Achieving second order advantage with multi-way partial least squares and residual bi-linearization with total synchronous fluorescence data of monohydroxy-polycyclic aromatic hydrocarbons in urine samples.

An attractive approach to handle matrix interference in samples of unknown composition is to generate second- or higher-order data formats and process them with appropriate chemometric algorithms. Several strategies exist to generate high-order data in fluorescence spectroscopy, including wavelength time matrices, excitation-emission matrices and time-resolved excitation-emission matrices. This article tackles a different aspect of generating high-order fluorescence data as it focuses on total synchronous fluorescence spectroscopy. This approach refers to recording synchronous fluorescence spectra at various wavelength offsets. Analogous to the concept of an excitation-emission data format, total synchronous data arrays fit into the category of second-order data. The main difference between them is the non-bilinear behavior of synchronous fluorescence data. Synchronous spectral profiles change with the wavelength offset used for sample excitation. The work presented here reports the first application of total synchronous fluorescence spectroscopy to the analysis of monohydroxy-polycyclic aromatic hydrocarbons in urine samples of unknown composition. Matrix interference is appropriately handled by processing the data either with unfolded-partial least squares and multi-way partial least squares, both followed by residual bi-linearization.

Solid-phase extraction, sample stacking and capillary zone electrophoresis for the analysis of urinary polycyclic aromatic hydrocarbon metabolites.

A capillary zone electrophoresis method is presented for the analysis of six biomarkers of polycyclic aromatic hydrocarbons in urine samples. Baseline resolution of 2-hydroxyfluorene, 2-hydroxynaphthalene, 1-hydroxypyrene, 9-hydroxyphenanthrene, 3-hydroxybenzo[a]pyrene, 4-hydroxybenzo[a]pyrene and 5-hydroxybenzo[a]pyrene was achieved in approximately 17 min with a 20 mM borate buffer prepared in 50% methanol-water (volume/volume). Competitive limits of detection were obtained for all the studied metabolites using commercial instrumentation equipped with an ultraviolet-visible absorption detector. Detection at the sub-parts-per-billion concentration levels was made possible via sample pre-concentration based on solid-phase extraction and sample stacking. Solid-phase extraction was performed with the aid of a twelve port vacuum manifold. Sample stacking was carried out in methanol, i.e. the eluting solvent from the solid-phase extraction procedure. To the extent of our literature search, this is the first application of sample stacking to the analysis of monohydroxy-polycyclic aromatic hydrocarbons in urine samples. Metabolite recoveries varied from 93.2 ± 7.7% (5-hydroxybenzo[a]pyrene) to 108.7 ± 7.8% (2-hydroxynaphthalene). Limits of detection were at the trace level ranging from 0.99 ng mL(-1) (3-hydroxybenzo[a]pyrene) to 8.54 ng mL(-1) (2-hydroxynaphthalene). The new method was found to be free of interference from four pharmacological drugs - naproxen, ibuprofen, diclofenac and amoxicillin - that might be found in urine samples of unhealthy individuals.

Multi-way partial least-squares and residual bi-linearization for the direct determination of monohydroxy-polycyclic aromatic hydrocarbons on octadecyl membranes via room-temperature fluorescence excitation emission matrices.

Multi-way partial least-squares (N-PLS) is combined to the residual bi-linearization procedure (RBL) for the direct analysis of metabolites of polycyclic aromatic hydrocarbons in urine samples. Metabolite analysis is carried out via a two-step experimental procedure based on solid-phase extraction and room temperature fluorescence spectroscopy. Excitation-emission matrices are recorded from octadecyl (C18) membranes that serve as solid substrates for sample extraction and spectroscopic measurements. Excellent metabolite recoveries were obtained in all cases, which varied from 96.2±1.35% (9-hydroxyphenanthrene) to 99.7±0.49% (3-hydroxybenzo[a]pyrene). Background correction of extraction membranes is carried out with a new alternating least-squares (ALS) procedure adapted to second order data. The performance of N-PLS/RBL is compared to the well-established multivariate curve resolution-alternating least-squares (MCR-ALS) algorithm. Both algorithms provided similar analytical figures of merit, including their ability to handle unknown interference in urine samples. With only 10 mL of sample, the limits of detection varied between 0.06-0.08 ng mL(-1) (1-hydroxypyrene) and 0.016-0.018 ng mL(-1) (2-hydroxyfluorene). When compared to previously reported univariate calibration data, the limits of detection via N-PLS/RBL and MCR-ALS are approximately one order of magnitude higher. This was somehow expected due to the effect of unexpected components in multivariate figures of merit, i.e. a more realistic approach to the analysis of metabolites in human urine samples.

Room-temperature fluorescence spectroscopy of monohydroxy metabolites of polycyclic aromatic hydrocarbons on octadecyl extraction membranes.

Urine analysis of monohydroxy metabolites is recognized as an accurate assessment of human exposure to polycyclic aromatic hydrocarbons. Despite the sophisticated arsenal of analytical tools, monitoring of monohydroxy metabolites via simple, cost effective and direct methods of analysis still remains a challenge. This article evaluates the analytical potential of solid-phase extraction room-temperature fluorescence spectroscopy for the problem at hand. Extraction membranes serve the dual purpose of sample pre-concentration and solid substrate for RTF measurements. The potential of our proposition is demonstrated with the analysis of 2-hydroxy-fluorene, 1-hydroxy-pyrene, 3-hydroxy-benzo[a]pyrene and 9-hydroxy-phenanthrene in synthetic urine samples. Signal reproducibility is improved with the aid of a sample holder specifically designed for the manual optimization of luminescence signals. Background correction of solid substrates is carried out with the aid of Asymmetric Least Squares. Recovery values for the studied metabolites varied from 99.0 ± 1.2% (3-hydroxy-benzo[a]pyrene) to 99.9 ± 0.05% (1-hydroxy-pyrene). With only 10 mL of urine sample, the limits of detection varied from 57 pg mL(-1) (2-hydroxy-fluorene) to 2 pg mL(-1) (1-hydroxy-pyrene). Additional figures of merit include a simple experimental procedure for routine screening of numerous samples and compatibility with portable instrumentation for field analysis. Because of the non-destructive nature of fluorescence measurements, membranes can be brought to the lab for subsequent elution and confirmation of compounds via high-resolution techniques.

Gold nanoparticles deposited capillaries for in-capillary microextraction capillary zone electrophoresis of monohydroxy-polycyclic aromatic hydrocarbons.

This article presents the first application of gold nanoparticles deposited capillaries as pre-concentration devices for in-capillary microextraction CZE and their use for the analysis of monohydroxy-polycyclic aromatic hydrocarbons in synthetic urine samples. The successful separation of 1-hydroxypyrene, 9-hydroxyphenanthrene, 3-hydroxybenzo[a]pyrene (3-OHbap), 4-hydroxybenzo[a]pyrene and 5-hydroxybenzo[a]pyrene under a single set of electrophoretic conditions is demonstrated as well as the feasibility to obtain competitive ultraviolet absorption LOD with commercial instrumentation. Enrichment factors ranging from 87 (9-OHphe) to 100 (3-OHbap) made it possible to obtain LOD ranging from 9 ng/mL (9-OHphe and 3-OHbap) to 14 ng/mL (4-hydroxybenzo[a]pyrene).