Metrohm's Aquatrode Plus A combined pH glass electrode with ground-joint diaphragm is recommended for measuring the pH in organic solvents. As a result of the expected low conductivity of the sample, the electrode should be particularly well shielded in order to suppress electrostatic influences. The Aquatrode Plus is an electrode that can be used for ethanol measurements. With separable ground-joint diaphragm, the Aquatrode Plus is suitable for measuring the pH of bioethanol.The pH meter used for the measurement should possess the following GLP functions, among others: three-point calibration with automatic buffer recognition; temperature compensation; calibration data monitoring; automatic measured-value recording; and result memory with identification. The pH meter 827 pH lab for laboratory use and the battery-operated 826 pH mobile offer these functions. The chloride content in bioethanol fuels is the subject of ASTM D 512.
Determinations can be carried out by mercurimetric or argentometric titration or by direct titration with a Cl-sensitive electrode. Argentometric determination (with silver nitrate) is the method of choice because of its environmental advantages and high precision. A defined volume of the sample is pipetted into the titration cell, treated with 5ml of 2M nitric acid and then titrated against 0.01M silver-nitrate solution.
A proven method for sulphate determination is potentiometric titration with lead nitrate using a Pb-sensitive electrode. The pH of the sample is adjusted to pH 3-5 with perchloric acid and the sulphate is then precipitated out with lead-nitrate solution. The Pb-selective electrode detects the first excess of lead ions at the equivalence point. The wide range of potentiometric applications for bioethanol requires a flexible titrator, such as the Metrohm Titrando.
The determinations can be carried out with excellent reproducibility due to the range of high-specification electrodes provided by Metrohm. For the pH measurement, the Aquatrode Plus electrode (6.0257.000) is recommended, but for acidity titration the well-shielded Solvotrode (6.0229.100) non-aqueous electrode is used. For the chloride determination, the low-maintenance Silver Titrode (6.0431.100) is used and for the sulphate determination, the Pb-selective ion-selective electrode is used.
