Table of Contents
Advertisement
temporarily set the temperature to 365 °C and drying gas flow to 10 L/min, and bake out the
interface assembly for a few hours or overnight.
O:
When I plot a TIC or BPC, all I see is a high baseline offset from the IRM compounds
and little peaks or no peaks from my sample.
A:
In the data analysis program, use a mass range that does not include the IRM masses;
for example, plot the BPC from 302—1221 m/z.
O:
I can see the IRM peaks, but the mass assignments for the IRM compounds and my
sample are off by a large error.
A:
A mass error window is used to detect the reference masses, typically 100 ppm (+/-50
ppm about the true value) and specified in the Reference Mass tab of the method. Calibrate
the instrument and the problem should disappear. The use of reference masses does not
eliminate the need to calibrate the instrument on a regular basis. Data that has been collected
already may be recalibrated using the <recalibrate> feature in the Data Analysis portion of the
software.
Another cause of this effect is that the mass range during acquisition does not include the
mass peak from the IRM compound. Change the mass range to fix this.
O:
There is no hose and drain bottle on the bottom of the interface assembly. Do I need
this?
A:
Yes. The hose and drain bottle need to be connected. The drain bottle needs to have a
restrictor added to its vent. These additions close off the ionization region from the laboratory
air or vent line, which often has contaminants contributing to background signals in the MS.
See part number G1995-90000 (instructions for G1995A Low Background Site Preparation kit)
for details.
O:
After I add the IRM solutions, I see masses in my spectrum that are from background
contaminants: 281, 297, 371, 391, 445, and 519 m/z.
A:
The modified top plate, IRM solutions, and/or their method of preparation may have
some of these contaminants from their manufacture, packaging, or preparation. These signals
normally decay rapidly during the first hour or so of operation.
Page 30 of 33
18 July 2011
Advertisement
Table of Contents
