Appendix N Trace Level Measurements - Thermo Scientific SOLA II User Manual

Appendix N
Trace level measurements
Description of the SOLA II Trace
The SOLA II Trace analyser is a modified version of the standard SOLA II, all characteristics of the
SOLA II operation are applicable to the SOLA II Trace, it is available for both liquid and vapour
samples; the primary function of the SOLA II Trace is to implement improvements to the limits of
detection performance at low concentrations of total sulphur.
The SOLA II Trace utilizes a modified analytical PUVF bench for the determination of total sulphur
in liquid and vapour samples, the modification consists of replacing the standard PUVF bench with a
version configured with an additional set of reflectance mirrors. The function of the additional set of
mirrors is to enhance the selectivity of UV light at wavelengths specific to the excitation of SO2
molecules.
Calibration method
The SOLA II requires a two-point linear calibration. High Calibration is conducted with a standard
that is, ideally, close to the full scale range of the analyzer. Low calibration is commonly conducted
by zeroing with no injections, for the SOLA II Trace it is recommended that a low concentration
standard is used instead of no injections, implementation of the low calibration method is also
subject to the combustion gas used with the SOLA II Trace, refer to the next paragraph.
Combustion gas for the SOLA II Trace
Results reported from the field as well as measurements conducted in the factory indicate that, when
the sample matrix is combustible and when air (rather than heliox) is used for combustion of the
sample in the pyrolyzer, re-zeroing with no injections can lead to significant overestimation of sulfur
content of low-level samples on SOLA II Trace. In order to prevent incorrectly reported sulphur
levels one of two calibration methods can be selected dependant on the combustion gas.
Method a: the analyzer is calibrated with both low and high calibration standards that are
representative of the sample matrix – e.g. to calibrate a SOLA II Trace for an ethylene stream,
perform low calibration on pure ethylene and high calibration on standards made up in ethylene.
Recommendation
Method b: heliox (21mol% oxygen in helium, zero grade) is used in place of clean air - this has been
observed to give satisfactory results when the analyzer is zeroed with no injections.
Lowest recommended
Model full scale range
SOLA II Trace 2ppm (2,000 ppb)
Table N-1 Performance specification table for the SOLA II Trace
Thermo Fisher Scientific
Highest recommended
full scale range ‐ Limit of Detection
consult factory for (2 injections per
higher ranges minute)
5ppm (5,000 ppb) 1.25% of full scale 25
Limit of Detection
at lowest available Repeatability with 2
range (in ppb) injections per minute
1% of range
SOLA II User Guide N-1