Institute of Analytical Chemistry and Food Chemistry

Graz, Austria

Institute of Analytical Chemistry and Food Chemistry

Graz, Austria

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Quaranta M.,Institute of Analytical Chemistry and Food Chemistry | Nugroho Prasetyo E.,Institute of Environmental Biotechnology | Koren K.,Institute of Analytical Chemistry and Food Chemistry | Nyanhongo G.S.,Institute of Environmental Biotechnology | And 4 more authors.
Analytical and Bioanalytical Chemistry | Year: 2013

It is estimated that up to 50 % of the adult population take antioxidant products on a daily basis to promote their health status. Strangely, despite the well-recognized importance of antioxidants, currently there is no international standard index for labeling owing to the lack of standardized methods for antioxidant measurement in complex products. Here, an online high-performance liquid chromatography (HPLC)-based method to detect and measure the total antioxidant capacity of antioxidant samples is presented. In this approach, complex samples containing antioxidants are separated by the HPLC system, which is further coupled to an antioxidant measuring system consisting of an optical oxygen sensor, laccase, and tetramethoxy azobismethylene quinone (TMAMQ). The antioxidants, separated via HPLC, reduce TMAMQ to syringaldazine, which is then reoxidized by laccase while simultaneously consuming O2. The amount of consumed oxygen is directly proportional to the concentration of antioxidants and is measured by the optical oxygen sensor. The sensor is fabricated by coating a glass capillary with an oxygen-sensitive thin layer made of platinum(II) meso-tetra(4-fluorophenyl)tetrabenzoporphyrin and polystyrene, which makes real-time analysis possible (t 90 = 1.1 s in solution). Four selected antioxidants (3 mM), namely, catechin, ferulic acid, naringenin (used as a control), and Trolox, representing flavonol, hydrocinnamic acid, flavanone, and vitamin E, respectively, were injected into the online antioxidant monitoring system, separated, and then mixed with the TMAMQ/laccase solution, which resulted in oxygen consumption. This study shows that, with the use of such a system, the antioxidant activity of individual antioxidant molecules in a sample and their contribution to the total antioxidant activity of the sample can be correctly assigned. © 2013 Springer-Verlag Berlin Heidelberg.


Strobl M.,Institute of Analytical Chemistry and Food Chemistry | Rappitsch T.,Institute of Analytical Chemistry and Food Chemistry | Borisov S.M.,Institute of Analytical Chemistry and Food Chemistry | Mayr T.,Institute of Analytical Chemistry and Food Chemistry | Klimant I.,Institute of Analytical Chemistry and Food Chemistry
Analyst | Year: 2015

New aza-BODIPY indicators which cover the pH scale from 1.5 to 13 are presented. The new indicators feature absorption/emission bands in the red/near-infrared (NIR) spectral region, exhibit high molar absorption coefficients (∼ 80 000 M-1 cm-1) and show good quantum yields (∼20%). All dyes represent promising building blocks for the development of a broad-range sensor for various pH ranges. Combination of four of these pH indicators yields a pH sensor with an extended dynamic range from pH 2 to 9. © 2015 The Royal Society of Chemistry.


Larndorfer C.,Institute of Analytical Chemistry and Food Chemistry | Borisov S.M.,Institute of Analytical Chemistry and Food Chemistry | Lehner P.,Institute of Analytical Chemistry and Food Chemistry | Klimant I.,Institute of Analytical Chemistry and Food Chemistry
Analyst | Year: 2014

This study highlights possible errors in luminescence lifetime measurements when using bright optical oxygen sensors with high excitation light intensities. An analysis of the sensor with a mathematical model shows that high light intensities will cause a depopulation of the ground state of the luminophore, which results in a non-linear behaviour of the luminescence emission light with respect to the excitation light. The effect of this non-linear behaviour on different lifetime determination methods, including phasefluorometry, is investigated and in good agreement with the output of the model. Furthermore, the consequences of increasingly high light intensities on phase fluorometric lifetime measurements are illustrated for different oxygen sensors based on benzoporphyrin indicators. For the specific case of PdTPTBPF-based sensors an error as high as 50% is possible under high light conditions (0.25 mol m-2 s-1 ≈ 50 mW mm-2). A threshold of applied excitation light intensity is derived, thus enabling the point at which errors become significant to be estimated. Strategies to further avoid such errors are presented. The model also predicts a similar depopulation of the ground state of the quencher; however, the effect of this process was not seen in lab measurements. Possible explanations for this deviation are discussed. © The Royal Society of Chemistry 2014.


PubMed | Institute of Analytical Chemistry and Food Chemistry
Type: Journal Article | Journal: The Analyst | Year: 2015

New aza-BODIPY indicators which cover the pH scale from 1.5 to 13 are presented. The new indicators feature absorption/emission bands in the red/near-infrared (NIR) spectral region, exhibit high molar absorption coefficients ( 80,000 M(-1) cm(-1)) and show good quantum yields (20%). All dyes represent promising building blocks for the development of a broad-range sensor for various pH ranges. Combination of four of these pH indicators yields a pH sensor with an extended dynamic range from pH 2 to 9.


PubMed | Institute of Analytical Chemistry and Food Chemistry
Type: Journal Article | Journal: The Analyst | Year: 2014

This study highlights possible errors in luminescence lifetime measurements when using bright optical oxygen sensors with high excitation light intensities. An analysis of the sensor with a mathematical model shows that high light intensities will cause a depopulation of the ground state of the luminophore, which results in a non-linear behaviour of the luminescence emission light with respect to the excitation light. The effect of this non-linear behaviour on different lifetime determination methods, including phase-fluorometry, is investigated and in good agreement with the output of the model. Furthermore, the consequences of increasingly high light intensities on phase fluorometric lifetime measurements are illustrated for different oxygen sensors based on benzoporphyrin indicators. For the specific case of PdTPTBPF-based sensors an error as high as 50% is possible under high light conditions (0.25 mol m(-2) s(-1) 50 mW mm(-2)). A threshold of applied excitation light intensity is derived, thus enabling the point at which errors become significant to be estimated. Strategies to further avoid such errors are presented. The model also predicts a similar depopulation of the ground state of the quencher; however, the effect of this process was not seen in lab measurements. Possible explanations for this deviation are discussed.

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