Broad Peaks

[Rob Burgess]

What are your samples - we may be able to give you a clearer direction to head in about what sample solvent you may be able to use. How about trying 100% AcN or MeOH as the solvent?

[hplc.chrom]

Thanks Rob

My analytes are PAHs and I use isooctane to extract them from plant materials.

[Mark Tracy]

I have tried to do that application. It is quite hard. Direct injection just won't cut it. The attempt to improve detection limits by large volume injection is defeated by the gross loss of efficiency.

If you are not afraid of complexity, there is an online SPE method that uses an exotic DACC concentrator column from Varian. This column will selectively extract PAHs from aliphatic solvents. After washing with iPA, it is switched inline with an analytical column (Varian again) for elution. Believe it or not, this is the basis of a well-established method in Europe. Dionex has an example implementation of the method: www1.dionex.com/en-us/webdocs/7503_summit_x2_poster_pah_application_isc04_sep042.pdf

[JI2002]

You can check out EPA method 8310 in which methylene chloride is used for extraction, then concentrated and finally exchanged to ACN.

Methylene chloride is a stronger solvent than isooctane, you can achieve better extraction efficiency by using MECL2.

By concentrating the extract, you can use smaller injetion volume for HPLC analysis.

Exchanging MECL2 to ACN will solve the immiscibility problem.

[Bruce Hamilton]

I'd agree with JI2002, unless there is a very good reason not to follow a standard procedure for PNAs ( eg EPA methods ), it's worthwhile to follow the method concept, even if you don't follow the detail ( such a the standard mixtures, internal stds etc ). Exchanging your solvent seems a very good idea.

As most PNAs are medium to low volatility, you should be able to cautiously concentrate your samples by evaporation.

The question about acceptable precision can only be resolved by the person using the the data. What's acceptable for a quick research scoping project probably will not be acceptable to a regulator being asked to use the data to grant consents or licences.

Please keep having fun,

Bruce Hamilton

[hplc.chrom]

Thanks a lot for all of you for the very nice discussion!

I think it is better to stop my game and follow one of the standard methods instead.

Thank you all again.