An environmentally-friendly gas chromatography technique from PerkinElmer offers an alternative to conventional infrared spectrometry
Historically, infrared spectrometry has been used to analyse low levels of hydrocarbons in water, extracting the hydrocarbons using solvents such as Freon or CCl4.
Responding to environmental and health concerns, an alternative method using n-Pentane extraction in combination with gas chromatography and flame ionisation detection has been approved.
PerkinElmer, in partnership with Westlab Services, has tested Method ISO 9377-2 against the IR method at all off-shore installations in Norway. The method is applicable to non-polar hydrocarbons with retention times between nC10 and nC40, which are extracted with n-pentane, do not adsorb on Florisil and can be detected by FID on a GC.
The method was developed in co-operation with the oil companies, and sample preparation is similar to the IR method.
PerkinElmer has now refined the method to eliminate the time-consuming sample concentration stage.
An AutoSystem XL GC, fitted with the Programmable Spilt/Splitless Injector and PreVent, allows the injection of up to 100 microlitres of sample into a special large volume liner.
The bulk of the solvent is purged off through the split vent before it is closed and the injector temperature is increased rapidly, vaporising the hydrocarbons onto the column. This prevents column overload from the solvent, while retaining the 'solvent effect' to produce sharp peaks.
Use of the PreVent technique removes the entire concentration step, and simplifies the basic procedure.
Calibration of the system is done on a weekly to monthly basis, with a run time for one sample of just 15 minutes.
