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Please scroll
down the list below to see if you have any questions answered
here. If not, please visit the Contact
Us page to enter a question. You may give us a call any
time between 9:00 to 5:00 Pacific Time or email
us your questions, comments, or concerns.
Phone number: 858-677-9432
Email address: Info@HT-Labs.com
Frequently asked questions:
Q: How much sample do I need to submit for mass analysis?
A: Ten micro-grams (10 µg) will be more than enough
for almost any type of mass analysis, including ESI, APCI,
MALDI, LC/MS, and even MSn structure elucidation. If the sample
is in a solution, it should be at least 10 µg/ml or 5 µmol
in concentration, and at least 200 µl in volume.
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Q: How do I submit a sample to HT Labs for analysis?
A: First, fill out a sample submission form, print it
out, and send it to us with your sample(s). You can find
our address in the upper right corner of the form. Go
to the form now .
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Q: What is your turn around time?
A: 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.
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Q: In what form I will receive the analytical results?
A: 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.
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Q: My sample contains a molecule with molecular weight
M, but the result shows a M+1 peak in the positive scanned
mass spectrum and M-1 in the negative spectrum. Why?
A: 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.
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Q: My sample has molecular weight M, but the result shows
a M+23 or M+40 peaks in the positive and M-34, M-36, M-77,
M-79 in the negative spectrum. Why?
A: 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.
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Q: My sample molecular weight is M, but the result shows
very little or no peak around M. There are instead a bunch
peaks in the spectrum with smaller mass. Why?
A: 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.
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Q: The result does not contain the mass of my molecule
but a bunch of unknown peaks. What are they?
A: 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.
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Q: What is the mass range that ESI, APCI, and MALDI can cover?
A: 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.
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