Exploiting gas diffusion for non-invasive sampling in flow analysis: determination of ethanol in alcoholic beverages

Abstract

A tubular gas diffusion PTFE membrane is exploited for non-invasive sampling in flow analysis, aiming to develop an improved spectrophotometric determination of ethanol in alcoholic beverages. The probe is immersed into the sample, allowing ethanol to diffuse through the membrane. It is collected into the acceptor stream (acidic dichromate solution), leading to formation of Cr(III), monitored at 600 nm. The analytical curve is linear up to 50% (v/v) ethanol, baseline drift is < 0.005 absorbance during four working-hours, and sample throughput is 30 h −1 , meaning 0.6 mmol K 2 Cr 2 O 7 per determination. Results are precise (r.s.d. < 2%) and in agreement with an official procedure.

Measurement of ethanol concentration using solvent extraction and dichromate oxidation and its application to bioethanol production process

“…Fletcher et al [11] established an ethanol determination method using sequential injection analysis with an assay range up to 6% (v/v), a 100-l sample, and an assay speed of 19 samples per hour. Based on the same principle, Vicente et al [20] carried out the determination of ethanol concentration, up to 50% (v/v) in alcoholic beverages, and at a rate of 30 samples per hour. In addition, Choengchan et al [8] also introduced the Xow injection analysis, up to 42.2% (v/v) ethanol in whiskey.…”

“…When ethanol is present in an aqueous solution, chromium ions oxidize ethanol, and these ions are reduced from the +6 oxidation state to +3, changing the color from orange to green. Dichromate oxidation method is recently used for the measurement of ethanol in a Xow injection analysis [8,11,20]. Moreover, the international ethanol reference solution is prepared by the dichromate oxidation method [3].…”

Inexpensive Procedure for Measurement of Ethanol: Application to Bioethanol Production Process

“…Based on the principle, Vicente et al [6] carried out the determination of ethanol concentration, up to 50% (v/v) in alcoholic beverages, and at a rate of 30 samples per hour. In addition, Choengchan et al [14] also introduced the flow injection analysis, up to 42% (v/v) ethanol in whiskey.…”

“…In saccharification, enzymatic degradation of complex sugars produces additional components as byproducts. These could react directly or indirectly with dichromate reagent, thus may interfere with reaction color [6] [7]. Therefore, the extraction of ethanol from the culture broth is essential before the assay is performed.…”

Flow Analysers

“…3.12) leads to an increase in the length of the entire sample zone. This does not result in a broader recorded peak, however, because the sample linear speed is 2 Non-ionic surfactant, (C 2 H 4 O) 23 increased, and the sample passes through the flow cell in a similar time (Fig. 5.7).…”