Quantitative analyses of multicomponent fluorescence data by the methods of least squares and non-negative least sum of errors

Review of Fluorescence Spectroscopy in Environmental Quality Applications

Fluorescence spectroscopy is an optical spectroscopic method that has been applied for the assessment of environmental quality extensively during the last 20 years. Most of the earlier works have used conventional light sources in spectrofluorometers to assess quality. Many recent works have used laser sources of light for the same purpose. The improvement of the energy sources and of the higher resolution spectrometers has led to a tremendous increase in applications. The motivation for the present review study is the increasing use of laser sources in environmental applications. The review is divided in two parts. The fundamental principles of fluorescence spectroscopy are described in the first part. The environmental applications are described in the second part.

Introducing Principal Coordinate Analysis (PCoA) Assisted EEMF Spectroscopic Based Novel Analytical Approach for the Discrimination of Commercial Gasoline Fuels

In the present work, a novel analytical procedure by integrating principal coordinate analysis (PcoA) with excitation-emission matrix fluorescence (EEMF) spectroscopy was introduced for discriminating the commercial gasoline fuels. The PcoA technique involved analysis of the distance matrices containing the dissimilarity information and it can serve as an efficient tool for capturing the major as well as subtle compositional differences among the analyzed commercial gasoline samples. The utility of the proposed PcoA assisted EEMF analytical procedure was successfully tested by discriminating gasoline fuel samples belonging to five different industrial brands. The obtained results clearly showed that combination of PcoA and EEMF could provide a simple, sensitive and economical analytical procedure to carry out the rapid analyses of the gasoline samples belonging to different brands.

The Right Answer for the Right Reason: My Personal Goal for Quantum Chemistry

A brief history of quantum theory is given to illustrate the barriers to progress caused by preconceived ideas. The biases in my own thinking which I had to overcome to approach the right answer for the right reason are discussed. This is followed by a personal autobiography illustrating how I have led a life of serendipity with no real sense of purpose. Chance events have shaped my life. The algorithms for which I am best known are briefly discussed. Then highlights from the many applications of theory to excited states, bonding in ice, spin properties and magnetism, (e,2e) shake-up spectra, and organic reactions are mentioned. This wide range of applications is mostly due to accidental collaboration with colleagues who sought my help. My real interest was in developing methods which could address these problems.

Analysis of dilute aqueous multifluorophoric mixtures using excitation-emission matrix fluorescence (EEMF) and total synchronous fluorescence (TSF) spectroscopy: a comparative evaluation

Excitation-emission matrix fluorescence (EEMF) and total synchronous fluorescence (TSF) spectroscopy are two conceptually different fluorescence techniques that have been used to map the fluorescence responses of the fluorophores present in a multifluorophoric mixture. EEMF was introduced four decades back and most of the fluorimeters have the suitable computer program which allows the acquisition EEMF spectra. Recently introduced TSF spectroscopy has been shown to possess good application potential in analytical fluorimetry and has started attracting the attention of analytical chemists. TSF data structure, however, is intrinsically different from EEMF data structure and a better understanding of TSF data structure is crucial to utilising its application potential. In the present work, a comprehensive comparative study between EEMF and TSF spectroscopic data set was performed by taking aqueous mixtures containing low concentrations of benzo[a]pyrene, chrysene, and pyrene as test case. The EEMF and TSF data structures were clearly explained by taking pyrene as an example. The effects of Rayleigh and Raman scattering on the quality of EEMF and TSF data sets were studied. EEMF and TSF data sets of dilute aqueous mixtures of benzo[a]pyrene, chrysene, and pyrene were subjected to three chemometric techniques PARAFAC, N-PLS, and MCR-ALS analysis. TSF data set in particular was found to be highly attuned to MCR-ALS analysis. Obtained results of chemometric analyses on EEMF and TSF data sets show that TSF data of dilute aqueous mixtures provides more accurate spectral and concentration information than EEMF data sets. Therefore, TSF spectroscopy could be considered as an alternate to the EEMF for the analyses of dilute multifluorophoric mixtures.

An in-depth study linking the infrared spectroscopy and photoluminescence of porous silicon during ambient hydrogen peroxide oxidation

We carefully tailored a porous silicon (pSi) surface by oxidation with hydrogen peroxide (H2O2) to determine the time-dependent changes in nanocrystallite surface chemistries (e.g., Si-O-Si, SiH(x) [x = 1, 2], OySiH [y = 2, 3], and SiOH/H2O) and their influence on the pSi photoluminescence (PL). The relationship between infrared band amplitudes and PL intensity were evaluated under H2O2 and O3 (previously studied) oxidation. The pSi surface composition under O3 and H2O2 oxidation conditions tended to, save the O(y)SiH (y = 2, 3) species, approach similar values at the longest oxidation times studied, but they took very different paths in reaching these end points. Furthermore, the pSi surface compositions that exhibit maximum/minimum PL under each oxidant are very different.

Link between O2SiH infrared band amplitude and porous silicon photoluminescence during ambient O3 oxidation

We carefully evaluate how porous silicon (pSi) surface oxidation by ozone (O(3)) and the resulting changes in nanocrystallite surface chemistries (e.g., SiOSi, SiH(x) (x = 1-3), O(y)SiH (y = 1-2), and SiOH) influence the pSi photoluminescence (PL). We discover a relationship between the pSi PL and the O(2)SiH band amplitude.

Problem of mixtures with known compositions and IRONFLEA method for multivariate curve resolution

A special case of gray spectral data systems [(a) F.-T. Chau, Y.-Z. Liang, J. Gao, X.-G. Shao (Eds.), Chemometrics: From Basics to Wavelet Transform, Chemical Analysis Series, vol. 164, John Wiley & Sons, Inc., 2004; (b) Y.Z. Liang, O.M. Kvalheim, R. Manne, Chemom. Intell. Lab. Syst. 18 (1993) 235-250] is discussed here and the least-squares method for the multivariate curve resolution (MCR) named IRONFLEA is proposed. The system under consideration is the bilinear spectral data of the samples with known chemical compositions and unknown concentration matrix. If the spectra of samples (A(i)) and (Q+A(i)) (i = 1, ..., n, n > or = 2) are available, then the spectrum and the concentrations of Q could be found and the solution is unique. A practical chemical model for this problem could be mixtures, polymers, peptides, oligosaccharides, or supramolecular formations made of a limited number of monomeric components. In the cases of polymeric or oligomeric samples the spectral contributions and the concentrations of the particular monomeric units are extracted. The method is capable of extracting chemically meaningful spectra of components. The method is implemented in SAS IML code and tested for the deconvolution of spectra of polymers made of styrene derivatives with known monomeric compositions [(a) H. Fenniri, L. Ding, A.E. Ribbe, Y. Zyrianov, J. Am. Chem. Soc. 123 (2001) 8151-8152; (b) H. Fenniri, S. Chun, L. Ding, Y. Zyrianov, K. Hallenga, J. Am. Chem. Soc. 125 (2003) 10546-10560]. The method performs calculations fast enough to allow the incorporation of leave-one-out outlier removal procedure.

Excitation-emission matrix fluorescence spectroscopy in conjunction with multiway analysis for PAH detection in complex matrices

A field portable, single exposure excitation-emission matrix (EEM) fluorometer has been constructed and used in conjunction with parallel factor analysis (PARAFAC) to determine the sub part per billion (ppb) concentrations of several aqueous polycyclic aromatic hydrocarbons (PAHs), such as benzo(k)fluoranthene and benzo(a)pyrene, in various matrices including aqueous motor oil extract and asphalt leachate. Multiway methods like PARAFAC are essential to resolve the analyte signature from the ubiquitous background in environmental samples. With multiway data and PARAFAC analysis it is shown that reliable concentration determinations can be achieved with minimal standards in spite of the large convoluting fluorescence background signal. Thus, rapid fieldable EEM analyses may prove to be a good screening method for tracking pollutants and prioritizing sampling and analysis by more complete but time consuming and labor intensive EPA methods.

Three- and four-way parallel factor (PARAFAC) analysis of photochemically induced excitation–emission kinetic fluorescence spectra

Independently emerging fluorescence profiles of unknown, photochemically induced degradation products of several naturally non-fluorescent pesticides were monitored using single exposure excitation-emission fluorescence spectroscopy. Three-way parallel factor analysis (PARAFAC) was employed to uniquely resolve the pure fluorescent spectra of the overlapping photolysis products. The quantitative utility of EEM photolysis-based determinations was demonstrated by employing four-way PARAFAC models built from EEM time cubes of multiple fenvalerate samples. The 4-way PARAFAC models were then used to predict original pesticide concentrations resulting in conservative limit of detection and root mean square errors of calibration (RMSEC) of 3 microM each.

Evaluation of Nd:YAG-pumped Raman shifter as a broad-spectrum light source

We have examined the utility of a gas-filled, Nd:YAG-laser-pumped Raman shifter as a possible broad-spectrum light source. Six to nine new output frequencies with pulse energies above 1 µJ are produced when a pure-hydrogen or pure-methane Raman shifter is pumped with 40 mJ of secondharmonic, 20 mJ of third-harmonic, or 11 mJ of fourth-harmonic pump pulse energy. Optimum output occurs at pressures of approximately 10 atm for the pure-gas experiments. We also report the output frequencies and pulse energies of a mixed hydrogen-methane Raman shifter pumped by 20 mJ of the third harmonic of the laser for various proportions of the two gases at pressures up to nearly 20 atm. Depending on composition and pressure, over a dozen new output lines with pulse energies over 1 µJ can be produced. We discuss the nonlinear processes involved, the optimum operating conditions, and the suitability of the source for our application of groundwater monitoring.

Fluorescence lidar detection with shot noise and sky radiance

Rank annihilation-factor analysis is potentially the best method of analyzing fluorescence lidar returns because of the following capability. Rank annihilation can recognize a fluorescence signal of a component that is hidden by a large fluorescence background without a spectrum of that background. Theoretical models were developed to analyze the effectiveness of rank annihilation-factor analysis in the interpretation of lidar returns. Interferents such as background fluorescence, photon-counting noise, sky radiance, and atmospheric extinction degraded the lidar-return spectra in numerical simulations. The rank annihilation-factor analysis detection algorithm was most severely biased by the combination of photon-counting noise and sky radiance. Rank annihilation calculations were also compared with calculations done by two other detection algorithms: finding peak wavelengths and the least-squares technique. Rank annihilation is better than both techniques.

Chemical Sensing in Process Analysis

Improvements in process control, which determine production efficiency and product quality, are critically dependent upon on-line process analysis. The technology of the required instrumentation will be substantially expanded by advances in sensing devices. In the future, the hardware will consist of sensor arrays and miniaturized instruments fabricated by microlithography and silicon micromachining. Chemometrics will be extensively used in software to provide error detection, selfcalibration, and correction as well as multivariate data analysis for the determination of anticipated and unanticipated species. A number of examples of monolithically fabricated sensors now exist and more will be forthcoming as the new paradigms and new tools are widely adopted. A trend toward not only on-line but even in-product sensors is becoming discernible.

Video fluorometer

Details of a unique computer controlled multichannel fluorometer are given. Features include: a novel optical system enabling simultaneous acquistion of excitation and emission data over broad spectral ranges, a highly sensitive silicon intensified target (SIT) vidicon detector, and a video interface to a minicomputer allowing data acquisition at the standard television rate.