HPLC/MS compared to GC/FID (MDHS 83/2) for analysis of resin acids in wood dust

Objectives
Comparison of our HPLC/MS method with a GC/FID method for determination of abietic acid (AA), dehydroabietic acid (DHAA) and 7-oxodehydroabietic acid (7-OXO) in wood dust.

Results
The correlation for DHAA between the two methods was good (r2 = 0.862, Figure 1).
On average the amount of 7-OXO, estimated in a wood dust sample using our HPLC/MS method was 50 % of the amount determined using the GC/FID method (regression: y = (0.45 ± 0.09)b + (0.16 ± 0.33), 95 % confidence, r2 = 0.862).
Due to interference by an unknown compound during analysis using the GC/FID method no correlation for AA could be calculated.

Större bild

Methods

Samples
25 air samples were collected on PVC-membrane filters at wood pellet production plants in Sweden. The dust loading were <0.1 – 16 mg. Each filter was cut into three subsamples prior to analysis.

HPLC/MS
The subsample was extracted with methanol with dehydroabietic acid-6,6-d2 as internal standard, filtered (0.22 μm) and analysed. The HPLC/MS analysis was run in SIM-mode. Quantification was done using reference substances in methanol.

GC/FID (MDHS 83/2)
The subsample was extracted with diethyl ether. A part of the solution was evaporated to dryness and methylated in methanol at 75 °C prior to analysis. Standard compounds in diethyl ether were used for quantification and they were treated as a wood sample.

CONCLUSION
The two methods correlate well and the differences in resin acid determination between the HPLC/MS and the GC/FID method is probably due to differences in extraction conditions and specificities, which warrants further investigation.