Samples of red and white wine were diluted (10–50-fold) in ultrapure water (UPW). To minimize oxidation, vials were capped with polyester lids. Using Inline Ultrafiltration, samples were automatically filtered through a 0.22 μm (regenerated cellulose) membrane prior to injection.

Since all organic acids easily ionize, their conjugate bases can be analyzed by ion chromatography with suppressed conductivity detection.

For fast screening analysis the chromatographic separation was performed on A Metrosep A Supp 10 column with isocratic elution (Figure 1). Within less than 20 minutes the organic acids acetate, malate, tartrate, oxalate and the anions chloride, phosphate, sulfite, and sulfate are separated. Sulfite was calibrated separately to avoid a potential sulfate contamination. It was stabilized with 2-propanol (2% in working standard solutions). Although sulfite can be determined within in this multi-component run, for dedicated sulfite analysis please refer to the described methods [3].

A comprehensive view of the organic acid composition for complex monitoring can be obtained by separation with a Metrosep A Supp 7 column using a binary gradient (Figure 2). With the carbonate-UPW gradient the following 15 organic acids could be resolved: gluconate, lactate, acetate, propionate, isobutyrate, butyrate, methacrylate, valerate, methyl sulfate, dichloroacetate, malonate, malate, glutarate, adipate, and phthalate.

The experimental setup is shown in Figure 3.

Ionic composition profiles in wines are readily quantified with IC and conductivity detection. Ion exchange chromatography allows the simultaneous determination of inorganic anions and organic acids in one run, in contrast to ion-exclusion which only separates organic acids. With the fast multi-component screening analysis sample throughput in laboratories can be maximized. Sample preparation can be facilitated with Inline Ultrafiltration, protecting the column and enhancing instrument performance. Further increase of the economic potential can be achieved by combination with Metrohm Inline Dilution including the possibility of automatic calibration. The manual error-prone dilution step of samples and standards is omitted while laboratory time is saved, and accuracy and precision improved.

The complex organic acid monitoring with suppressed conductivity detection benefits from higher sensitivity compared to UV-detection methods and reduced interferences from UV-active sugars and phenols in such wine samples.

If peak identity needs confirmation, or very low detection limits are required, the IC setup can be combined with a sensitive mass specific detector (Figure 3).