BUCHI ELS Detector C-650 - Manual (Page 36)

C-650 Operation Manual, Version B 5 Putting into operation 36
5.9.4 Solvent noise test
To determine the solvent noise:
Ensure that the gas is flowing at 2 bar (29 psi), the temperature is set to 50 °C and stable and
the pump is switched off.
Switch on the light source and set the gain to 12 and monitor the signal. Do not autozero the
detector. The signal may be negative.
Bypass the column and connect the detector to the mobile phase delivery system and pump the
solvent that you expect to use for your analyses through it at a flow rate of 1 mL/min.
Monitor the baseline for a few minutes.
If water is used as the solvent, the signal should be less than 10 mV. Higher values could be ob-
served if non-HPLC grade water (with a higher non-volatile residue) is used.
If an organic solvent is used, the signal should be less than 200 mV.
For mixed aqueous/organic solvents, the expected signal is approximately linear with respect to
the concentration of organic phase in the solvent (e.g. a water/organic solvent (50:50) mixture
should provide a signal of approximately less than 100 mV).
NOTE
The purity of the solvent is critical for a low background noise. The sensitivity is inversely propor-
tional to the solvent noise.
In most cases, distilled water and HPLC grade solvents are satisfactory. When you are compar-
ing solvents from different sources, the most critical parameter is the Residue After Evaporation;
this parameter should be less than 1 ppm to maximize the sensitivity of the detector.
If the device fails the Solvent Noise test, it is most likely due to an impurity in the solvent rather
than a fault with the device. If changing the solvent source does not solve the problem, it may be
necessary to decontaminate the device as described in section 8.7.2 or clean the nebulizer as
described in section 8.5.
When filtering the solvent, verify that it does not extract any contaminant from the filter.
The mobile phase should not contain non-volatile solvent modifiers. Volatile solvent modifiers
(e.g. CHOOH, CH
3
COOH, CF
3
COOH, NH
4
Formate, NH
4
, Acetate, (C
2
H
5
)
3
N)…) can be used, but
they may increase the noise level at high gain settings. In addition, the solvent should not contain
preservatives, (e.g. Tetrahydrofuran may contain BHT as a stabilizer).