The standard method for the determination of oxygen in gaseous fuels and fuel type gases (ASTM D7607-11) employs an electrochemical sensor. Whilst in theory quantification of oxygen at single 1 µL/L (ppm v/v) concentrations should be possible, in practice accurate, on-site measurements below 100 µL/L are rarely achieved due to system leaks and ingress of atmospheric oxygen into the system.
Qa3 have developed a sampling apparatus and analysis protocol designed to (i) prevent contamination from atmospheric oxygen (ii) reduce equilibration time and (iii) achieve an LOQ for O2 that is commensurate with the specifications imposed by many pipeline operators, which are generally around 10 µL/L.
The suitability of the methodology and sampling technique developed by Qa3 has been successfully witness demonstrated to BP’s CATS Terminal and validated using a bespoke synthetic CATS entrant gas mixture with certified oxygen content.
The O2 in this synthetic mixture determined by Qa3 was found to be 9.2 µL/L, which was in very good agreement with the certified value (9.5 µL/L) taking into account the uncertainty associated with the method (± 1 µL/L or ± 10% relative, whichever is the greater).
For hydrocarbon gas samples, the limit of detection (LOD) for oxygen determination following the Qa3 method is 0.1 µL/L; however, the practical limit of quantification (LOQ) is of the order of 1 µL/L.
- Guaranteed true LOQ for O2 of 1 µL/L ppm.
- No interference from H2S (up to 100 µL/L).
- No interference from CO2.
- H2S & CO2 quantified as part of standard analysis.
- Method approved for BP’s CATS Terminal entrants.
- LPG module available on request