Ultratrace-level determination of glyphosate,aminomethylphosphonic acid and glufosinate in natural waters by solid-phase extraction followed by liquid chromatography–tandem mass spectrometry: performance tuning of derivatization,enrichment and detection

A sensitive and robust analytical method for the quantification of glyphosate, aminomethylphosphonic acid (AMPA) and glufosinate in natural water has been developed on the basis of a derivatization with 9-fluorenylmethylchloroformate (FMOC-Cl), solid-phase extraction (SPE) and liquid chromatography followed by electrospray tandem mass spectrometry (LC-ESI-MS/MS). In order to maximize sensitivity, the derivatization was optimized regarding organic solvent content, amount of FMOC-Cl and reaction time. At an acetonitrile content of 10% a derivatization yield of 100% was reached within two hours in groundwater and surface water samples. After a twofold dilution the low acetonitrile content allowed solid-phase extraction of a sample of originally 80 mL over 200 mg Strata-X cartridges. In order to decrease the load of the LC column and mass spectrometer with derivatization by-products (e.g., 9-fluorenylmethanol FMOC-OH), a rinsing step was performed for the SPE cartridge with dichloromethane. Acidification of the sample and addition of EDTA was used to minimize complexation of the target compounds with metal ions in environmental samples. Due to the large sample volume and the complete FMOC-OH removal, limits of quantification of 0.7 ng/L, 0.8 ng/L and 2.3 ng/L were achieved in surface water for glyphosate, AMPA and glufosinate, respectively. The limits of detection were as low as 0.2 ng/L, 0.2 ng/L and 0.6 ng/L for glyphosate, AMPA and glufosinate, respectively. Surface water and ground water samples spiked at 2 ng/L showed recoveries of 91–107%. Figure LC-MS/MS chromatogram of a water sample from a remote alpine region spiked at 1 ng/L     

Re-evaluation of glyphosate determination in water by liquid chromatography coupled to electrospray tandem mass spectrometry

An analytical method based on on-line solid-phase extraction-liquid chromatography coupled to electrospray tandem mass spectrometry (SPE-LC-ESI-MS/MS) for the determination of glyphosate and aminomethylphosphonic acid (AMPA) residues has been applied to the analysis of water samples within a Round Robin Study. The method had been previously validated in a variety of water samples and it fulfilled all the parameters of precision, accuracy, sensitivity and unequivocal confirmation. The results within the study that we participated were highly satisfactory in all cases with the only exception of glyphosate in groundwater samples, where surprisingly recoveries around 15% were obtained despite the use of isotope-labeled glyphosate as internal standard (I.S.). A slight modification has been introduced in the method, simply consisting of the acidification of sample with hydrochloric acid (HCl) to pH 1. Then, the sample is neutralized and immediately derivatized with 9-fluorenylmethylchloroformate (FMOC) before LC-MS/MS determination. Round Robin Study samples were reanalyzed using this approach, and the recoveries increased up to 98%. A possible explanation might be the slow kinetic interaction between glyphosate and some components of the matrix. These components might act as chelating agents, making glyphosate unavailable for derivatization and therefore for analysis. Several water samples collected at the Mediterranean area of Spain, and previously analyzed and being found to contain glyphosate, were also reanalyzed using this approach, obtaining higher concentrations (between 2 and 14 times) in most of cases.     

Direct aqueous determination of glyphosate and related compounds by liquid chromatography/tandem mass spectrometry using reversed-phase and weak anion-exchange mixed-mode column

Analysis of the broad-spectrum herbicide glyphosate and its related compounds is quite challenging. Tedious and time-consuming derivatization is often required for these substances due to their high polarity, high water solubility, low volatility and molecular structure which lacks either a chromophore or fluorophore. A novel liquid chromatography/tandem mass spectrometry (LC/MS–MS) method has been developed for the determination of glyphosate, aminomethylphosphonic acid (AMPA) and glufosinate using a reversed-phase and weak anion-exchange mixed-mode Acclaim^® WAX-1 column. Aqueous environmental samples are directly injected and analyzed in 12 min with no sample concentration or derivatization steps. Two multiple reaction monitoring (MRM) channels are monitored in the method for each target compound to achieve true positive identification, and ¹³C,¹⁵N-glyphosate is used as an internal standard to carry out isotope dilution mass spectrometric (IDMS) measurement for glyphosate. The instrument detection limits (IDLs) for glyphosate, AMPA and glufosinate are 1, 2 and 0.9 μg/L, respectively. Linearity of the detector response with a minimum coefficient of determination (R²) value (R² > 0.995) was demonstrated in the range of ∼10 to 10³ μg/L for each analytes. Spiked drinking water, surface water and groundwater samples were analyzed using this method and the average recoveries of analytes in three matrices ranged from 77.0 to 102%, 62.1 to 101%, 66.1 to 93.7% while relative standard deviation ranged from 6.3 to 10.2%, 2.7 to 14.8%, 2.9 to 10.7%, respectively. Factors that may affect method performance, such as metal ions, sample preservation, and storage time, are also discussed.     

Issues pertaining to the analysis of buprenorphine and its metabolites by gas chromatography–mass spectrometry

“Substitution therapy” and the use of buprenorphine (B) as an agent for treating heroin addiction continue to gain acceptance and have recently been implemented in Taiwan. Mature and widely utilized gas chromatography–mass spectrometry (GC–MS) technology can complement the low cost and highly sensitive immunoassay (IA) approach to facilitate the implementation of analytical tasks supporting compliance monitoring and pharmacokinetic/pharmacogenetic studies. Issues critical to GC–MS analysis of B and norbuprenorphine (NB) (free and as glucuronides), including extraction, hydrolysis, derivatization, and quantitation approaches were studied, followed by comparing the resulting data against those derived from IA and two types of liquid chromatography–tandem mass spectrometry (LC–MS/MS) methods. Commercial solid-phase extraction devices, highly effective for recovering all metabolites, may not be suitable for the analysis of free B and NB; acetyl-derivatization products exhibit the most favorable chromatographic, ion intensity, and cross-contribution characteristics for GC–MS analysis. Evaluation of IA, GC–MS, and LC–MS/MS data obtained in three laboratories has proven the 2-aliquot GC–MS protocol effective for the determination of free B and NB and their glucuronides.     

Nonderivatization method for determination of glyphosate,glufosinate, bialaphos,and their main metabolites in environmental waters based on magnetic metal‐organic framework pretreatment

A novel magnetic metal‐organic framework composite was prepared by a self‐assembly approach. The material properties were characterized by Fourier‐transform infrared spectroscopy, vibrating sample magnetometry, thermogravimetry and differential thermogravimetric analysis, and X‐photoelectron spectroscopy. Then, the as‐prepared material was used as an adsorbent and indicated great enrichment ability toward glyphosate, glufosinate, bialaphos, and their main metabolites aminomethylphosphonic acid and 3‐methylphosphinicopropionic acid. Based on this, an efficient magnetic solid‐phase extraction method combined with ultra high performance liquid chromatography with high‐resolution mass spectrometry for the pretreatment and determination of five target compounds in environmental waters was established. Parameters that could impact on the adsorption performance had been studied in detail. The proposed method was successfully applied for the simultaneous determination of glyphosate, glufosinate, bialaphos, and their main metabolites aminomethylphosphonic acid and 3‐methylphosphinicopropionic acid in environmental water with recoveries in range of 86.2–104.6% with relative standard deviations less than 10%. Desired linearity was achieved varying from 1 to 100 μg/L for five target analytes, respectively. The limits of detection were between 0.01 and 0.03 μg/L.     

Analysis of diphenylarsinic acid in human and environmental samples by HPLC–ICP‐MS

A simple, rapid and robust analytical method for determining diphenylarsinic acid in human and environmental samples was developed based on a combination of hydrophilic polymer‐based gel‐permeation high‐performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP‐MS). Hair and nail samples were digested with alkali, and liberated diphenylarsinic acid (derivative) was extracted with diethyl ether, redissolved in water and injected for HPLC–ICP‐MS analysis. Human urine, groundwater and water extracts from soils were injected for HPLC–ICP‐MS directly after filtration. Using the method, diphenylarsinic acid in a solution was quantified in 7 min duration for an analysis with a detection limit of sub‐nanograms per milliliter. The method has been applied to groundwater arsenic pollution recently uncovered in Japan. Copyright © 2005 John Wiley & Sons, Ltd.     

Cyclohexane‐1,3‐dione as a derivatizing agent for the analysis of aldehydes by micelar electrokinetic chromatography with diode array detection

Aldehydes are important compounds in a large number of samples, especially food and beverages. In this work, for the first time, cyclohexane‐1,3‐dione (CHD) was used as a derivatizing reagent aiming aldehyde (formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) analysis by MEKC‐DAD. The optimized separation of the derivates was performed using a voltage program (+20 kV, 0–15 min.; +23 kV, 15–17 min.) at a temperature of 26°C, and using as the running buffer a mixture containing 100 mmol/L of sodium dodecyl sulfate and 29 mmol/L of sodium tetraborate at pH 9.2, with maximum absorbance at 260 nm. CHD was compared with two other derivatizing agents: 3‐methyl‐2‐benzothiazolinone hydrazone and phenylhydrazine‐4‐sulfonic acid. The CHD‐aldehyde derivatives were also characterized by LC‐MS. The calibration curves for all aldehydes had r² above 0.999 and LODs ranged from 0.01 to 0.7 mg/L. The optimized methodology was applied in sugar cane brandy (cachaça) samples successfully. CHD showed to be an alternative derivatization reagent due to its stability, aqueous solubility, high selectivity and sensitivity, reduced impurities, and simple preparation steps.     

Ionic liquid chemically bonded basalt fibers for in‐tube solid‐phase microextraction

Ionic liquids have been widely used in different fields by advantage of their specific properties. In this work, 1‐methyl‐3‐(3‐trimethoxysilyl propyl)imidazolium chloride was prepared and chemically bonded onto basalt fibers for in‐tube solid‐phase microextraction. Through combining in‐tube extraction device with high‐performance liquid chromatography equipped with a diode array detector, an online enrichment and analysis method for eight polycyclic aromatic hydrocarbons was established under the optimum conditions. A good enrichment factor (52–814), good linearity (0.10–15 and 0.20–15 μg/L), low limits of detection (0.03–0.05 μg/L), and low limits of quantitation (0.10–0.20 μg/L) were achieved using a sample volume of 50 mL. Analysis method was applied to the real samples including the groundwater and wastewater from a chemical industry park, some target analytes were detected and the relative recoveries were in the range of 80.4–116.8%.     

Determination of glyphosate and aminomethylphosphonic acid in surface water and vegetable oil by capillary zone electrophoresis

A procedure is developed for the determination of glyphosate and aminomethylphosphonic acid in surface water and vegetable oil by means of capillary zone electrophoresis with preliminary derivatization with phenylisothiocyanate and UV-detection. The analytical ranges are 0.05–10 mg/L, the detection limits for glyphosate and aminomethylphosphonic acid make 0.005 and 0.02 mg/L, respectively. The analysis takes 1–2 hours, the relative standard deviation of the results of analysis does not exceed 7%.     

Urinary profile of methylprednisolone acetate metabolites in patients following intra-articular and intramuscular administration

A study on urinary metabolites of methylprednisolone acetate (MPA) has been performed by liquid chromatography–electrospray ionization–tandem mass spectrometry (LC-ESI-MS/MS) in precursor ion scanning (PIS) and neutral loss (NL) modes. Patients suffering from joint inflammation have been treated with Depo-Medrol? (MPA marketed suspension, 40 mg) intra-articularly (IA) and after a wash-out period, intramuscularly (IM) at the same dose. Urine samples have been collected after both the administration routes. Metabolites were identified in PIS mode by setting the fragment ion at m/z 161 which is specific for MPA, methylprednisolone (MP), methylprednisolone hemisuccinate, and in NL mode by selecting the losses of 54, 72, 176 and 194 Da. The MP-related structure of each target ion detected in both the MS modes was then confirmed by MS/MS acquisitions, and by accurate mass experiments. By using this approach, 13 MPA metabolites (M1–M13) have been identified, nine already reported in the literature and four unknown and for which the chemical structures have been proposed. No differences in the metabolic pattern of MPA when administered IM or IA were observed. The relative abundances of metabolites compared with the internal standard (MP-D2) were monitored by multiple reaction monitoring analysis for 19 days after both the administration routes.     

Quantitative analysis of bucillamine in blood using high-performance liquid chromatography-mass spectrometry technique

A fast and sensitive method has been developed and validated for the determination of bucillamine in human blood by derivatizing the free sulfhydryl groups with isobutyl acrylate (IA), by APCI-LC/MS/MS. The collected blood sample was immediately mixed with a mixture of IA and 0.05 m Tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer, pH 9.2, to stabilize the sulfyhydryl moieties. The derivatized samples were then extracted by protein precipitation, evaporated, reconstituted and injected using an LC-APCI/MS/MS instrument. Separation was achieved using a C18 analytical column and a gradient mobile phase within a chromatographic run time of 5 min. A quadratic (weighted 1/concentration(2)) relationship was observed during validation over a concentration range of 0.4-40 microg/mL with a correlation value of r > or = 0.9966. The inter-batch precision and accuracy at low, medium and high concentrations were 8.1, 8.4 and 7.3%; 113.3, 104.9 and 103.9%, respectively, and the intra-batch precision and accuracy at low, medium and high concentrations were 7.7, 5.4 and 2.7%; 105.1, 111.9 and 113.2%, respectively.     

Development and application of immunoaffinity column chromatography for atrazine in complex sample media

A rabbit antibody immunoaffinity (IA) column procedure was evaluated as a cleanup method for the determination of atrazine in soil, sediment, and food. Four IA columns were prepared by immobilizing a polyclonal rabbit anti-atrazine antibody solution to HiTrap Sepharose columns. Atrazine was bound to the IA columns when the loading solvents were either 100% water, 2% acetonitrile in water, or 10% methanol in phosphate buffered saline (PBS). Quantitative removal of atrazine from the IA columns was achieved with elution solvents of either 70% ethanol in water, 70% methanol in water, or 100% methanol. One control column was prepared using nonspecific rabbit IgG antibody. This control column did not retain any applied atrazine indicating atrazine did not bind indiscriminately to protein or the Sepharose support. The four IA columns showed reproducible coupling efficiency for the immobilization of the atrazine antibody and consistent binding and releasing of atrazine. The coupling efficiency (4.25 mg of antibody in 1 mL of resin bed) for the four IA columns ranged from 93 to 97% with an average of 96 ± 2% (2.1%). Recoveries of the 500, 50, and 5 ng mL⁻¹ atrazine standard solutions from the four IA columns were 107 ± 7% (6.5%), 122 ± 14% (12%), and 114 ± 9% (8.0%) respectively, based on enzyme-linked immunosorbent assay (ELISA) data. The maximum loading was approximately 700 ng of atrazine for each IA column (∼0.16 μg of atrazine per mg of antibody). The IA columns could withstand 100% methanol as the elution solvent and could be reused more than 50 times with no change in performance. The IA columns were challenged with soil, sediment, and duplicate-diet food samples and effectively removed interferences from these various matrices for subsequent gas chromatography/mass spectrometry (GC/MS) or ELISA analysis. The log-transformed ELISA and GC/MS data were significantly correlated for soil, sediment and food samples although the ELISA values were slightly higher than those obtained by GC/MS. The IA column cleanup procedure coupled with ELISA analysis could be used as an alternative effective analytical method for the determination of atrazine in complex sample media such as soil, sediment, and food samples.     

Residue determination of glyphosate, glufosinate and aminomethylphosphonic acid in water and soil samples by liquid chromatography coupled to electrospray tandem mass spectrometry

This paper describes a method for the sensitive and selective determination of glyphosate, glufosinate and aminomethylphosphonic acid (AMPA) residues in water and soil samples. The method involves a derivatization step with 9-fluorenylmethylchloroformate (FMOC) in borate buffer and detection based on liquid chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS). In the case of water samples a volume of 10 mL was derivatized and then 4.3 mL of the derivatized mixture was directly injected in an on-line solid phase extraction (SPE)-LC-MS/MS system using an OASIS HLB cartridge column and a Discovery chromatographic column. Soil samples were firstly extracted with potassium hydroxide. After that, the aqueous extract was 10-fold diluted with water and 2 mL were derivatized. Then, 50 microL of the derivatized 10-fold diluted extract were injected into the LC-MS/MS system without pre-concentration into the SPE cartridge. The method has been validated in both ground and surface water by recovery studies with samples spiked at 50 and 500 ng/L, and also in soil samples, spiked at 0.05 and 0.5 mg/kg. In water samples, the mean recovery values ranged from 89 to 106% for glyphosate (RSD <9%), from 97 to 116% for AMPA (RSD < 10%), and from 72 to 88% in the case of glufosinate (RSD < 12%). Regarding soil samples, the mean recovery values ranged from 90 to 92% for glyphosate (RSD <7%), from 88 to 89% for AMPA (RSD <5%) and from 83 to 86% for glufosinate (RSD <6%). Limits of quantification for all the three compounds were 50 ng/L and 0.05 mg/kg in water and soil, respectively, with limits of detection as low as 5 ng/L, in water, and 5 microg/kg, in soil. The use of labelled glyphosate as internal standard allowed improving the recovery and precision for glyphosate and AMPA, while it was not efficient for glufosinate, that was quantified by external standards calibration. The method developed has been applied to the determination of these compounds in real water and soil samples from different areas. All the detections were confirmed by acquiring two transitions for each compound.     

Study of the effects of operational parameters on multiresidue pesticide analysis by LC-MS/MS

In this paper, the influence of several operational parameters on a well established multiresidue LC-MS/MS method has been studied in relation to the analysis of 150 pesticides commonly present in vegetable samples. The operational parameters investigated are: (i) the influence of different modifiers (0.1% formic acid; 5 mM ammonium formiate; 5 mM ammonium acetate in aqueous phase) - both on the retention time and on the analytical response of the studied compounds; (ii) the effect of the analytical column's temperature on the retention time and on the analytical response of the pesticides investigated; (iii) the effects of co-elution in mixture containing 150 pesticides and, additionally, (iv) the carrying out of a study about the common transitions obtained by LC-MS/MS. Various common transitions were found among the 150 pesticides, but there were only two problematic cases, the pairs diuron-fluometuron and prometryn-terbutryn, which have common scanned transitions and have very close retention times. The use of ammonium salts as modifier instead of formic acid reports enhancement or suppression of the response depending on the pesticides. No great influence on the retention time or on the response of the pesticides and commodities studied was observed with relation to the column temperature. Two different columns: an HPLC (5 μm particle size) and an UHPLC analytical column (1.8 μm particle size) have been used. As was expected, shorter run times and lower peak width was achieved with the UHPLC column.In this paper, the effect of the compounds on each other in the MS analysis when the number of co-eluting compounds is quite high is also described. Mainly small suppression or enhancement co-elution effect was observed, but some particular pesticides presented high sensitivity (>±60% effect) when they elute together with others. This is an important factor and it has to be taken into account when performing multiresidue pesticide analysis.     

Multiresidue analysis of quinolones in water by ultra‐high perfomance liquid chromatography with tandem mass spectrometry using a simple and effective sample treatment

A rapid and simple analytical method has been developed for the determination of 19 quinolones in environmental water samples using ultra high performance liquid chromatography with tandem mass spectrometry. Chromatographic and detection conditions have been optimized and the separation was achieved in less than 4 min. The separation was carried out using a new‐generation column filled with superficially porous particles, resulting in lower backpressure and better resolution than totally porous particle columns. The quinolones were detected by electrospray ionization in positive mode using multiple‐reaction monitoring mode for acquisition. A sample treatment based on liquid–liquid extraction and phase separation via salting‐out was employed to achieve a fast and simple extraction that enables the multiresidue analysis. The method has been validated for an environmental well water sample from a mountain area. Very low limits of detection (between 10 and 90 ng/L) with relative standard deviations lower than 16.5% and recoveries higher than 73% were achieved. Moreover, well waters from different origins (mountain and coast areas and irrigated land) have been evaluated and similar results were obtained.     

Synthesis of core‐shell magnetic molecularly imprinted polymer for the selective determination of imidacloprid in apple samples

This work demonstrates the synthesis and characterization of core‐shell magnetic molecularly imprinted polymers based on surface imprinting using methacryloyl chloride as a functional monomer for the selective extraction of imidacloprid (template) from apple fruit. The characterization analysis results ensured the successful synthesis of the magnetic molecularly imprinted polymers owing to their heterogeneous structure and good magnetic properties. An isothermal binding test was assessed with a pseudo‐second‐order kinetic model, and the kinetic results fit well to the Freundlich isothermal model. The polymers exhibited an adsorption capacity of 5.75 mg/g for the target analyte with a good selective extraction ability. In addition, the polymers can be reused several times without significant performance loss. The molecularly imprinted polymers showed good performance in the analysis of spiked apple sample with a linear range of 0.05–1.0 mg/L, a limit of detection of 0.048 mg/L and a limit of quantification of 0.146 mg/L (S/N = 3/10). The recoveries of the samples were 77.66–96.57% and their respective relative standard deviations were 3.36–0.45%. All the results indicated that the proposed method provided good selective extraction, as qualifying the analytical standards.     

Facile synthesis of spherical covalent organic frameworks for enrichment and quantification of aryl organophosphate esters in mouse serum and tissues

Here, an imine-linked-based spherical covalent organic framework (COF) was prepared at room temperature. The as-synthesized spherical COF served as an adsorbent in dispersive solid-phase extraction (dSPE), by its virtue of great surface area (1542.68 m²/g), regular distribution of pore size (2.95 nm), and excellent stability. Therefore, a simple and high-efficiency dispersive solid phase extraction method based on a spherical COF coupled with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established to determine aryl organophosphate esters in biological samples. This approach displayed favorable linearity in the range of 10.0–1000.0 ng/L (r > 0.9989), a high signal enhancement factor (58.8–181.8 folds) with low limits of detection (0.3–3.3 ng/L). Moreover, it could effectively eliminate complex matrix interference to accurately extract seven aryl organophosphate esters from mouse serum and tissue samples with spiked recoveries of 82.0%–117.4%. The as-synthesized spherical COF has been successfully applied in sample preparation. The dSPE-HPLC-MS/MS method based on a spherical COF has potential application to study the pollutants' metabolism in vivo.     

直接进样超高效液相色谱-三重四极杆质谱法快速测定环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利残留

建立了一种简便、直接进样的超高效液相色谱-三重四极杆质谱法（UPLC-MS/MS）快速测定环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利的残留。环境水样经0.22 μm滤膜过滤或冷冻离心去除杂质后,滤液无需衍生化直接进行定量分析。4种农药通过Metrosep A Supp 5柱（150 mm×4.0 mm,5 μm）分离,以碳酸氢铵-氨水溶液为流动相进行梯度洗脱,在负离子模式下以MRM方式进行检测。结果表明,4种农药在0.50~50.0 μg/L范围内相关系数（r）均大于0.999,线性关系良好,方法检出限为0.05~0.09 μg/L。实际水样在低、中、高3种加标浓度水平下,回收率分别为76.3%~108%、83.0%~107%和87.0%~105%,相对标准偏差分别为2.0%~12.3%、2.4%~5.6%和2.7%~6.8%。使用该方法对海南省34个水样进行测定,其中30个饮用水源地水样中均未检出4种农药,槟榔园附近3个水样均检出草甘膦和氨甲基膦酸,香蕉园附近的1个水样检出草铵膦和氨甲基膦酸。与传统的衍生化方法比较,该方法操作简便,重现性好,准确性高,不受基体干扰,适用于环境水样中草甘膦、氨甲基膦酸、草铵膦及乙烯利的残留检测。     

Analytical determination of selenium in medical samples,staple food and dietary supplements by means of total reflection X-ray fluorescence spectroscopy

Selenium is essential for many aspects of human health and, thus, the object of intensive medical research. This demands the use of analytical techniques capable of analysing selenium at low concentrations with high accuracy in widespread matrices and sometimes smallest sample amounts.In connection with the increasing importance of selenium, there is a need for rapid and simple on-site (or near-to-site) selenium analysis in food basics like wheat at processing and production sites, as well as for the analysis of this element in dietary supplements. Common analytical techniques like electrothermal atomic absorption spectroscopy (ETAAS) and inductively-coupled plasma mass spectrometry (ICP-MS) are capable of analysing selenium in medical samples with detection limits in the range from 0.02 to 0.7 μg/l. Since in many cases less complicated and expensive analytical techniques are required, TXRF has been tested regarding its suitability for selenium analysis in different medical, food basics and dietary supplement samples applying most simple sample preparation techniques.The reported results indicate that the accurate analysis of selenium in all sample types is possible. The detection limits of TXRF are in the range from 7 to 12 μg/l for medical samples and 0.1 to 0.2 mg/kg for food basics and dietary supplements. Although this sensitivity is low compared to established techniques, it is sufficient for the physiological concentrations of selenium in the investigated samples.     

Triple quadrupole tandem mass spectrometry: A real alternative to high resolution magnetic sector instrument for the analysis of polychlorinated dibenzo-p-dioxins,furans and dioxin-like polychlorinated biphenyls

This paper reports on the optimisation, characterisation, validation and applicability of gas chromatography coupled to triple quadrupole mass spectrometry in its tandem operation mode (GC-QqQ(MS/MS) for the quantification of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs, dioxins) and dioxin-like polychlorinated biphenyls (DL-PCBs) in environmental and food matrices. MS/MS parameters were selected to achieve the high sensitivity and selectivity required for the analysis of this type of compounds and samples. Good repeatability for areas (RSD = 1–10%, for PCDD/Fs and DL-PCBs) and for ion transition ratios (RSD = 0.3–10%, for PCDD/Fs, and 0.2–15%, for DL-PCBs) and low instrumental limits of detection, 0.07–0.75 pg μL⁻¹ (for dioxins) and 0.05–0.63 pg μL⁻¹ (for DL-PCBs), were obtained. A comparative study of the congener specific determination using both GC-QqQ(MS/MS) and gas chromatography-high resolution mass spectrometry (GC-HRMS) was also performed by analysing several fortified samples and certified reference materials (CRMs) with low (feed and foodstuffs), median (sewage sludge) and high (fly ash) toxic equivalency (TEQ) concentration levels, i.e. 0.60, 1.83, 72.9 and 3609 pg WHO-TEQ(PCDD/Fs) g⁻¹. The agreement between the results obtained for the total TEQs (dioxins) on GC-QqQ(MS/MS) and GC-HRMS in all the investigated samples were within the range of ±4%, and that of DL-PCBs at concentration levels of 0.84 pg WHO-TEQs (DL-PCBs) g⁻¹, in the case of feedstuffs, was 0.11%. Both instrumental methods have similar and comparable linearity, precision and accuracy. The GC-QqQ(MS/MS) sensitivity, lower than that of GC-HRMS, is good enough (iLODs in the down to low pg levels) to detect the normal concentrations of these compounds in food and environmental samples. These results make GC-QqQ(MS/MS) suitable for the quantitative analysis of dioxins and DL-PCBs and a real alternative tool to the reference sector HRMS instruments.