Quantitative Analysis Of Environmental Samples Research Articles

Nanostructured polyaniline SPME fiber coating for chemical warfare agents analysis

Nanostructured polyaniline (PANI) was electrochemically obtained as a fiber coating of solid-phase microextraction (SPME) and then used in the analysis of selected organoarsenic and organophosphorus compounds in soil samples. Also, comparative studies of the obtained PANI fibers with seven commercially available fibers for varying miscellaneous polarity, and various absorption and/or adsorption natures, were carried out. Quantitative analysis of environmental samples was performed using a gas chromatograph coupled with a tandem mass spectrometer. During the analysis of organophosphorus compounds, the PANI fiber showed at least 20% greater sorption efficiency than any commercially available fiber, whereas, in the case of organoarsenic compounds, the sorption efficiency of the PANI fiber increased with the expansion in the number of phenyl rings in the molecule. The PANI coating material was characterised by N2 adsorption–desorption, scanning electron microscopy, infrared spectroscopy and thermogravimetric analysis. SEM imaging confirmed a nanostructured form of PANI. The repeatability for one fiber (n = 7), expressed as the relative standard deviation ranges from 3.2% to 4.4% depending on the kind of tested chemical compound. The reproducibility (calculated as relative standard deviation of the 9 prepared fibers) was not greater than 7.2% Under the optimized conditions, the proposed method was linear over approximately 4 orders for organophosphorus compounds (0.02–100 ng g−1) and 5 orders for organoarsenic compounds (0.12–5000 ng g−1) of magnitude for the tested compounds, with linear determination coefficients (R2) greater than 0.972, and the limit of detection for the home-made PANI fiber was relatively low (0.006–0.45 ng g−1). In comparison with all commercially available SPME fibers, the new PANI fiber was more selective for the tested aromatic and organophosphorus compounds and easily as well as inexpensively prepared. The resulting stationary phase allowed for quantitative analysis of selected organophosphorus and organoarsenic compounds from the group of warfare agents.

Surface‐enhanced Raman spectroscopy coupled with advanced chemometric models for quantification of sulfide anion in environmental water samples

AbstractIn this work, surface‐enhanced Raman spectroscopy (SERS) was employed for the quantification of sulfide anion (S2−) in aqueous samples. Silver nanoparticles modified with trithiocyanuric acid were used as the SERS enhancing substrate. To address the problem of poor reproducibility of SERS signal caused by the uncontrollable variations in physical properties of enhancing substrate, the performance of several calibration models for quantitative analysis of the SERS measurements of S2− samples were evaluated and compared. The calibration models studied were univariate ratiometric model based on the intensity ratio between the characteristic SERS peaks of trithiocyanuric acid, PLS models built on the raw and preprocessed SERS measurements, and the generalized ratiometric indicator based multiplicative effects model (MEMGRI). Experimental results showed that among the calibration models considered in this contribution, only MEMGRI model achieved accurate and precise concentration predictions for S2− in the spiked environmental water samples with recovery rates varying within the range of 94% to 106%. Therefore, it is reasonable to expect that the combination of SERS technique with MEMGRI model may be a competitive alternative for quantitative analysis of environmental samples.

Azaindole modified imine moiety as fluorescent probe for highly sensitive detection of Fe3+ ions

An azaindole based schiff base AzIm was synthesized that serve as a luminescent turn “off” switch for the detection of Fe3+ ions. The photoluminescence intensity of AzIm was quenched significantly in the presence of 30μM Fe3+ ions. The sensing response of the probe was tested at different ranges of pH and at different cation concentrations between 2 and 25μM. Analytical characteristics were evaluated using standard Benesi-Hildebrand equation and the system displayed micromolar sensitivity for these ions. The specific diminished emission signal upon Fe3+ binding was interpreted in terms of the enhanced photoelectron transfer from azaindole group, which induces very fast and efficient non-radiative decay of the excited states of the sensor. In addition, practical utilization of luminescent AzIm was further supported by significant ion selective stability against the presence of extraneous charged species that makes this system compatible for quantitative analysis of environmental samples.

Characterizing and Compensating for Matrix Effects Using Atmospheric Pressure Chemical Ionization Liquid Chromatography−Tandem Mass Spectrometry: Analysis of Neutral Pharmaceuticals in Municipal Wastewater

Matrix effects are a great challenge for the quantitative analysis of environmental samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Signal suppression or enhancement can compromise the accuracy of analytical results. While matrix effects have been relatively well studied for applications of LC-MS/MS instrumentation with electrospray ionization, there have been relatively few studies to evaluate matrix effects when using atmospheric pressure chemical ionization (APCI) as the ion source. In this study, we determined the effects of sample matrix on the analysis of six neutral pharmaceuticals (i.e., caffeine, cotinine, carbamazepine and its major metabolite, carbamazepine-10,11-dihydrodiol, trimethoprim, and fluoxetine) in samples of municipal wastewater using LC-APCI-MS/MS and evaluated whether isotope-labeled internal standards can be used to compensate for matrix effects. The matrix effects were measured using postextraction spikes and postcolumn direct infusion, respectively. The results showed that the matrix in the extracts prepared from municipal wastewater enhanced the signals for four of the six analytes when using an APCI source. Without correction for signal enhancement, apparent recoveries of the analytes from wastewater samples were overestimated to levels as high as 178% of the spiked amount. Isotope-labeled compounds corrected for these overestimates that occurred as a result of interferences from the sample matrix.

Circuit Board Analysis for Lead by Atomic Absorption Spectroscopy in a Course for Nonscience Majors

Disposal of electronic waste is a growing problem. This article describes an experiment for nonmajors that was developed (i) to demonstrate the concept of atomic absorption (AA) to the students by qualitative screening of circuit board materials and (ii) to demonstrate the use of AA for quantitative analysis of environmental samples. Circuit board samples are digested in aqua regia and analyzed following dilution. This experiment provides an effective demonstration of the lead content of consumer products that students can readily identify with. For nonmajors, the lab provides a significant introduction to major quantitative techniques of environmental analysis. The experiment can readily be extended to projects for science majors in the general chemistry or analytical chemistry courses. The experiment can also easily be connected to discussions of the potential environmental hazards of unsafe disposal of used electronic equipment and discussion of the various public policy options for dealing with this growing problem.

Evaluation of N-methyl-N-tert-butyldimethylsilyl trifluoroacetamide for environmental analysis under both EIMS and electron capture NICIMS conditions and comparison to trimethylsilyl reagents under EIMS

N-Methyl-N-tert-butyldimethylsilyltrifluoroacetamide (MTBSTFA) is a silylating agent with a range of applicability in clinical and environmental analysis, particularly when substrates possess at least moderate acidity. In this paper, we demonstrate its applicability and limitations as a reagent for environmental analysis by comparing and contrasting two different target analyte problems in a sewage effluent matrix. In one case, electron ionization was used for the determination of three potential endocrine disrupting compounds: 17β-oestradiol, ethynyl oestradiol, and oestrone where the phenolic functionality was silylated with MTBSTFA and compared with results using N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA) as the reagent. In this instance, a large volume of effluent was subjected to either solid-phase extraction followed by cleanup using high-performance gel permeation chromatography (AppI) or liquid/liquid extraction followed by SPE fractionation and HPLC fractionation (AppII). The method using BSTFA rather than MTBSTFA was demonstrated to work down to low and sub-ppt levels where the target compounds were found. In a parallel and contrasting study, sewage effluent was analysed for 3,5,6-trichloropyridinol (TCP) by extracting one liter of water using liquid–liquid extraction and determined by GC/MS operated in the negative ion chemical ionization (electron capture) mode after derivatization with MTBSTFA. TCP is the major metabolite of the commonly used insecticide, chlorpyrifos, and herbicide trichlorpyr. The recoveries using dichloromethane as the extractant were 59%, with a relative standard deviation of 2%. This method was used to investigate levels of TCP in sewage effluent. During this analysis, a tentatively identified additional isomer of TCP (X-TCP) was found. The 3,5,6-TCP, the common chlorpyrifos metabolite and the synthesized isomer, 3,4,5-TCP were compared with X-TCP. All three isomers have significantly different retention times. The average level of 3,5,6-TCP was 3.4 ng L−1, while the level of X-TCP was 39.8 ng L−1. The two approaches are compared and contrasted with respect to artefact formation and matrix component effects. The reagent MTBSTFA is found to be suitable for quantitative analysis of environmental samples for relatively acidic substrates (e.g. phenols and carboxylic acids). More powerful silylating agents such as N-methyl-N-trimethylacetamide or BSTFA are required for sterols and similar substrates. The stability of the two silylating reagents appears to be similar and practical for accurate quantitative analysis. Differences in EI spectra with respect to fragmentation may also dictate which reagent is preferred.

Adduct formation in LC–ESI–MS of nonylphenol ethoxylates: mass spectrometrical, theoretical and quantitative analytical aspects

The analysis of nonylphenol ethoxylate (A 9PEO n ) surfactants with LC–ESI–MS was investigated in a detailed study of the formation of different types of adducts. Part of the observations was explained by calculating their relative stabilities using molecular dynamics techniques. Strong differences in adduct formation behaviour were found for different oligomers. Beside the common sodium adducts, surfactant dimer adducts [2 × A 9PEO 1,2 + Na] +, adducts including a solvent molecule [A 9PEO 1,2 + MeOH + Na] + and doubly charged adducts [A 9PEO >11 + 2 × Na] 2+ were found. Molecular dynamics calculations showed that the A 9PEO n molecule wraps itself around the complexing sodium ion in a way that negative electronic charges on oxygen have optimum electrostatic interaction with this ion. van der Waals interactions between alkyl chains are of less importance for the stability of these adducts. Both [2 × A 9PEO 2,5 + Na] + dimer and [A 9PEO 2,5 + Na] + monomer adducts turned out to be stable from an energetic point of view with adducts of A 9PEO 5 being more stable than adducts of A 9PEO 2. Only for the monomer adduct the latter is in accordance with experimental observations. Consequences of the formation of several adducts per A 9PEO n oligomer for the quantitative analysis of environmental samples were evaluated. In clean samples, it was found that the presence of short-chain A 9PEO 1,2 can cause an overestimation of long-chain A 9PEO >2. In real environmental extracts, other processes like matrix effects have a stronger influence on the quantitative result, and therefore no significant influence of adduct formation processes could be observed. However, inclusion of [A 9PEO 1,2 + MeOH + Na] + adduct signals does improve the detection limits of the two short-chain oligomers. Correct quantitative results are obtained when A 9PEO 1 and A 9PEO 2 are quantified separately, and longer oligomers with a molar calibration followed by correction of the average molar weight of the A 9PEO >2 in the sample.

Operational options to reduce matrix effects in liquid chromatography–electrospray ionisation-mass spectrometry analysis of aqueous environmental samples

Matrix effects like signal enhancement or suppression can severely compromise quantitative analysis of environmental samples with liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS). Several operational options were studied to reduce such matrix effects in the determination of polar organic trace contaminants from water, like non-steroidal anti-inflammatory drugs, among them ibuprofen, diclofenac and naproxen, lipid regulators like bezafibrate and clofibric acid and industrial chemicals (2-substituted benzothiazoles). A step-wise removal of organic matrix from a wastewater sample by ultrafiltration showed that the majority of matrix effects in that sample was due to low molecular weight compounds <1 kDa. For such wastewaters samples size-exclusion, as in restricted access material (RAM), is not a useful clean-up strategy. Reducing the eluent flow entering the ESI interface by post-column splitting increased instrumental sensitivity and reduced matrix effects. The flow optimum was analyte-dependent and ranged from 20 to 100 μL/min. Sensitivity in the positive ion mode increased up to nine-fold upon flow-reduction for some analytes detected in the positive ion mode. At low flow rates matrix effects are reduced by 45–60% on average. If moderate matrix effects occurred, post-column splitting may allow obtaining reliable quantitative data even with external calibration.

Evaluation of three calibration methods to compensate matrix effects in environmental analysis with LC-ESI-MS

In quantitative analysis of environmental samples using high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) one of the major problems is the suppression or, less frequently, the enhancement of the analyte signals in the presence of matrix components. Standard addition is the most suitable method for compensating matrix effects, but it is time-consuming and laborious. In this study we compare the potential of three calibration approaches to compensate matrix effects that occurred when seven analytes (naphthalene sulfonates) were quantified in time series samples of waters with different matrices (untreated and treated industrial wastewater). The data obtained by external calibration, internal calibration with one standard, and external sample calibration (corresponding to matrix-matched calibration) were compared with those obtained by standard addition. None of the three approaches were suitable for a sample series of highly loaded, untreated wastewater with highly variable matrix. For less heavily loaded and less variable samples (treated wastewater effluents), the external sample calibration provided reasonable results for most analytes with deviations mostly below 25% as compared to standard addition. External sample calibration can be suitable to compensate matrix effects from moderately loaded samples with more uniform matrices, but it is recommended to verify this for each sample series against the standard addition approach.

TRXRF analysis of environmental lead and heavy metals to monitor pollution in Caracas, Venezuela

Environmental monitoring has been one of the major issues worldwide since the Rio Conference 1992. In Venezuela several projects started to assess the industrial activity as a burden on the living environment. In this work we present a quantitative analysis of environmental samples collected in a residential and industrial sector of the Capital using the powerful technique of total reflection X-ray fluorescence. Sample preparation is described and results are shown of lead and other heavy metals. The elements with higher concentration were Fe, Sn and Pb which reported values in the range of 1.9–2.9 wt.%, 0.8–1.4 wt.% and 0.2–0.4 wt.%, respectively. Total heavy element concentration in street dust is in the range of 3–4 wt.% underscoring the need for governmental programs to implement pollution limiting measures by displacing the heavy industries away from Caracas and to implement advanced instrumental techniques to monitor the environment.

The application of micro-PIXE simulation code in the quantitative analysis of environmental samples

An interactive software package, VIBA-Lab, has been developed by our group for the simulation of PIXE/RBS energy spectra and elemental maps. The program allows the user to define a wide range of experimental parameters, including sample microstructure. In this work, the program has been used to examine the effects of sample morphology and sample size on intensity profiles of specimens, which have distinct microstructure, e.g. single aerosol particles and cascade impactor samples.Sample concentrations have been computed by taking into account geometrical factors, and compared to concentrations where these factors have not been considered. Our studies show that for aerosol samples, correction factors often exceed factors of 2–5 for elements below Ti. We demonstrate in this paper that the use of simulation software in quantitative analysis is indispensable to gauge the significance of the geometrical correction factors for environmental (and other) samples of intermediate thickness.

Analysis of Volatile Organic Compounds in Environmental Water Samples and Soil Gas by Solid-Phase Microextraction

The basic principle of solid-phase microextraction (SPME) is equilibration. Therefore, all possible interferences on the extraction process should be taken into account in order to perform a reliable calibration for the quantitative analysis of environmental samples. Humic acids and suspended mineral oxides showed no effect on the SPME analysis of volatile organic compounds (VOCs), whereas salt had a positive effect on the extraction efficiency. The linearity was good in all cases, the precision of repeated analysis was around 5% average standard deviation, and detection limits were in the ng/1 range. Thus, SPME can be applied for the quantitative analysis of VOCs in various environmental water samples, such as sea water, groundwater and heterogeneous samples like river and lake water containing suspended solids. SPME was established also as an alternative to liquid-liquid extraction in the study of TiO2-catalysed photodegradation mechanisms. Finally, two new SPME sampling probes were designed and tested for rapid, on-site measurements of organic micro pollutants in groundwater and soil gas. SPME is suited ideally to provide low-cost evaluation of groundwater properties in unconventional hydrogeologic settings, such as underground excavations, and to provide preliminary data on which to base the selection of boreholes for more extensive casing installation and instrumentation.

Evaluation of Gas Chromatography/Matrix Isolation-Infrared Spectroscopy for the Quantitative Analysis of Environmental Samples

Gas chromatography/matrix isolation-infrared spectrometry (GC/MI-IR) is being applied to many analyses previously done only by gas chromatography/mass spectrometry (GC/MS). Qualitatively, the infrared spectra of matrix-isolated compounds contain much information about their structure. The information obtained from the infrared spectrum is complementary to the information obtained from mass spectrometry. The technique of GC/MI-IR should also be useful as a quantitative detector. In this study, semivolatile priority pollutant mixtures were analyzed quantitatively by GC/MI-IR. Results were compared with results obtained by GC/MS. Calibration curves were obtained on the GC/MI-IR for several semivolatile priority pollutants to measure the precision and linearity of this technique. The results indicated that GC/MI-IR, in its current form, is only suitable for semiquantitative work.