Semiautomatic Flow-Injection Method for Determination of Volatile Acidity in Wines

Abstract

A flow-injection (FI) method based on analytical pervaporation was assessed for its routine use in the determination of volatile acidity in winery laboratories. The new method was compared with both the official method and the Mathieu method, which is most often used in Spanish wineries, by testing 30 different wines, including young and aged, and sweet and dry wines from Montilla-Moriles appellation d'origine. The robustness of the new method was established, and then all 3 methods were studied in terms of range of linearity and regression of the calibration curve, repeatability, reproducibility, sensitivity, detection and quantitation limits (LOD and LOQ, respectively), and time of analysis. The FI method surpassed the Mathieu method in reproducibility and both the Mathieu and official methods in LOD and LOQ and sensitivity; it also required less personnel involvement and shorter analysis time. The statistical criteria established by the Office International de la Vigne et du Vin were applied to the data and the results obtained indicated that the differences between the analytical parameters of the 3 methods are not significant and can be applied indistinctly. The correlation of the methods was studied by taking them 2 by 2, and the corresponding equations, coefficients, and deviations confirmed the statistical results. Thus, the new method can be used in winery laboratories with clear advantages over its 2 counterparts (the routine and official methods).

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

“…The developed novel, automated flow-based system with spectrophotometric detection for determination of VA integrates procedures of steam distillation to separate volatile acids and titration for their determination. Comparing with other methods reported in the literature, they usually use pervaporation or gas diffusion for separating volatile acids [21][22][23][24][25][26][27][28].…”

“…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].…”