Temperature-dependent schlieren effect in liquid flow for chemical analysis

Jintana Suwanrut; Nattapong Chantipmanee; Wichayaporn Kamsong; Supatana Buking; Thitirat Mantim; Phoonthawee Saetear; Duangjai Nacapricha

doi:10.1016/j.talanta.2018.05.055

Temperature-dependent schlieren effect in liquid flow for chemical analysis

Talanta. 2018 Oct 1:188:74-80. doi: 10.1016/j.talanta.2018.05.055. Epub 2018 May 18.

Authors

Jintana Suwanrut¹, Nattapong Chantipmanee², Wichayaporn Kamsong², Supatana Buking², Thitirat Mantim³, Phoonthawee Saetear⁴, Duangjai Nacapricha⁵

Affiliations

¹ Flow Innovation-Research for Science and Technology Laboratories (FIRSTLabs), Thailand; Department of Chemistry, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand. Electronic address: kanejintana@gmail.com.
² Flow Innovation-Research for Science and Technology Laboratories (FIRSTLabs), Thailand; Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
³ Flow Innovation-Research for Science and Technology Laboratories (FIRSTLabs), Thailand; Department of Chemistry, Faculty of Science, Srinakharinwirot University, Bangkok 10110, Thailand.
⁴ Flow Innovation-Research for Science and Technology Laboratories (FIRSTLabs), Thailand; Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand. Electronic address: phoonthawee.sae@mahidol.ac.th.
⁵ Flow Innovation-Research for Science and Technology Laboratories (FIRSTLabs), Thailand; Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand. Electronic address: duangjai.nac@mahidol.ac.th.

PMID: 30029441
DOI: 10.1016/j.talanta.2018.05.055

Abstract

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.

Keywords: Ascorbic acid; Ethanol; Exothermic oxidation reaction; Heat exchanger unit; Schlieren effect; Thermal sensing.