Determination of trace impurities in boron nitride by graphite furnace atomic absorption spectrometry and electrothermal vaporization inductively coupled plasma optical emission spectrometry using solid sampling

Two digestion-free methods for trace analysis of boron nitride based on graphite furnace atomic absorption spectrometry (GFAAS) and electrothermal vaporization inductively coupled plasma spectrometry optical emission (ETV-ICP-OES) using direct solid sampling have been developed and applied to the determination of Al, Ca, Cr, Cu, Fe, Mg, Mn, Si, Ti and Zr in four boron nitride materials in concentration intervals of 1–23, 54–735, 0.05–21, 0.005–1.3, 1.6–112, 4.5–20, 0.03–1.8, 6–46, 38–170 and 0.4–2.3 μg g^− 1, respectively. At optimized experimental conditions, with both methods, effective in-situ analyte/matrix separation was achieved and calibration could be performed using calibration curves measured with aqueous standard solutions. In solid sampling GFAAS, before sampling, the platform was covered with graphite powder and, for determination of Si, also the Pd/Mg(NO₃)₂ modifier was used. In the determination of all analyte elements by solid sampling ETV-ICP-OES, Freon R12 was added to argon carrier gas. For solid sampling GFAAS and ETV-ICP-OES, the achievable limits of detection were within 5 (Cu)–130 (Si) ng g^− 1 and 8 (Cu)–200 (Si) ng g^− 1, respectively. The results obtained by these two methods for four boron nitride materials of different purity grades are compared each with the other and with those obtained in analysis of digests by ICP-OES. The performance of the two solid sampling methods is compared and discussed.     

Determination of organic compounds from wood combustion aerosol nanoparticles by different gas chromatographic systems and by aerosol mass spectrometry

Organic compounds in atmospheric nanoparticles have an effect on human health and the climate. The determination of these particles is challenged by the difficulty of sampling, the complexity of sample composition, and the trace-level concentrations of the compounds. Meeting the challenge requires the development of sophisticated sampling systems for size-resolved particles and the optimization of sensitive, accurate and simple analytical techniques and methods. A new sampling system is proposed where particles are charged with a bipolar charger and size-segregated with a differential mobility analyzer. This system was successfully used to sample particles from wood pyrolysis with particle sizes 30–100 nm. Particles were analyzed by four techniques: comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry, gas chromatography–time-of-flight mass spectrometry, gas chromatography–quadrupole mass spectrometry, and aerosol mass spectrometry (aerosol MS). In the chromatographic techniques, particles were collected on a filter and analyzed off-line after sample preparation, whereas in the aerosol MS, particle analysis was performed directly from the particle source. Target compounds of the samples were polyaromatic hydrocarbons and n-alkanes. The analytical techniques were compared and their advantages and disadvantages were evaluated. The sampling system operated well and target compounds were identified in low concentrations.     

Development of a versatile,easy and rapid atmospheric monitor for benzene,toluene, ethylbenzene and xylenes determination in air

A new procedure for the passive sampling in air of benzene, toluene, ethylbenzene and xylene isomers (BTEX) is proposed. A low-density polyethylene layflat tube filled with a mixture of solid phases provided a high versatility tool for the sampling of volatile compounds from air. Several solid phases were assayed in order to increase the BTEX absorption in the sampler and a mixture of florisil and activated carbon provided the best results. Direct head-space-gas chromatography–mass spectrometry (HS-GC–MS) measurement of the whole deployed sampler was employed for a fast determination of BTEX. Absorption isotherms were used to develop simple mathematical models for the estimation of BTEX time-weighted average concentrations in air. The proposed samplers were used to determine BTEX in indoor air environments and results were compared with those found using two reference methodologies: triolein-containing semipermeable membrane devices (SPMDs) and diffusive Radiello samplers. In short, the developed sampling system and analytical strategy provides a versatile, easy and rapid atmospheric monitor (VERAM).     

Simultaneous determination of 3-monochloropropane-1,2-diol and acrylamide in food by gas chromatography-triple quadrupole mass spectrometry with coupled column separation

Both 3-monochloropropane-1,2-diol (3-MCPD) and acrylamide are contaminants found in heat-processed foods and their related products. A quantitative method was developed for the simultaneous determination of both contaminants in food by gas chromatography-triple quadrupole mass spectrometry (GC–MS/MS). The analytes were purified and extracted by the matrix solid-phase dispersion extraction (MSPDE) technique with Extrelut NT. A coupled column (a 3 m Innowax combined with a 30 m DB-5 ms) was developed to separate both compounds efficiently without derivatization. Triple quadrupole mass spectrometry in multiple reaction monitoring mode (MRM) was applied to suppress matrix interference and obtain good sensitivity in the determination of both analytes. The limit of detection (LOD) in the sample matrix was 5 μg kg⁻¹ for 3-MCPD or acrylamide. The average recoveries for 3-MCPD and acrylamide in different food matrices were 90.5–107% and 81.9–95.7%, respectively, with the intraday relative standard deviations (RSDs) of 5.6–13.5% and 5.3–13.4%, respectively. The interday RSDs were 6.1–12.6% for 3-MCPD and were 5.0–12.8% for acrylamide. Both contaminants were found in samples of bread, fried chips, fried instant noodles, soy sauce, and instant noodle flavoring. Neither 3-MCPD nor acrylamide was detected in the samples of dairy products (solid or liquid samples) and non-fried instant noodles.     

Direct determination of trace elements in boron nitride powders by slurry sampling total reflection X-ray fluorescence spectrometry

The use of slurry sampling total reflection X-ray fluorescence spectrometry (SlS-TXRF) for the direct determination of Ca, Cr, Cu, Fe, Mn and Ti in four boron nitride powders has been described. Measurements of the zeta potential showed that slurries with good stabilities can be obtained by the addition of polyethylenimine (PEI) at a concentration of 0.1 wt.% and by adjusting the pH at 4. For the optimization of the concentration of boron nitride in the slurries the net line intensities and the signal to background ratios were determined for the trace elements Ca and Ti as well as for the internal standard element Ga in the case of concentrations of boron nitride ranging from 1 to 30 mg mL⁻¹. As a compromise with respect to high net line intensities and high signal to background ratios, concentrations of 5 mg mL⁻¹ of boron nitride were found suitable and were used for all further measurements. The limits of detection of SlS-TXRF for the boron nitride powders were found to range from 0.062 to 1.6 μg g^– 1 for Cu and Ca, respectively. Herewith, they are higher than those obtained in solid sampling and slurry sampling graphite furnace atomic absorption spectrometry (SoS-GFAAS, SlS-GFAAS) as well as those of solid sampling electrothermal evaporation inductively coupled plasma optical emission spectrometry (SoS-ETV-ICP-OES). For Ca and Fe as well as for Cu and Fe, however, they were found to be lower than for GFAAS and for ICP-OES subsequent to wet chemical digestion, respectively. The universal applicability of SlS-TXRF to the analysis of samples with a wide variety of matrices could be demonstrated by the analysis of certified reference materials such as SiC, Al₂O₃, powdered bovine liver and borate ore with a single calibration. The correlation coefficients of the plots for the values found for Ca, Fe and Ti by SlS-TXRF in the boron nitride powders as well as in the before mentioned samples versus the reference values for the respective samples over a concentration range from 2.5 to 1470 μg g^– 1 were found to be 0.995, 0.991 and 0.997, respectively.     

Determination of trace impurities in titanium dioxide by direct solid sampling electrothermal atomic absorption spectrometry

A true direct solid sampling electrothermal atomic absorption spectrometry method with Zeeman-effect background correction (Analytik Jena ZEEnit 60 AAS) was developed for the determination of As, Cd, Hg, Pb, Sb and Zn in powdered titanium dioxide of pharmaceutical, food and cosmetics grade. The interaction of the titanium matrix and graphite surface of the sample carrier boat in a transversely heated graphite tube atomizer was investigated. Conversion of titanium dioxide to interfering TiO₂–TiC-liquid phase, running out the sampling boat, was observed at temperatures above 2000 °C. The temperature program was optimized accordingly for these volatile analytes in atomization and cleaning steps in order to prevent this interference and to prolong significantly the analytical lifetime of the boat to more than one thousand runs. For all elements, calibration by aqueous standard addition method, by wet-chemically analyzed samples with different content of analytes and/or by dosing one sample in different amounts, were proved as adequate quantification procedures. Linear dynamic calibration working ranges can be considerably expanded up to two orders of magnitude within one measurement run by applying three-field dynamic mode of the Zeeman background correction system. The results obtained by true direct solid sampling technique are compared with those of other independent, mostly wet-chemical methods. Very low limits of detection (3σ criterion) of true solid sampling technique of 21, 0.27, 24, 3.9, 6.3 and 0.9 ng g^− 1 were achieved for As, Cd, Hg, Pb, Sb and Zn, respectively.     

Investigation of acidic pharmaceuticals in river water and sediment by microwave-assisted extraction and gas chromatography–mass spectrometry

Investigations were performed along the Danube river at Budapest (Hungary) by collecting water and sediment samples simultaneously for 1 year in order to clarify the possible hazard of selected acidic pharmaceuticals (ibuprofen, naproxen, ketoprofen, and diclofenac) on the water supply used for the production of drinking water by bank filtration. In the case of water samples, the sample preparation procedure included solid phase extraction (SPE), meanwhile, in the case of sediment samples, microwave-assisted extraction (MAE) followed by dispersive matrix extraction (DME) for pre-cleaning as well as SPE for enrichment. The quantification was carried out using gas chromatography–mass spectrometry (GC–MS). The calculated recoveries were 97–99% (± 7%) for the water and 95–103% (± 12%) for the sediment samples. In the river water, ketoprofen concentration was always below the limit of quantification (LOQ) level; ibuprofen, naproxen and diclofenac could be quantified in the range of 8–50, 2–30, 7–90 ng/L. In sediments, only naproxen and diclofenac were found in the range of 2–20 and 5–38 ng/g, respectively. According to the obtained results, the concentration ratios of the two phases linearly depended on the total organic carbon content (TOC) of the sediments at each sampling date. The linear regressions were 0.925 and 0.946 for naproxen and diclofenac, respectively.     

Quantification of organic acids in particulate matter by coupling of thermally assisted hydrolysis and methylation with thermodesorption-gas chromatography–mass spectrometry

A quantitative method for the determination of organic acids in atmospheric particles is developed. The method couples a derivatisation step (thermally assisted hydrolysis and methylation) and a Curie point pyrolyser as a thermal desorption technique and gas chromatography–mass spectrometry (CPP-GC–MS). Among the reagents tested (tetramethylammonium hydroxide (TMAH), tetramethylammonium acetate (TMAAc) and phenyltrimethylammonium hydroxide (TMPAH)), the best performance was found using TMAAc as a derivatisation reagent for the reaction time of 4 s at 510 °C as heating temperature. Calibration was performed for a series of fatty acids (FA), dicarboxylic acids (DCA) and terpenoic acids (TA) under these conditions. Coefficients of determination (R²) were between 0.94 and 0.98. Limits of detection (LOD) were in the nanogram-range between 0.1 and 3.6 ng. The method is applied on atmospheric particle samples to obtain the quantification reproducibility and quantification limits. Reproducibility was determined in terms of relative standard deviations (RSD) for ambient aerosol samples collected by a high-volume-sampler (HVS, RSD = 6–45%, n = 10) and a Berner impactor (BI, RSD = 5–34%, n = 10). Based on 24 h sampling time the developed method enables quantification of all three classes of acids for both sampling techniques. Calibration data and presented volume concentrations are compared with literature data. A comparison with an off-line methylation-GC–MS using BF₃ as a derivatisation reagent and capillary electrophoresis coupled mass spectrometry (CE-MS) showed a good agreement. Minimal sample preparation is the main advantage of the developed method. Depending on the sensitivity requirements the present method can be a fast and simple alternative to GC–MS techniques with conventional sample preparation steps for semi-volatile organic acids.     

Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.     

Trace determination of sulphur mustard and related compounds in water by headspace-trap gas chromatography–mass spectrometry

A method for trace determination of sulphur mustard (HD) and some of its cyclic decomposition compounds in water samples has been developed using headspace-trap in combination with gas chromatography–mass spectrometry (GC–MS). Factorial design was used for optimisation of the method. The trap technology allows enrichment and focusing of the analytes on an adsorbent, hence the technique offers better sensitivity compared to conventional static headspace. A detection limit of 1 ng/ml was achieved for HD, while the cyclic sulphur compounds 1,4-thioxane, 1,3-dithiolane and 1,4-dithiane could be detected at a level of 0.1 ng/ml. The method was validated for the stable cyclic compounds in the concentration range from the limit of quantification (LOQ: 0.2–0.4 ng/ml) to hundred times LOQ. The within and between assay precisions at hundred times LOQ were 1–2% and 7–8% relative standard deviation, respectively. This technique requires almost no sample handling, and the total time for sampling and analysis was less than 1 h. The method was successfully employed for muddy river water and sea water samples.     

Solid sampling coupled to flame furnace atomic absorption spectrometry for Mn and Ni determination in petroleum coke

A solid sampling flame furnace atomic absorption spectrometry (SS-FF-AAS) system was developed for Mn and Ni determination in petroleum coke. The proposed system for solid sampling was a quartz cell with two perpendicular tubes (T-shaped tubes), positioned above the burner. Manganese and Ni determination was made using an atomic absorption spectrometer with deuterium background corrector, air-acetylene flame and a single slit burner. Powdered samples of coke were introduced as pellets (up to 62 mg) into the quartz cell with a movable hollow quartz piston. When the sample pellet reached the end of quartz cell (T-connection), in the presence of a constant oxygen flow, it quickly burned and the combustion products were transferred to the upper slit tube where the atomic absorption process occurs. Calibration was possible using aqueous reference solutions applied directly on high purity graphite pellets. Results obtained for Mn and Ni using the proposed SS-FF-AAS system were compared to those obtained by inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS) after sample decomposition by high pressure microwave assisted acid digestion and also by microwave induced combustion. Agreement better than 96% was obtained for both methods employing a previous step of sample digestion (ICP OES and ICP-MS) and by SS-FF-AAS. Accuracy was evaluated using certified reference materials and also recovery tests. The relative standard deviation was lower than 9% for both analytes. The characteristic mass was 18.3 and 14.7 ng and the limit of detection was 0.6 and 0.8 µg g^− 1 for Mn and Ni, respectively. The proposed SS-FF-AAS system can be applied for Mn and Ni determination in petroleum coke, combining a relatively high sample throughput (9 determinations per h), and a suitable precision and accuracy.     

Inter-laboratory trials for analysis of perfluorooctanesulfonate and perfluorooctanoate in water samples: Performance and recommendations

The ISO 25101 (International Organization for Standardization, Geneva) describes a new international standard method for the determination of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) in unfiltered samples of drinking and surface waters. The method is based on the extraction of target analytes by solid phase extraction, solvent elution, and determination by high performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS). For the determination of the performance of this method, more than 20 laboratories from 9 different countries participated in an inter-laboratory trial in 2006. In addition, inter-laboratory trials were conducted in 2008 and 2009 for the analysis of perfluoroalkylsubstances (PFASs), including PFOS and PFOA, in water samples by following the protocols of Japanese Industrial Standard (JIS). Overall, the repeatability coefficients of variation (i.e., within-laboratory precision) for PFOS and PFOA in all water samples were between 3 and 11%, showing a adequate precision of the ISO and JIS methods. The reproducibility coefficients of variation (i.e., between-laboratory precision) were found to vary within a range of 7–31% for surface water and 20–40% for wastewater. The recoveries of PFOS and PFOA, as a measure of accuracy, varied from 84 to 100% for surface water and from 84 to 100% for wastewater among the samples with acceptable criteria for internal standards recovery. The determined concentrations of PFASs in samples compared well with the “true” values. The results of the inter-laboratory trial confirmed that the analytical methods are robust and reliable and can be used as a standard method for the analysis of target compounds in water samples.     

Design and Critical Evaluation of Improved Electrothermal Vaporization Flame Atomic Absorption/Emission Spectrometry for Direct Determination of Trace Metals in Microliter Samples

Improved tantalum-filament electrothermal vaporization flame atomic absorption spectrometry (ETV-FAAS) was developed and used for the direct determination of trace metals in microliter samples. Studies have been made for optimizing the experimental parameters that affect the performance of sample introduction to the flame. Linear calibration graphs are shown for the elements Mn (10–200 ng), Pb (5–200 ng), Cu (5–100 ng), Cd (5–50 ng), Li (1–20 ng), Na (10–80 ng), and K (10–80 ng), using only 10 μl of standard solutions. The detection limits of the elements by ETV-FAAS were much lower than those of conventional FAAS. Absolute detection limits for all elements studied were less than 0.1 ng. The relative standard deviation values for the elements were <10%. The developed method was also applied to the determination of lead concentration in blood samples.     

On-line solid phase extraction-liquid chromatography–mass spectrometry for trace determination of nerve agent degradation products in water samples

Three primary nerve agent degradation products (ethyl-, isopropyl- and pinacolyl methylphosphonic acid) have been determined in water samples using on-line solid phase extraction-liquid chromatography and mass spectrometry (SPE-LC–MS) with electrospray ionisation. Porous graphitic carbon was employed for analyte enrichment followed by hydrophilic interaction chromatography. Diethylphosphate was applied as internal standard for quantitative determination of the alkyl methylphosphonic acids (AMPAs). By treating the samples with strong cation-exhange columns on Ba, Ag and H form, the major inorganic anions in water were removed by precipitation prior to the SPE-LC–MS determination. The AMPAs could be determined in tap water with limits of detection of 0.01–0.07 μg L⁻¹ with the [M−H]⁻ ions extracted at an accuracy of ±5 mDa. The within and between assay precisions at analyte concentrations of 5 μg L⁻¹ were 2–3%, and 5–9% relative standard deviation, respectively. The developed method was employed for determination of the AMPAs in three natural waters and a simulated waste water sample, spiked at 5 μg L⁻¹. Recoveries of ethyl-, isopropyl- and pinacolyl methylphosphonic acid were 80–91%, 92–103% and 99–106%, respectively, proving the applicability of the technique for natural waters of various origins.     

Development of a gas chromatography-mass spectrometry method for the determination of pesticides in gaseous and particulate phases in the atmosphere

A reliable multi-residue method for determining gaseous and particulate phase pesticides in atmospheric samples has been developed. This method, based on full scan gas chromatography–mass spectrometry (GC–MS), allowed the proper determination of sixteen relevant pesticides, in a wide range of concentrations and without the influence of interferences. The pesticides were benfluralin, bitertanol, buprofezin, chlorfenvinphos, chlorpyrifos, chlorpyrifos-methyl, ethalfluralin, fenthion, lindane, malathion, methidathion, propachlor, propanil, pyriproxifen, tebuconazol and trifluralin. Comparisons of two types of sampling filters (quartz and glass fibre) and four types of solid-phase cartridges (XAD-2, XAD-4, Florisil and Orbo-49P) showed that the most suitable supports were glass fibre filter for particulate pesticides and XAD-2 and XAD-4 cartridges for gaseous pesticides (>95% recovery). Evaluations of elution solvents for ultrasonic-assisted extraction demonstrated that isooctane is better than ethylacetate, dichloromethane, methanol or a mixture of acetone:hexane (1:1).Recovery assays and the standard addition method were performed to validate the proposed methodology. Moreover, large simulator chamber experiments allowed the best study of the gas-particle partitioning of pesticides for testing the sampling efficiency for the validation of an analytical multiresidue method for pesticides in air. Satisfactory analytical parameters were obtained, with a repeatability of 5 ± 1%, a reproducibility of 13 ± 3% and detection limits of 0.05–0.18 pg m⁻³ for the particulate phase and 26–88 pg m⁻³ for the gaseous phase. Finally, the methodology was successfully applied to rural and agricultural samples in the Mediterranean area.     

Analysis of capsaicin and dihydrocapsaicin in peppers and pepper sauces by solid phase microextraction–gas chromatography–mass spectrometry

A simple method for the analysis of capsaicin and dihydrocapsaicin in peppers and pepper sauces by solid phase microextraction–gas chromatography–mass spectrometry has been developed. A novel device was designed for direct extraction solid phase microextraction in order to avoid damage to the fiber. The analysis was performed without derivatization for the gas chromatography–mass spectrometry analysis. Selection fiber, extraction temperature, extraction time and pH, were optimized. The method was linear in the range 0.109–1.323 μg/mL for capsaicin and 0.107–1.713 μg/mL for dihydrocapsaicin with correlation coefficient up to r = 0.9970 for both capsaicinoids. The precision of the method was less than 10%. The method was applied to the analysis of 11 varieties of peppers and four pepper sauces. A broad range of capsaicin (55.0–25 459 μg/g) and dihydrocapsaicin (93–1 130 μg/g) was found in the pepper and pepper sauces samples (4.3–717.3 and 1.0–134.8 μg/g), respectively.     

Ultra-trace determination of iodine in sediments and biological material using UV photochemical generation-inductively coupled plasma mass spectrometry

Several sample preparation techniques have been evaluated for the determination of iodine using UV-photochemical generation-quadrupole inductively coupled plasma mass spectrometry. Thermal decomposition of samples at 1000 °C followed by capture of the liberated iodine in dilute acetic acid permitted subsequent UV-photochemical generation of a volatile iodine species that serves to enhance sensitivity 25-fold over conventional solution nebulization, delivering reagent blank detection limits of 8.75 pg g^{–1 127}I and 0.075 pg g^–1 129I for solid samples (400 mg test mass). The methodology was validated through determination of total iodine in several Standard Reference Materials, including NIST 1572 Citrus leaves, NIST 1549 Non-fat milk powder, NIST 1566a Oyster tissue and NIST 2709 San Joaquin Soil. Liberation of iodine from samples and its collection as well as photochemical generation were quantitative, permitting calibration to be achieved using standards prepared in dilute acetic acid.     

A direct solid sampling electrothermal atomic absorption spectrometry method for the determination of silicon in biological materials

A solid sampling electrothermal atomic absorption spectrometry method for direct determination of trace silicon in biological materials was developed and applied to analysis of pork liver, bovine liver SRM 1577b and pure cellulose. The organic matrix was destroyed and expelled from the furnace in the pyrolysis stage involving a step-wise increasing the temperature from 160 °C to 1200 °C. The mixed Pd/Mg(NO₃)₂ modifier has proved to be the optimum one with respect to the achievement of maximum sensitivity, elimination of the effect of the remaining inorganic substances and the possibility of using calibration curves measured with aqueous standard solutions for quantification. For the maximum applicable sample amount of 6 mg, the limit of detection was found to be 30 ng g^− 1. The results were compared with those obtained by different spectrometric methods involving sample digestion, by electrothermal atomic absorption spectrometry using slurry sampling, by wavelength dispersive X-ray fluorescence spectrometry and by radiochemical neutron activation analysis. The method seems to be a promising one for analysis of biological materials containing no significant fraction of silicon in form of not naturally occurring volatile organosilicon compounds. The still incessant serious limitations and uncertainties in the determination of trace silicon in solid biological materials are discussed.     

Bismuth as a general internal standard for lead in atomic absorption spectrometry

Bismuth was evaluated as internal standard for Pb determination by line source flame atomic absorption spectrometry (LS FAAS), high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) and line source graphite furnace atomic absorption spectrometry (LS GFAAS). Analysis of samples containing different matrices indicated close relationship between Pb and Bi absorbances. Correlation coefficients of calibration curves built up by plotting A^Pb/A^Biversus Pb concentration were higher than 0.9953 (FAAS) and higher than 0.9993 (GFAAS). Recoveries of Pb improved from 52–118% (without IS) to 97–109% (IS, LS FAAS); 74–231% (without IS) to 96–109% (IS, HR-CS FAAS); and 36–125% (without IS) to 96–110% (IS, LS GFAAS). The relative standard deviations (n = 12) were reduced from 0.6–9.2% (without IS) to 0.3–4.3% (IS, LS FAAS); 0.7–7.7% (without IS) to 0.1–4.0% (IS, HR-CS FAAS); and 2.1–13% (without IS) to 0.4–5.9% (IS, LS GFAAS).     

Trace analysis of tetracycline antibiotics in human urine using UPLC–QToF mass spectrometry

A rapid, sensitive and specific ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC–QToF-MS) method has been developed and validated for simultaneous determination of three tetracyclines (TCs) including oxytetracycline, tetracycline, and chlortetracycline in human urine. Human urine sample preparation involves pH adjustment to 4 with hydrochloric acid, pre-concentration, and cleanup by solid phase extraction (SPE) process. The chromatographic separation of all TCs was achieved in less than 5 min using UPLC and ESI-QToF-MS was successfully employed for the identification and quantification. The accurate masses of the product ions were calculated using lock mass correction, and were deviated from the theoretical masses by 0.5–1.9 mDa and 1.1–4.5 ppm, respectively. The developed method was validated in terms of linearity, sensitivity, selectivity, decision limit, detection capability, accuracy, and precision. Limit of detection and limit of quantitation for all TCs were estimated in the range of 0.089–0.138 ng mL^{− 1} and 0.294–0.455 ng mL^{− 1}, respectively. High overall recoveries of greater than 90% were achieved with linear responses over the 0.5–2 ng mL^{− 1} range for all TCs in urine samples.