Dear Guruprasad,
Ideally the results are rather similar. However, some differences are obvious, due to many different factors.
With head space (HS) type gas extraction, used typically with GC, relatively small portion of gases are extracted from oil and measured. The total gas concentrations are then calculated using gas solubility coefficients. Those calculations increase uncertainty and deviation between different methods. However, the biggest uncertainty is always related to oil sample quality i.e. how it’s been collected, transported, stored and handled in laboratory.
Monitors again have their own uncertainties. However, monitors tend to provide better and more consistent gas trending over time.
This means there is often some bias between the different methods, but the trend should be similar.
Best regards,
Senja Leivo