Analyser Sample Contamination — Protecting Instruments from Process Interference
When your gas chromatograph drifts, your CEMS reads high, or your moisture analyser gives erratic results, the problem is almost never the instrument — it is what reaches the instrument.
Recognise the Symptoms
- Analyser readings drift over time or become erratic
- Blocked capillaries or sample lines requiring frequent cleaning
- Detector contamination and loss of sensitivity
- Increased maintenance intervals for sample conditioning systems
- Trace-level measurements (ppb H₂S, Hg) showing unexplained background levels
- CEMS failing QAL or AST audit requirements
Root Causes
Particulate breakthrough
even micron-sized particles can block analyser capillaries (typically 0.25–0.53 mm ID). Sample gas from process taps always contains particulate unless filtered
Liquid aerosol carryover
condensed hydrocarbons or water droplets reaching the analyser detector cause baseline interference and long-term contamination
Adsorption/desorption effects
reactive compounds (H₂S, SO₂, HCl, Hg) adsorb onto uncoated stainless steel surfaces, creating memory effects and delayed response
Dead volume in filter housings
large internal volumes cause sample transport delays and mix fresh sample with stale gas, smoothing out transient peaks the analyser should detect
Temperature drop in sample line
if sample gas cools below its dew point between the tap and the analyser, condensation forms and carries contaminants to the instrument
Diagnostic Checklist
- 1Is there an inline filter between the sample tap and the analyser?
- 2What is the filter element rating? For most analysers, 2 µm or finer is required
- 3Is the sample line heated and maintained above the dew point?
- 4For trace sulphur/mercury analysis: are all wetted surfaces inert-coated (e.g., SilcoNert®)?
- 5What is the internal volume of the filter housing? Minimise dead volume for fast response
- 6Are there signs of condensation in the sample line or filter housing?
- 7When was the filter element last replaced?
Related Applications
Related Problems
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