Analysis of chemical deposits on tooth enamel exposed to total particulate matter from cigarette smoke and tobacco heating system 2.2 aerosol by novel GC-MS deconvolution procedures.

Tobacco smoking contributes to tooth discoloration. Pigmented compounds in the smoke generated by combustion of tobacco can cause discoloration of dental hard tissues. However, aerosols from heated tobacco products cause less discoloration than cigarette smoke (CS) in vitro. The objective of the present study was to optimize a method for extracting the colored chemical compounds deposited on tooth enamel following exposure to total particulate matter (TPM) from CS or a heated tobacco product (Tobacco Heating System [THS] 2.2), analyze the extracts by gas chromatography coupled to time-of-flight mass spectrometry, and identify the key chemicals associated with tooth discoloration. Sixty bovine enamel blocks were exposed for 2 weeks to TPM from CS or THS 2.2 aerosol or to artificial saliva as a control. Brushing without toothpaste and color measurements were performed each week. Noticeable discoloration of enamel was observed following exposure to CS TPM. The discoloration following exposure to THS 2.2 aerosol TPM or artificial saliva was not distinguishable to the eye (ΔE < 3.3). Carbon disulfide was used to extract surface-deposited chemicals. Untargeted analyses were followed by partial least squares correlation against discoloration scores (R2 = 0.96). Eleven compounds had variable importance in projection scores greater than 2. Discriminant autocorrelation matrix calculation of their mass spectral information identified eight of the eleven compounds as terpenoids. None of the compounds were related to nicotine. Several of these compounds were also detected in THS 2.2 aerosol TPM-exposed enamel, but at lower levels, in line with our findings showing less discoloration. Compared with CS TPM exposure, THS 2.2 aerosol TPM exposure resulted in lower deposition of color-related compounds on enamel surface, consistent with minimal discoloration of dental enamel.

Monitoring changes in the structure and properties of humic substances following ozonation using UV-Vis, FTIR and (1)H NMR techniques.

The main objective of this work is to conduct a comprehensive structural characterization of humic substances using the following experimental techniques: FTIR, 1H NMR and several UV­Vis parameters (Specific UV Absorbance at 254 nm or SUVA254, SUVA280, A400, the absorbance ratios A210/254, A250/365, A254/203, A254/436, A265/465, A270/400, A280/350, A465/665, the Absorbance Slope Index (ASI), the spectral slopes S275­295, S350­400 and the slope ratio SR). These UV­Vis parameters have also been correlated with key properties of humic substances such as aromaticity, molecular weight (MW) and trihalomethane formation potential (THMFP). An additional objective of this work is also to evaluate the usefulness of these techniques to monitor structural changes in humic substances produced by the ozonation treatment. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard: SRFA, Suwannee River Humic Acid Standard: SRHA and Nordic Reservoir Fulvic Acid Reference: NLFA) and the other one was a terrestrial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: AHA). The UV­Vis parameters showing the best correlations with aromaticity in this study were SUVA254, SUVA280, A280/A350 ratio and A250/A364 ratio. The best correlations with molecular weight were for SUVA254, SUVA280 and A280/A350 ratio. Finally, in the case of the THMFP it was STHMFP-per mol HS the parameter showing good correlations with most of the UV­Vis parameters studied (especially with A280/A350 ratio, A265/A465 ratio and A270/A400 ratio) whereas STHMFP-per mg C showed poor correlations in most cases. On the whole, the UV­Vis parameter showing the best results was A280/A350 ratio as it showed excellent correlations for the three properties studied (aromaticity, MW and THMFP). A decrease in aromaticity following ozonation of humic substances can be readily monitored by 1H NMR and FTIR; the latter technique also allows to monitor an increase in carboxylic acidity with ozone dosage. This organic matter originated following ozonation (more aliphatic in character and more polar) is expected to be recalcitrant to further oxidation. The terrestrial humic acid (AHA) showed some structural differences with the aquatic humic substances and its behavior upon ozonation also differed in some extent from that shown by them.

A comprehensive structural evaluation of humic substances using several fluorescence techniques before and after ozonation. Part I: structural characterization of humic substances.

The main objective of this work (Part I) is to conduct a comprehensive structural characterization of humic substances, using all the current fluorescence techniques: emission scan fluorescence (ESF), synchronous fluorescence spectroscopy (SFS), total luminescence spectroscopy (TLS or EEM) through the use of both 2-D contour maps and 3-D plots, fluorescence index and the λ0.5 parameter. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard, Suwannee River Humic Acid Standard and Nordic Reservoir Fulvic Acid Reference) and the other one was a commercial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: ALHA). The EEM spectra for the three natural aquatic substances were quite similar, showing two main peaks of maximum fluorescence intensity: one located in the ultraviolet region and centered at around Ex/Em values of 230/437 nm (peak A) and another one in the visible region, centered at around 335/460 nm (peak C); however, the EEM spectrum of ALHA is completely different to those of natural aquatic humic substances, presenting four poorly resolved main peaks with a high degree of spectral overlap, located at 260/462, 300/479, 365/483 and 450/524 nm. The synchronous spectra at Δλ=18 and 44 nm (especially at Δλ=18 nm) allowed the identification of a protein-like peak at λsyn around 290 nm, which was not detected in the EEM spectra; as it happened with EEM spectra, the synchronous spectra of ALHA are quite different from those of the aquatic humic substances, presenting a higher number of bands that suggest greater structural complexity and a higher degree of polydispersity. Good correlations were achieved between (13)C NMR aromaticity and both fluorescence index and λ0.5 parameter. The different spectra presented by ALHA compared to those shown by the natural aquatic humic substances for all the fluorescence techniques studied suggest an important structural difference between them, which cast doubt on the use of commercial humic acids as surrogates for natural humic substances.

A comprehensive structural evaluation of humic substances using several fluorescence techniques before and after ozonation. Part II: evaluation of structural changes following ozonation.

The main objective of this work (Part II) is to evaluate the usefulness of fluorescence techniques to monitor structural changes in humic substances produced by the ozonation treatment, using all the current fluorescence techniques: Emission scan fluorescence (ESF), synchronous fluorescence spectroscopy (SFS), total luminescence spectroscopy (TLS or EEM) through the use of both 2-D contour maps and 3-D plots, fluorescence index and the λ0.5 parameter. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard: SUFA, Suwannee River Humic Acid Standard: SUHA and Nordic Reservoir Fulvic Acid Reference: NOFA) and the other one was a commercial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: ALHA). The lowest ozone dosage tested (0.25mg O3/mg TOC) caused no appreciable change in the different types of fluorescence spectra under study, therefore the structural change produced in the humic macromolecules may be considered of little significance. Concerning EEM and synchronous spectra, the two natural fulvic acids (SUFA and NOFA) showed a decrease in fluorescence intensity as ozone dosage increased, but the natural humic acid (SUHA) showed a different behaviour: an initial increase in fluorescence intensity at medium ozone dosages (1.5 mg O3/mg TOC) followed by an intensity decrease for the higher ozone dose (7.5 mg O3/mg TOC). Regarding synchronous spectra, the moderate dosage of 1.5 mg O3/mg TOC led to an increase in the fluorescence of the protein-like peak at λsyn=285 nm for the natural humic substances. The results obtained for the fluorescence index and λ0.5 may suggest that the greatest degradation of aromatic structures within the humic macromolecule occurs at high ozone dosages, whereas the predominant effect at moderate dosages would be the break-up of the humic macromolecule into lower molecular weight fragments. The behaviour of the commercial humic acid (ALHA) upon ozonation was very different from that of the natural humic substances (SUFA, SUHA and NOFA), a result that was confirmed with all the fluorescence techniques used in this study and that would cast doubt on the use of commercial humic acids as surrogates for natural humic substances.