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E Michael Thurman

Publications and source records attributed to E Michael Thurman.

At least 19 recordsLinked to original sources
PubMed2006

Analysis of herbicides in olive oil by liquid chromatography time-of-flight mass spectrometry.

The application of liquid chromatography time-of-flight mass spectrometry (LC/TOF-MS) for the identification and quantitation of four herbicides (simazine, atrazine, diuron, and terbuthylazine) in olive oil samples is reported here. The method includes a sample treatment step based on a preliminary liquid-liquid extraction followed by matrix solid-phase dispersion (MSPD) using aminopropyl as a sorbent material. A final cleanup step is performed with florisil using acetonitrile as an eluting solvent. The identification by LC/TOF-MS is accomplished with the accurate mass (and the subsequent generated empirical formula) of the protonated molecules [M + H]+, along with the accurate mass of the main fragment ion and the characteristic chlorine isotope cluster present in all of them. Accurate mass measurements are highly useful in this type of complex sample analyses since they allow us to achieve a high degree of specificity, often needed when other interferents are present in the matrix. The mass accuracy typically obtained is routinely better than 2 ppm. The sensitivity, linearity, precision, mass accuracy, and matrix effects are studied as well, illustrating the potential of this technique for routine quantitative analyses of herbicides in olive oil. Limits of detection (LODs) range from 1 to 5 microg/kg, which are far below the required maximum residue level (MRL) of 100 microg/kg for these herbicides in olive oil.

Atrazine↗
PubMed2006

Accurate-mass identification of chlorinated and brominated products of 4-nonylphenol, nonylphenol dimers, and other endocrine disrupters.

LC/ToF-MS was used to identify new chlorination and bromination products of 4-nonylphenol (4-NP), such as 4-NPBr2, 4-NPBrCl, 4-NP dimer (2 isomers), 4-NPCl dimer (2 isomers), 4-NPBr dimer, and a series of methoxy bromo and chloro 4-NPs from a laboratory study of nonylphenol chlorination. The identification procedure used the exact mass, exact mass of the isotope cluster, and their relative intensities, at an average mass accuracy of approximately 1 ppm. The products were produced by a simulated study of industrial cleaning procedures where 4-NP, nonylphenol ethoxylate (NPEO-1 and 2), and nonylphenol carboxylate (NPEC-1) were in contact with sodium hypochlorite solutions (with and without bromide) of various strengths (possible environmental scenarios) at neutral pH. The formation of the products was measured as a function of chlorine concentration, and it was found that 4-NP was the most reactive, producing 4-NPCl, 4-NPCl2, 4-NP (dimers), and the 4-NPCl (dimers). In the presence of bromide ions, a mixture results with products of 4-NPBr2, 4-NPCl, 4-NPCl2, 4-NPBrCl, 4-NPBr, and a 4-NPBr dimer. Less reactive to halogenation was NPEO, which formed only the monochloro and monobromo products, and the least reactive was NPEC. A simple stereochemical model is used to explain halogenation reactivity for the family of 4-NPs and NPEOs at neutral pH. The presence of halogenated 4-NP dimers (bromo and chloro diphenyl ethers) is discussed as a possible source of new endocrine disrupters.

Electrons↗
PubMed2006

Exact-mass library for pesticides using a molecular-feature database.

An automated molecular-feature database (MFD) consisting of the exact monoisotopic mass of 100 compounds, at least one exact mass product ion for each compound, and chromatographic retention time were used to identify pesticides in food and water samples. The MFD software compiles a list of accurate mass ions, excludes noise, and compares them with the monoisotopic exact masses in the database. The screening criteria consisted of +/-5 ppm accurate mass window, +/-0.2 min retention time window, and a minimum 1000 counts (signal-to-noise (S/N) ratio of approximately 10:1). The limit of detection for 100 tested compounds varied from <0.01 mg/kg for 72% of the compounds to <0.1 mg/kg for 95% of the compounds. The MFD search was useful for rapid screening and identification of pesticides in food and water, as shown in actual samples. The combined use of accurate mass and chromatographic retention time eliminated false positives in the automated analysis. The major weakness of the MFD is matrix interferences and loss of mass accuracy. Strengths of the MFD include rapid screening of 100 compounds at sensitive levels compared with a manual approach and the ease of use of the library for any accurate mass spectrometer instrumentation capable of routine sub-5-ppm mass accuracy.

Algorithms↗
PubMed2006

Feasibility of LC/TOFMS and elemental database searching as a spectral library for pesticides in food.

Traditionally, the screening of unknown pesticides in food has been accomplished by GC/MS methods using conventional library-searching routines. However, many of the new polar and thermally labile pesticides are more readily and easily analysed by LC/MS methods and no searchable libraries currently exist (with the exception of some user libraries, which are limited). Therefore, there is a need for LC/MS libraries that can detect pesticides and their degradation products. This paper reports an identification scheme using a combination of LC/MS time-of-flight (accurate mass) and an Access database of 350 pesticides that are amenable to positive ion electrospray. The approach differs from conventional library searching of fragment ions. The concept consists of three parts: (1) initial screening of possible pesticides in actual market-place fruit extracts (apple and orange) using accurate mass and generating an accurate mass via an automatic ion-extraction routine, (2) searching the Access database manually for screening identification of a pesticide, and (3) identification of the suspected compound by accurate mass of at least one fragment ion and comparison of retention time with an actual standard. Imazalil and iprodione were identified in apples and thiabendazole in oranges using this database approach.

Aminoimidazole Carboxamide↗
PubMed2005

Photo-fenton degradation of diclofenac: identification of main intermediates and degradation pathway.

In recent years, the presence of pharmaceuticals in the aquatic environment has been of growing interest. These new contaminants are important because many of them are not degraded under the typical biological treatments applied in the wastewater treatment plants and represent a continuous input into the environment. Thus, compounds such as diclofenac are present in surface waters in all Europe and a crucial need for more enhanced technologies that can reduce its presence in the environment has become evident. In this sense, advanced oxidation processes (AOPs) represent a good choice for the treatment of hazardous nonbiodegradable pollutants. This work deals with the solar photodegradation of diclofenac, an antiinflammatory drug, in aqueous solutions by photo-Fenton reaction. A pilot-scale facility using a compound parabolic collector (CPC) reactor was used for this study. Results obtained show rapid and complete oxidation of diclofenac after 60 min, and total mineralization (disappearance of dissolved organic carbon, DOC) after 100 min of exposure to sunlight. Although diclofenac precipitates during the process at low pH, its degradation takes place in the homogeneous phase governed by a precipitation-redissolution-degradation process. Establishment of the reaction pathway was made possible by a thorough analysis of the reaction mixture identifying the main intermediate products generated. Gas chromatography-mass spectrometry (GC/ MS) and liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOF-MS) were used to identify 18 intermediates, in two tentative degradation routes. The main one was based on the initial hydroxylation of the phenylacetic acid moiety in the C-4 position and subsequent formation of a quinone imine derivative that was the starting point for further multistep degradation involving hydroxylation, decarboxylation, and oxidation reactions. An alternative route was based on the transient preservation of the biphenyl amino moiety that underwent a similar oxidative process of C-N bond cleavage. The proposed degradation route differs from those previously reported involving alternative degradation processes (ozonization, UV/H2O2, or photolysis), indicating that diclofenac degradation follows different pathways, depending on the treatment applied.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Multi-residue pesticide analysis in fruits and vegetables by liquid chromatography-time-of-flight mass spectrometry.

In this work, a new multi-residue methodology using liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS) for the quantitative (routine) analysis of 15 pesticide residues has been developed. The analytical performance of the method was evaluated for different types of fruit and vegetables: pepper, broccoli, tomato, orange, lemon, apple and melon. The accurate mass measurements were compared in different matrices at significantly different concentration levels (from 0.01 to 0.5 mg/kg) obtaining accuracy errors lower than 2 ppm, which is well within the accepted limits for elemental confirmation. Linearity of response over two orders of magnitude was demonstrated (r > 0.99). Matrix effects resulting in suppression or enhancement of the response were frequently observed, most notably in broccoli and citrus. Instrumental limits of detection (LOD) were between 0.0005 and 0.03 mg/kg depending on the commodity and pesticide studied, all being within European Union regulations for food monitoring program. Finally, the methodology was applied to the analysis of two samples from an inter-laboratory exercise. The high degree of confirmation for target pesticides by accurate mass measurements demonstrated the applicability of the method in routine analysis. This study is a valuable indicator of the potential of LC-TOF-MS for quantitative multi-residue analysis of pesticides in vegetables and fruits.

Chromatography, Liquid↗
PubMed2005

Discovering metabolites of post-harvest fungicides in citrus with liquid chromatography/time-of-flight mass spectrometry and ion trap tandem mass spectrometry.

In this study, we benefit from the combination of liquid chromatography (LC)/time-of-flight (TOF) MS accurate mass measurements to generate elemental compositions of ions and LC/ion trap multiple MS (MSn) providing complementary structural information, which is useful for the elucidation of unknown organic compounds at trace levels in complex food extracts. We have applied this approach to investigate different citrus fruits extracts, and we have identified two post-harvest fungicides (imazalil and prochloraz), the main degradation product of imazalil ([M + H]+, m/z 257) and a non-previously reported prochloraz degradation product ([M + H]+, m/z 282). The database-mediated identification of the parent compounds was based on the generated elemental composition obtained from accurate mass measurements and additional qualitative information from the high resolution chlorine isotopic clusters of both the protonated molecules (imazalil, [M + H]+ 297.0556, <0.1 ppm error, 2-Cl; prochloraz, [M + H]+ 376.0381, 1.9 ppm error, 3-Cl) and their characteristic fragments ions (imazalil: m/z 255 and 159; prochloraz: m/z 308 and 266). The correlation between the structural information provided by ion trap MS/MS fragmentation pathways of the parent species and the TOF accurate mass elemental composition data of the degradation products were the key to elucidate the structures of the degradation products of both post-harvest fungicides. Finally, where standards were not available (prochloraz), further confirmation was obtained by synthesizing the proposed degradation product by acid hydrolysis of the parent standard and confirmation by LC/TOF-MS.

Chromatography, Liquid↗
PubMed2005

Measuring the mass of an electron by LC/TOF-MS: a study of "twin ions".

While investigating the in-source CID fragmentation of nonsteroidal antiinflammatory drugs (NSAIDs), it was noticed that the same fragment ion (nominal mass) formed in either positive or negative ion electrospray for a suite of NSAIDs. For example, ibuprofen with a molecular mass of 206, fragments to the m/z 161 ion in negative ion from its deprotonated molecule (m/z 205, [M - H]-) and fragments to the m/z 161 ion in positive ion from its protonated molecule (m/z 207, [M + H]+). This fragment ion was euphemistically called a "twin ion"because of the same nominal mass despite opposite charge. The CID fragmentation of the twin ions was confirmed also by LC/MS/MS ion trap. Accurate mass measurements in negative ion show that the loss was due to CO2 (measured loss of 43.9897 atomic mass units (u) versus calculated loss of 43.9898 u for N = 10) and in positive ion the loss is due to HCOOH (measured loss of 46.0048 u versus calculated loss of 46.0055 u, N = 10). It was realized that, in fact, the ions were not "identical mass twins of opposite charge" but separated in accurate mass by two electrons. The accurate mass measurement by liquid chromatography/time-of-flight-mass spectrometry (LC/TOF-MS) can distinguish between the two fragment ions of ibuprofen (161.13362 +/- 0.00019 and 161.13243 +/- 0.00014 for N = 20). This experiment was repeated for two other NSAIDs, and the mass of an electron was measured as the difference between the twin ions, which was 0.00062 u +/- 14.8% relative standard deviation (N = 20 analyses). Thus, the use of continuous calibration makes it possible to measure the mass of an electron within one significant figure using the NSAID solution. This result shows the importance of including electron mass in accurate mass measurements and the value of a benchmark test for LC/TOF-MS mass accuracy.

Algorithms↗
PubMed2005

Quantitation and accurate mass analysis of pesticides in vegetables by LC/TOF-MS.

A quantitative method consisting of solvent extraction followed by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) analysis was developed for the identification and quantitation of three chloronicotinyl pesticides (imidacloprid, acetamiprid, thiacloprid) commonly used on salad vegetables. Accurate mass measurements within 3 ppm error were obtained for all the pesticides studied in various vegetable matrixes (cucumber, tomato, lettuce, pepper), which allowed an unequivocal identification of the target pesticides. Calibration curves covering 2 orders of magnitude were linear over the concentration range studied, thus showing the quantitative ability of TOF-MS as a monitoring tool for pesticides in vegetables. Matrix effects were also evaluated using matrix-matched standards showing no significant interferences between matrixes and clean extracts. Intraday reproducibility was 2-3% relative standard deviation (RSD) and interday values were 5% RSD. The precision (standard deviation) of the mass measurements was evaluated and it was less than 0.23 mDa between days. Detection limits of the chloronicotinyl insecticides in salad vegetables ranged from 0.002 to 0.01 mg/kg. These concentrations are equal to or better than the EU directives for controlled pesticides in vegetables showing that LC/TOF-MS analysis is a powerful tool for identification of pesticides in vegetables. Robustness and applicability of the method was validated for the analysis of market vegetable samples. Concentrations found in these samples were in the range of 0.02-0.17 mg/kg of vegetable.

Chromatography, Liquid↗
PubMed2005

Determination of pesticide residues in olives and olive oil by matrix solid-phase dispersion followed by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry.

A novel analytical approach has been developed and evaluated for the quantitative analysis of a selected group of widely used pesticides (dimethoate, simazine, atrazine, diuron, terbuthylazine, methyl-parathion, methyl-pirimiphos, endosulfan I, endosulfan II, endosulfan sulphate, cypermethrin and deltamethrin), which can be found at trace levels in olive oil and olives. The proposed methodology is based on matrix solid-phase dispersion (MSPD), (with a preliminary liquid-liquid extraction in olive oil samples) using aminopropyl as sorbent material with a clean-up performed in the elution step with Florisil, followed by mass spectrometric identification and quantitation of the selected pesticides using both gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode and liquid chromatography tandem mass spectrometry (LC-MS-MS) in positive ionization mode. The recoveries obtained (with mean values between 85 and 115% (obtained at different fortification levels) with RSD values below 10% in most cases, confirm the usefulness of the proposed methodology for the analyses of these kind of complex samples with a high fat content. Moreover, the obtained detection limits, which were below 5 microg kg(-1) by LC-MS analyses and ranged from 10 to 60 microg kg(-1) by GC-MS meet the requirements established by the olive oil pesticide regulatory programs. The method was satisfactorily applied to different olives and olive oil samples.

Dimethoate↗
PubMed2005

Urban contributions of glyphosate and its degradate AMPA to streams in the United States.

Glyphosate is the most widely used herbicide in the world, being routinely applied to control weeds in both agricultural and urban settings. Microbial degradation of glyphosate produces aminomethyl phosphonic acid (AMPA). The high polarity and water-solubility of glyphosate and AMPA has, until recently, made their analysis in water samples problematic. Thus, compared to other herbicides (e.g. atrazine) there are relatively few studies on the environmental occurrence of glyphosate and AMPA. In 2002, treated effluent samples were collected from 10 wastewater treatment plants (WWTPs) to study the occurrence of glyphosate and AMPA. Stream samples were collected upstream and downstream of the 10 WWTPs. Two reference streams were also sampled. The results document the apparent contribution of WWTP effluent to stream concentrations of glyphosate and AMPA, with roughly a two-fold increase in their frequencies of detection between stream samples collected upstream and those collected downstream of the WWTPs. Thus, urban use of glyphosate contributes to glyphosate and AMPA concentrations in streams in the United States. Overall, AMPA was detected much more frequently (67.5%) compared to glyphosate (17.5%).

Atrazine↗
PubMed2005

Matching unknown empirical formulas to chemical structure using LC/MS TOF accurate mass and database searching: example of unknown pesticides on tomato skins.

Traditionally, the screening of unknown pesticides in food has been accomplished by GC/MS methods using conventional library searching routines. However, many of the new polar and thermally labile pesticides and their degradates are more readily and easily analyzed by LC/MS methods and no searchable libraries currently exist (with the exception of some user libraries, which are limited). Therefore, there is a need for LC/MS approaches to detect unknown non-target pesticides in food. This report develops an identification scheme using a combination of LC/MS time-of-flight (accurate mass) and LC/MS ion trap MS (MS/MS) with searching of empirical formulas generated through accurate mass and a ChemIndex database or Merck Index database. The approach is different than conventional library searching of fragment ions. The concept here consists of four parts. First is the initial detection of a possible unknown pesticide in actual market-place vegetable extracts (tomato skins) using accurate mass and generating empirical formulas. Second is searching either the Merck Index database on CD (10,000 compounds) or the ChemIndex (77,000 compounds) for possible structures. Third is MS/MS of the unknown pesticide in the tomato-skin extract followed by fragment ion identification using chemical drawing software and comparison with accurate-mass ion fragments. Fourth is the verification with authentic standards, if available. Three examples of unknown, non-target pesticides are shown using a tomato-skin extract from an actual market place sample. Limitations of the approach are discussed including the use of A + 2 isotope signatures, extended databases, lack of authentic standards, and natural product unknowns in food extracts.

Chromatography, Liquid↗
PubMed2005

Searching for non-target chlorinated pesticides in food by liquid chromatography/time-of-flight mass spectrometry.

In this study the unique and most salient features of liquid chromatography/time-of-flight-mass spectrometry (LC/TOFMS) were applied for the identification of non-target chlorinated pesticides in complex food extracts 'a priori', i.e., without the use of standards. The combination of high sensitivity full-scan spectra incorporating accurate mass measurements (routinely better than 2 ppm accuracy) of the protonated molecules with the evidence from resolved isotopic clusters provides the ability to obtain a reduced number of possible elemental compositions (typically 1-2). Databases were then used to find the identity of the suspected species using the elemental composition as a searching criterion. The accurate mass and the generated elemental composition of characteristic fragment ions of the suspected species provide further evidence for the proposed species. With this approach we have identified the following chlorinated pesticides in different market-purchased fruit and vegetable extracts: Chlorotoluron (tomato), iprodione (apple), and procymidone (grapes). Finally, the confirmation and quantitation of these suspected species were successfully accomplished with standards. Other unknown compounds could be partially identified based on the data obtained within this study. As an example, a chlorinated species ('m/z 311') is discussed; the elemental composition and possible structures were proposed and the analytical potential, advantages and disadvantages of the proposed approach critically discussed.

Algorithms↗
PubMed2005

Widespread detection of N,N-diethyl-m-toluamide in U.S. streams: comparison with concentrations of pesticides, personal care products, and other organic wastewater compounds.

One of the most frequently detected organic chemicals in a nationwide study concerning the effects of wastewater on stream water quality conducted in the year 2000 was the widely used insect repellant N,N-diethyl-m-toluamide (DEET). It was detected at levels of 0.02 microg/L or greater in 73% of the stream sites sampled, with the selection of sampling sites being biased toward streams thought to be subject to wastewater contamination (i.e., downstream from intense urbanization and livestock production). Although DEET frequently was detected at all sites, the median concentration was low (0.05 microg/L). The highest concentrations of DEET were found in streams from the urban areas (maximum concentration, 1.1 microg/L). The results of the present study suggest that the movement of DEET to streams through wastewater-treatment systems is an important mechanism that might lead to the exposure of aquatic organisms to this chemical.

Cities↗
PubMed2004

Combination of LC/TOF-MS and LC/Ion trap MS/MS for the identification of diphenhydramine in sediment samples.

Diphenhydramine (Benadryl) is a popular over-the-counter antihistaminic medication used for the treatment of allergies. After consumption, excretion, and subsequent discharge from wastewater treatment plants, it is possible that diphenhydramine will be found in environmental sediments due to its hydrophobicity (log P = 3.27). This work describes a methodology for the first unequivocal determination of diphenhydramine bound to environmental sediments. The drug is removed from the sediments by accelerated solvent extraction and then analyzed by liquid chromatography with a time-of-flight mass spectrometer and an ion trap mass spectrometer. This combination of techniques provided unequivocal identification and confirmation of diphenhydramine in two sediment samples. The accurate mass measurements of the protonated molecules were m/z 256.1703 and 256.1696 compared to the calculated mass of m/z 256.1701, resulting in errors of 0.8 and 2.3 ppm. This mass accuracy was sufficient to verify the elemental composition of diphenhydramine in each sample. Furthermore, accurate mass measurements of the primary fragment ion were obtained. This work is the first application of time-of-flight mass spectrometry for the identification of diphenhydramine and shows the accumulation of an over-the-counter medication in aquatic sediments at five different locations.

Anti-Allergic Agents↗
PubMed2004

Intramolecular isobaric fragmentation: a curiosity of accurate mass analysis of sulfadimethoxine in pond water.

Liquid chromatography with time-of-flight mass spectrometry (TOF-MS) and quadrupole-time-of-flight (Q-TOF) mass spectrometry/mass spectrometry (MS/MS) were used for the accurate mass analysis of sulfadimethoxine in pond water of a fish hatchery. Sulfadimethoxine is the most important sulfa antimicrobial used in aquaculture to treat bacterial disease in a wide variety of fish. Because correct identification is essential to environmental monitoring of antimicrobial pharmaceuticals, accurate mass analyses (TOF and Q-TOF-MS/MS) were compared to nominal mass measurement (quadrupole ion trap). It was known that all six members of the sulfa antimicrobial family gave a common 6-sulfanilamido ion at a nominal mass of m/z 156; thus, this ion was the focus of TOF confirmation (exact mass 156.0119 u) along with the protonated molecule (exact mass 311.0814 u). In the process of accurate mass confirmation of the 156 m/z fragment ion, a second isobaric ion (exact mass m/z 156.0773), was discovered at the same nominal mass, which was not differentiated by quadrupole ion trap. The structure was assigned as 2-4-dimethoxypyridine and is exactly the other protonated half of the sulfadimethoxine molecule. This discovery led to the subsequent use of Q-TOF-MS/MS and high-resolution identification of five other important ion fragments for the identification of sulfadimethoxine in pond water at environmental concentrations. The caveats of using low-resolution mass spectrometry without MS/MS for environmental monitoring are discussed in the light of high profile monitoring of sulfa antimicrobial pharmaceuticals in the aquatic environment.

Anti-Infective Agents↗
PubMed2004

Liquid chromatography/time-of-flight mass spectrometric analyses for the elucidation of the photodegradation products of triclosan in wastewater samples.

Liquid chromatography coupled with time-of-flight mass spectrometry (LC/TOFMS) was applied for the identification of four new photodegradation products of triclosan, a major antimicrobial agent used in personal care products. Wastewater samples, spiked at 7 microg/mL with triclosan, were irradiated with natural sunlight in order to generate the photodegradation products. Aliquots of the spiked water samples were taken at different times of irradiation and compounds were isolated from the water samples by solid-phase extraction. Separation and detection of the compounds and degradation products were accomplished by LC/TOFMS, which provided highly selective information about elemental compositions. Accurate mass measurements for the four degradation products permitted postulation of proposed empirical formulae in this study. Replacement of chlorine atoms by hydroxyl groups and chlorine losses are the major degradation pathways proposed. The degradation products were formed also under environmental conditions in wastewater matrices, thus suggesting their presence in real wastewater treatment processes.

Anti-Infective Agents, Local↗