Chromatography
The analysis of volatile fatty acids by Headspace GC-FID Dr Claire Rossouw1 , Mr Jonathan Angove2
1 Omex Environmental, Estuary Road, King’s Lynn, UK. 2 Ellutia Ltd, 200 Lancaster Way Business Park, Ely, UK.
Volatile fatty acids (VFAs) are analysed to aid in the optimisation of the anaerobic digestion process. The role of anaerobic digestion is the decomposition of organic matter and thus the production of gasses, such as methane and carbon dioxide.
The typical methods to analyse VFAs include titration, distillation, steam distillation and chromatographic.
Titration: Titration provides approximate results and is a quick analysis method. This is widely used in the treatment of wastewater to track the status of the microorganisms available.
Distillation: Distillation provides approximate results, though a signifi cant percentage of the VFAs may be lost during the analysis due to volatility of the various VFAs. As with titration, this is often used in wastewater treatment plants.
Steam distillation: This tends to exhibit greater recoveries of the VFAs and is more precise than the titration and distillation methods but is more time consuming.
Chromatographic techniques: These tend to give the most precise and accurate results, while having the capability of qualitatively and quantitively analysing each VFA.
Ellutia Ltd was approached by Omex Environmental to increase throughput and to reduce the consumable cost of their current, validated method. This method involved a pH adjustment of the samples, followed by a large volume liquid:liquid extraction prior to their
GC-FID analysis. As Omex Environmental is analysing VFAs between C2 and C6, it was proposed that a headspace analysis method could achieve similar results to the liquid:liquid extraction, but with the desired increase in productivity and also the elimination of the use of a solvent, hence the generation of hazardous solvent waste.
The equipment proposed was the Ellutia 500 series GC-FID with a CTC PAL-RSI mounted to perform the headspace sampling.
Method Summary
The liquid:liquid extraction involved a series of repeated steps involving sample acidifi cation, centrifugation and agitation, addition of an internal standard together with addition of a drying salt.
The headspace technique involved much fewer steps, with only sample acidifi cation, centrifugation, addition of an internal standard together with addition of a drying salt.
Results
Calibration curves were prepared for the analytes, correcting the area responses using the internal standard response.
10 15 20 25 30 35 40 45 50
0 5
0 500
Propionic Acid
Propionic Acid
y = 0.0233x + 0.4331 R² = 0.9931
1000 1500 Concentration (µg/mL) 2000 2500
INTERNATIONAL LABMATE - APRIL 2022
Area (mV/sec)
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
