FAQ

For ESI and MALDI samples, we guarantee a 12 hour turn-around, (We will send you the analytical results within 12 hours after receiving your sample). Most of the time we deliver the results to you within 6 hours. You should get your LC/MS results the next day after your sample has arrived in our lab. Turn around time for PK studies and elemental analysis is three days. Turn-around time for all other services can vary depending on the complexity and urgency of the job.

All mass analysis results (including ESI, APCI, MALDI, LC/MS, and high-accuracy mass) are either emailed or faxed to you as soon as the analysis is done. Emailed data will be in PDF file format. Data in other electronic format may be furnished upon request and at an extra charge of $15/sample.

Since we are using an API (Atmospheric Pressure Ionization) source, the molecules under detection are charged, becoming ions by gaining a proton (H+) in the positive scan mode, and by losing a proton in the negative scan mode. A mass spectrometer measures (counts) the ions.

In the positive scan mode, a molecule can become ionized by grabbing a Na+ (23) or K+ (40) ion. The source of Na+ and K+ is mostly from the sample itself (e.g. the buffer, reagents residue, contamination from glassware, etc). Please note that Na+ and K+ are detected everywhere by the mass spectrometer.Similarly, in negative scan mode, the molecule may be ionized by attaching to a Cl- (34 and 36) or Br-.(79 and 81) ion. You should find the isotope pattern shown in the spectrum if ionization occurs in this way. Any other deviation from the expected molecular weight should be considered to be something existing in the sample. Other types of adduct are very rare and has to be confirmed by further experiments before asserting their existence.

Although the API source usually reveals a molecular ion to be the strongest ion in the spectrum, there is still a significant possibility of fragmentation, in which the molecule gets chopped apart. It is relatively rare in the case of ESI or MALDI that there is no molecular ion find in the mass spectrum unless the molecule is highly unstable. If you do not find any expected molecular ion at all in the result, chances are that the expected molecule does not exist in the sample.

If you do not know what they are, we don’t know, either. Besides the background peaks that we usually label out for you, these peaks are solely indicative of the substances existing in your sample. It is impossible to tell what the substances are only judging by their masses. Please also note that we are not responsible for interpreting the data any further than answering yes/no to whether your expected mass exists. A look at only the molecular ions is insufficient to answer any further questions.

ESI and APCI can scan exactly the same mass range, usually from 50 to 2000 Dalton; some instruments get up to a limit of 4000 or even 6000 Dalton. However, since API machines always cause multiple charge to large molecules, a 6000 Da peptide may bear 10 to 20 charges and therefore show in the 300 to 1000 mass range. Therefore, large mass ranges for API spectrometers are not very useful anyway.MALDI can measure up to 500,000 Dalton, but mostly can only get high quality signals within about 200,000 range. Larger molecules are difficult to be laser desorped and then ionized.