On-line pervaporation-capillary electrophoresis for the determination of volatile acidity and free sulfur dioxide in wines

Abstract

Pervaporation has been coupled on-line to capillary electrophoresis (CE) by a simple interface consisting of a modified CE vial. The approach allows volatile analytes to be removed and injected into the capillary meanwhile the sample matrix remains in the pervaporator. By this approach volatile acidity and free sulfur dioxide have been simultaneously determined in wines. The detection limits (LODs) are 1.25 and 5.00 microg/mL, the quantification limits 4.12 and 16.50 microg/mL, and the linear dynamic ranges between LOD and 50 microg/mL and between 0.1 and 0.9 g/L for free sulfur dioxide and volatile acidity, respectively. The repeatability and within laboratory reproducibility, expressed as relative standard deviation (RSD), are 1.61% and 3.00% for free sulfur, and 3.35% and 4.58% for volatile acidity, respectively. The optimal pervaporation time and the time necessary for the individual separation-detection of the target analytes are 6 and 5 min, respectively. The analysis frequency is 7 h(-1) and the sample amount necessary is less than 7 mL. The proposed method and official methods for the analytes were applied to 32 wine samples. A two-tailed t-test was used to compare the methods, which yielded similar results. The errors, expressed as RSD for the two parameters, ranged between 1.3 and 4.1%.

Recent trends in CE of inorganic ions: From individual to multiple elemental species analysis

“…Pervaporation has been coupled online to CE using a simple interface (a modified CE vial) that allowed volatile analytes (e.g., HSO À 3 ) to be isolated and interferences from complex matrices thus avoided [88]. Another option when the performance of a CE system can be improved at the stage of sample introduction concerns the application of flow injection (FI)-CE systems [89].…”

Novel Integrated Flow-Based Steam Distillation and Titration System for Determination of Volatile Acidity in Wines

“…It was found that using 28 mL of water for SD resulted in collecting about 25 mL of distillate, therefore this volume of the sample after distillation was obtained in further studies. These volumes ensured that all the analyte was transferred to the distillate, hence, unlike other methods [21][22][23][24][25][26][27][28], there was no need to calibrate the system. There was no significant difference observed between the results obtained for different sample volumes, but due to the low relative error of the obtained results and better precision, sample volume of 6 mL was selected.…”

“…Many flow-based methods were developed to determine titratable acidity in wines [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. However, only a few of them were simultaneously adapted to VA determination [21][22][23][24][25][26][27][28]. The procedure of VA determination is laborious and time-consuming.…”

“…It includes two stages: the separation of volatile fraction and the VA determination. To improve and automate these processes, membrane-based methods utilizing pervaporation (PV) [22][23][24][25] or gasdiffusion (GD) [21,[26][27][28] modules were implemented using FIA [21][22][23][24]27] or SIA [25,26] systems. The systems employed electrophoretic separation [22] and spectrophotometric [21][22][23][24][25][26], conductometric [21] detection, bulk acoustic wave-impedance sensor [27], or pH-ISFET (Ion-Sensitive Field Effect Transistor) [28].…”

“…The reaction product formed in an acceptor solution was transported to the spectrophotometric detection system, where the change of the color of BTB in the presence of the acidity compounds was monitored [25,26]. Using the PV systems, the VA was determined in the range of 0.1-0.9 g L −1 [22][23][24] or 0.1-1.5 and 1.5-6.0 g L −1 [25,29] with precision reported only in two methods (relative standard deviation, RSD) at 25% [22] and 5% [25]. Using the GD systems, the VA was determined generally up to 0.6 [27] or 1.1 g L −1 [21,26] with precision lower than 1.0 [21] or 5.1% [26].…”