Application of a custom-synthesized molecularly imprinted polymer for the selective isolation of total glucose and fructose from `100%` fruit juice prior to instrumental analysis

Abstract

This thesis presents a novel sample preparation strategy that employed a custom-synthesized glucose – fructose (G-F) specific molecularly imprinted polymer (MIP) powder as an adsorbent for the simultaneous, selective extraction, isolation, pre-concentration of total glucose and fructose from the complex and `dirty` sample matrix of ‘100%’ fruit juices in order to improve their accurate analysis. The ‘100%’ fruit juice samples were purchased from retail shops in Palapye, Botswana. Scanning electron microscopy (SEM) revealed G-F MIP particles that were somewhat spherical with an estimated particle size of > 20 μm. Both of which are excellent morphological characteristics for adsorption. The prepared G-F MIP powder demonstrated high selectivity, effective extraction and isolation for glucose and fructose from real samples of `100%` fruit juice samples as evidenced by the calculated high extraction efficiencies (EEs) of over 90%, with low percentage relative standard deviations (%RSD) of below 7% for n = 6, for both glucose and fructose when compared to the low EEs of below 28% by the non-imprinted polymer (NIP), regarded as the control. Furthermore, the G-F MIP showed lower selectivity towards the analogue molecules; maltose and lactose as supported by the low EEs of below 34%. All binding studies were performed at optimal conditions; 60 mg and 20 min for sorbent dose and reaction time respectively. With the high affinity for glucose and fructose, the selective sample preparation strategy proposed herein presented itself as a potential procedure to be employed to improve the accurate analysis of juices adulterated by artificial sugar sweeteners that are usually illegally added to the so-called `100%` fruit juices by producers to improve their taste.