Posted By Dave Morris I have recently measured an airborne contaminant involving hydrocarbons, specifically Alkanes. My measurement is in PPM but EH40 (page 52) suggests a guidance value of 1200mg/m3 for alkanes. My problem therefore is the need to convert mg/m3 to ppm. For my online conversion calculator I require the molecular weight of Alkanes, for this I require the chemical formula for Alkanes so I can add the atomic weights of all atoms present in the chemical formula. The manufacturer has not specified this chemical formula on the safety data sheet. Does anyone know of another way (other than sampling in mg/m3) that I can find out these molecular weights?

Posted By Adrian Watson Dave, Unfortunately, you cannot convert between the two unless you have either a full and complete analysis of the material sampled by GCMS or know the average molecular weight. The Molecular Weights can be obtained from a chemistry database or textbook. Regards Adrian

Posted By Dave Morris Paul, the CAS no is 90622-57-4 with a 50-100% concentration. The boiling point is 173C. How does this help me?

Posted By Paul Leadbetter Dave From the CAS number, your solvent mixture is otherwise known as Isopar G which, if memory serves me correctly, is a mixture of C10 - C11 alkanes and cycloalkanes. The boiling point of n-decane is 174ºC which fits closely with the bp you quote. The methylnonanes boil at 165 - 168, the dimethyloctanes at 155 - 161 and undecane at 196. In the absence of compositional data (although you may be able to find that on the internet), you can get a rough conversion by assuming that the solvent is n-decane. Paul

Posted By Dave Morris Bob It's a close loop solvent degreasing process where the hydrocarbon is heated in an ultrasonic bath. I believe the chiller unit is malfunctioning and I wanted to ensure we didn't exceed any WEL's.