Generating Data Augmented Spectroscopic Data For Performance Enhancement

The application of chemometrics in food science has revolutionized the field by allowing the creation of models able to automate a broad range of applications such as food authenticity and food fraud detection. In order to create effective and general models able to address the complexity of real life problems, a vast amount of varied training samples are required. Training dataset has to cover all possible types of sample and instrument variability. However, acquiring a varied amount of samples is a time consuming and costly process, in which collecting samples representative of the real world variation is not always possible, specially in some application fields. To address this problem, a novel framework for the application of data augmentation techniques to spectroscopic data has been designed and implemented. This is a carefully designed pipeline of four complementary and independent blocks which can be finely tuned depending on the desired variance for enhancing model's robustness: a) blending spectra, b) changing baseline, c) shifting along x axis, and d) adding random noise.
This novel data augmentation solution has been tested in order to obtain highly efficient generalised classification model based on spectroscopic data. Fourier transform mid-infrared (FT-IR) spectroscopic data of eleven pure vegetable oils (106 admixtures) for the rapid identification of vegetable oil species in mixtures of oils have been used as a case study to demonstrate the influence of this pioneering approach in chemometrics, obtaining a 10% improvement in classification which is crucial in some applications of food adulteration.

Microextração adsortiva em barra (BAuE) : fundamentos avanços e aplicações na análise vestigial de compostos emergentes em matrizes reais

Tese de doutoramento, Química (Química Analítica), Universidade de Lisboa, Faculdade de Ciências, 2014

Electrochemical study of butylate: application to the analysis of water

The electroactivity of butylate (BTL) is studied by cyclic voltammetry (CV) and square wave voltammetry (SWV) at a glassy carbon electrode (GCE) and a hanging mercury drop electrode (HMDE). Britton–Robinson buffer solutions of pH 1.9–11.5 are used as supporting electrolyte. CV voltammograms using GCE show a single anodic peak regarding the oxidation of BTL at +1.7V versus AgCl/ Ag, an irreversible process controlled by diffusion. Using a HMDE, a single cathodic peak is observed, at 1.0V versus AgCl/Ag. The reduction of BTL is irreversible and controlled by adsorption. Mechanism proposals are presented for these redox transformations. Optimisation is carried out univaryingly. Linearity ranges were 0.10–0.50 mmol L-1 and 2.0–9.0 µmolL-1 for anodic and cathodic peaks, respectively. The proposed method is applied to the determination of BTL in waters. Analytical results compare well with those obtained by an HPLC method.

Determination of carbamate and urea pesticide residues in fresh vegetables using microwave-assisted extraction and liquid chromatography

An analytical multiresidue method for the simultaneous determination of seven pesticides in fresh vegetable samples, namely, courgette (Cucurbita pepo), cucumber (Cucumis sativus), lettuce (Lactuca sativa, Romaine and Iceberg varieties) and peppers (Capsicum sp.) is described. The procedure, based on microwave-assisted extraction (MAE) and analysis by liquid chromatography– photodiode array (LC–PDA) detection was applied to four carbamates (carbofuran, carbaryl, chlorpropham and EPTC) and three urea pesticides (monolinuron, metobromuron and linuron). Extraction solvent and the addition of anhydrous sodium sulphate to fresh vegetable homogenate before MAE were the parameters optimised for each commodity. Recovery studies were performed using spiked samples in the range 250–403 µgkg- 1 in each pesticide. The pesticide residues were extracted using 20mL acetonitrile at 60 ºC, for 10 min. Acceptable recoveries and RSDs were attained (overall average recovery of 77.2% and RSDs are lower than 11%). Detection limits ranged between 5.8 µgkg- 1 for carbaryl to 12.3 µgkg- 1 for carbofuran. The analytical protocol was applied for quality control of 41 fresh vegetable samples bought in Oporto Metropolitan Area (North Portugal). None of the samples contained any detectable amounts of the studied compounds.

Electroanalytical study of the pesticide asulam

The electrochemical behaviour of the herbicide Asulam was studied by cyclic and square wave voltammetry. Asulam may be irreversibly oxidised at a glassy carbon electrode. Maximum currents were obtained at pH=1.9 in aqueous electrolyte solution. Based on the electrochemical behaviour of Asulam, two analytical methodologies were developed for its determination in water samples, using square wave voltammetry (SWV) and flow injection analysis (FIA) coupled with an amperometric detector. Limits of detection of 7.1x10-6 mol L-1 and 1.2x10-8 mol L-1 for SWV and FIA respectively, were achieved. Repeatability was calculated by assessing the relative standard deviation (%) for 10 consecutive determinations of one sample. The found values were 2.1% for SWV and 5.0% for FIA. Validation of the results provided by SWV and FIA methodologies was performed by comparison with results from an HPLC-DAD technique. Good relative deviations were found (<5%). Recovery trials were performed to assess the accuracy of the results and the obtained values were between 84% and 107% for both methods.

Chlormequat selective electrodes: construction, evaluation and application at FIA systems

A flow injection analysis (FIA) system having a chlormequat selective electrode is proposed. Several electrodes with poly(vinyl chloride) based membranes were constructed for this purpose. Comparative characterization suggestedthe use of membrane with chlormequat tetraphenylborate and dibutylphthalate. On a single-line FIA set-up, operating with 1x10-2 mol L-1 ionic strength and 6.3 pH, calibration curves presented slopes of 53.6±0.4mV decade-1 within 5.0x10-6 and1.0x10-3 mol L-1, andsquaredcorrelation coefficients >0.9953. The detection limit was 2.2x10-6 mol L-1 and the repeatability equal to ±0.68mV (0.7%). A dual-channel FIA manifold was therefore constructed, enabling automatic attainment of previous ionic strength andpH conditions and thus eliminating sample preparation steps. Slopes of 45.5±0.2mV decade -1 along a concentration range of 8.0x10-6 to 1.0x10-3 mol L-1 with a repeatability ±0.4mV (0.69%) were obtained. Analyses of real samples were performed, and recovery gave results ranging from 96.6 to 101.1%.

Analysis of PCBs in soils and sediments by microwave-assisted extraction, headspace-SPME and high resolution gas chromatography with ion-trap tandem mass spectrometry

A procedure for the determination of seven indicator PCBs in soils and sediments using microwave-assisted extraction (MAE) and headspace solid-phase microextraction (HS-SPME) prior to GC-MS/MS is described. Optimization of the HS-SPME was carried out for the most important parameters such as extraction time, sample volume and temperature. The adopted methodology has reduced consumption of organic solvents and analysis runtime. Under the optimized conditions, the method detection limit ranged from 0.6 to 1 ng/g when 5 g of sample was extracted, the precision on real samples ranged from 4 to 21% and the recovery from 69 to 104%. The proposed method, which included the analysis of a certified reference material in its validation procedure, can be extended to several other PCBs and used in the monitoring of soil or sediments for the presence of PCBs.

Secondary effects of catalytic diesel particulate filters: copper-induced formation of PCDD/Fs.

Potential risks of a secondary formation of polychlorinated dibenzodioxins/furans (PCDD/Fs) were assessed for two cordierite-based, wall-through diesel particulate filters (DPFs) for which soot combustion was either catalyzed with an iron- or a copper-based fuel additive. A heavy duty diesel engine was used as test platform, applying the eight-stage ISO 8178/4 C1 cycle. DPF applications neither affected the engine performance, nor did they increase NO, NO2, CO, and CO2 emissions. The latter is a metric for fuel consumption. THC emissions decreased by about 40% when deploying DPFs. PCDD/F emissions, with a focus on tetra- to octachlorinated congeners, were compared under standard and worst case conditions (enhanced chlorine uptake). The iron-catalyzed DPF neither increased PCDD/F emissions, nor did it change the congener pattern, even when traces of chlorine became available. In case of copper, PCDD/F emissions increased by up to 3 orders of magnitude from 22 to 200 to 12 700 pg I-TEQ/L with fuels of &lt; 2, 14, and 110 microg/g chlorine, respectively. Mainly lower chlorinated DD/Fs were formed. Based on these substantial effects on PCDD/F emissions, the copper-catalyzed DPF system was not approved for workplace applications, whereas the iron system fulfilled all the specifications of the Swiss procedures for DPF approval (VERT).

Drop-In Clinics for Environmental Studies Students

The delivery of library instruction to students in those areas of the sciences and the social sciences dealing with biology and the environment has a long history (Bowden & Di Benedetto 2001; Kutner 2000; Kutner & Danks 2007; Sapp 2006; Sinn 1998). Often these instruction sessions take the form of a one hour lecture or workshop at the start of a semester before the students have begun their projects or papers. This "one-shot" approach, though popular, has its limitations. It may not be offered at a time when the students will actually start making use of library resources, it may not be tied very specifically to a particular assignment, or it may be too general in nature to be of much use to students later on when they need to look at particular topics in much more depth than can be addressed in one such session. The following article describes another approach: the strategic use of drop-in clinics as a method of instruction in which the students themselves determine how the instruction proceeds.

Development of Electrochemical Sensors for Various Pharmaceuticals

The development of electrochemical sensors is currently one of the active areas of research in analytical chemistry.Voltammetric sensors as an important class of electrochemical sensors are extensively used in pharmaceutical applications.In voltammetric analysis,many active compounds in dosage forms,in contrast to excipients,can be readily oxidised or reduced at the electrode surface by applying a potential.Chemically modified electrodes have great significance in the electrochemical determination of pharmaceuticals.The modification of electrode results in efficient determination of electroactive species at very lower potential without any major interferences.The present study involves the fabrication of 8 voltammetric sensors for the drugs Metronidazole Benzoate, Sulfamethoxazole, Acyclovir, Pam Chloride , Trimethoprim , Tamsulosin Hydrochloride and Ceftriaxone Sodium.Two sensors were developed for the drug tamsulosin hydrochloride while one sensor each was developed for the other drugs.

Studies On Chelating Ion-Exchange Resins

Ion-exchange chromatography has emerged as a practical and rapid method of separation and analysis. A review of literature on chelating resins reveals that eventhough investigations on highly selective resins are intensively pursued from early 1940s, such resins are still insufficiently used in analytical chemistry and process technology. This is mainly due to the complexity of their synthesis and high cost. In this context, it is worthwhile to develop novel chelating resins which are specific or at least selective towards a group of metal ions. Synthesis, characterization and analytical applications of two such resins are presented in this thesis.

Development of Electrochemical and Fluorescent Sensors

Chemical sensors have growing interest in the determination of food additives, which are creating toxicity and may cause serious health concern, drugs and metal ions. A chemical sensor can be defined as a device that transforms chemical information, ranging from the concentration of a specific sample component to total composition analysis, into an analytically useful signal. The chemical information may be generated from a chemical reaction of the analyte or from a physical property of the system investigated. Two main steps involved in the functioning of a chemical sensor are recognition and transduction. Chemical sensors employ specific transduction techniques to yield analyte information. The most widely used techniques employed in chemical sensors are optical absorption, luminescence, redox potential etc. According to the operating principle of the transducer, chemical sensors may be classified as electrochemical sensors, optical sensors, mass sensitive sensors, heat sensitive sensors etc. Electrochemical sensors are devices that transform the effect of the electrochemical interaction between analyte and electrode into a useful signal. They are very widespread as they use simple instrumentation, very good sensitivity with wide linear concentration ranges, rapid analysis time and simultaneous determination of several analytes. These include voltammetric, potentiometric and amperometric sensors. Fluorescence sensing of chemical and biochemical analytes is an active area of research. Any phenomenon that results in a change of fluorescence intensity, anisotropy or lifetime can be used for sensing. The fluorophores are mixed with the analyte solution and excited at its corresponding wavelength. The change in fluorescence intensity (enhancement or quenching) is directly related to the concentration of the analyte. Fluorescence quenching refers to any process that decreases the fluorescence intensity of a sample. A variety of molecular rearrangements, energy transfer, ground-state complex formation and collisional quenching. Generally, fluorescence quenching can occur by two different mechanisms, dynamic quenching and static quenching. The thesis presents the development of voltammetric and fluorescent sensors for the analysis of pharmaceuticals, food additives metal ions. The developed sensors were successfully applied for the determination of analytes in real samples. Chemical sensors have multidisciplinary applications. The development and application of voltammetric and optical sensors continue to be an exciting and expanding area of research in analytical chemistry. The synthesis of biocompatible fluorophores and their use in clinical analysis, and the development of disposable sensors for clinical analysis is still a challenging task. The ability to make sensitive and selective measurements and the requirement of less expensive equipment make electrochemical and fluorescence based sensors attractive.

Desenvolupament de mètodes de determinació de compostos fenòlics en aigües i sòls. Caracterització dels processos d'adsorció en diferents tipus de sòls.

El desenvolupament de mètodes d'anàlisi de compostos fenòlics és una pràctica habitual en molts laboratoris des de l'establiment de mesures legislatives de control de les concentracions d'aquestes substàncies en el medi ambient. Les tècniques cromatogràfiques representen la primera opció per a la determinació de la major part de compostos orgànics, en els que s'inclouen els fenols. Aquests, per les seves propietats de volatilitat i polaritat, poden analitzar-se emprant tant la cromatografia líquida com la cromatografia de gasos i aquesta dualitat s'ha aplicat en aquest treball.