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Simple flow system with in-line gas-diffusion unit for determination of ethanol employing hypsochromic shift of visible absorbance band of methyl orange
(2020-01-01)
Ratanawimarnwong, Nuanlaor
;
Sinpun, Montatip
;
Chankaw, Panuwat
;
Choengchan, Nathawut
;
Nacapricha, Duangjai
The effect of solvent composition on the uv–visible spectrum of methyl orange was investigated for application to the quantitative determination of ethanol. At fixed pH, there was a hypsochromic shift of the absorbance band of methyl orange with increasing ethanol concentration. Using acetate buffer at pH 3.40 the change of absorbance at 530 nm of a solution of methyl orange containing known concentrations of standard ethanol was measured to provide a calibration curve. In order to apply this method to the analysis of alcoholic samples, such as distilled spirits, blended spirits and liquid herbal medicines, a simple gas-diffusion unit coupled with flow system was employed to separate the ethanol from sample matrices. Using the gas diffusion-flow system and employing an evaporation time of 2 min, a linear calibration range of 5–45% (v/v) ethanol was achieved ((ΔA = (0.0078 ± 0.0002)x(ethanol, %(v/v)) + (0.040 ± 0.005)), r<sup>2</sup> = 0.998). The limit of detection (3σ blank/slope) was 2.23% (v/v). The developed gas diffusion-flow system was applied to the analysis of colorless distilled spirits, yellow blended spirits and dark brown herbal medicines that are available in the local markets of Bangkok, Thailand. Validation of the method was carried out by comparing the results with analysis using gas chromatography. There was no statistically significant difference at the 95% confidence level for all alcoholic samples analyzed.
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A "dual-acceptor channel" membraneless gas-diffusion unit for simultaneous determination of ethanol and acetaldehyde in liquors using reverse flow injection
(2018-01-01)
Choengchan, Nathawut
;
Poontong, Bangerdsuk
;
Mathaweesansurn, Arjnarong
;
Maneerat, Noppadol
;
Motomizu, Shoji
A new design of membraneless gas-diffusion unit with dual acceptor channels for separation, collection and simultaneous determination of two volatile analytes in liquid sample is presented. The unit is comprised of three parallel channels in a closed module. A sample is aspirated into the central channel and two kinds of reagents are introduced into the other two channels. Two analytes are isolated from the sample matrix by diffusion into head-space and absorbed into the specific reagents. Non-absorbed vapor is released by opening the programmable controlled lid. The unit was applied to liquors for measurement of ethanol and acetaldehyde using reverse flow injection. Dichromate and nitroprusside were exploited as reagents for colorimetric detection of ethanol and acetaldehyde, respectively. Good linearity ranges (r2 > 0.99) with high precision (RSD < 2%) and high accuracy (recovery: 90 - 105%) were achieved. The results were compared to the results by GC-FID and no significant difference was observed by paired t-test (95% confidence).
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Quality control of gasohol using a micro-unit for membraneless gas diffusion
(2009-01-01)
Muncharoen, Sasithorn
;
Sitanurak, Jirayu
;
Tiyapongpattana, Warawut
;
Choengchan, Nathawut
;
Ratanawimarnwong, Nuanlaor
This work describes the development of a new spectrophotometric flow technique suitable for monitoring of ethanol content in gasohol fuel. Membraneless gas-diffusion (MBL-GD) was applied with one-step aqueous extraction of gasohol (1:2 gasohol/water). Segments of aqueous extract and color developing reagent were allowed to flow into two separate channels in the MBL-GD device. Inside the device, ethanol vapor can diffuse across a small headspace between the two channels (donor and acceptor). Introduction of an air-segment behind the zone of acceptor reagent to stop dispersion of the colored zone greatly improves the rapidity of analysis using this MBL-GD technique. Two methods were developed for quality control of gasohol by measuring ethanol content. Method I is suitable for direct calibration of E5 and E10. Method II is recommended for E20. These methods have high accuracy with good precision (% RSD: 1 to 4.9, n=45) and have a sample throughput of 26 samples per hour. E10 samples were compared with analysis using a standard GC method. © 2008 Springer-Verlag.

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