or nanopure water (e.g. > 0.5 mL). This will concentrate non-volatile contaminants that are in all solvents (even HPLC-grade solvents and nanopure water).
- Do not use glass vials with screw-on caps that can contaminate your sample. Paper or foil-lined caps will contaminate your sample when the solvent contacts the cap. Preferrably, use cleaned polypropylene microcentrifuge tubes (when the solvent is compatible with polypropylene).
- Be careful not to touch microcentrifuge tubes or caps with fingers, and don’t use gloves coated with powder on the inside. This will contaminate samples. Gloves should be rinsed with nanopure water.