35
MSD SourceNut
(Similar toAgilent part # 05988-20066.)
Description
qty. cat.#
(Detector)MSDSource Nut
2-pk. 20643
Figure 38.
To check for leaks, cap the split vent and
septum purge vent lines on theGC and the
column, then shut off the gas supply.
System pressure should remain constant.
Cap both
Connect the capillary column, 0.25mm ID or smaller, to the injection port, but not to the
MS source, and condition the column.When the column has been conditioned, remove
50cm from the detector end of the column to ensure complete removal of siloxanes and
other potential contaminants. Then, with theMS still turned off, insert the column end into
theMS source. Cut the column several centimeters from the connection to the injection port.
Use septa to cap the short length of column that is left in the injection port and the new,
unconnected inlet end of the column.Also cap the split vent and septum purge vent lines on
theGC (Figure 38). Perform a pressure decay test on the injection port by setting the pres-
sure to 30psi, then shutting off the gas supply. The pressure should remain constant for at
least 1minute. If the pressure drops in less than 1minute, turn on the gas supply and begin
leak checking, using an electronic leak detector, such as theRestekLeakDetective
TM
II (cat.
#20413, page 36).
Once you have confirmed theGC system is leak-tight, andwhile the injection port end of
the column is capped and there is no flow in the column, evacuate theMS and record the
source pressure in yourmaintenance logbook.After several hours equilibration, perform the
instrument leak-check using PFTBA (seeMSCalibration andTuning, page 32). If a leak is
present, draw 500µL ofmethanol into a syringe and apply drops of this solvent on areas
where leaksmight be suspected, while scanning formass 31.Alternatively, bathe these areas
with argon gas and scan form/z 40. The brass source nut is the primary place for leaks in an
MS, this nut should be replaced every time the column is changed (cat. #20643, page 35).
Other areas to examine include the rubber seals and the PFTBA vial.
After you confirm theMS is leak-free, quickly install the inlet end of the column into the
injection port. TheMSwill draw air into the source during this connection time; after anoth-
er 2-hour equilibration theMS is ready for tuning/leak checking using PFTBA.
Figure 37.
Cl andBr are examples ofA+2 elements (isotopes vary by 2amu ormore).
Element
Mass
%Abundance
Mass
%Abundance
carbon
12
100
13
1.1
nitrogen
14
100
15
0.37
chlorine
35
100
37
32.5
bromine
79
100
81
98
oxygen
16
100
18
0.2
Br
Cl
Cl
2
Br
2
Table V.
Fragment ions can offer clues to compound composition.
Compound Class
Fragment Ions
Aldehydes, amides, amines
44, 58, 72, 59, 30
Aliphatic hydrocarbons
43, 57, 71, 85, 99
Alkylbenzenes
104, 91
Aromatic hydrocarbons
39, 50, 51, 52, 63, 65, 76, 77, 91
Fluorine-containing
50, 69
Methacrylates
41, 69
Methyl ketones
43, 58
Oxygen-containing
31,45,59,73
Sulfur-containing
47,61
Unsaturated hydrocarbons
41, 55, 69
