Beverage analysis methods must be fast and robust to fulfill many quality control regulations. Optimal product quality is critical for consistent taste and other sensory characteristics in mass produced beverages.
In the case of beer, the ionic composition heavily influences the taste. For example, potassium chloride salts lead to a bitter, astringent, and soapy taste while magnesium sulfates form more sweet-sour flavors. Therefore, analytical control of anions and cations in beer is essential to guarantee the quality and meet consumer needs.
Major anions in beer are precisely determined with ion chromatography (IC) and suppressed conductivity detection, while cations are quantified with non suppressed conductivity. With a two-channel system, cations and anions can be determined simultaneously for the same sample. To reduce manual preparation steps, beer samples are automatically filtered with Inline Ultrafiltration. Features like automatic calibration and logical sample dilution streamline such beverage analyses and ensure the fast analysis of samples in high-throughput laboratories.
Beer samples from different providers (e.g., WarsteinerTM) were automatically diluted and filtered through a 0.22 μm membrane in the Ultrafiltration cell (Figure 1). Analyte concentrations outside of the calibration range are diluted with an optimal dilution factor and analyzed again with logical dilution, a feature of the chromatographic software MagIC Net. Hence, the results always fit within the calibration range.
After Inline Sample Preparation is performed, the sample is injected into two analytical channels that simultaneously analyze cations and anions under isocratic elution conditions (Table 1). Conductivity is a universal and sensitive detector to determine all relevant ions present in the beer sample. The MagIC Net software offers time-saving reliable calibration from a single standard solution by injecting increasing volumes on to the separation column (MiPT – Metrohm intelligent Partial Loop Injection Technique). This avoids pipetting errors during standard preparation. Furthermore, samples can be injected with the most suitable injection volume. Together with logical dilutions, sample concentrations in the range 1:10,000 can be analyzed reliably. High accuracy of results is achieved by an optimal fit for the calibration points (feature: high-low calibration).
| Method parameter | Anions | Cations |
|---|---|---|
| Column | Metrosep A Supp 10 - 100/4.0 | Metrosep C 6 - 150/4.0 |
| Eluent | 4 mmol Na2CO3 + 6.0 mmol/L NaHCO3 + 5.0 μmol/L NaClO4 | 2.3 mmol HNO3 + 1.7 mmol/L dipicolinic acid |
| Flow rate | 0.7 mL/min | 0.9 mL/min |
| Temperature | 30 °C | 35 °C |
| Injection | 20 μL | 20 μL |
| Detection | Suppressed conductivity | Non-suppressed conductivity |
Potassium was identified as a major cation in all beer samples, while the concentration of other cations (e.g., Na+, Ca2+, and Mg2+) was lower than 100 mg/L (Figure 2). The results reveal the effect of K+ in beer, as it provides a bitter and astringent taste. Other ions such as ammonium (eluting between Na+ and K+) can also be determined.
Chloride, phosphate, nitrate, and sulfate were the main anions detected in beer (Figure 2). Sulfite, a common preservative, can be determined next to other anions in the same run (retention time approximately 11 minutes).
Ion chromatography is a robust and straightforward analytical technique to monitor beer production and to control its quality. Beverage samples are automatically diluted and filtered prior to analysis to protect the analytical system. All essential anions and cations are simultaneously quantified in one analysis run. Features like logical dilution further save time and reduce manual work.
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Internal reference: AW IC BE6-0113-092015