Reagent-free analytical flow methods for the soft drink industry: Efforts for environmentally friendly chemical analysis

Abstract

The evolution of an entirely green analytical system for industrial quality control of carbonated drinks is described. The developed flow system is capable of providing analytical data of the dissolved CO2, sucrose, and color of a sample consecutively in real-time. The system has been carefully designed on the basis of “reagent-free”, meaning that no added chemicals are required for the analysis. The system first vaporizes CO2 from the soft drink in a gas–liquid separation chamber, with a channel for a flow of pure water as the CO2 acceptor. The dissolved CO2 alters the conductivity of the water stream, which is directly related to the concentration of CO2 in the soft drink. The sucrose content is measured based on the “schlieren effect”, the sample plug flows out of the vaporization chamber into a colorimeter with a near-infrared/light-emitting diode (NIR/LED) as light source. The schlieren effect arises at the boundary of pure water and soft drink with refraction of light in proportion to the sugar concentration. The system also measures the absorbance of the sample using an RGB-LED. The related principles and preliminary experiments as proof of concept are described as well as the construction of the flow system for this completely reagent-free analyzer. A simple flow injection system using the schlieren effect was also developed for rapid quantitative analysis of sugar in noncarbonated soft drinks.

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

“…With using standard sucrose solutions (1.0 to 7.0 • Bx), the signal profiles in Figure 3 show two positive (+ve) signals: 1st (+ve) and 2nd (+ve) signals, representing the liquid boundary for zone head (S/H 2 O) and zone tail (H 2 O/S), respectively. The profiles were similar to those from previous report [21], except for 1.0 • Bx, due to differences in optical alignment and type of light detector. However, the schlieren signal were well-defined and reproducible for triplicate injections (see Figure 3).…”

“…The schlieren effect in FIA was first mentioned by Krug et al in 1977 [24]. Nonetheless, the schlieren effect can be useful in flow-based analysis [19][20][21]. Herein, we manipulate a positive aspect of the 'schlieren effect' (sometimes called as 'refractive index effect' or 'lens effect'), as an in-line detection method for • Bx analysis in raw sugarcane juice.…”

“…Sucrose (equivalent to • Bx) and orthophosphate was carried out using a benchtop spectrophotometer. Sucrose was detected based on the schlieren effect at the interface between sample and pure water plugs [19][20][21][22][23][24], as our reported for analysis of sucrose in beverages [19][20][21]. Orthophosphate analysis was achieved by the molybdenum blue method, instead of turbidimetry [19], to avoid the adsorption of the in-line precipitates on the inner wall of PTFE tubing.…”

Contactless conductivity detection for analytical techniques—Developments from 2012 to 2014

“…A formerly developed reagent‐free SIA system with C 4 D was used by Mantim and co‐workers for determination of dissolved carbon dioxide in beverages . Newill et al.…”

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

“…When using a segment of water less than 1000 µL, the two signal peaks were not baseline separated. For photometric measurements, the schlieren effect may occur at the interface of the sample zone and the water carrier due to differences in the refractive indices [19,44,58,59]. This was also observed with the PEDD signal for some urine samples.…”