Comparison of gas chromatography–mass spectrometry and high-performance liquid chromatography with coulometric electrode array detection for determination of alkylresorcinol metabolites in human urine

Alkylresorcinols (AR) are amphiphilic compounds present at high concentrations in the outer parts of wheat and rye kernels. Due to their specificity to whole grain and bran products of these cereals, AR and their metabolites have been proposed as biomarkers for intake of such foods. Two alkylresorcinol metabolites, 3,5-dihydroxybenzoic acid (DHBA) and 3-(3,5-dihydroxyphenyl)-1-propanoic acid (DHPPA), have previously been quantified in human urine using two different methodologies: high-performance liquid chromatography coupled to a coulometric electrode array detector (HPLC–CEAD) and gas chromatography in combination with mass spectrometry (GC–MS). In this study, these two methodologies were compared by analysing 114 urine samples from free-living Swedish subjects consuming their habitual diet. Data were evaluated by graphical investigation of difference-plots and statistical inference of agreement was assessed by weighted Deming regression analysis. The median DHBA concentrations were 11 μM (GC–MS) and 13 μM (HPLC–CEAD), respectively. Both difference-plot and regression analysis showed a small but statistically significant additive bias, with HPLC–CEAD resulting in a slightly higher DHBA concentration than GC–MS. The median concentration of DHPPA was 18 μM for both methods. Examination of the difference-plot of DHPPA did not indicate any systematic difference between the methods, but regression analysis showed small but statistically significant constant and proportional biases. The conclusion was that the two methodologies are equally suitable for analysis of alkylresorcinol metabolites in human urine and that any small systematic differences observed are most likely of limited practical importance.