Resolution of ternary mixtures of salicylic, salicyluric and gentisic acids by partial least squares and principal component regression: Optimization of the scanning path in the excitation-emission matrices

Source Apportionment of Environmental Combustion Sources using Excitation Emission Matrix Fluorescence Spectroscopy and Machine Learning

The link between particulate matter (PM) air pollution and negative health effects is well-established. Air pollution was estimated to cause 4.9 million deaths in 2017 and PM was responsible for 94% of these deaths. In order to inform effective mitigation strategies in the future, further study of PM and its health effects is important. Here, we present a method for identifying sources of combustion generated PM using excitation-emission matrix (EEM) fluorescence spectroscopy and machine learning (ML) algorithms. PM samples were collected during a health effects exposure assessment panel study in Seattle. We use archived field samples from the exposure study and the associated positive matrix factorization (PMF) source apportionment based on X-ray fluorescence and light absorbing carbon measurements to train convolutional neural network and principal component regression algorithms. We show EEM spectra from cyclohexane extracts of the archived filter samples can be used to accurately apportion mobile and vegetative burning sources but were unable to detect crustal dust, Cl-rich, secondary sulfate and fuel oil sources. The use of this EEM-ML approach may be used to conduct PM exposure studies that include source apportionment of combustion sources.

Application of time-resolved fluorescence to the determination of metabolites

A simple fluorescent methodology for the simultaneous determination of two major metabolites of acetylsalicylic acid--salicylic and gentisic acids--in pharmaceutical preparations and human urine is proposed. Due to the overlapping between the fluorescence spectra of both analytes, the use of the more selective fluorescence decay curves is proposed. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed with a simplex optimization procedure. A calibration matrix of thirteen standards plus two blank samples was processed using a partial least-squares (PLS) analysis. To assess the goodness of the proposed method, a prediction set of nine synthetic samples was analyzed, obtaining recovery percentages between 95% and 106%. Limits of detection, calculated by means of a new criterion, were 3.49 μg L(-1) and 1.66 μg L(-1) for salicylic and gentisic acids, respectively. The method was also tested in three pharmaceutical preparations containing salicylic acid, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of thirteen standards plus five analyte blanks. Although spectra of analytes and urine overlap strongly, no extraction method neither prior separation of the analytes were needed.

Direct determination of closely overlapping drug mixtures of diflunisal and salicylic acid in serum by means of derivative matrix isopotential synchronous fluorescence spectrometry

A direct method for the simultaneous fluorimetric determination of two anti-inflammatory drugs in serum is proposed. The combination of matrix isopotential synchronous fluorescence (MISF) and first derivative technique provides good analytical results and permits the simultaneous determination of diflunisal and salicylic acid in human serum. MISF spectra are obtained by calculating the isopotential trajectory in the three-dimensional fluorescence spectrum for a serum solution. In the spectral contour, the trajectory is taken to be the portion of the line that passes by the fluorescence maxima of both compounds ensuring a sensitivity level similar to that of a direct determination in absence of background fluorescence. Analysis was carried out in water using a pH of 7.2 provides by 0.1 M sodium dihydrogen phosphate buffer. Serum samples are diluted 100 times and provide linear calibration plots at diflunisal and salicylic acid concentrations up to 800 ng mL(-1). The goodness of the analytical signal was checked by using variance analysis. Signals recorded throughout the calibration range were subjected to three calibrations per each analyte, both in the absence and in the presence of variable amounts of the other analyte. Differences between individual calibrations and slopes were compared with those within individual calibrations. Based on the results, diflunisal and salicylic acid can be accurately quantified in the presence of each other. The limit of detection calculated according to Clayton who uses error propagation throughout the calibration curve and a non-centralized security factor was 36.8 and 37.3 ng mL(-1) for diflunisal and salicylic acid, respectively.

Simultaneous spectrofluorimetric determination of (acetyl)salicylic acid, codeine and pyridoxine in pharmaceutical preparations using partial least-squares multivariate calibration

A partial least-squares calibration (PLS) method for the simultaneous spectrofluorimetric determination of salicylic acid (SA), codeine (CO) and pyridoxine (PY) is proposed. The determination of SA, CO, and PY has been carried out in mixtures of up to three components by recording the emission fluorescence spectra between 300 and 500 nm (lambda(exc) = 220 nm). Due to the fact of the strong spectral overlap among the excitation and also among the emission spectra of these compounds, a previous separation should be carried out in order to determine them by conventional spectrofluorimetric methodologies. Here, a full-spectrum multivariate calibration PLS method is developed. The experimental calibration matrix was constructed with 14 samples. The concentration ranges considered were 0.1-2.0 (SA), 0.25-3.0 (CO) and 0.10-2.0 (PY) mg x l(-1). The optimum number of factors was selected by using the cross-validation method. The method also allows the simultaneous determination of acetylsalicylic acid (ASA), CO and PY by previous alkaline hydrolysis of ASA to SA. To check the accuracy of the proposed method, it was applied to the determination of these compounds in synthetic mixtures and in pharmaceuticals.

Enhanced synchronous spectrofluorometric determination of tetracycline in blood serum by chemometric analysis. Comparison of partial least-squares and hybrid linear analysis calibrations

Tetracycline has been determined in human serum samples by a combination of: (1) synchronous fluorescence spectra of whole sera treated with Mg2+, and (2) the multivariate calibration methods of partial least-squares (PLS-1) and a variant of the recently introduced hybrid linear analysis (HLA), which does not require the knowledge of pure-component spectra. The calibration set was designed with 50 sera spiked with concentrations of tetracycline in the range 0.0-4.0 micrograms mL-1'. Studies concerning validation, precision, accuracy and figures of merit (selectivity, sensitivity and limit of determination) were also carried out. A novel wavelength-selection procedure was applied to minimize the effect of nonmodeled interferents present in serum samples containing bilirubin, triglycerides, and salicylate. Overall, the performance of the newly developed HLA approach seems to be better than that of PLS-1.