• Flush buffers from the system, with aqueous solvent, if you keep the system idle for extended
periods (longer than 24 hours). Use 10 to 20% organic solvent in water as a “storage” solvent.
Prime the sample manager with purge solvent for a minimum of 10 cycles.
• Running continuously with salt concentrations higher than 1M can result in a need to change
pump seals more frequently than the scheduled PM. To help increase seal life and prevent
salt crystal buildup on the pump seals, flush the pump, high salt line, and reservoir
periodically. Salt concentration, flow rate, and other factors can affect the frequency of flush
procedures. Some applications can require weekly flushing.
Follow proper shutdown procedures
• Flush all flow paths, including the needle wash, with plenty of non-buffered solvent before
shutting down the system. For extended shutdown periods (longer than 24 hours), use 10% to
20% methanol in water.
• Do not use the
Load Ahead
or
Loop Offline
options when you are troubleshooting carryover
problems.
2.2 Dispersion
UPLC systems and autosamplers exhibit low dispersion—a fixed, instrument characteristic
measured by the extent of peak broadening that occurs because of the system design.
Small particle chromatography uses small, high-efficiency columns. A typical 2.1 × 50 mm UPLC
column has an approximate 174-µL volume, compared with 2.5 mL for a typical 4.6 × 150 mm
HPLC column. The smaller column and particle size require a system whose low dispersion
reduces dilution and band broadening, thus maintaining the peak shape, height, and sensitivity
produced by the high efficiency column.
An ACQUITY UPLC H-Class system typically exhibits a bandspread between 10 and 12 µL,
depending on system configuration. An Alliance HPLC system can exhibit a bandspread between
35 µL and 50 µL. Because of the dispersion differences, a band on an Alliance system
experiences a threefold increase in dilution, compared with an ACQUITY UPLC H-Class system.
As a result, UPLC peak concentrations are higher than HPLC concentrations. Because solubility
effects are more apparent in low dispersion, high pressure systems, it is important to adjust
column load appropriately.
2.3 Carryover
You observe carryover in chromatographic systems when a previously injected analyte appears
as a peak in the chromatogram of subsequent samples. Carryover tends to occur when a small
amount of analyte remains in the system after a sample is injected. You can measure carryover
by observing analyte peaks that appear when you run a blank sample immediately after an
analytical sample.
August 8, 2016, 715005049 Rev. C
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