Optimizing the Analysis of Volatile Organic Compounds
Optimizing the Analysis of Volatile Organic Compounds
Optimizing the Analysis of Volatile Organic Compounds
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36<br />
Leak Detective II<br />
Leak Detector<br />
Affordable <strong>the</strong>rmal conductivity leak<br />
detector—every analyst should have one*<br />
Compact, ergonomic design is easy to<br />
hold and operate with one hand.<br />
Helium, hydrogen, and nitrogen can be<br />
detected at 1x10 -4 cc/sec. or at an absolute<br />
concentration as low as 100ppm**<br />
Fast results—responds in less than 2 seconds<br />
to trace leaks <strong>of</strong> gases with <strong>the</strong>rmal<br />
conductivities different than air.<br />
Micro-chip design improves sensitivity<br />
and response time over previous models.<br />
Auto zeroing with <strong>the</strong> touch <strong>of</strong> a button.<br />
Battery-operated for increased portability<br />
(one 9-volt).<br />
Description qty. cat.#<br />
Leak Detective II Leak Detector ea. 20413<br />
* Never use liquid leak detectors on a capillary<br />
system. Liquids can be drawn into <strong>the</strong><br />
system.<br />
** Caution: NOT designed for determining<br />
leaks <strong>of</strong> combustible gases. A combustible<br />
gas detector should be used for determining<br />
combustible gas leaks in possibly hazardous<br />
conditions.<br />
www.restekcorp.com<br />
MS Contamination<br />
A universal detector, <strong>the</strong> MS responds to all organic compounds and, consequently, any contamination<br />
potentially can interfere with target analyte identification. The common sources<br />
<strong>of</strong> contamination are column bleed and septum bleed. High column bleed can be an indication<br />
<strong>of</strong> oxygen entering <strong>the</strong> system and degrading <strong>the</strong> stationary phase in <strong>the</strong> column. If high<br />
column bleed is suspected, conduct a leak check <strong>of</strong> <strong>the</strong> system, using <strong>the</strong> procedure<br />
described on page 34 and 35. Septum bleed introduces silicon fragments, characterized by<br />
ion 73, into <strong>the</strong> system. Silicon compounds also are components <strong>of</strong> GC and MS seals. Table<br />
VI lists common contaminants and <strong>the</strong> ions by which <strong>the</strong>y can be identified.<br />
Water / Methanol: The introduction <strong>of</strong> water and/or methanol vapor from <strong>the</strong> purge and trap<br />
system can cause problems in an MS system. Excess water vapor entering <strong>the</strong> MS can<br />
decrease <strong>the</strong> ionization <strong>of</strong> target analytes eluting at <strong>the</strong> same time. To overcome problems<br />
associated with water vapor, use a trap containing hydrophobic adsorbents, such as <strong>the</strong><br />
Vocarb ® 3000 trap. If you are using an ion trap system, increase <strong>the</strong> split ratio in <strong>the</strong> injection<br />
port. This will prevent overloading <strong>the</strong> ion trap and will increase overall linearity for <strong>the</strong><br />
gaseous analytes.<br />
Table VI.<br />
Common contaminants and <strong>the</strong>ir identifying ions.<br />
Contaminant Characteristic Fragmentation Ions<br />
Silicon 73, 147, 207, 221, 281, 355, 429, 503<br />
Rough vacuum pump oil 55-57, 61-67, 81-85, 95-99<br />
Diffusion pump oil 77, 115, 141, 168, 223, 260, 446<br />
Plasticizers 149, 223, 278<br />
Practical Introduction to GC/MS <strong>Analysis</strong> with Quadrupoles<br />
The text gives answers to questions such as: how does <strong>the</strong> mass<br />
spectrometer work, what problems can occur and how do I detect<br />
<strong>the</strong>m, how must separation and detection be adapted to each o<strong>the</strong>r,<br />
and what pitfalls can be avoided when elucidating structures and<br />
quantifying compounds.<br />
M. Oehme, Wiley-VCH<br />
1999, 195pp., ISBN 3-527-29748-0<br />
cat.# 21098<br />
Interpretation <strong>of</strong> Mass Spectra, 4 th Edition<br />
This updated version builds on <strong>the</strong> strengths <strong>of</strong> <strong>the</strong> previous editions<br />
and presents <strong>the</strong> information required to clearly and concisely interpret<br />
mass spectra. Chapters include information on elemental composition,<br />
molecular ions, mechanisms <strong>of</strong> ion fragmentations, unimolecular<br />
ion decompositions, and mass spectra <strong>of</strong> common compound<br />
classes. It is valuable and necessary resource for every person practicing<br />
mass spectrometry.<br />
F.W. McLafferty and F. Turecek, University Science<br />
1993, 371pp., ISBN 0-935702-25-3<br />
cat.# 20498