Table of Contents
Advertisement
2007), it is recommended to keep the abundances below the value of 90 * (number of transients
per scan) to avoid saturation effects. For 2 scans/second (4,880 transients/scan), the
desirable range is between ca. 5,000—440,000 counts abundance. The ion signals from the
IRM compounds decay quickly at first but should stabilize at a lower usable level for days.
Increasing the drying gas temperature increases the abundances for the IRM compounds but
also leads to a faster rate of decline of the IRM abundances. The IRM response may be
reduced when using mobile phase compositions containing high organic content, particularly
high amounts of ACN. (This is especially true for methyl stearate.) Upon repeated use of the
IRM solutions, a residual amount of the IRM compounds builds up in the interface assembly
itself, requiring less frequent addition of the IRM solutions to maintain usable abundances.
The IRM compounds specifically have been selected to persist in the interface assembly and
yield signals for an extended period of time. If the presence of these IRM signals no longer is
desired, the interface assembly may be cleaned in the usual fashion using wipes and organic
solvents (e.g., ACN and isopropyl alcohol) to remove the IRM compounds. However, traces of
them will remain and be removed only by prolonged heating (350-365 °C and 10-12 L/min
drying gas flow for several days).
If it is necessary to clean the modified top plate, remove the IRM wick from the holder. Then,
soak the entire top plate in the appropriate organic solvent.
Over time, an increase in background signals may result from material being adsorbed on or
deposited in the wick in the top plate. To clean the wick, remove the top plate from the HPLC
Chip Cube Interface. Turn the plate over to access the two screws which hold the wick
retainer in place. Remove the two screws using a T-6 driver. Remove the wick using tweezers.
Clean the wick by soaking it in a suitable organic solvent such as ACN. Allow the wick to dry
completely before reinstalling it in the top plate. Reinsert the wick into the slot of the top plate
using tweezers, or press it firmly into place while wearing clean gloves. The wick is longer and
wider than the slot and so must be compressed to fit. No portion should bulge out of the slot
(see Figure 1), and the surface of the wick should barely be visible above the plate surface.
Remove any stray fibers with tweezers, or blow them off with e.g., compressed air or nitrogen,
and reinstall the top plate. A replacement wick is available if needed (part number G1982-
20000).
Troubleshooting Tips
The following observations are not common but may help in some situations.
Observation (O): The spray from the chip tip is unstable.
Answer (A): There are multiple causes for this situation. This document assumes that air is
being added to the drying gas. If air is not being added to the drying gas, the chip is charging
Page 28 of 33
18 July 2011
Advertisement
Table of Contents
