TRACE METHANOL IN PROPYLENE CONCENTRATES BY GAS CHROMATOGRAPHY: ASTM D4864
EXPLANATION
Methanol is a common impurity in propylene. It can have a deleterious effect on various processes that use propylene as a feedstock. The range of this method is approximately 4 to 40 mg/kg.
TEST SUMMARY
A known weight of water is pressured into a sample cylinder containing a known amount of liquefied propylene. The contents in the cylinder are shaken and the water/methanol phase is withdrawn. A reproducible volume of the extract is then injected into a gas chromatograph equipped with either a thermal conductivity or a flame ionization detector. The methanol concentration is calculated from the area of the methanol peak using calibration and extraction factors obtained from synthetic blends of known methanol content. There are no interferences using the GC columns referenced in this test method. However, any water-soluble component that co-elutes with methanol on any other GC column used would interfere.
TEST PRECISION
Repeatability: 2.4
Reproducibility: 8.0
Above precision values are expressed in terms of the maximum allowable ratio of the larger to the smaller result. Since there is no accepted reference material suitable for determining the bias for this procedure, the bias is not available.
