A heating-assisted liquid-liquid microextraction (HA-LLME) procedure was developed as a new approach for pretreatment of complex sample matrix. The procedure was applied for HPLC-UV determination of preservative (benzoic acid) in juices. Menthol was investigated as an extractant for the HA-LLME. The procedure consists in heating of an aqueous sample in a polymeric vial with solid-phase menthol located at the bottom of extraction vial. The heating promotes the melting of menthol and its dispersion in a sample phase. The extractant drops are moving from the bottom to the surface of the sample, forming a liquid organic phase containing target analyte. Thus separation is taken place without centrifugation. It was found that menthol provides for microextraction of benzoic acid from fruit and berry juice samples with recovery from 93 to 117%. The conditions of the HA-LLME were optimized using factorial experimental designs. Under optimal experimental conditions the linear detection range was found to be 0.5–50 mg L⁻¹ with LOD at 0.15 mg L⁻¹. The HA-LLME with menthol allowed for significant improvement of the selectivity of benzoic acid determination. The advantages of the HA-LLME are the simplicity, low cost, and using of environmentally friendly extractant.

开发了一种加热辅助的液-液微萃取（HA-LLME）程序，作为预处理复杂样品基质的新方法。该方法用于HPLC-UV法测定果汁中的防腐剂（苯甲酸）。研究了薄荷醇作为HA-LLME的萃取剂。该程序包括在聚合物小瓶中加热含水样品，并在萃取小瓶底部放置固相薄荷醇。加热促进薄荷醇的熔化及其在样品相中的分散。萃取剂滴从样品的底部移动到表面，形成了包含目标分析物的液态有机相。因此，分离无需离心即可进行。发现薄荷醇可从水果和浆果汁样品中微萃取苯甲酸，回收率从93％到117％。HA-LLME的条件使用析因实验设计进行了优化。在最佳实验条件下，线性检测范围为0.5–50 mg L^-1的LOD为0.15 mg L ^-1。带有薄荷醇的HA-LLME极大地提高了苯甲酸测定的选择性。HA-LLME的优点是简单，低成本以及使用环保的萃取剂。