Operating instructions

Charged Aerosol Detectors
Corona Veo and Corona Veo RS
Page 42 Operating Instructions
The following table is to assist you with typical additives and buffers.
Additive/Buffer pKa Buffer Range
Trifluoroacetic Acid (TFA) 0.3
Formic Acid 3.75 2.8 – 4.8
Ammonium Formate 3.75 2.8 – 4.8
Acetic Acid 4.76 3.8 – 5.8
Ammonium Acetate 4.76 3.8 – 5.8
• Exposure of the detector to non-volatile salts will lead to increased background currents
and noise. It may also adversely affect the nebulizer performance. If the detector is
inadvertently exposed to non-volatile salts, use HPLC-grade water as mobile phase to
remove the salts from the detector. Avoid using inorganic buffer salts.
• Use nitrogen with highly combustible mobile phases such as tetrahydrofuran (THF) and
other ethers or ketones.
4.5.2 Mobile Phase Delivery System
The pump should deliver continuous flow and at the same time ensure the intermixing of the
mobile phase (if gradient elution is used). Fluctuations in pump backpressure can cause
baseline noise. If the noise is synchronized with the pump stroke, check your HPLC pump.
The mobile phase reservoir should be glass. In some applications, however, it may be
necessary to use plastic solvent reservoirs. In carbohydrate applications, for example, PTFE
solvent reservoirs should be used to prevent carbon dioxide build up in the mobile phase.
4.5.3 Gas Supply
• The gas supplied to the detector must be either air or nitrogen. Always use nitrogen with
tetrahydrofuran (THF) or other highly combustible solvents. Do not use helium, as it
does not charge the aerosol particles properly.
• If nitrogen gas is used, it must be pure (typically ≥ 95 %), free from particulates, and
must not contain volatile hydrocarbons or solvent vapors (e.g. compressor oils).
Tip: If necessary, use a sub-micron filter in combination with a water
condensation trap located close to the nitrogen gas source.
• The supplied gas is filtered through a charcoal filter and a high-efficiency particulate air
(HEPA) filter within the detector. Make sure that the filters are maintained properly to
ensure optimal gas quality.
• If you use a nitrogen generator, observe the manufacturer's user documentation on
recommended service intervals for the generator to provide optimum performance of the
detector.