It may not be necessary to perform a calibration when using the Ethanol Sensor in the classroom. If your experiment or application is evaluating the rate of ethanol production, such as determining fermentation rates with yeast, or the relative change in ethanol concentration, then the stored calibration works well.
For quantitative analysis of ethanol samples, it is best to use a two-point calibration to improve accuracy. The two points you choose for your calibration will depend on the expected amount of ethanol in your sample. For best results at low concentrations (0.1–1%), calibrate using 1% and 0.1% ethanol. For best results at high concentrations (1.0–3.0%), calibrate using 3.0% and 1% ethanol. If you are measuring an intermediate range you can also calibrate using 0.2% and 2.0% ethanol. Use the higher standard first for any calibration.
The instructions for calibration are dependent on the data collection interface you are using.
Making Ethanol Standards for Calibration
To make solutions for the ethanol calibration, you will need to dilute fresh, stock ethanol to the appropriate concentration. Denatured ethanol or non-denatured, grain ethanol may be used. Ethanol that is 70% is more stable than 95%. For the most accurate results, use a volumetric flask to make the standards. Use the following equation to guide you:
C1V1 = C2V2
- C1 is the concentration of the stock solution (typically 70% or 95%).
- V1 is the amount of stock solution to be added (you will solve for this).
- C2 is the desired concentration in %.
- V2 is the total final volume.
- V2 – V1 = amount of distilled water to add to the stock solution
It may be necessary to do a serial dilution in order to get the precision you need for your standards. The following table shows an example of a serial dilution to make 0.1% ethanol starting with 70% ethanol.
|Amount of ethanol
(ethanol and water)