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- In-line monitoring of the coffee roasting process with near infrared spectroscopy: Measurement of sucrose and colourPublication . Santos, João Rodrigo; Viegas, Olga; Páscoa, Ricardo N. M. J.; Ferreira, Isabel M. P. L. V. O.; Rangel, António O. S. S.; Lopes, João AlmeidaIn this work, a real-time and in-situ analytical tool based on near infrared spectroscopy is proposed to predict two of the most relevant coffee parameters during the roasting process, sucrose and colour. The methodology was developed taking in consideration different coffee varieties (Arabica and Robusta), coffee origins (Brazil, East-Timor, India and Uganda) and roasting process procedures (slow and fast). All near infrared spectroscopy-based calibrations were developed resorting to partial least squares regression. The results proved the suitability of this methodology as demonstrated by rangeerror- ratio and coefficient of determination higher than 10 and 0.85 respectively, for all modelled parameters. The relationship between sucrose and colour development during the roasting process is further discussed, in light of designing in real-time coffee products with similar visual appearance and distinct organoleptic profile.
- Sistema de fluxo com célula de percurso óptico longo para a determinação de ferro em águasPublication . Páscoa, Ricardo N. M. J.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Review on recent applications of the liquid waveguide capillary cell in flow based analysis techniques to enhance the sensitivity of spectroscopic detection methodsPublication . Páscoa, Ricardo N.M.J.; Tóth, Ildikó V.; Rangel, António O.S.S.Incorporation of long path length liquid waveguide capillary cell (LWCC or LCW) into spectrometric detection systems can increase the sensitivity of these by orders of magnitude (up to 500 times), and consequently can reduce the detection limits. The combination of the long path length spectrophotometry with flow methodologies can provide analytical solutions for various challenges in the field of environmental, biochemical and food chemistry. In this present work, the analytical applications of the long capillary cells are summarised and critically discussed. A historical overview of the cell development is given; applications in different areas are presented and grouped by analyte type. Major improvements achieved based on the use of the LWCC in the analytical characteristics (like sensitivity and detection limit) are emphasised while some of the limitations are also discussed.
- A double-line sequential injection system using a long pathlength liquid waveguide capillary flow cell for the spectrophotometric iron determination in watersPublication . Páscoa, Ricardo N. M. J.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Exploiting the use of a liquid waveguide capillary cell for spectrophotometric determinations in flow-based systemsPublication . Páscoa, Ricardo Nuno Mendes de Jorge; Rangel, António O. S. S.; Tóth, Ildikó V.In this thesis, the use of a liquid waveguide capillary cell (LWCC) was exploited for the spectrophotometric determination of several analytes in different types of water. With the purpose of in-line sample handling, different flow approaches were used for the development of simple, robust, cheap and automated analytical procedures. The first procedure was based on a sequential injection analysis (SIA) system for the determination of iron in coastal waters. With the goal of reaching low levels of iron, a LWCC was coupled to the system. This procedure used a doubled-line SIA system to improve mixing conditions between sample and reagents. The detection was based on a colorimetric reaction and two different reagents (ferrozine and 1,10-phenanthroline) were tested. The absorbance measurements were carried out at the wavelengths of 512 and 562 nm for the detection of iron-1,10-phenathroline and iron-ferrozine complex, respectively. An interference study was performed for both reagents. The developed method was also applied to natural waters (river, well, ground, potable and sea waters) and then compared with the reference procedure. One certified reference water sample was used to test the accuracy of the developed method. The objective of the second work was to determine iron at lower levels than the previous work and, as a consequence, to measure the levels of iron in ocean waters. With this in mind, a LWCC and a pre-concentration resin were coupled to a multisyringe flow injection analysis (MSFIA) system. Two different pre-concentration resins (Chelex 100 and NTA Superflow) were tested and evaluated. The determination of iron was also based on a colorimetric reaction and two reagents were tested, ferrozine and ammonium thiocyanate. The reactions were monitored at the wavelengths of 480 and 562 nm for the detection of iron-ammonium thiocyanate and iron-ferrozine complex, respectively. The accuracy was assessed using a certified reference water sample. A multi-parametric system for the spectrophotometric determination of zinc and copper at low levels in waters was the third work of this thesis. To attain this objective, a LWCC was coupled to a MSFIA system. The developed procedure for both analytes was based on a colorimetric reaction with zincon reagent at different pH values and monitored at 620 nm. Zincon reagent reacts only with copper at pH 5 and with copper and zinc at pH 9. An interference study for both determinations was carried out. The developed work was also applied to natural waters and three certified reference water samples. Subsequently, a multi-pumping flow system (MPFS) coupled with a LWCC was developed for the determination of titanium. This determination was based on the colorimetric reaction of titanium with chromotropic acid and the absorbance measurements were carried out at 425 nm. An interference study was performed in order to evaluate possible interferences. The developed procedure was applied to natural waters as well as to sunscreen formulations (the results were compared with the reference procedure). The accuracy was assessed with one certified lake sediment. The development of a spectrophotmetric method for bromate determination in waters at trace levels was the last work of this thesis. With this objective, a LWCC was coupled to a MPFS. The proposed methodology was based on a colorimetric reaction and two different colour reagents were tested, chlorpromazine and trifluoperazine. The lack of repeatability detected in this approach led to the development of a FIA approach in order to find out the reasons of this occurrence.
- A double-line sequential injection system using a long path length liquid waveguide capillary flow cell for the spectrophotometric iron determination in watersPublication . Páscoa, Ricardo N. M. J.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Determination of zinc in natural waters using a multisyringe flow injection analysis approach coupled with a long liquid waveguide capillary flow cellPublication . Páscoa, Ricardo N.M.J; Tóth, Ildikó; Rangel, António O.S.S.
- Spectrophotometric determination of zinc and copper in a multisyringe injection analysis system using a liquid waveguide capillary cell: Application to natural watersPublication . Páscoa, Ricardo N. M. J.; Tóth, Ildikó V.; Rangel, António O. S. S.This work exploits a multisyringe injection analysis (MSFIA) system coupled with a long liquid waveguide capillary cell for the spectrophotometric determination of zinc and copper in waters. A liquid waveguide capillary cell (1.0mpathlength, 550mmi.d. and 250mL internal volume) was used to enhance the sensitivity of the detection. The determination for both ions is based on a colorimetric reaction with zincon at different pH values. The developed methodology compares favourably with other previously described procedures, as it allows to reach low detection limits for both cations (LODs of 0.1 and 2mg L−1, for copper and zinc, respectively), without the need for any preconcentration step. The system also provided a linear response up to 100mg L−1 with a high throughput (43 h−1) and low reagent consumption and effluent production. The developed work was applied to natural waters and three certified reference water samples.
- Flow injection system using a liquid waveguide capillary cell for the determination of bromated in mineral watersPublication . Santos, Inês C.; Mesquita, Raquel; Páscoa, Ricardo N .M. J.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Sequential injection system for the enzymatic determination of ethanol in winePublication . Páscoa, Ricardo N. M. J.; Vidigal, Susana S. M. P.; Tóth, Ildikó Varga; Rangel, António O. S. S.A sequential injection system was developed for the enzymatic determination of ethanol in wine. The spectrophotometric determination is based on the enzymatic reaction catalyzed by alcohol dehydrogenase in the presence of NAD+. The system was applied to the determination of ethanol in a range of 0.008-0.024% (v/v) with good repeatability; RSDn)10 < 2.3%. The results obtained with the developed system showed good agreement with those obtained by using the reference method. The determination rate was 25 h-1; 1 ímol of NAD+, 1.1 units of enzyme, and 50 íL of sample were consumed per determination; and the waste produced was 2.2 mL per assay.
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