coupling of new mass spectrometric techniques with new and
significant research problems requires considerable interaction
between mass spectrometrist and mass spectrometry user. For this
reason, Purdue University created the Campus-wide Mass Spectrometry
Center (CWMSC) in October of 1985, with the following goals:
1) to coordinate the operation and maintenance of mass spectrometers
which are located in different departments
and are used for routine analyses,
2) to provide research groups working on significant problems with
access to all of the mass spectrometers on campus,
3) to increase awareness in the University community of the
opportunities for problem solving by mass spectrometry and
4) to coordinate the acquisition of new instrumentation as needs
Decentralization and shared resources are important features of this
facility. Key to the success of the facility is the Director, who
supervises the staff mass spectrometrists providing routine service across campus,
assists investigators in defining (and recognizing) their needs in
mass spectrometry, coordinates access to research mass spectrometers
and through clinics, research group seminars, and other means
educates the University in mass spectrometry. The CWMSC which
utilizes mass spectrometers located in the Departments of
Biochemistry, Chemistry and Medicinal Chemistry and Pharmacognosy,
insures a high level of quality control for the more routine types
of analyses, and provides a collaborative analytical mass
spectrometry capability to the Purdue research community. In order
to more efficiently utilize the mass spectrometry resources on
campus the CWMSC has pursued a plan designed to maximize the
utilization of the mass spectrometers in the three departments. This
is being done in a variety of ways:
(a) the coordination of sample analyses, since differing capabilities
are available in different departments (Biochemistry -
capillary GC/MS, electron impact and chemical ionization probe,
plasma desorption, matrix-assisted laser desorption; Chemistry -
electron impact and positive and negative chemical ionization probe,
desorption chemical ionization ICPMS; Medicinal Chemistry and
Pharmacognosy - electrospray ionization, electron impact and chemical
ionization probe, high resolution mass measurement),
(b) the education of researchers campus-wide as to availability and
capabilities of modern mass spectrometry,
(c) maintaining close investigator-operator ties such that the
analysis is not done without the necessary background for providing
quality results, and
(d) the presence of a director to coordinate access to the mass spectrometers,
address questions relating to the interpretation of the spectra,
train instrument operators, assist users in their search for new
research funds and provide troubleshooting expertise to minimize
The CWMSC is organized as shown in Table 1. The department
heads (or their designated representative) meet with the director
individually on a regular basis and as a group at least once per
year. They act as a resource for the Director as well as to provide
their input from a departmental perspective for new initiatives in
steering the direction of mass spectrometry at Purdue. Each
department head (or their representative) is a mass spectrometry
user and is committed to the decentralized, but coordinated concept
of mass spectrometry at Purdue. This can be seen by the
collaborative effort used to obtain funds from all three
departments/schools to purchase the matrix-assisted laser desorption
instrument located in the Department of Biochemistry. In addition,
the central administration is strongly supportive of mass
spectrometry. A former Vice President for Research launched the
concept of a Campus-wide Mass Spectrometry Center and provided the
Director's salary for the first three years.
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Status of Instruments
Spectrometers at CWMSC
(click on the
instrument to view picture)
Biosystems Voyager DE PRO
Laser Desorption) Nonvolatile
components to m/z 100000
|Agilent 5975C GC/MS
probe and capillary GC/MS)
Volatile components to m/z 1000
coupled Argon plasma)
probe and capillary GC/MS)
Volatile components to m/z 1000
and Atmospheric Pressure Chemical Ionization, LC/MS/MS)
components to m/z 50,000
Chemistry & Molecular Pharmacology
Resolution Mass Measurements)
EI, CI and ESl
Nonvolatile components to m/z 50,000
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can be submitted at any of the three mass spectrometry laboratories.
The electronic sample submission form can be accessed at: www.ras.itap.purdue.edu. First you will need to log-in with your career account. At this point you will want to ‘Create a new job’ which involves giving a sample name and selecting ‘next’. On the next page first time users will be asked for their phone number. Then you will need to provide your account information and the type of mass spectrometric service you require (drop down box). On the opposite side of the page you can provide a description if needed as well as relevant sample information including molecular formula, molecular weight, structure (at present as a downloaded file), solvent, etc. Once you hit submit, the system will check your account number and indicate to you all is okay, do you want to proceed. Assuming yes the next step is to print a copy of the sample submission form. Once printed all you need to do is select done. The final step is to bring the sample submission form and your sample to one of the mass spectrometry labs. At present I would request that you also draw the structure of your reaction and/or expected product on the sample form or provide it on a separate sheet of paper (we sometimes have problems reading the files you include). If you run into any difficulties please contact Karl V. Wood (firstname.lastname@example.org).
you have questions about the best method for obtaining mass spectral
results, please give the Director or any of the staff mass
spectrometrists a call to discuss.
This also includes any special needs that your sample might
require like; being kept in the freezer, the need to analyze right
after reaction is completed due to stability, some unique solubility
you need to utilize GC/MS or LC/MS capabilities we request that you
first determine the methodology, for separation prior to submitting
the sample. In this way
we can best try to duplicate your chromatogram and provide you with
the information you need. LC/MS
is particularly demanding in terms of the sample and mobile phase
requirements, as seen in the next few paragraphs.
following is needed to submit a sample for LC/MS
A new or clean (provide blank chromatogram) LC column and at
least one liter of the mobile phase
The LC elution conditions, including (a) flow rate (less than
1 ml per minute is preferred), (b) mobile phase, (c) stationary
phase and (d) gradient
The amount of sample injected and the concentration of the
A copy of the LC chromatogram showing the peak(s) of interest
as well as the wavelength used
A standard where applicable
The expected component(s) of interest, as well as the
reactants and solvents involved
The mass range of interest
If possible supply at least 50 microliters of sample
routine operation the sample size should be in the range 1-100
picomoles per microliter.
commentary on acceptable buffering agents:
LC/MS can only utilize VOLATILE components (and only below
acceptable molar concentrations) or else the electrospray capillary
will become plugged. This
includes common solvents like methanol, water, acetonitrile and
salts (below 25mM) like ammonium acetate and ammonium bicarbonate.
This also explains why acetic acid is preferred over
or mineral acids can be used.
the more information you can provide about your sample and its
chemical characteristics the better mass spectra we can obtain for
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The Following is a brief description of selected mass
spectrometer ionization techniques:
Electron Impact (EI) utilizes 70eV electrons for ionization of volatile compounds.
This relatively harsh ionization technique can produce
molecular ions (M+) as well as fragment ions.
If fragmentation is extensive little or no molecular ion
intensity may be observed.
Chemical Ionization (CI) is a softer ionization technique for volatile compounds.
The basis for ionization centers on proton transfer from a
reagent gas ion, present in great excess relative to the sample of
reagent gases are isobutane, methane and ammonia.
The following three ionization techniques are used to
analyze non-volatile components.
Laser Desorption Ionization (MALDI) typically utilizes a nitrogen
laser at 337nM as the ionization source.
The sample is mixed with a matrix, and allowed to dry prior
to insertion into the mass spectrometer.
Crystallization of the sample within the matrix is an
important component of successful MALDI analysis.
A variety of matrices, present in great excess relative to
the sample amount, are used to span the range of compounds classes
amenable to MALDI mass analysis.
Formation of sample ions, upon laser irradiation, involves a
proton transfer reaction involving the matrix (which absorbs the UV
photon) and the analyte. The
ions are then accelerated into a time-of-flight mass analyzer for
mass analysis. Typical
matrices include, a-cyano-4-hydroxycinnamic
acid, sinapinic acid and 2,5-dihydroxybenzoic acid. MALDI can be done routinely to m/z 100,000 and there are many
examples of analyses going well above this mass range.
Electrospray (ESI) Samples can be analyzed by ESI using either direct
injection or through liquid chromatographic introduction.
Typically ESI forms protonated molecules with little or no
molecular weight molecules can also be ionized using ESI.
In this case the molecule becomes multiply charged and the
molecule of interest is observed at its respective m/z.
(For example a 20,000 molecular weight protein that has 20
protons attached would be detected at 20,020/20 or m/z 1001.)
The choice of solvents and related components, which must be
volatile, are very important for obtaining quality electrospray
spectra. This results
because sample introduction is through a liquid medium, but
eventually the solvent needs to be volatilized away.
If a nonvolatile solvent or buffer is used the result is
frequent plugging of the capillary tubing and/or some of the beam
defining components. In
ESI the solvated sample is passed through a needle held at a high
potential typically 3-10kV. As
the molecule exits from the needle, the resulting spray undergoes
electrostatic nebulization, which places a charge(s) on the droplet.
The charged droplet passes through a variety of focusing
elements, which are differentially pumped.
One result is desolvation of the droplet.
Depending on the size and chemical makeup of the analyte the
resulting stable ion can have a single charge or may be multiply
charged. Mass analysis
of this ion can be carried out with any type of mass analyzer,
including magnetic sector, quadrupole, ion trap or time-of-flight.
Sample concentrations that can routinely be analyzed are
10-50picomoles / microliter, however the detection limit for many
components is considerably lower.
amenable to liquid samples, for this reason it is used for liquid
chromatography / mass spectrometry. The sample is typically
dissolved in a volatile organic solvent, like methanol or
acetonitrile, and then injected into the mass spectrometer through a
Plasma Desorption Mass Spectrometry (PDMS)
utilizes fission fragments from 252Californium for
ionization. The sample
is applied to a nitrocellulose matrix, either by droplet or
electrospraying, allowed to dry and then inserted into the mass
sample ions, which are formed, are accelerated into a time-of-flight
mass spectrometer for mass analysis. The useful mass range for PDMS
is up to m/z 5000. Typically
the observed ion is the protonated molecule, however, PDMS has
proven to be well suited for the analysis of pre-charged species,
Coupled Argon Plasma (ICP) multi-element analyses are
carried out using ICP. The
sample is vaporized an Argon plasma, with the resulting ions being
limits for selected elements can be sub part per trillion
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