ABSTRACT
In this work, it is shown that the quartz crystal microbalance (QCM) can be a powerful and simple tool for quick and precise kinetic enzymatic assays. This is shown by measuring immobilized acetylcholinesterase (AChE) activity with variations of pH as a case study.
Subject(s)
Acetylcholinesterase/chemistry , Quartz Crystal Microbalance Techniques/methods , Biosensing Techniques , Enzyme Assays/methods , Hydrogen-Ion Concentration , KineticsABSTRACT
Gas-diffusion microextraction (GDME) is an innovative technique that combines the advantages of membrane-aided gas-diffusion with microextraction concepts. GDME makes uses of a novel portable and low-cost device that comprises a small, commercially available, semi-permeable membrane. Furthermore, if derivatization is integrated into the GDME concept, considerable enrichment factors can be obtained. It may become a powerful tool for any analyst who intends to quantify volatile and semi-volatile analytes in various kinds of matrices. The analysis of vicinal diketones in beer was used as a case study to show GDME applicability and capabilities. Vicinal diketones were derivatized with o-phenylenediamine and then determined by HPLC-UV. Obtained results showed good repeatability and precision with extraction periods at the minute time span.
ABSTRACT
In this work, a recently developed extraction technique for sample preparation aiming the analysis of volatile and semi-volatile compounds named gas-diffusion microextraction (GDME) is applied in the chromatographic analysis of aldehydes in beer. Aldehydes-namely acetaldehyde (AA), methylpropanal (MA) and furfural (FA)-were simultaneously extracted and derivatized with 2,4-dinitrophenylhydrazine (DNPH), then the derivatives were separated and analyzed by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was confirmed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass-spectrometry detection in the negative ion mode (HPLC-APCI-MS). The developed methodology showed good repeatability (ca. 5%) and linearity as well as good limits of detection (AA-12.3, FA-1.5 and MA 5.4microgL(-1)) and quantification (AA-41, FA-4.9 and MA 18microgL(-1)); it also appears to be competitive in terms of speed and cost of analysis.
Subject(s)
Aldehydes/analysis , Beer/analysis , Chemical Fractionation/methods , Chromatography, High Pressure Liquid/methods , Mass Spectrometry/methods , Acetaldehyde/analysis , Acetaldehyde/chemistry , Aldehydes/chemistry , Furaldehyde/analysis , Furaldehyde/chemistry , Linear Models , Sensitivity and SpecificityABSTRACT
A membraneless extraction module (MLEM) for the sample preparation of volatile compounds and its use for the chromatographic analysis of vicinal diketones in beer are reported. The extraction process is based on the same principles of gas diffusion (GD) and pervaporation (PV); however it does not use a membrane. This module has a lower chamber where the sample continuously flows, while volatile compounds evaporate to the headspace. Inside the module there is a suspended small reactor, where a small volume of a suitable acceptor solution is placed. This extraction module was tested in the determination of vicinal diketones (VDKs) in beer (CV=5%; LOD=4 microg L(-1)), showing applicability with real samples. Several parameters of the extraction process, such as temperature, sample flow and extraction time, were studied and optimized. This module proved to be a good tool for the sampling of volatile compounds, since the extraction is made without using a membrane avoiding all the robustness problems related with its use.
