[rajaijah]

I am trying to develop method for hydrocarbon fractions in water samples. I am having trouble with preparing a sample to analyse. When I have samples to analyse, I can understand the hexane extraction part and analysis with GC-MS and GC-FID.  But I would like to prepare a spiked sample for method validation. If I mix few drops of motor oil in water and shake it, I can not get an emulsion. Same if I add a little bit of methanol or acetone.

Is there a better way of preparing a spiked sample of HC in water? Any help appreciated.
Thanks

[Arkcon]

You might have better results if you selected hydrocarbons of the sort you expect to find in your water samples.  Besides that, your motor oil in water samples, after to allow the oil to separate, is there detectable levels of hydrocarbon dissolved in the water?

[rajaijah]

I am trying to develop method for petroleum hydrocarbon in water. A typical sample I would get would have the fractions found in motor oil, including BTEX.

[Stepan]

For low concentrations at ppb-ppm level: Dissolve reference materials in methanol and spike water with this solution to achieve desirable concentration. For high concentration, add oil + HC + surfactant to the water and sonicate it.

[rajaijah]

Thanks.

I would like to get a higher conc so I can analyse by fractions ( F1-F4G) . Any idea on what surfactant to use. I read somewhere that cetyl alcohol can be used.

[Stepan]

Number of surfactants is available from soap to alcohols and ethanol amines. You need to select one which: a) can be potentially present (or can be added)  in the water you are trying to purify, b) works in pH range of the water you are testing; c) doesn't interfere and is is not removed by the process you are working on.