Flow-injection conductometric determination of acidity in industrial hydrated ethyl alcohol Original Research Article

A flow-injection (FI) conductometric procedure is proposed for the determination of acidity in industrial 96% v/v hydrated ethyl alcohol. The method consists in a single-line system in which an alkaline solution (sodium hydroxide), in excess, is used as carrier. When the sample is inserted in the flow system, it mixes with and partially neutralizes the carrier solution, causing a decrease on the sample zone conductance, proportional to the sample acidity. The best conditions found were an analytical path of 100 cm, injection sample volume of 50 μl, temperature of 20°C and 1.0×10−3 mol l−1 sodium hydroxide as reagent carrier. With a single-channel manifold, 96% v/v ethyl alcohol acidity was determined in the 0.60–15.00 mg HOAc/100 ml concentration range (expressed as acetic acid) (calibration graph: H=−49.141–2.447C, r=0.9989, where H is the peak height in mm and C is the acetic acid concentration in 96% v/v ethyl alcohol in mg HOAc/100 ml) with a detection limit (three times the signal blank/slope) of 0.51 mg HOAc/100 ml. The throughput was 120 results h−1 and potassium chloride solution up to concentration of 11.48 mg KCl/100 ml injected together 2.40 mg HOAc/100 ml 96% v/v ethyl alcohol solution does not cause any effect in the conductometric response. A 2.40 mg HOAc/100 ml 96%v/v ethyl alcohol solution gave a relative standard deviation lower than 1% (n=15) and the results obtained for four industrial, hydrated ethyl alcohol with this procedure are in close agreement with those obtained using the titration procedure (r=0.9991).