Simplified measures of copper fractions in wine: colorimetric and filtration‐based approaches

Abstract

Background and Aims Simple methods for determining Cu forms in wine do not currently exist. This study demonstrates the relevance of measuring a specific fraction of Cu in wine, and introduces simplified methods for its measurement utilising either colorimetry, or filtration in combination with routine measures of total Cu in wine. Methods and Results Electrochemically detectable Cu provided a threshold level of Cu that related directly to the accumulation of free hydrogen sulfide and free methanethiol in bottled wines. A simple colorimetric method using bicinchoninic acid was optimised to allow a rapid approximation of this fraction of Cu in white wine. By modification of the measurement conditions, an extra fraction of Cu associated with the partial release of Cu from thiols could also be quantified. The use of diatomaceous earth depth filters to isolate these fractions of Cu was also assessed. After passing red wine through the filters, the concentration of Cu in the filtrate correlated well with the electrochemically detectable Cu. Alternatively, for white wine the concentration of filtrate Cu overestimated this fraction of Cu and this was attributed to its inability to distinguish sulfhydryl‐free Cu from Cu loosely bound to thiols. Conclusions Multiple and simplified approaches have been devised to allow measurement of Cu fractions in wine. Significance of the Study These methodologies will allow an important fraction of Cu in wine to be measured with a spectrophotometer.

Comparison of Techniques for the Quantitation of Reductive Aroma Compounds in White Wine: Links to Sensory Analysis and Cu Fractions

“…Consistent with past results 15,16 and the known complexation reaction between Cu(II) and H 2 S, once the combined Cu fractions I and II fell below 0.02 mg/L, a link to potential GC-SCD free H 2 S accumulation (i.e., >1.0 μg/L) was evident (Figure 4a). This was also demonstrated for the first time when free H 2 S was measured by GDT (Figure 4b).…”

“…Total concentrations of Al, Cu, Fe, Mn, Mg, and Zn were determined by ICPOES at Laboratory 2 as described by Kontoudakis et al 14 The colorimetric analysis of white wine for total Cu and Cu fractions was determined at Laboratory 2 as described by Kontoudakis et al 22 and Clark, Zhang, and Kontoudakis. 16 In brief, total Cu concentration was measured after incubating 10 mL of wine with 12 mg/L bichinchonic acid (BCA), 380 mg/L ascorbic acid and 10 mg/L silver(I) for 30 min, while Cu fractions I and II were determined after 0 and 30 min of incubation of wine with 12 mg/L BCA and 380 mg/L ascorbic acid but without silver(I) addition. The concentration of Cu fraction III was calculated as the difference between the total Cu concentration and the combined concentrations of Cu fractions I and II.…”

“…In parallel with the advances made in the measurement of the sulfhydryl compounds in wine (Table ), methodologies for the quantitation of Cu fractions in wine were developed that were inextricably linked to the measured free sulfhydryl concentrations. , Electrochemical, diatomaceous earth depth filtrationICPOES and colorimetric methods afforded the measurement of Cu fractions attributed to Cu­(II)–organic acid complexes (Cu fraction I), Cu­(I)–thiol complexes (Cu fraction II), and Cu­(I)/Cu­(II) sulfides (Cu fraction III). , Studies of white wines have shown that wines with elevated concentrations of Cu fractions I and II (>0.02 μg/L) have low free H 2 S concentrations (i.e., <1 μg/L by GC-SCD) . This is consistent with Cu­(II)–organic acids and Cu­(I)–thiol complexes readily reacting with free H 2 S to prevent its accumulation.…”

Development of a Composite Cu(II)-Selective Potentiometric Sensor Based on a Thiourea Derivative Symmetric Schiff Base

“…In the last part of the optimization studies, the influence of the ionic additive percentage on the sensor performance was examined. Therefore, a series of all-solid-state composite electrodes were produced by adding ionic additives in the ratios varying between (w/w) 0.5-2.5 % to the composition of (w/w) 20.0 % paraffin oil, (w/w) 5.0 % MWCNT, and (w/w) 3.0 % ionophore (NaTPB) (Composition [13][14][15][16][17] and their performance characteristics were compared. The data given in Table 2 indicate that none of the studied compositions including ionic additive had any premptory effect on the electrode performances.…”

“…Considering the toxic effects of copper, its determination is quite critical. There are a number of analytical techniques that have been reported for the determination of copper ions at very low concentration levels, including ion chromatography [7,8], UV-Vis Spectrophotometry [9,10], flame atomic absorption spectrometry (FAAS) [11,12], graphite-furnace atomic absorption spectrometry (GF AAS) [13], Colorimetry [14][15][16], fluorescence spectroscopy [17,18], ICP-MS [19], ICP-OES [20], ICP-AES [21], Capilarry Electrophoresis-UV [22], titrimetry [23], gravimetry [24], electrogravimetry [25] and electrochemical methods [26][27][28][29][30].…”