Plasma Spectroscopic Techniques Applied to Biological and Environmental Matrices

The purpose of this research was to apply the use of direct ablation plasma spectroscopic techniques, including spark-induced breakdown spectroscopy (SIBS) and laser-induced breakdown spectroscopy (LIBS), to a variety of environmental matrices. These were applied to two different analytical problems. SIBS instrumentation was adapted in order to develop a fieldable monitor for the measurement of carbon in soil. SIBS spectra in the 200 nm to 400 nm region of several soils were collected, and the neutral carbon line (247.85 nm) was compared to total carbon concentration determined by standard dry combustion analysis. Additionally, Fe and Si were evaluated in a multivariate model in order to determine their impacts on the model\u27s predictive power for total carbon concentrations. The results indicate that SIBS is a viable method to quantify total carbon levels in soils; obtaining a good correlation between measured and predicated carbon in soils. These results indicate that multivariate analysis can be used to construct a calibration model for SIBS soil spectra, and SIBS is a promising method for the determination of total soil carbon. SIBS was also applied to the study of biological warfare agent simulants. Elemental compositions (determined independently) of bioaerosol samples were compared to the SIBS atomic (Ca, Al, Fe and Si) and molecular (CN, N2 and OH) emission signals. Results indicate a linear relationship between the temporally integrated emission strength and the concentration of the associated element. Finally, LIBS signals of hematite were analyzed under low pressures of pure CO2 and compared with signals acquired with a mixture of CO2, N2 and Ar, which is representative of the Martian atmosphere. This research was in response to the potential use of LIBS instrumentation on the Martian surface and to the challenges associated with these measurements. Changes in Ca, Fe and Al lineshapes observed in the LIBS spectra at different gas compositions and pressures were studied. It was observed that the size of the plasma formed on the hematite changed in a non-linear way as a function of decreasing pressure in a CO2 atmosphere and a simulated Martian atmosphere

Honey authentication: effect of irradiation and ageing on near-infrared (NIR) spectroscopy classification models

Thesis (MScFoodSc)--Stellenbosch University, 2020.ENGLISH ABSTRACT: Near-infrared (NIR) spectroscopy was used to investigate the effects of syrup dilution, ageing, storage temperature and irradiation treatment on the NIR spectra of honey. Additionally, NIR spectroscopy and partial least squares discriminant analysis (PLS-DA) were employed to develop a classification model for the rapid screening of high-fructose corn syrup (HFCS) and invert cane sugar syrup (ICSS) diluted honey. Detection of irradiation treatment was also investigated, to assess NIR spectroscopy-based models as a potential screening tool for detecting mislabelled honey. Unfiltered and unheated honey samples (n = 17) obtained from South African beekeepers were uniformly strained and subjected to treatment combinations of 10 kGy gamma irradiation and dilution with 0, 10 or 20% (w/w) ICSS or HFCS to create sub-samples (n = 174) which were stored at 25°C. Another three undiluted subsets were stored at 4°C, 40°C and in uncontrolled ambient conditions (n = 51). A benchtop BÜCHI Fourier transform-near infrared (FT-NIR) spectrometer and a portable MicroNIR NIR spectrometer, with ranges of 1000–2500 nm and 908-1676 nm respectively, were used to acquire triplicate spectral measurements, over a period of 9 months. ANOVA-simultaneous component analysis (ASCA) indicated that honey type, diluent type, storage temperature and age had significant (p > 0.05) effects on the spectral dataset, while diluent level and irradiation treatment did not. Despite this, irradiation treatment was found to reduce the validation accuracy and efficacy of authentication models, by 5.82% and 7.19% respectively, when PLS-DA models based on only irradiated and only non-irradiated spectral data were compared, suggesting that authentication may be impeded by irradiation treatment to some degree. However, a PLS-DA model discriminating on the basis of irradiation treatment obtained an unsuccessful validation classification of 59.7%, suggesting that there is little or no utilisable effect of irradiation on the spectral data. The best-performing authentication solutions were individual two-class PLS-DA models for detecting ICSS (75.95% accuracy, 86.31% sensitivity) and HFCS (73.95% accuracy, 82.14% sensitivity) dilution, which demonstrated predictive power adequate for screening purposes. PLS-DA models based on spectral data acquired with the benchtop BÜCHI instrument performed best when compared with the portable MicroNIR instrument and its two sample presentation formats. Despite this, the MicroNIR with Teflon cup sample presentation was shown to be a feasible and cost-effective alternative, demonstrating similar accuracies (70.0-75.47%) and efficiencies (68.22-74.51%). In addition, quantification of the level of diluent with partial least squares regression (PLSR) was poor for both ICSS (R2 Pred = 0.118, RMSEP = 6.795%) and HFCS (R2 Pred = 0.147, RMSEP = 6.596%) dilutions. This was attributed to an inadequate range of dilution levels in the reference data, as well as the insignificant effect (p < 0.05) of diluent level on the overall variation in the spectral data. The findings of this study highlighted the potential shortcomings of NIR spectroscopy models in providing definite authentication, while demonstrating the capabilities of this technique for authenticity screening.AFRIKAANSE OPSOMMING: Naby-infrarooi (NIR) spekroskopie is gebruik om die effekte van stroop verdunning, veroudering, stoortemperatuur en bestraling behandeling op heuning se NIR spektra te ondersoek. NIR spekroskopie, gekombineer met parsiёle kleinste kwadrate diskriminantanalise (PLS-DA), is ook aangewend om ’n klassifikasie model te ontwikkel wat kan onderskei tussen outentieke heuning en heuning wat met hoё- fruktose mieliestroop (HFCS) of omgekeerde suikerriet stroop (ICSS) verdun is. Bepaling van vorige bestraling behandeling is ook ondersoek, om NIR spekroskopie-gebasseerde modelle te assesseer as ‘n moontlike hulpmiddel vir die identifisering van bedrieglik-geetiketteerde heuning. Rou, ongefiltreerde heuningmonsters (n = 17) verkry van Suid-Afrikaanse byeboere is eenvormig gesyg en met behandelingskombinasies van 10 kGy bestraling en verdunning met 0, 10 en 20% (w/w) ICSS en HFCS onderverdeel (n = 174). Nog drie outentiek en onverdunde deelversamelings is by 4°C, 40°C en in onbeheerde omringende toestande gebêre (n = 51). ’n Laboratorium BÜCHI Fourier-transformasie nabyinfrarooi (FT-NIR) spekrofotometer en ‘n draagbare MicroNIR NIR spekrofotometer, met golflengte reekse van 1000–2500 nm en 908-1676 nm, onderskeidelik, is gebruik om spektra in triplikaat te versamel, oor ’n tydperk van 9 maande. ANOVA-gelyktydige komponentanalise (ASCA) het aangedui dat heuningtipe, verdunningsmiddeltipe, stoortemperatuur en ouderdom beduidende (p > 0.05) effekte op die spektrale datastel het, terwyl verdunningsvlak en bestraling geen beduidende effek het nie. Ten spyte hiervan, is bestraling verantwoordelik vir ‘n 5.82% en 7.19% vermindering van validasie akkuraatheid en doeltreffenheid, onderskeidelik, wanneer PLS-DA modelle wat op bestraalde en onbestraalde spektrale data gebou is, vergelyk is. Dit dui daaraan dat bestraling behandeling, heuning egtheid verifikasie tot ’n mate kan belemmer. Egter kon PLS-DA onderskeiding van bestraling behandeling ’n onsuksesvolle validasie akkuraatheid van slegs 59.7% behaal. Dié resultaat stel voor dat bestraling geen bruikbare effek op die spektrale data het nie. Afsonderlike twee-klas PLS-DA modelle vir ICSS (75.95% akkuraatheid, 86.31% sensitiwiteit) en HFCS (73.95% akkuraatheid, 82.14% sensitiwiteit) verdunningbepaling is as die mees effektiewe verifikasieoplossing bevind, en het voldoende voorspellingskrag vir keuring gedemonstreer. PLS-DA modelle wat op die BÜCHI laboratorium spekrofotometer data gebou is, het beter opgetree as dié wat op die draagbare MicroNIR spekrofotometer, en albei die MicroNIR se monsterhouers, gebaseer is. Ten spyte hiervan, bied die MicroNIR, met die Teflonhouer, soortgelyke akkuraatheid (70.0-75.47%) en doeltreffenheid (68.22- 74.51%) aan, en is dus bewys as ’n haalbare en koste-effektiewe alternatief. Kwantifisering van verdunningsvlak met parsiёle kleinste kwadrate regressie (PLSR) het swak vertoning gewys vir beide ICSS (R2 Pred = 0.118, RMSEP = 6.795%) en HFCS (R2 Pred = 0.147, RMSEP = 6.596%) verdunnings. Hierdie resultaat is toegeskryf aan die onvoldoende verskeidenheid van verdunningsvlakke in die verwysingsdata, asook die onbeduidende (p < 0.05) effek van verdunningsvlak op die algehele variasie van die spektrale data. Die resultate van hierdie studie beklemtoon NIR spekroskopie se moontlike tekortkominge vir die doeleindes van heuning egtheid verifikasie, maar demonstreer ook die geskiktheid van hierdie tegniek vir heuning egtheid keuring.Master

Application of metabolomic profiling and fingerprinting approaches to food fraud cases

[eng] Food fraud is an intentional and misleading act in food that generally does not comply with food law and is motivated by economic gain. It encompasses several fraudulent practices such as deception during manufacture, diversion into illicit supply chains, interventions with the food product, or misrepresentation. In this context, the coming to light of the horse meat scandal at the beginning of 2013 highlighted the shortcomings of the European system against food fraud, increasing concern and interest among European citizens and administrative bodies. Under these circumstances, in recent years, omics tools —comprising genomics, transcriptomics, proteomics, metabolomics, and elementomics/isotopollomics— have been applied to solve food fraud issues, along with biostatistics and chemometrics. In most cases, their application has relied on profiling (focusing on determining targeted secondary chemical markers) or fingerprinting approaches (based on the unspecific detection of instrumental responses without assuming any previous knowledge about the sample composition), overcoming the traditional targeted analysis. In particular, since a food product’s metabolome varies according to its biological nature and several external conditions (i.e., either from a natural or anthropogenic origin), metabolomics has shown excellent potential to assess several issues related to its authenticity and quality. Therefore, in this thesis, several metabolomic profiling and fingerprinting approaches were developed to address different food fraud cases. In this line, liquid chromatography coupled to low- or high-resolution mass spectrometry (LC–LRMS, LC–HRMS) was proposed for the targeted approaches. In contrast, non-targeted methods were based on liquid chromatography with ultraviolet detection (LC-UV) or fluorescence detection (LC-FLD), LC–HRMS, or direct mass spectrometry (MS)-based techniques. Furthermore, non-supervised and supervised chemometric techniques allowed sample assignation and classification. As a result, the proposed analytical methodologies were successfully applied to several food products —including paprika, nuts and seeds, hen eggs, vegetable oils, and red wine— guaranteeing their classification and authentication regarding the geographical origin, botanical origin, production system, or quality category.[cat] El frau alimentari és un acte intencionat i enganyós produït en els aliments que, generalment, no compleix amb la legislació alimentària i que està motivat per un benefici econòmic. La sortida a la llum de l’escàndol de la carn de cavall a principis del 2013 va posar de manifest les mancances del sistema europeu contra el frau alimentari, augmentant la preocupació i l’interès entre els ciutadans i els organismes administratius europeus. En aquestes circumstàncies, en els darrers anys, s’han aplicat eines òmiques —que inclouen la genòmica, la transcriptòmica, la proteòmica, la metabolòmica i l’elementòmica/isotopol·lòmica— per resoldre qüestions relacionades amb el frau alimentari, juntament amb bioestadística i quimiometria. En la majoria dels casos, la seva aplicació s’ha efectuat mitjançant estratègies basades en perfils (centrant-se en la determinació dirigida de marcadors químics secundaris) o empremtes dactilars (basades en la detecció inespecífica de respostes instrumental sense assumir cap coneixement previ sobre la composició de la mostra), superant l’anàlisi dirigida tradicional. En concret, com que el metaboloma d’un producte alimentari varia segons la seva naturalesa biològica i un seguit de condicions externes (siguin d’origen natural o antropogènic), la metabolòmica ha demostrat un excel·lent potencial per avaluar diverses qüestions relacionades amb la seva autenticitat i qualitat. En aquesta tesi, es van desenvolupar diverses estratègies de perfils i empremtes dactilars metabolòmiques per abordar alguns casos de frau alimentari. Així, es va proposar la cromatografia líquida acoblada a l’espectrometria de masses de baixa o alta resolució (LC–LRMS, LC–HRMS) per als enfocaments dirigits. En canvi, els mètodes no dirigits es van basar en la cromatografia líquida amb detecció ultraviolada (LC-UV) o fluorescent (LC-FLD), LC–HRMS o tècniques basades en l’espectrometria de masses (MS) directa. A més, tècniques quimiomètriques no supervisades i supervisades van permetre l’assignació i classificació de les mostres. Com a resultat, les metodologies analítiques proposades es van aplicar amb èxit a diferents productes alimentaris —incloent el pebre vermell, fruits secs i llavors, ous de gallina, olis vegetals i vi negre— garantint-ne la classificació i autenticació pel que fa a l’origen geogràfic, l’origen botànic, el sistema de producció o la categoria de qualitat