Mould growth on building materials - Statens Byggeforskningsinstitut

2.6.1.2 Gas chromatography
As previously mentioned, mycotoxins are generally not volatile and hence gas chromatographic
detection of them will always have to face instability problems during injection and
chromatography 344 . On the other hand capillary GC gives 10-100 times higher separation
power 345 than LC (packed column) and runs very stable with flame ionisation, electron capture
detection (ECD), and MS, which are significantly more sensitive than UV and refraction
index detectors used in LC.
Almost all GC methods for mycotoxins start with derivatisation of free OH and N-H groups 346
to decrease the thermal lability. Acid groups are usually methylated, and alcohol groups are
reacted to their TMS ether or esterficied to their acetyl or pentafluoropropionyl esters 340,344 .
GC methods on most mycotoxins have been published, inter alia AFB1 and ST 346 , Alternaria
mycotoxins 347 , penicillic acid 348 , patulin 349 , the backbone of the AAL toxins and the fumonisins
350 , and especially the TR 340 . The latter, is the only group where GC-MS or GC-ECD has
been the primary analytical method. 351-365 .
2.6.1.2.1 GC-MS for trichothecenes
The use of MS detection of the pentafluoropropionyl- (PFP) or heptafluorobuturyl (HPB) esters
will give the highest sensitivity if the MS has a mass range > m/z 800 340 . These derivatives
can be formed by the imidazoles PFPI and HFBI respectively or acid anhydrides PFPA
and HFBA respectively, although the latter needs a nucleophilic catalyst such as triethylamine,
dimethylaminopyridin or imidazole 340 . Unfortunately the TB react slowly with both types
of reagents and can undergo isomerisation giving more than one peak 352 . The fluorinated
derivatives can be detected selectively to very low levels using negative ion chemical ionisation
(NICI)-MS or ECD, but also positive electron impact ionisation (EI + )-MS or positive
chemical ionisation (PCI)-MS can been used 360,366,367 .
TR lacking free OH groups cannot be detected using NICI and ECD unless they are hydrolysed
to their parent alcohols prior to derivatisation 353,360 .
2.6.1.2.2 GC-MS for sterols
GC-MS has also been used, usually based on an internal standard, such as cholesterol or
dehydrocholesterol 335,368 , as a isotope substituted standard is not commercially available. Erg
has usually been derivatised to its tertiary-butyldimethylsilyl or trimethylsilyl (TMS) ether to
reduce decomposition during injection and chromatography. On-column injection can also be
used to further reduce decomposition 330 , but this method requires cleaner samples and is not
as robust as splitless injection 368 .
2.6.1.3 High performance liquid chromatography
Since the late 1980s and the start of the 1990s HPLC have been the most important analytical
method for mycotoxins 337,369,370 .
The success of HPLC compared with the other methods have several reasons. Firstly the
instruments have decreased in price as well as getting easier to maintain. They are easily
automated and PCs can sample and do automated detection of target compounds. Many
column materials are available from many different manufactures, and significantly larger
samples can be injected than in a GC. More over samples do generally not demand derivatisation
as GC does.
From the mid 1990s the use of HPLC with MS detection employing atmospheric pressure
ionisation techniques (API) 371 such as electrospray 372 and atmospheric pressure chemical
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