A critical examination of the components of the Schlieren effect in flow analysis

Dias, Ana Cristi Basile; Borges, Eduardo P.; Zagatto, Elias A.G.; Worsfold, Paul J.

doi:10.1016/j.talanta.2005.06.071

Cited by 79 publications

(45 citation statements)

References 30 publications

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“…[24][25][26][27] This effect was also observed in the present work. The Schlieren effect is a phenomenon caused by refractive index and concentration gradients formed during the transport of solutions in the flow or in the sample zone, which disturb the transient signals.…”

Section: Optimization Of Variablessupporting

confidence: 92%

Flow Injection Analysis of 5-(Hydroxymethyl)-2-furaldehyde in Honey by a Modified Winkler Method

et al. 2016

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One of the quality indicators for honey is 5-(hydroxymethyl)-2-furaldehyde (HMF), which is formed during the heating or aging of honey. The International Honey Commission recommends three methods for the determination of HMF in honey: the Winkler method, the White method, and determination by HPLC. The Winkler method uses the carcinogenic substance p-toluidine, which is not in accordance with the principles of Green Chemistry. The present work describes the determination of HMF in honey by flow injection analysis (FIA) using a modified Winkler method, replacing p-toluidine with p-aminobenzoic acid. The linear range was 1.00 to 40.0 mg L -1 , the limit of detection (LOD) was 0.43 mg L -1, and the limit of quantification (LOQ) was 1.32 mg L -1 . The method is an efficient and environmentally friendly technique for the analysis of HMF in honey.

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Section: Optimization Of Variablessupporting

confidence: 92%

Flow Injection Analysis of 5-(Hydroxymethyl)-2-furaldehyde in Honey by a Modified Winkler Method

et al. 2016

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“…This is because a boundary layer is generated when fluids with varying densities and refractive indices are not well mixed (the Schlieren effect). This fluidic interface can act as liquid lens resulting in a loss of light intensity along the optical path (Zagatto et al, 1990;Dias et al, 2006). The boundary layer disappears with time by diffusive mixing.…”

Section: Response Time Of Analyzermentioning

confidence: 99%

Evaluation of a Ferrozine Based Autonomous in Situ Lab-on-Chip Analyzer for Dissolved Iron Species in Coastal Waters

et al. 2017

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The trace metal iron (Fe) is an essential micronutrient for phytoplankton growth and limits, or co-limits primary production across much of the world's surface ocean. Iron is a redox sensitive element, with Fe(II) and Fe(III) co-existing in natural waters. Whilst Fe(II) is the most soluble form, it is also transient with rapid oxidation rates in oxic seawater. Measurements of Fe(II) are therefore preferably undertaken in situ. For this purpose an autonomous wet chemical analyzer based on lab-on-chip technology was developed for the in situ determination of the concentration of dissolved (<0.45 µm) Fe species (Fe(II) and labile Fe) suitable for deployments in a wide range of aquatic environments. The spectrophotometric approach utilizes a buffered ferrozine solution and a ferrozine/ascorbic acid mixture for Fe(II) and labile Fe(III) analyses, respectively. Diffusive mixing, color development and spectrophotometric detection take place in three separate flow cells with different lengths such that the analyzer can measure a broad concentration range from low nM to several µM of Fe, depending on the desired application. A detection limit of 1.9 nM Fe was found. The microfluidic analyzer was tested in situ for nine days in shallow waters in the Kiel Fjord (Germany) along with other sensors as a part of the SenseOCEAN EU-project. The analyzer's performance under natural conditions was assessed with discrete samples collected and processed according to GEOTRACES protocol [acidified to pH < 2 and analyzed via inductively coupled plasma mass spectrometry (ICP-MS)]. The mechanical performance of the analyzer over the nine day period was good (consistent high precision of Fe(II) and Fe(III) standards with a standard deviation of 2.7% (n = 214) and 1.9% (n = 217), respectively, and successful completion of every programmed data point). However, total dissolved Fe was consistently low compared to ICP-MS data. Recoveries between 16 and 75% were observed, indicating that the analyzer does not measure a significant fraction of natural dissolved Fe species in coastal seawater. It is suggested that an acidification step would be necessary in order to ensure that the analyzer derived total dissolved Fe concentration is reproducible and consistent with discrete values.

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“…The refractive index or schlieren effect occurs when light passes through a medium with refractive index gradients, resulting in the variable refraction of light into streaks [74]. In flow injection systems with spectrophotometric analysis, the schlieren effect can be quite problematic where the refractive index of the sample differs from that of the carrier stream into which it is injected.…”

Section: Consideration Of the Schlieren (Refractive Index) Effect In mentioning

confidence: 99%

Flow injection analysis as a tool for enhancing oceanographic nutrient measurements—A review

Worsfold

Clough

Lohan

et al. 2013

Analytica Chimica Acta

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A critical examination of the components of the Schlieren effect in flow analysis

Cited by 79 publications

References 30 publications

Flow Injection Analysis of 5-(Hydroxymethyl)-2-furaldehyde in Honey by a Modified Winkler Method

Flow Injection Analysis of 5-(Hydroxymethyl)-2-furaldehyde in Honey by a Modified Winkler Method

Evaluation of a Ferrozine Based Autonomous in Situ Lab-on-Chip Analyzer for Dissolved Iron Species in Coastal Waters

Flow injection analysis as a tool for enhancing oceanographic nutrient measurements—A review

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