Measurement of sucrose concentration using Imbibition length on paper: A device for equipment-free and environmentally-friendly detection

The Lucas-Washburn equation is commonly used to predict the distance (L) that a liquid travels through paper. This equation establishes that L2 is linear with time and inversely proportional to the viscosity of the liquid. However, there is currently no theoretical equation connecting the viscosity of a solution to its concentration. In this study, the imbibition flow of a sucrose solution was measured along the length of a horizontal strip of filter paper, featuring a printed, thermometer-shaped hydrophobic boundary. A sample (38 μL) was dispensed onto the bulb area, and the solution's flow was visually tracked using a red dye added to the sample. The imbibition length (L) was measured by a vernier caliper at 10.0 min after the sample addition. An empirical equation, based on literature values of the viscosity (η) and concentration (C) of sucrose solutions, was proposed. By integrating this empirical equation with the Lucas-Washburn equation, the following equation was derived: L = a⋅exp{-(bC + cC2)}, where 'a', 'b' and 'c' are parameters. This equation was fitted to the dataset of L and C, covering C values from 0 to 60 % w/w standard sucrose solutions, resulting in a coefficient of determination of 0.9987. The plot of L against C was observed to closely follow a linear line, with a fitting providing a coefficient of determination of 0.9986. The sucrose contents in samples, such as soft drinks, syrups, and sugarcanes, determined using the imbibition length method and conventional refractometry, were in statistical agreement via the paired t-test at the 95 % confidence level. This method is simple, instrument-free, requiring only a small amount of safe red food dye, and can be conducted on-site.

Home-Made Membraneless Vaporization Gas-Liquid Separator for Colorimetric Determination of Ethanol in Alcoholic Beverages

This work utilized the simplicity of a so-called membraneless vaporization (MBL-VP) unit as a gas separator for the colorimetric determination of ethanol in alcoholic beverages. A beverage sample with a volume of 1 mL was directly injected into a small container which was hung from a lid inside a closed 40 mL reused glass bottle without pretreatment such as distillation. An acidified potassium dichromate (Cr₂O₇ ^2-) acceptor solution, preadded to the glass bottle, was reduced to Chromium (III) ion by the diffusion of vaporized ethanol from the sample. After 5 min, the absorbing solution was collected for colorimetric detection at 590 nm. The unit manually quantifies ethanol in the range 1.0-90% (v/v) with satisfactory interday precision but without matrix effect (recovery 89-109%). The method was validated with the conventional distillation/pycnometer method which showed no significant difference of ethanol contents between those two methods and the declared values of 12 alcoholic beverages, indicating sufficient accuracy. Analyses of alcoholic beverages using this method were successful with benefits of simplicity, cheapness, and less energy consumption.

Sequential Injection System for Analysis of Degree Brix, Orthophosphate and pH in Raw Sugarcane Juice Applicable to Sugar Industry

This work presents, for the first time, a new sequential injection analysis (SIA) method to simultaneously analyze degree Brix, orthophosphate and pH in raw cane juice. These key parameters relate to price of harvested sugarcane and quality of cane juice for sugar production. The SIA system employed two detectors: the first detector is a diode-array spectrophotometer, equipped with a regular flow cell, for measurements of degree Brix and orthophosphate. Quantitative of degree Brix (°Bx; ca. % (w/w) sucrose) was based on manipulation of the schlieren effect at the interface between plugs of sample and water. Orthophosphate analysis was carried out based on the molybdenum blue method with significant reduction in consumption of the reagents. Compensation of the schlieren effect from sucrose for determination of orthophosphate was achieved by using a dual-wavelength spectrometric detection. Second detector is a pH-sensing device, called ion-selective field-effect transistors (ISFET). The ISFET is based on the current through the ISFET arising according to the H⁺ concentration in solution. Our developed SIA system provides linear calibration graphs fitting for purpose in analysis of sugarcane juice (pH: 0–14, °Bx: 1.0–7.0 and P₂O₅: 20–200 mg L⁻¹). Simultaneous analysis of sugarcane juice for pH, °Bx and P₂O₅ is carried out within 5 min (12 sample per h). Precision of SIA system is acceptable (RSD < 3%). Our SIA system gave quantitative results insignificantly different, as compared with conventional methods for analysis of pH, °Bx and P₂O₅ in sugarcane juice.

Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter-detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 × 2 × 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffé reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm-1).

Temperature-dependent schlieren effect in liquid flow for chemical analysis

In flow analysis, such as flow injection analysis, liquid lens is formed at the boundary between two adjacent liquid media which have different refractive indices. Light refraction at the liquid interface gives the so-called 'schlieren signal'. Schlieren effect is both concentration-dependent and temperature-dependent. In this work, the schlieren signal from temperature difference was quantitatively investigated for application in enthalpimetric measurement. The schlieren phenomena was then exploited for chemical analysis. A thermal insulated single flow line manifold was constructed using deionized water at 23 °C as the carrier. Deionized water at various temperatures in the range of 5-85 °C was injected into the carrier flow. A correlation between the schlieren signal and sample temperature was observed. A heat exchanger unit (HEU), consisting of a small volume glass-reaction chamber with a surrounding water jacket, was constructed. The unit was thermally insulated in a double layer cylindrical PVC unit. For demonstrating the applicability of temperature-dependent schlieren effect in chemical analysis, the exothermic oxidation reaction between acid dichromate and ethanol or ascorbic acid was employed with heat transferring to the surrounding water layer. When an aliquot of water from the HEU is injected into the constant temperature flow line the observed schlieren signal was dependent on the analyte concentration. Linear calibration (r² > 0.99) were obtained covering the concentration range of ethanol and ascorbic acid as found in samples. The developed flow system provides good precision (RSD < 5%) with sample throughput of 4 sample h^-1. The system were applied to the determination of ethanol in Thai white spirit and ascorbic acid in vitamin C tablets, respectively. The quantitative results obtained from the schlieren method were in agreement with the comparative methods.

Recent advances in flow injection analysis

A dynamic development of methodologies of analytical flow injection measurements during four decades since their invention has reinforced the solid position of flow analysis in the arsenal of techniques and instrumentation of contemporary chemical analysis.

New membraneless vaporization unit coupled with flow systems for analysis of ethanol

This work presents the development of a new design for a membraneless vaporization (MBL-VP) unit, called dual chamber MBL-VP for measurement of volatile compounds. With this unit, exact volumes of sample and reagent are introduced into their respective cone-shaped chambers from the base of the cones. Diffusion of volatile analyte then takes place. After an appropriate time interval, the acceptor solution is withdrawn from the chamber into the detector flow-cell, while the sample solution is withdrawn to waste. Unlike the previous MBL-VP design, problems with overflow of solutions are eliminated by precise control of the input volume to be less than the volume of the chamber. The developed flow system with the dual chamber MBL-VP unit was applied to the determination of the ethanol content of various liquid samples, using the oxidation reaction between potassium dichromate and the diffused ethanol. In addition, in order to accelerate the gas diffusion process, the donor chamber was aerated. As the result, relatively short analysis time of 144 s was achieved for ethanol content in the range of 5-50% (v/v). The proposed method was successfully validated against a gas chromatographic method for 17 alcoholic samples. Percentage recovery was in the range of 96-109%.