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Optimisation of the on-fibre derivatisation of volatile fatty acids in the simultaneous determination together with phenols and indoles in cow slurries.

Analytical and bioanalytical chemistry (2007-09-06)
J Larreta, A Usobiaga, N Etxebarria, G Arana, O Zuloaga
ABSTRACT

The on-fibre derivatisation of volatile fatty acids (VFAs) using N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA) was optimised in the simultaneous determination of VFAs together with phenols and indoles by headspace solid-phase microextraction (SPME)-gas chromatography-mass spectrometry. Firstly, the nature of the SPME fibre was optimised and four different fibres were studied (100 microm polydimethylsiloxane, 85 microm Carboxen/polydimethylsiloxane, 5/30 microm divinylbenzene/Carboxen/polydimethylsiloxane and 85 microm polyacrylate). The optimum fibre (50/30 microm divinylbenzene/Carboxen/polydimethylsiloxane) was used to study the exposure time of the fibre to the derivatisation agent and the desorption time and temperature. Firstly, a factorial design was built but since the three variables had a significant effect, a central composite design was used to build the response surfaces. The best signals were obtained after the exposure of the fibre in the headspace of the MTBSTFA derivatisation reagent for 1 h and desorption at 300 degrees C for 9 min. The determination of underivatised phenols and indoles was not affected by the presence of the derivatisation reagent in the fibre.

MATERIALS
Product Number
Brand
Product Description

Supelco
Tenax® TA / Carboxen® 1018, glass TD tube, preconditioned, O.D. × L 1/4  in. × 3 1/2  in., Sealed with (Swagelok® End-Fittings), pkg of 10 ea
Supelco
Carboxen®-1010 PLOT Capillary GC Column, L × I.D. 30 m × 0.53 mm, average thickness 30 μm
Supelco
Carboxen® Adsorbent, matrix Carboxen® 569, 20-45 mesh, bottle of 10 g
Supelco
ORBO 78 HBr on Carboxen® 564 specially cleaned (20/45), 400/200 mg, W,W,W separators, O.D. × L 6 mm × 110 mm, pkg of 25 ea
Supelco
Carboxen®-1006 PLOT Capillary GC Column, L × I.D. 30 m × 0.53 mm, average thickness 30 μm
Supelco
Carboxen® Adsorbent, matrix Carboxen® 1000, 60-80 mesh, bottle of 10 g
Supelco
ORBO 90 Carboxen® 564 (20/45), 160/80 mg, W,F,F separators, O.D. × L 6 mm × 75 mm, pkg of 25 ea, for analyte group MEK (methylethyl ketone)
Supelco
Carboxen®-1010 PLOT Capillary GC Column, L × I.D. 30 m × 0.32 mm, average thickness 15 μm
Supelco
Carboxen® Adsorbent, matrix Carboxen® 569, 20-45 mesh, bottle of 500 g
Supelco
Carboxen®-1006 PLOT Capillary GC Column, L × I.D. 30 m × 0.32 mm, average thickness 15 μm
Supelco
Carboxen® Adsorbent, matrix Carboxen® 1003, 40-60 mesh, bottle of 10 g
Supelco
Carboxen® Adsorbent, matrix Carboxen® 1000, 40-60 mesh, bottle of 50 g
Supelco
Carboxen® Adsorbent, matrix Carboxen® 563, 20-45 mesh, bottle of 10 g
Supelco
Carboxen® Adsorbent, matrix Carboxen® 564, 20-45 mesh, bottle of 10 g
Supelco
Carboxen® 1000 Reversible SPE Tube, 200 mg/mL, pk 30
Supelco
Carboxen® 572 for Tobacco Smoke, Adsorbent Bed Wt: (300 mg), cartridge volume 3 mL, pkg of 10 ea
Supelco
ORBO-93 Sorbent Tube, matrix Carboxen® 1000, ORBO tube I.D. × L 6 mm × 95 mm, Bed B 90 mg, Bed A 180 mg, 60/80 mesh, pkg of 25 ea
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 75 μm (CAR/PDMS), for use with manual holder, needle size 24 ga
Supelco
SPME fiber assembly Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS), needle size 24 ga, for use with manual holder
Supelco
Carboxen® 569, O.D. × L 1/4  in. × 3 1/2 , glass TD tube, fritted, Sealed with Brass Endcaps, preconditioned, pkg of 10 ea
Supelco
Carboxen® 572 for Tobacco Smoke, Adsorbent Bed Wt: 300 mg, cartridge size 3 mL, pkg of 50 ea
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 75 μm (CAR/PDMS), needle size 23 ga, for use with manual holder
Supelco
SPME fiber assembly Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS), needle size 24 ga, StableFlex, for use with manual holder/autosampler
Supelco
Carboxen® 569, glass TD tube, fritted, O.D. × L 1/4  in. × 3 1/2  in., preconditioned, pkg of 10 ea
Supelco
Carboxen® Adsorbent, matrix Carboxen® 564, 20-45 mesh, pack of 144 × 290 mg
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 75 μm (CAR/PDMS), needle size 24 ga, for use with autosampler
Supelco
SPME fiber assembly Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS), needle size 24 ga, StableFlex, for use with autosampler
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 75 μm (CAR/PDMS), needle size 23 ga, for use with autosampler
Supelco
SPME fiber assembly Divinylbenzene/Carboxen/Polydimethylsiloxane (DVB/CAR/PDMS), needle size 23 ga, StableFlex, for use with manual holder/autosampler, fiber L 2 cm
Supelco
SPME fiber assembly Carboxen/Polydimethylsiloxane (CAR/PDMS), df 85 μm (CAR/PDMS), needle size 24 ga, for use with manual holder, StableFlex fiber