ISQ User Guide - Write Frame of Mind

7 Optimizing Your Method
Improving the Way You Prepare Samples
Improving the Way You Prepare Samples
Changing the Scan Rate
Narrowing the Mass Range
Although sample preparation adds time and expense to the overall analysis, a more focused
method can give you better results. Try extracting your sample in a solvent that increases the
solubility of the analytes of interest, but does not increase the solubility of the other
compounds. Try switching solvents if your method will allow it.
You can also use or change the phase of a solid phase extraction cartridge, which gives you
similar results as changing a solvent. You can affect the way you prepare samples by changing
the type of cartridge you are using.
The precision of your data depends on how well you define your chromatographic peak.
Typically, you get good precision when sampling ten times across the chromatographic peak.
Increasing the scan rate increases the number of times you’ve sampled across the peak.
However, increasing the scan rate too much results in mass spectral noise, which decreases
your analytical precision. To optimize your scan rate, select a rate that will give you 8-12
points across a chromatographic peak.
By narrowing your mass range, you can look directly at the compounds of interest. However,
if you’re looking at a large number of compounds that have a broad range of mass fragments,
a wide mass range makes sense. To narrow the mass range, refine your scan parameters to a
smaller number. A narrower mass range will also allow you to decrease the scan rate and get
the same chromatographic peak sampling.
Adjusting the Transfer Line Temperature
If your transfer line temperature is set too low, the less volatile compounds may get stuck in
the transfer line and never make it into the ion source. On the other hand, if your transfer line
is too hot, you could damage the column or cause a thermal breakdown in the compounds
you are analyzing. Typically, the transfer line temperature should be 10 °C over the highest
boiling point of the compounds of interest, but no more than the maximum safe operating
temperature of the column.
76 ISQ User Guide Thermo Scientific