If sensitivity is less than you expect, check the following possible causes:
Make sure the tune file specified in the method is a valid file. Make sure it is appropriate for the analytical technique and for the type of sample you are analyzing. Do not acquire data if the MSD cannot pass tune.
Make sure the tune file specified in the method is appropriate for the type of chemicals being analyzed.
Increase the repeller voltage slightly and see if sensitivity improves.
Incorrect temperatures in the MSD can decrease sensitivity. See MS Temperature Guidelines.
Make sure the sample concentration is correct. A sample that is lower in concentration than you think it is can make sensitivity appear poor when in fact it is good.
Leaks in the septum, injection port seal, and column nut allow sample to escape. Tighten fittings or replace injection port components as necessary.
Make sure the split ratio is correct and appropriate for the sample size. If necessary, reduce the split ratio or switch to a splitless injection.
If the purge off time is too short, part of the sample will be lost when the purge turns back on. Lengthen the purge off time.
At typical column flow rates (0.1 - 2.0 mL/minute), the foreline pressure will be approximately 20 to 100 mTorr. The vacuum manifold pressure will be approximately 1 × 10^-6 to 1.4 × 10^-4 Torr. These pressures can vary widely from instrument to instrument so it is very important that you are familiar with the pressures that are typical for your instrument at given carrier gas flows.
If the foreline or vacuum manifold pressure in your MSD seems too high, refer to Foreline pressure is too high and Vacuum manifold pressure is too high
Increase the electron multiplier voltage. If increasing the voltage does not improve sensitivity, check other possible causes. If the electron multiplier voltage is at or near its limit (3000 V), replace the electron multiplier horn.
See the MSD maintenance documentation for instructions for replacing the electron multiplier horn.
Look for mass spectral peaks associated with air (m/z 18, 28, 32, and 44 or m/z 14 and 16). If you find significant peaks at these masses, check for air leaks.
Switch a filament and when propmted to autotune click YES.
If sensitivity improves, use the new filament.
Replace the original filament when convenient.
See the MSD maintenance documentation for instructions for replacing a filament.
Switch the dc polarity on the quadrupole mass filter (quad). Retune the MSD. If performance improves, continue to use the new dc polarity.