| Autor: |
Liao PH; Department of Chemistry , National Tsing Hua University , 101, Section 2, Kuang-Fu Road , Hsinchu 30013 , Taiwan.; Department of Applied Chemistry , National Chiao Tung University , 1001 University Road , Hsinchu 300 , Taiwan., Yang HH; Department of Chemistry , National Tsing Hua University , 101, Section 2, Kuang-Fu Road , Hsinchu 30013 , Taiwan.; Department of Applied Chemistry , National Chiao Tung University , 1001 University Road , Hsinchu 300 , Taiwan., Wu PC; Department of Chemistry , National Tsing Hua University , 101, Section 2, Kuang-Fu Road , Hsinchu 30013 , Taiwan.; Department of Applied Chemistry , National Chiao Tung University , 1001 University Road , Hsinchu 300 , Taiwan., Abu Bakar NH; Department of Chemistry , National Tsing Hua University , 101, Section 2, Kuang-Fu Road , Hsinchu 30013 , Taiwan., Urban PL; Department of Chemistry , National Tsing Hua University , 101, Section 2, Kuang-Fu Road , Hsinchu 30013 , Taiwan.; Frontier Research Center on Fundamental and Applied Sciences of Matters , National Tsing Hua University , 101, Section 2, Kuang-Fu Road , Hsinchu 30013 , Taiwan. |
| Abstrakt: |
Simultaneous distillation-extraction (SDE) using the Likens-Nickerson apparatus is a convenient technique used to isolate volatile organic compounds (VOCs) from complex liquid matrices. The technique combines steam distillation with solvent extraction. While analytical extractions are normally followed by off-line separation/detection, it is advantageous to couple extractions on-line with separation and detection systems that are employed in the same analytical workflow. Here, we have coupled the Likens-Nickerson apparatus on-line with a gas chromatograph hyphenated with a mass spectrometer. For that purpose, we have devised an automated liquid transfer setup comprising a peristaltic pump, control unit, customized transfer vial with a drain port, and an autosampler arm to deliver liquid extract aliquots at defined time points. The on-line SDE-GC/MS system enables one to record real-time extraction profiles. These profiles reveal extraction kinetics of various VOCs present in the extracted samples. The data sets were fitted with the first order kinetic equation to obtain numeric values characterizing the extraction process (rate constants ranging from 0.21 to 0.01 min -1 for the ethyl esters from C 6 to C 19 ). A comparison of on-line and off-line results reveals that the on-line system is more dependable, while the off-line analysis leads to artifacts. To demonstrate the operation of the on-line SDE-GC/MS system, we performed analyses of selected real samples (beer). The real-time data sets revealed extraction kinetics for VOCs present in these samples. The devised extraction-analysis system allows the analysts to make an evidence-based decision on the extraction time for different groups of analytes in order to maximize extraction yield and minimize analyte losses. |
