inquiry about VFA internal standard

[badiss]

i am using FFAP column to analyze VFA volatile fatty acid (C2-C6)( n- and iso-) in waste water .
what can i use as internal standard ? tried many substnce between C2 and C6,and it has a peak interfere with the VFA i want to detect !!!!
is (caprylic) octanoic acid C8 (low dissolution in water to achieve the desire concentration - 20 mmol-) appropriate ?
any idea ???
thanx every one

[AICMM]

badiss,

Don't do VFA but someone else posted here an application that uses crotonic acid. Since no else has posted, I thought I would offer it as a suggestion.

Best regards,

AICMM

[Consumer Products Guy]

I don't see why C7 or C8 fatty acid wouldn't work at those low concentrations, likely worth a try. Or 2-ethylhexanoic acid.

[Peter Apps]

Any internal standard needs to mimic the behaviour of the analytes. The problem with the short chain VFAs is that the only things that mimic their behaviour are other short chain VFAs, which are already present in the sample and even then the different molecules have markedly different properties (e.g. pH vapour pressure).

How about a fluorinated analogue ?

Peter

[badiss]

thank you all for respond
solubility of c8 is 0.068 g/100g water and the wanted concentration need 0.2884 g/100g water ( if i am not mistaken ) ,just to check if it is accurate to use c8 !!
the standard chromatogram for VFA shown below

http://postimage.org/image/17v6w5af8

but practically the peak is wide at low temp and overlapping occur at high temp ,peaks not completely separated