36
Table VI.
Common contaminants and their identifying ions.
Contaminant
Characteristic Fragmentation Ions
Silicon
73, 147, 207, 221, 281, 355, 429, 503
Rough vacuum pump oil
55-57, 61-67, 81-85, 95-99
Diffusion pump oil
77, 115, 141, 168, 223, 260, 446
Plasticizers
149, 223, 278
MSContamination
A universal detector, theMS responds to all organic compounds and, consequently, any con-
tamination potentially can interferewith target analyte identification. The common sources
of contamination are column bleed and septum bleed. High column bleed can be an indica-
tion of oxygen entering the system and degrading the stationary phase in the column. If high
column bleed is suspected, conduct a leak check of the system, using the procedure
described on page 34 and 35. Septum bleed introduces silicon fragments, characterized by
ion 73, into the system. Silicon compounds also are components of GC andMS seals. Table
VI lists common contaminants and the ions bywhich they can be identified.
Water /Methanol:
The introduction of water and/ormethanol vapor from the purge and trap
system can cause problems in anMS system. Excesswater vapor entering theMS can
decrease the ionization of target analytes eluting at the same time. To overcome problems
associatedwithwater vapor, use a trap containing hydrophobic adsorbents, such as the
Vocarb
®
3000 trap. If you are using an ion trap system, increase the split ratio in the injec-
tion port. Thiswill prevent overloading the ion trap andwill increase overall linearity for the
gaseous analytes.
LeakDetective
™
II
LeakDetector
* Never use liquid leak detectors on a capil-
lary system. Liquids can be drawn into the
system.
**
Caution:
NOT designed for determining
leaks of combustible gases. A combustible
gas detector should be used for determin-
ing combustible gas leaks in possibly haz-
ardous conditions.
Description
qty. cat.#
Leak Detective
™
II
Leak Detector ea.
20413
• Affordable thermal conductivity leak
detector—everyanalystshouldhaveone*
• Compact, ergonomic design is easy to
holdandoperatewithonehand.
• Helium, hydrogen, and nitrogen can be
detectedat1x10
-4
cc/sec. orat anabsolute
concentrationas lowas100ppm**
• Fast results—responds in less than2sec-
onds to trace leaksof gaseswith thermal
conductivitiesdifferent thanair.
• Micro-chip design improves sensitivity
and response timeover previousmodels.
• Autozeroingwith the touchof abutton.
• Battery-operatedfor increasedportability
(one9-volt).
Practical Introduction toGC/MSAnalysiswithQuadrupoles
The text gives answers to questions such as: how does themass
spectrometer work, what problems can occur and how do I detect
them, howmust separation and detection be adapted to each other,
andwhat pitfalls can be avoidedwhen elucidating structures and
quantifying compounds.
M. Oehme,Wiley-VCH
1999, 195pp., ISBN 3-527-29748-0
cat.# 21098
InterpretationofMassSpectra, 4
th
Edition
This updated version builds on the strengths of the previous editions
and presents the information required to clearly and concisely inter-
pret mass spectra. Chapters include information on elemental com-
position, molecular ions, mechanisms of ion fragmentations, unimol-
ecular ion decompositions, andmass spectra of common compound
classes. It is valuable and necessary resource for every person prac-
ticingmass spectrometry.
F.W. McLafferty andF. Turecek, University Science
1993, 371pp., ISBN 0-935702-25-3
cat.# 20498
