Ethanol concentrations in complex matrices such as beer can be measured directly and quickly using any YSI 2900 Series Biochemistry Analyzer. YSI’s unique biosensor technology provides for rapid ethanol measurement. Measurements are virtually unaffected by color, turbidity, density, or pH.
When a sample is injected into the sample chamber, the ethanol diffuses into the membrane containing alcohol oxidase. The ethanol is immediately oxidized to hydrogen peroxide and acetaldehyde. The hydrogen peroxide is detected amperometrically at the platinum electrode surface. The current flow at the electrode is directly proportional to the hydrogen peroxide concentration, and hence to ethanol concentration.
Other alcohols can interfere with ethanol measurement by also oxidizing and producing a signal. Fortunately, most alcohols have much lower responses to alcohol oxidase than ethanol. One notable exception is methanol, which is over three times as sensitive to the enzyme as ethanol. Therefore, samples must be methanol-free.
This application note demonstrates how simply and quickly ethanol concentrations can be determined using the following method. Precision of replicate samples was determined from selected samples; and percent recovery was determined for samples spiked with ethanol. The results section demonstrates typical precision and accuracy when using a YSI Biochemistry Analyzer in process applications.
Materials and Instrument Settings
A. YSI 2900 Series Biochemistry Analyzer - equipped with a 2786 Ethanol Membrane and 1579 Ethanol Buffer.
B. 2790 Ethanol standards (2.00 g/L, 3.20 g/L). Place the 2.00 g/L calibrator solution in Station 2.
C. Connect the 2900 Series Biochemistry Analyzer to a suitable power source.
D. Perform the instrument and membrane check described in the Operations Manual.
E. Volumetric glassware (Class A recommended).
F. The following instrument setup is recommended:
Probe A Parameters
Calibrator: 2.00 g/L
Sample size: 15 μL
End Point: 45 Sec
Cal Station: 21
Probe B Parameters
B Chemistry: None
Time (min): 30
T Shift (°C): 1
Cal Shift (%): 2
A. Dilute sample to bring ethanol concentration into the linear range of the instrument, which is 0.04 to 3.20 g/L. Samples with 1.5 to 2.5 g/L ethanol will give the best results.
B. Calibrate the 2900 Series Biochemistry Analyzer with a 2.00 g/L ethanol standard solution.
C. Check the linearity of the membrane at least once a day with an ethanol linearity check solution (3.20 g/L). Refer to the User’s Manual for specifications.
D. Assay the sample prepared in A by aspiration into the 2900 Series Biochemistry Analyzer. The linear range of the system is 0.04 to 3.20 g/L ethanol. If the value reported exceeds this, further dilution is required.
E. Calibrate frequently as described in the User’s Manual.
To calculate % ethanol, multiply the reported value by the appropriate dilution factor.
Example: 5.00 mL of beer was diluted to 100 mL in a Class A volumetric flask. When assayed, the value reported was 1.56 g/L ethanol.
For a v/v result, divide the mass by the density of ethanol (0.789 g/mL at 20°C).
Several beers were analyzed for their ethanol concentrations (w/v) using the YSI biochemistry analyzer and Sigma Test Kit 332-BT. The YSI analyzer results and Sigma Test Kit results are compared in the following table:
YSI’s proprietary immobilized enzyme membrane technology provided accurate ethanol results within one minute of sampling. The YSI 2900 Biochemistry Analyzer’s ability to provide rapid, precise analyses makes it ideal for brewing process monitoring and control and QC analysis of beer harvest samples.
YSI Part Numbers:
2900 Series Biochemistry Analyzer
2786 Ethanol Membrane Kit
2790 Ethanol Standards Kit
1579 Carbonate Buffer Concentrate
2363 Potassium Ferrocyanide Test Solution
2392 NaCl Solution (for membrane installation)
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