In Situ Derivatization/Solid-Phase Microextraction: Determination of Polar Aromatic Amines

Comparison of gas chromatographic techniques for the analysis of iodinated derivatives of aromatic amines

Some aromatic amines (AA) have been classified as carcinogens to humans. After entering the body, mainly through tobacco smoke, they can be detected in urine. Thus, their trace analysis as biomarkers in biofluids is of high relevance and can be achieved with gas chromatography (GC-MS), usually after derivatization. This study compares three gas chromatographic methods for the analysis of ten iodinated derivatives of AA: GC-MS in single-ion monitoring (SIM) mode with (1) electron ionization (GC-EI-MS) and (2) negative chemical ionization (GC-NCI-MS), and (3) GC-EI-MS/MS in multiple reaction monitoring (MRM) mode using electron ionization. All methods and most analytes showed good coefficients of determination (R² > 0.99) for broad linear ranges covering three to five orders of magnitude in the picogram-per-liter to nanogram-per-liter range, with one and two exceptions for (1) and (2) respectively. Excellent limits of detection (LODs) of 9-50, 3.0-7.3, and 0.9-3.9 pg/L were observed for (1), (2), and (3) respectively, and good precision was achieved (intra-day repeatability < 15% and inter-day repeatability < 20% for most techniques and concentration levels). On average, recoveries between 80 and 104% were observed for all techniques. Urine samples of smokers and non-smokers were successfully analyzed, and p-toluidine and 2-chloroaniline could be found at significantly (α = 0.05) higher concentrations among smokers.

Carboxylated mesoporous carbon hollow spheres for the efficient solid-phase microextraction of aromatic amines

An efficient and stable fiber coating is of great importance for solid-phase microextraction (SPME). In this study, carboxylated mesoporous carbon hollow spheres (MCHS-COOH) were developed as an efficient SPME coating of polar aromatic amines (AAs) for the first time. The MCHS-COOH coating material with high specific surface area (1182.32 m² g^-1), large pore size (10.14 nm), and rich oxygen-containing groups was fabricated via a facile H₂O₂ post-treatment. The as-prepared MCHS-COOH-coated fiber exhibited fast adsorption rate and excellent extraction properties, mainly due to its π-π interactions, hollow structure, and abundant affinity sites (carboxyl groups). Subsequently, coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS), a sensitive method with low limits of detection (0.08-2.0 ng L^-1), a wide linear range (0.3-500.0 ng L^-1), and good repeatability (2.0-8.8%, n = 6) was developed for the analysis of AAs. The developed method was validated against three river water samples, with satisfactory relative recoveries being obtained. The above results demonstrated that the prepared MCHS-COOH-coated fiber exhibited good adsorption capacity, suggesting a promising application to monitor trace polar compounds in real environment.

Determination of Aniline in Soil by ASE/GC-MS

In this study, a rapid and simple method based on accelerated solvent extraction (ASE) combined with gas chromatography-mass spectrometry (GC-MS) was established to determine the levels of aniline in soil. The matrix spike recovery rates of aniline were investigated by changing several experimental parameters such as vacuum freeze-drying, accelerated solvent extraction, sample transfer, nitrogen-blowing concentration and solvent exchange. Under optimized pretreatment conditions, the linearity of the method ranged from 0.5 to 20 μg mL-1 for aniline, and the correlation coefficient was 0.999. Recoveries of aniline from quartz sand and soil ranged from 76% to 98%, while the precision was excellent with average inter-day and intraday values ranging (n = 6) from 3.1% to 7.5% and 2.0% to 6.9%, respectively. The limits of quantification of the method were 0.04 mg kg-1. Notably, the results show that the method we developed is simple, fast, low cost and can meet the requirements for the determination of aniline in soil samples, sewage sludge, river and pond sediments.

Optimization of a solid-phase microextraction technique for chloro‑ and nitro- substituted aromatic compounds using design of experiments

A rapid and sensitive direct immersion solid-phase microextraction (SPME) technique for the analysis of seven chloro (Cl-) and nitro (NO₂-) substituted anilines, toluenes, and nitrobenzenes from small volume (1.5 mL) aqueous samples was optimized for gas chromatography using Design of Experiments (DoE). Screening of the SPME factors was performed by a fractional factorial DoE, and the optimization of influential factors was achieved with a central composite multi-response surface DoE. Extraction time, pre-SPME agitation speed, extraction temperature, and desorption temperature were identified as significant factors and their values were set using a desirability function that maximized the extraction of the seven target analytes. Extraction time and agitation speed showed significant interactions for most analytes (α = 0.05). The relative standard deviations (RSDs) for within-day and between-day analyses were below 8%, suggesting that the method was repeatable and reproducible. The obtained limits of detection were in the low μg/L range (1-10) using a Flame Ionization Detector, far below what is needed for industrial contaminated sites (usually >1 mg/L). The optimized SPME method increased the analyte concentration up to 2-3 orders of magnitude compared with direct GC injection. The optimized SPME method was applied to two groundwater samples from a contaminated site in which the concentrations of three of the target analytes were ranged from 0.06 to 9.42 mg/L with RSDs <11%. When the concentrations of the target analytes in the sample matrix were higher than 0.5 mg/L, a competition for the SPME extraction sites was observed where analytes with higher affinity for the fiber material replaced the analytes with lower affinity. As a result, dilution of highly contaminated samples is recommended. This study provided for the first time an analytical method for the quantification of frequently co-occurring contaminants from the chloro‑ and nitro- substituted aniline, toluene, and nitrobenzene families.

Comparison between Different Extraction Methods for Determination of Primary Aromatic Amines in Food Simulant

The primary aromatic amines (PAAs) are food contaminants which may exist in packaged food. Polyurethane (PU) adhesives which are used in flexible packaging are the main source of PAAs. It is the unreacted diisocyanates which in fact migrate to foodstuff and then hydrolyze to PAAs. These PAAs include toluenediamines (TDAs) and methylenedianilines (MDAs), and the selected PAAs were 2,4-TDA, 2,6-TDA, 4,4'-MDA, 2,4'-MDA, and 2,2'-MDA. PAAs have genotoxic, carcinogenic, and allergenic effects. In this study, extraction methods were applied on a 3% acetic acid as food simulant which was spiked with the PAAs under study. Extraction methods were liquid-liquid extraction (LLE), dispersive liquid-liquid microextraction (DLLME), and solid-phase extraction (SPE) with C18 ec (octadecyl), HR-P (styrene/divinylbenzene), and SCX (strong cationic exchange) cartridges. Extracted samples were detected and analyzed by HPLC-UV. In comparison between methods, recovery rate of SCX cartridge showed the best adsorption, up to 91% for polar PAAs (TDAs and MDAs). The interested PAAs are polar and relatively soluble in water, so a cartridge with cationic exchange properties has the best absorption and consequently the best recoveries.

Differentiation of isomeric methylanilines by imidization and gas chromatography/mass spectrometry analysis

RATIONALE

Carcinogenic o-methylaniline is one of the banned aromatic amines in azo dyes, but it is very difficult to distinguish it from its noncarcinogenic isomers due to their identical retention time on chromatography and similar mass spectra.

METHODS

Imidization of the isomeric methylanilines was carried out by treatment with benzaldehyde under mild conditions. The formed derivatives were analyzed by gas chromatography/mass spectrometry (GC/MS). Theoretical calculations were carried out on the Gaussian 03 program by using the density functional theory method at the B3LYP/6-311+G(d,p) level.

RESULTS

Imidization of methylanilines occurred easily and gave rise to the corresponding N-methylbenzylidene benzenamines. The isomeric derivatives were completely separated by GC, and thus the three isomeric methylanilines could be determined simultaneously. Due to the ortho effect, the derivative from o-methylaniline has a characteristic fragment ion at m/z 118 with a stable bicyclic structure, and it could be easily differentiated from the meta- and para-isomers in electron ionization mass spectrometry.

CONCLUSIONS

These results provided a promising solution for simultaneous determination of isomeric methylanilines.

Simultaneous determination of isomeric substituted anilines by imidization with benzaldehyde and gas chromatography-mass spectrometry

The chromatographic separation of several isomeric anilines is a challenging issue. Herein, a simple method for the simultaneous determination of four groups of isomeric primary aromatic amines, including chloroanilines, methylanilines, methoxylanilines, and dimethylanilines, was presented. In this method, all of the 15 primary aromatic amines were easily transformed into the corresponding imine derivative by treatment with benzaldehyde under mild conditions. The formed isomeric imine derivatives were completely separated on a commercial capillary gas chromatography column. The effects of several derivatization parameters were investigated and optimized. Linearity in the optimized method ranged from 0.050 to 50 μg/mL with the squared correlation coefficients (R² ) between 0.9981 and 0.9999. Reasonable reproducibility was obtained, with the intraday relative standard deviation (N = 5) ranging from 0.89 to 4.57% and interday relative standard deviation ranging from 2.26 to 7.69% at the concentration of 5.0 μg/mL. The developed method has been successfully applied to determine these isomeric aromatic amines in real samples.

Sensitivity enhancement in the fluorometric determination of aliphatic amines using naphthalene-2,3-dicarboxaldehyde derivatization followed by vortex-assisted liquid-liquid microextraction

A highly sensitive liquid chromatographic method was developed for the fluorometric determination of trace amounts of linear aliphatic primary amines. Prior to extraction, amines were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA) in the presence of cyanide ion (CN) and extracted by vortex-assisted liquid-liquid microextraction (VALLME). The optimum conditions were as follows: derivatization reaction time for 5 min in 2.0 mL aqueous donor samples with 50 μM NDA/CN, and 10mM borate buffer at pH 9; vortex extraction time for 20s in the VALLME step with 50 μL of isooctane as the extractant phase; centrifugation for 1 min at 6000 rpm. Under the optimum conditions, the limits of detection (LOD) were between 0.01 and 0.04 nmol L(-1). The calibration curves showed good linearity in the range of 0.1-20 nmol L(-1). In comparison with previous work using o-phthalaldehyde/2-mercaptoethanol derivatization, the method has much more stable fluorescent derivatives, higher fluorescence intensities, and greater extraction efficiencies. The sensitivity enhancement factors (SEF) were between 2 and 70, which is in good agreement with the theoretical values calculated from partition coefficients in VALLME system.

Isomeric differentiation of chloroanilines by gas chromatography-mass spectrometry in combination with tosylation

p-Chloroaniline is one of the banned aromatic amines in azo dyes, but it is very difficult to distinguish it from its isomers due to their identical retention time in chromatography and similar mass spectra. In this work, derivatization of the isomeric chloroanilines was carried out to yield the corresponding N-tosyl chloroanilines, which were completely separated by gas chromatography and also possessed clearly different electron ionization mass spectra. Thus, the three isomers could be differentiated and determined at the same time. Density functional theory calculation results indicated that the effect of the substituent pattern in electron ionization mass spectrometry is mainly due to the difference in the stability of the product ion (P2) at m/z 126, originating from the loss of tosyl radical from the precursor ion.

Identification of specific organic contaminants in different units of a chemical production site

Due to the very limited number of studies dealing with the chemical composition of industrial wastewaters, many industrial organic contaminants still escape our view and consequently also our control. We present here the chemical characterization of wastewaters from different units of a chemical complex, thereby contributing to the characterization of industrial pollution sources. The chemicals produced in the investigated complex are widely and intensively used and the synthesis processes are common and applied worldwide. The chemical composition of untreated and treated wastewaters from the chemical complex was investigated by applying a non-target screening which allowed for the identification of 39 organic contaminants. According to their application most of them belonged to four groups: (i) unspecific educts or intermediates of industrial syntheses, (ii) chemicals for the manufacturing of pharmaceuticals, (iii) educts for the synthesis of polymers and resins, and (iv) compounds known as typical constituents of municipal sewage. A number of halogenated compounds with unknown toxicity and with very high molecular diversity belonged to the second group. Although these compounds were completely removed or degraded during wastewater treatment, they could be useful as "alarm indicators" for industrial accidents in pharmaceutical manufacturing units or for malfunctions of wastewater treatment plants. Three potential branch-specific indicators for polymer manufacturing were found in the outflow of the complex. Among all compounds, bisphenol A, which was present in the leachate water of the on-site waste deposit, occurred in the highest concentrations of up to 20 000 μg L(-1). The comparison of contaminant loads in the inflow and outflow of the on-site wastewater treatment facility showed that most contaminants were completely or at least significantly removed or degraded during the treatment, except two alkylthiols, which were enriched during the treatment process. The chemical composition of the inflow samples showed a very heterogenic composition and strongly varied, reflecting that large scale industrial synthesis is carried out in batches. The outflow contained mainly unspecific chlorinated educts or intermediates of industrial syntheses as well as compounds which are known as typical constituents of municipal wastewaters.

In situ aqueous derivatization as sample preparation technique for gas chromatographic determinations

The use of derivatization reactions is a common practice in analytical laboratories. Although in many cases it is tedious and time-consuming, it does offer a good alternative for the determination of analytes not compatible to gas chromatography. Many of the reactions reported in the literature occur in organic medium. However, in situ aqueous derivatization reactions, which can be performed directly in aqueous medium, offer important advantages over those mentioned above, such as no need of a previous extraction step and easy automation. Here we review the most recent developments and applications of in situ aqueous derivatization. The discussion focuses on the derivatization reactions used for the determination of alcohols and phenols, carboxylic acids, aldehydes and ketones, nitrogen-containing compounds and thiols in different aqueous matrices, such as environmental, biological and food samples. Several reactions are described for each functional group (acylation, alkylation, esterification, among others) and, in some cases, the same reagents can be used for several functional groups, such that there is an unavoidable overlap between sections. Finally, attention is also focused on the techniques used for the introduction of the derivatives formed in the aqueous medium into the chromatographic system. The implementation of in situ aqueous derivatization coupled to preconcentration techniques has permitted the enhancement of recoveries and improvements in the separation, selectivity and sensitivity of the analytical methods.

Synthesis of highly luminescent cobalt(II)-bis(8-hydroxyquinoline) nanosheets as isomeric aromatic amine probes

Highly luminescent and water-soluble cobalt(ii)-bis(8-hydroxyquinoline) (CoQ(2)) nanosheets have been successfully synthesized via a simple, rapid sonochemical method. The water-soluble CoQ(2) nanosheets were characterized by luminescence spectroscopy, UV-vis spectroscopy, FT-IR spectroscopy and transmission electron microscopy (TEM). The CoQ(2) nanosheets allow highly sensitive and selective determination of p-nitroaniline via fluorescence quenching. Under optimal conditions, the relative fluorescence intensities of nanosheets decreased linearly with increasing p-nitroaniline. However, the sensitivity of CoQ(2) nanosheets toward other aromatic amines including o-diaminobenzene, m-diaminobenzene, p-diaminobenzene, p-toluidine, o-nitroaniline, m-nitroaniline, p-chloroaniline and aniline is negligible. It is found that p-nitroaniline can quench the luminescence of CoQ(2) nanosheets in a concentration-dependent manner that is best described by a Stern-Volmer-type equation. The possible underlying mechanism is discussed.

Analysis of fatty acids in sputum from patients with pulmonary tuberculosis using gas chromatography-mass spectrometry preceded by solid-phase microextraction and post-derivatization on the fiber

A method based on solid-phase microextraction (SPME) and post-derivatization on the fiber coupled to gas chromatography-mass spectrometry (GC-MS) was developed for the analysis of fatty acids in sputum from patients with pulmonary tuberculosis. The sputum specimens were digested, hydrolyzed, extracted, derivertized, injected and analyzed without cultivation or isolation of the microorganism. Under optimized conditions, the relative standard deviations (RSD, n=5) for all analytes were below 17% and the limits of detection varied from 1.68 (C(24:0)) to 150.4 microg L(-1) (C(12:0)). Good linearity was observed for all the fatty acids studied except for C(12:0) within a wide concentration range of three orders of magnitudes with the correlation coefficients ranging from 0.91 (C(24:0)) to 0.99 (C(14:0)). Fatty acids in sputum specimens from 21 persons were directly analyzed using the proposed method. The results show that in all the sputum specimens from patients, who were clinically diagnosed with tuberculosis (TB), tuberculosis stearic acid (TBSA) was detected, while in all the sputum samples from persons without TB, TBSA was not found. The possibility of using the proposed method to detect mycobacterium tuberculosis (MTB) via the identification of TBSA in sputum was discussed. The comparison with other methods including sputum culture and microscopy of direct smears indicated that the proposed method is fast and sensitive for the analysis of fatty acids in sputum and offers an alternative for the detection of MTB in sputum.

Analysis of aromatic amines asN-propoxycarbonyl derivatives by gas chromatography with nitrogen-phosphorus selective detection

A selective and sensitive method for the analysis of aromatic amines by GC was developed. Aromatic amines were converted to their N-n-propoxycarbonyl derivatives and measured by GC with nitrogen-phosphorus selective detection (NPD) using an HP-5 fused-silica capillary column. The derivatives of the 20 aromatic amines provided excellent NPD responses, and were resolved both quantitatively and reproducibly within 15 min. The calibration curves for aromatic amines in the range 20-500 ng were linear and the detection limits at an S/N of 3 were ca. 19-139 pg injected. This method was applied successfully to combustion smoke and human urine samples, and analyzed without any interference from coexisting substances.

Development and application of microporous hollow fiber protected liquid-phase microextraction via gaseous diffusion to the determination of phenols in water

A new organic solvent-free microextraction technique termed liquid-gas-liquid microextraction (LGLME) was developed. In this technique, a small amount (6 microl) of aqueous acceptor solution (0.5M NaOH) is introduced into the channel of a 2.65 cm polypropylene hollow fiber. The hollow fiber is then immersed in an aqueous sample donor solution. The aqueous acceptor phase in the channel of the hollow fiber is separated from the sample solution by the hydrophobic microporous hollow fiber wall with air inside its pores. The analytes (phenols) passed through the microporous hollow fiber membrane by gas diffusion and were then trapped by the basic acceptor solution. After extraction, the acceptor solution was withdrawn into a microsyringe and injected into a capillary electrophoresis sample vial for subsequent analysis. Limits of detection of between 0.5 and 10 microg/l for eight phenols could be achieved. The relative standard deviations (n=6) of this technique between 2.7 and 7.6%. The technique also provides good enrichment factors for all the eight analytes.

SPME in environmental analysis

Recent advances in the use of solid-phase microextraction (SPME) in environmental analysis, including fiber coatings, derivatization techniques, and in-tube SPME, are reviewed in this article. Several calibration methods for SPME, including traditional calibration methods, the equilibrium extraction method, the exhaustive extraction method, and several diffusion-based calibration methods, are presented. Recent developed SPME devices for on-site sampling and several applications of SPME in environmental analysis are also introduced.

Strategies for the microextraction of polar organic contaminants in water samples

In this paper the most recent developments in the microextraction of polar analytes from aqueous environmental samples are critically reviewed. The particularities of different microextraction approaches, mainly solid-phase microextraction (SPME), stir-bar-sorptive extraction (SBSE), and liquid-phase microextraction (LPME), and their suitability for use in combination with chromatographic or electrically driven separation techniques for determination of polar species are discussed. The compatibility of microextraction techniques, especially SPME, with different derivatisation strategies enabling GC determination of polar analytes and improving their extractability is revised. In addition to the use of derivatisation reactions, the possibility of enhancing the yield of solid-phase microextraction methods for polar analytes by using new coatings and/or larger amounts of sorbent is also considered. Finally, attention is also focussed on describing the versatility of LPME in its different possible formats and its ability to improve selectivity in the extraction of polar analytes with acid-base properties by using separation membranes and buffer solutions, instead of organic solvents, as the acceptor solution.

Specific determination of 20 primary aromatic amines in aqueous food simulants by liquid chromatography–electrospray ionization-tandem mass spectrometry

A multi-analyte method without any pre-treatment steps using reversed-phase liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) was developed and applied for the determination of 20 primary aromatic amines (PAA) associated with polyurethane (PUR) products or azo-colours. The method was validated in-house for water and 3% acetic acid food simulants using spiked migrates from plastic laminates. Detection limits ranged from 0.27 to 3 microg amine/L food simulants, and RSD values of within-laboratory reproducibility at the 2 microg PAA/L level ranged from 3.9 to 19%. PAA migration from plastic laminates and black nylon cooking utensils were determined with the method, and high levels of 4,4'-methylenedianiline and aniline were found in migrates from about half of the tested cooking utensils. The method fulfils present legislative demands in the EU for screening and verification of PAA migration from food contact materials.

Stir bar sorptive extraction with in situ derivatization and thermal desorption-gas chromatography–mass spectrometry for measurement of phenolic xenoestrogens in human urine samples

A high-sensitivity analytical method that uses stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS) for the simultaneous measurement of trace amounts of phenolic xenoestrogens (PXs), such as 2,4-dichlorophenol (DCP), 4-tert-butylphenol (BP), 4-tert-octylphenol (OP), 4-nonylphenol technical isomers (NP), pentachlorophenol (PCP) and bisphenol A (BPA), in human urine samples was developed. The urine sample (1 ml) was de-conjugated by adding beta-glucuronidase and sulfatase. Then, protein precipitation was performed by the addition of acetonitrile. After centrifugation, the supernatant was diluted with purified water and subjected to SBSE with in situ derivatization and TD-GC-MS. The detection limits of DCP, BP, OP, NP, PCP and BPA in the urine samples were 20, 10, 10, 50, 20 and 20 pg ml-1 (ppt), respectively. The calibration curves for PXs were linear and had correlation coefficients higher than 0.99. The average recoveries of those analytes in the urine samples were higher than 95% (RSD: <10%, n=6) with correction using the added surrogate standards. This simple, accurate, sensitive and selective method can be used in the determination of PXs in human urine samples.

Determination of 2,4,6-tribromoaniline in the color additives D&C Red Nos. 21 and 22 (Eosin Y) using solid-phase microextraction and gas chromatography-mass spectrometry

The present work demonstrates the presence of an impurity, 2,4,6-tribromoaniline (TBA), in the color additives D&C Red Nos. 21 and 21 lake (21L) and describes the determination of TBA in certified lots of D&C Red Nos. 21, 21L and 22 (Eosin Y). A method was developed using solid-phase microextraction with [13C6]TBA as an internal standard followed by gas chromatography-mass spectrometry analysis. Test portions from 23 lots of US-certified color additives D&C Red Nos. 21, 21L and 22 were analyzed for TBA using the new method. These lots represent domestic (four) and foreign (four) manufacturers that requested certification for the color additives during the past 2 years. Of the test portions analyzed, 12 (52.2%) contained TBA in amounts ranging from 19.9 to 638.9 ppm with an average value of approximately 278.7 ppm. The remaining 11 (47.2%) test portions contained no detectable TBA or less than 0.01 ppm, which is the limit of quantification of the present method. The wide range of TBA levels found in lots submitted for certification suggest that the contamination with TBA may be avoided or significantly decreased through appropriate changes in the color-manufacturing process.