Anthrone method combined with adsorption of interferents as a new approach towards reliable quantification of total carbohydrate content in pyrolysis bio-oils

Carbohydrates are a group of compounds abundantly present in pyrolysis bio-oils. Their quantitative analysis however presents many challenges such as possible co-elution with other oxygenates when liquid chromatographic methods are used. For a cheaper and faster analysis, spectrophotometric methods are a convenient alternative. Most of the absorption spectrometry-based methods stem from the reaction scheme, where the carbohydrates are converted into furfural or 5-hydroxymethylfurfural (HMF) derivatives and simultaneously react with colorizing agents such as phenol or anthrone. Alternatively, the produced compounds can be determined in the UV region without the addition of colorizing agent. An obvious problem arises when these furanic compounds are already present in the mixture, which is the case with most biomass-based pyrolysis bio-oils. In this study, we quantified the responses of 26 potential interferents that are expected to be present in the water-soluble fraction of bio-oils as well as 13 different carbohydrates. To mitigate the interferences, we used styrene-divinylbenzene polymeric resin adsorbents to separate the less polar interferents from the aqueous bio-oil extract and naturally formed bio-oil aqueous phases. A derivatization-GC-MS method was used as a reference for comparison of the results. We found that the adsorption step is crucial for acquiring more precise and accurate results. The anthrone method was the least susceptible to interferences and simultaneously produced results that were the closest to the reference GC-MS method. Statistical analysis showed no significant differences between the optimized anthrone method and the reference GC-MS method.