Thermo Scientific Dionex UltiMate 3000 Series, Operating Instructions Manual

Page: 146 / 270

UltiMate 3000 Series:
NCS-3500RS and NCP-3200RS
Page 138 Operating Instructions
5.8 Recommendations for Optimally Running Systems (Best
Practice)
The best stability with any chromatographic system is achieved when running the system
uninterruptedly.
This is true also for the NC pump that uses extremely precise pressure transducers or
thermal flow sensors to control the flow rate and gradients. The best stability is reached
when the pressure transducers or thermal flow sensors are always used in the same
operating range, as is the case, for example, with gradient runs.
If a Classic flow meter is installed, note the following: When the pump flow has been
interrupted or when the pressure has been down to zero, a certain time of operation will be
required until the pump has reached full stability again.
However, over time, such sensors can have a small drift. Over time, the drift can change
the zero point of the sensors, and thus can cause retention time shifts. With the following
tests, you can check and correct the zero points of the sensors:
• If a Classic flow meter is installed, you can check and correct the offset of the pressure
transducers if required. To do so, run the Pressure Transducer Test ( → page 172).
• If a ProFlow flow meter is installed, you can check and adjust the zero balance of the
flow sensors, if required. To do so, run the
Zero Balance Test
( → page 172).
A drift or shift in retention times can also have other reasons that are not connected to the
sensors. For example, you may observe also a drift or shift in retention times when you use
pre-mixed solvents. If pre-mixed solvents are not refreshed for a long time, the solvent
composition can change due to evaporation of volatile solvent components (for example,
ACN, (T)FA)).
Observe the following recommendations:
1. As long as the system provides stable retention times in the expected range, you
should
not
interrupt operation unnecessarily by measuring the viscosity, re-calibrating
the pressure transducers or flow sensors, or purging the module.
2. For ultimate reproducibility, run the system continuously. For example, use blank runs
if the system is not in use for sample analysis. As an alternative, you can run the
system at the same flow rate and 50 % of solvent channel B. With nano LC, it is
generally not recommended to reduce the flow rate or run the pump at low %B
concentrations for a long period of time.