Rapid and sensitive methodology for determination of ethyl carbamate in fortified wines using microextraction by packed sorbent and gas chromatography with mass spectrometric detection

This work presents a new methodology to quantify ethyl carbamate (EC) in fortified wines. The presented approach combines the microextraction by packed sorbent (MEPS), using a hand-held automated analytical syringe, with one-dimensional gas chromatography coupled with mass spectrometry detection (GC–MS). The performance of different MEPS sorbent materials was tested, namely SIL, C2, C8, C18, and M1. Also, several extraction solvents and the matrix effect were evaluated. Experimental data showed that C8 and dichloromethane were the best sorbent/solvent pair to extract EC. Concerning solvent and sample volumes optimization used in MEPS extraction an experimental design (DoE) was carried out. The best extraction yield was achieved passing 300 μL of sample and 100 μL of dichloromethane. The method validation was performed using a matrix-matched calibration using both sweet and dry fortified wines, to minimize the matrix effect. The proposed methodology presented good linearity (R² = 0.9999) and high sensitivity, with quite low limits of detection (LOD) and quantification (LOQ), 1.5 μg L⁻¹ and 4.5 μg L⁻¹, respectively. The recoveries varied between 97% and 106%, while the method precision (repeatability and reproducibility) was lower than 7%. The applicability of the methodology was confirmed through the analysis of 16 fortified wines, with values ranging between 7.3 and 206 μg L⁻¹. All chromatograms showed good peak resolution, confirming its selectivity. The developed MEPS/GC–MS methodology arises as an important tool to quantify EC in fortified wines, combining efficiency and effectiveness, with simpler, faster and affordable analytical procedures that provide great sensitivity without using sophisticated and expensive equipment.     

Ultrasonic energy as a tool in the sample treatment for polymer characterization through matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Different ultrasonic devices including ultrasonic bath with dual frequency, sonoreactor and ultrasonic probe, were tested for their viability in the sample treatment for polymer characterization by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis. The effect of sonication frequency (35 kHz, 40 kHz and 130 kHz), sonication amplitude, and sonication time on the polymer's number-average molecular weight (M_n) and weight-average molecular weight (M_w) were investigated. The effect of those variables in the molecular mass distribution of three polymer standards, poly(styrene) 2000 Da and 10,000 Da and poly(ethylene glycol) 1000 Da, was evaluated. In addition, the influence of ultrasonic energy on the sample treatment as a function of the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI) matrix was also studied through two common standard matrices, dithranol and 2,5-dihydroxybenzoic acid. The results obtained show that the ultrasonic bath at 35 kHz is the best option for the purpose of fast sample treatment for polymer characterization. The M_n and M_w values obtained for this ultrasonic device and for the three polymers tested using dithranol as MALDI matrix, were not statistically different from the ones acquired with vortex mixing and also were in concordance with the values recommended by the polymer manufacturers.     

An improved clean sonoreactor-based method for protein identification by mass spectrometry-based techniques

A new clean fast (8 min) method for in-solution protein digestion without detergent or urea for protein identification by peptide mass fingerprint and mass spectrometry-based techniques is proposed. The new method avoids the use of time consuming desalting procedures entailing the following four steps done under the effect of an ultrasonic field provided by a sonoreactor: denaturation (1 min) in a mixed solution of water:acetonitrile 1/1 (v/v); protein reduction (1 min); protein alkylation (1 min); and protein digestion (5 min). Five proteins with masses comprised between 14.4 kDa and 97 kDa and the protein split-soret cytochrome c from D. desulfuricans ATCC27774, were successfully identified with this procedure. No differences were found in the sequence coverage or in the number of peptides matched when the new clean method was compared to another one using urea. Twofold better signal-to-noise ratios were obtained in the MALDI spectra from protein samples prepared with the new method when comparing it with a method using urea. The new digestion method avoids the need to remove salt content and increases throughput (six samples at once) while reducing sample loss and contamination from sample handling.     

Automated polyvinylidene difluoride hollow fiber liquid-phase microextraction of flunitrazepam in plasma and urine samples for gas chromatography/tandem mass spectrometry

A new polyvinylidene difluoride (PVDF) hollow fiber (200 μm wall thickness, 1.2 mm internal diameter, 0.2 μm pore size) was compared with two other polypropylene (PP) hollow fibers (200, 300 μm wall thickness, 1.2 mm internal diameter, 0.2 μm pore size) in the automated hollow fiber liquid-phase microextraction (HF-LPME) of flunitrazepam (FLNZ) in biological samples. With higher porosity and better solvent compatibility, the PVDF hollow fiber showed advantages with faster extraction efficiency and operational accuracy. Parameters of the CTC autosampler program for HF-LPME in plasma and urine samples were carefully investigated to ensure accuracy and reproducibility. Several parameters influencing the efficiency of HF-LPME of FLNZ in plasma and urine samples were optimized, including type of porous hollow fiber, organic solvent, agitation rate, extraction time, salt concentration, organic modifier, and pH. Under optimal conditions, extraction recoveries of FLNZ in plasma and urine samples were 6.5% and 83.5%, respectively, corresponding to the enrichment factor of 13 in plasma matrix and 167 in urine matrix. Excellent sample clean-up was observed and good linearities (r² = 0.9979 for plasma sample and 0.9995 for urine sample) were obtained in the range of 0.1–1000 ng/mL (plasma sample) and 0.01–1000 ng/mL (urine sample). The limits of detection (S/N = 3) were 0.025 ng/mL in plasma matrix and 0.001 ng/mL in urine matrix by gas chromatography/mass spectrometry/mass spectrometry.     

A chemiluminescence sensor for the determination of hydrogen peroxide

A chemiluminescence one-shot sensor for hydrogen peroxide is described. It is prepared by immobilization of cobalt chloride and sodium lauryl sulphate in hydroxyethyl cellulose matrix cast on a microscope cover glass. Luminol, sodium phosphate and the sample are mixed before use and applied on the membrane by a micropipette. The calibration graph is linear in the range 20-1600 μg/L, and the detection limit of the method (3σ) is 9 μg/L. A relative standard deviation of 4.5% was obtained for 100 μg/L H₂O₂ (n = 11). The sensor has been applied successfully to the determination of hydrogen peroxide in rainwater.     

Improved peptide mass fingerprinting matches via optimized sample preparation in MALDI mass spectrometry

Peptide mass fingerprinting (PMF) is a powerful technique in which experimentally measured m/z values of peptides resulting from a protein digest form the basis for a characteristic fingerprint of the intact protein. Due to its propensity to generate singly charged ions, along with its relative insensitivity to salts and buffers, matrix-assisted laser desorption and ionization (MALDI)-time-of-flight mass spectrometry (TOFMS) is the MS method of choice for PMF. The qualitative features of the mass spectrum can be selectively tuned by employing different methods to prepare the protein digest and matrix for MALDI-TOFMS. The selective tuning of MALDI mass spectra in order to optimize PMF is addressed here. Bovine serum albumin, carbonic anhydrase, cytochrome c, hemoglobin alpha- and beta-chain, and myoglobin were digested with trypsin and then analyzed by MALDI-TOFMS. 2,5-dihydroxybenzoic acid (DHB) and alpha-cyano-4-hydroxycinnamic acid (CHCA) were prepared using six different sample preparation methods: dried droplet, application of protein digest on MALDI plate followed by addition of matrix, dried droplet with vacuum drying, overlayer, sandwich, and dried droplet with heating. Improved results were obtained for the matrix alpha-cyano-4-hydroxycinnamic acid using a modification of the died droplet method in which the MALDI plate was heated to 80 °C prior to matrix application, which is supported by observations from scanning electron microscopy. Although each protein was found to have a different optimum sample preparation method for PMF, in general higher sequence coverage for PMF was obtained using DHB. The best PMF results were obtained when all of the mass spectral data for a particular protein digest was convolved together.     

Aggregation-induced emission compounds as new assisted matrices for laser desorption/ionization time-of-flight mass spectrometry

Here, N,N′-bis(4-hydroxylsalicylidene)-p-phenylenediamine (BSPD-OH), N,N′-bis(4-methoxylsalicylidene)-p-phenylenediamine (BSPD-OMe) and N,N′-bis(salicylidene)-p-phenylenediamine (BSPD), which belong to the same category of aggregation-induced emission (AIE) compounds based on Schiff base reactions, were synthesized and applied as new matrices in the analysis of small molecules by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). This type of AIE compounds can be good MALDI matrices. Conventional organic matrices often produce large amounts of matrix ions, hindering the analysis of low molecular weight (LMW) compounds. However, these AIE compounds generate few matrix ions and less background interference because their presence as aggregates decreases the generation of matrix interference. The sensitivity of the AIE matrix is high because the aggregates can improve the absorption of the applied laser emissions. We can regulate the ionization efficiency of the AIE matrix by changing its aggregation state. During this study, BSPD-OH exhibited better ionization efficiency than the other two AIE matrices because it has more phenolic hydroxyl groups. BSPD-OH was successfully applied to the analysis of various LMW compounds including amino acids, organic amine compounds, isoquinoline compounds and fluoroquinolones compounds. This material also can be employed during the qualitative and quantitative analysis of LMW metabolites in human urine without requiring complicated separation processes.     

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L⁻¹ (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L⁻¹ (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L⁻¹) seawater sample were in good agreement with the certified values.     

Palladium-citric acid-ammonium fluoride as a matrix modifier for overcoming of interferences occurring during the direct determination of Sn in aqua regia extracts from environmental samples by D2-ETAAS

When tin is to be determined in such a complex matrix like aqua regia extracts of environmental samples by electrothermal atomic absorption spectrometry (ETAAS), spectral interferences occur when deuterium-lamp (D₂) background correction is used, even using high pyrolysis temperature of 1400 °C achieved with palladium with citric acid chemical modifier. We have found that the further addition of NH₄F to palladium with citric acid chemical modifier is essential for overcoming the above-mentioned problems for which aluminium oxide is most probably responsible. It is supposed, that NH₄F enables volatilization of the alumina matrix formed by hydrolysis from the chloride salt and interfering in a gas phase via the formation of AlF₃ which could be, in contrast to aluminium oxide, removed from the graphite furnace during the pyrolysis stage. Using the proposed chemical modifier, the direct and accurate determination of Sn in aqua regia extracts from rocks, soils and sediments is possible even when using matrix free standard solutions. This presumption was confirmed by the analysis of certified reference samples and by the comparison with inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) method. Characteristic mass and LOD value for the original sample (10-μL aliquots of sample) was 17 pg and 0.055 μg g⁻¹, respectively.     

Determination of total mercury in nuts at ultratrace level

Total mercury, at μg kg⁻¹ level, was determined in different types of nuts (cashew nut, Brazil nuts, almond, pistachio, peanut, walnut) using a direct mercury analyser after previous sample defatting and by cold vapour atomic fluorescence spectrometry. There is not enough sensitivity in the second approach to determine Hg in previously digested samples due to the strong matrix effect. Mercury levels in 25 edible nut samples from Brazil and Spain were found in the range from 0.6 to 2.7 μg kg⁻¹ by using the pyrolysis of sample after the extraction of the nut fat. The accuracy of the proposed method was confirmed by analysing certified reference materials of Coal Fly Ash-NIST SRM 1633b, Fucus-IAEA 140 and three unpolished Rice Flour NIES-10. The observed results were in good agreement with the certified values. The recoveries of different amounts of mercury added to nut samples ranged from 94 to 101%. RSD values corresponding to three measurements varied between 2.0 and 14% and the limit of detection and quantification of the method were 0.08 and 0.3 μg kg⁻¹, respectively.     

Ion chromatography for rapid and sensitive determination of fluoride in milk after headspace single-drop microextraction with in situ generation of volatile hydrogen fluoride

In this article, we report a new method that involves headspace single-drop microextraction and ion chromatography for the preconcentration and determination of fluoride. The method lies in the in situ hydrogen fluoride generation and subsequent sequestration into an alkaline microdrop (15 μL) exposed to the headspace above the stirred aqueous sample. The NaF formed in the drop was then determined by ion chromatography. The influences of some crucial single-drop microextraction parameters such as the extraction temperature, extraction time, sample stirring speed, sulphuric acid concentration and ionic strength of the sample, on extraction efficiency were investigated. In the optimal condition, an enrichment factor of 97 was achieved in 15 min. The calibration working range was from 10 μg L⁻¹ to 2000 μg L⁻¹ (R² = 0.998), and the limit of detection (signal to noise ratio of 3) was 3.8 μg L⁻¹ of fluoride. Finally, the proposed method was successfully applied to the determination of fluoride in different milk samples. The recoveries of fluoride (at spiked concentrations of 200 μg L⁻¹ and 600 μg L⁻¹ into milk) in real samples ranged from 96.9% to 107.7%. Intra-day precision (N = 3) in terms of peak area, expressed as relative standard deviation, was found to be within the range of 0.24-1.02%.     

Development and validation of a high-performance liquid chromatography-tandem mass spectrometric method for quantification of daunorubicin in rat plasma

A high-performance liquid chromatography-tandem mass spectrometric method (LC-MS/MS) has been developed and validated for the determination of daunorubicin in K₃EDTA rat plasma. The 100 μL plasma samples were extracted by a methanol:acetone protein precipitation step in the presence of additional 50 μL of 70% (w/v) zinc sulfate, and subsequently analyzed by LC/MS/MS using positive turbo-ion spray ionization mode. The LC/MS/MS instrument was operated in the multiple-reaction-monitoring (MRM) mode. Doxorubicinol was better than doxorubicin as the internal standard because its recovery and absolute matrix effect data exactly matched with those for daunorubicin. In addition, HPLC gradient condition was optimized to thoroughly separate daunorubicin from the background interference. The validated concentration range was from 0.250 to 100 ng/mL. The true recoveries of daunorubicin and doxorubicinol were 93.2% and 93.6%, respectively. In addition, the ion-suppression data of daunorubicin and doxorubicinol were 78.2% and 78.4%, respectively. Absence of the relative matrix effect from six unique lots was confirmed. Results obtained from the GLP validation study demonstrated very good accuracy (95-105%) and precision (less than 10% CV).     

Simple fabrication of hydrophobic surface target for increased sensitivity and homogeneity in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of peptides,phosphopeptides, carbohydrates and proteins

To enhance sample signals and improve homogeneity in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) analysis, a simple, rapid, and efficient sample preparation method was developed in this study. Polydimethylsiloxane (PDMS) was coated on a stainless steel MALDI plate, forming a transparent, hydrophobic surface that enhanced sample signals without producing observable background signals. Compared to the use of an unmodified commercial metal MALDI plate, peptide signals were enhanced by ~7.1–11.0-fold due to the reduced sample spot area of the PDMS-coated plate, and showed improved peptide mass fingerprinting (PMF) and MS/MS peptide sequencing results. In the analysis of phosphopeptides and carbohydrates with a 2,5-dihydroxybenzoic acid (DHB) matrix, the PDMS-coated plate showed improved sample homogeneity and signal enhancements of ~5.2–8.2-fold and ~2.8–3.2-fold, respectively. Improved sensitivity in the observation of more unique fragment ions by MS/MS analysis, to successfully distinguish isomeric carbohydrates, was also illustrated. In protein analysis with a sinapinic acid (SA) matrix, a ~3.4-fold signal enhancement was observed. The PDMS film coating was easily removed and refabricated to avoid sample carryover, and was applicable to diverse commercial MALDI plates. The PDMS-coated approach is a simple, practical, and attractive method for enhancing analyte signals and homogeneity.     

Short monolithic columns for purification and fractionation of peptide samples for matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry analysis in proteomics

This study records a novel application of methacrylate-based monolithic columns for MALDI-TOF/TOF MS analyses in proteomics for pre-concentration and separation of peptides derived from protein digestion. Reversed-phase monolithic capillary columns (30 mm × 0.32 mm i.d.) were created inside the fused silica capillary via thermal-initiated free-radical polymerization of ethylene glycol dimethacrylate and lauryl methacrylate monomers in the presence of 1-propanol and 1,4-butandiol as a porogen system. The elution of peptides was achieved using a linear gradient of acetonitrile from 0 to 60% in water with 0.1% trifluoroacetic acid formed in a microsyringe. Individual fractions of separated peptides were collected on the MALDI target spots covered with alpha-cyano-4-hydroxycinnamic acid used as a matrix and then they were analyzed using MALDI-TOF/TOF mass spectrometry. The developed method was tested with a mixture of tryptic peptides from bovine serum albumin and its applicability was also tested for tryptic in-gel digests from barley grain extracts of water soluble proteins separated using SDS gel electrophoresis. The number of detected peptides was approximately three to four times higher compared to the analysis without previous separation. These results show an improved quality of sample information with the higher amount of identified peptides which increased protein sequence coverage and improved sensitivity of mass spectrometry measurements.     

Comprehensive characterization of natural organic matter by MALDI- and ESI-Fourier transform ion cyclotron resonance mass spectrometry

Natural organic matter (NOM) is a complex and non-uniform mixture of organic compounds which plays an important role in environmental processes. Due to the complexity, it is challenging to obtain fully detailed structural information about NOM. Although Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) has been demonstrated to be a powerful tool for providing molecular information about NOM, multiple ionization methods are needed for comprehensive characterization of NOM at the molecular level considering the ionizing selectivity of different ionization methods. This paper reports the first use of matrix assisted laser desorption/ionization (MALDI) method coupled with FT-ICR-MS for molecular characterization of NOM within a mass range of 200–800 Da. The mass spectral data obtained by MALDI were systematically compared with data generated by electrospray ionization (ESI). It showed that complementary molecular information about NOM which could not be detected by ESI, were provided by MALDI. More unsaturated and aromatic constituents of NOM with lower O/C ratio (O/C ratio < 0.5) were preferentially ionized in MALDI negative mode, whereas more polar constituents of NOM with higher O/C ratio were preferentially ionized in ESI negative mode. Molecular anions of NOM appearing at even m/z in MALDI negative ion mode were detected. The results show that NOM molecules with aromatic structures, moderate O/C ratio (0.7 > O/C ratio > 0.25) and lower H/C ratio were liable to form molecular anions at even m/z, whereas those with higher H/C ratio are more likely to form deprotonated ions at odd m/z. It is speculated that almost half of the NOM molecules identified by MALDI may be aromatic or condensed aromatic compounds with special groups which are liable to absorb electron from other molecules to generate free radical anions during MALDI ionization.     

Measurement of laser activated electron tunneling from semiconductor zinc oxide to adsorbed organic molecules by a matrix assisted laser desorption ionization mass spectrometer

Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser (λ = 355 nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO₂ nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.     

Determination of 3-nitroaniline in water samples by directly suspended droplet three-phase liquid-phase microextraction using 18-crown-6 ether and high-performance liquid chromatography

Liquid–liquid–liquid microextraction (LLLME) with directly suspended droplet in high-performance liquid chromatography (HPLC) has been applied as a new, rapid and easy method for the determination of 3-nitroaniline in environmental water samples. The target compound was extracted from the aqueous sample solution (donor phase, pH 13) into an organic phase and then was back-extracted into a directly suspended droplet of an acidic aqueous solution (acceptor phase, pH 0.3). In this method, without using a microsyringe as supporting device, an aqueous large droplet is freely suspended at the top-center position of an immiscible organic solvent, which is laid over the aqueous sample solution while being agitated. Then, the droplet was withdrawn into the microsyringe and directly was injected into the HPLC system with UV detection at 227 nm. Up to 148-fold enrichment of the analyte could be obtained under the optimal conditions [i.e. donor phase: 0.1 M sodium hydroxide solution (4.5 mL); organic phase: o-xylene/1-octanol (90:10, v/v; 250 μL); acceptor phase: 0.5 M hydrochloric acid and 500 mM 18-crown-6 ether (6 μL); extraction time: 60 s; back-extraction time: 6 min and stirring rate: 600 rpm]. The limit of detection was 1 μg/L (n = 7) and the relative standard deviation (RSD, n = 5) was 4.9 at S/N = 3. The calibration graph was linear in the range of 5–1500 μg/L with r = 0.9983. All experiments were carried out at room temperature (22 ± 0.5 °C).     

A liquid chromatography-electrospray ionization-tandem mass spectrometry study of ethanolamines in high salinity industrial wastewaters

The detection and quantitation of four ethanolamines, tris(2-hydroxyethyl)amine (triethanolamine, TEA), N,N-bis(2-hydroxyethyl)methylamine (methyldiethanolamine, MDEA), N-(2-aminoethyl)ethanolamine (AEA), and N,N-diethylethanolamine (DEA), were achieved in wastewaters from two aerobic activated sludge bioreactors located in an industrial wastewater treatment plant. The streams had salt concentrations of approximately 3% and 7% by weight in Reactor 1 and Reactor 2, respectively. The use of liquid chromatography-electrospray ionization-tandem mass spectrometry avoided the need for some sample preparation steps such as extraction, concentration, and derivatization. Ion suppression in the electrospray, attributable to the presence of sodium clusters, was attenuated by a 10-fold dilution of the wastewaters with acetonitrile. A matrix-matched calibration model averted other potential interferences. For the compounds analyzed in selected reaction monitoring mode (TEA, MDEA, and DEA), the calibration curves presented linearity in a range of 10-1000 μg/L with corresponding detection limits ranging from 2 to 11 μg/L, depending upon the specific analyte and aqueous matrix. AEA was calibrated in selected ion monitoring mode (100-1000 μg/L), with corresponding detection limits in the two wastewaters of 74.6 and 85.3 μg/L, respectively. Overall good precision (<10%) and accuracy (97-110%) were achieved for both matrices, which fell within-laboratory reproducibility. Finally, the amines were introduced into six mixed liquor samples from both reactors and quantified following the reported protocol. Again, recoveries were close to 100% with a relative standard deviation of less than 10% in all cases.     

Interference-free determination of thallium in aqua regia leaches from rocks, soils and sediments by D(2)-ETAAS method using mixed palladium-citric acid-lithium chemical modifier

The mixture of palladium (chloride) with citric acid and lithium is proposed as a new chemical modifier for the elimination of interference occurred during the determination of Tl in aqua regia extracts from rocks, soils and sediments by electrothermal atomic absorption spectrometry using instrumentation with deuterium-lamp background correction (D₂-ETAAS). Palladium was preferred to rhodium and platinum as to analyte stabilization, citric acid served as an effective reducing agent facilitating formation of Pd-Tl stable covalent bonds playing an important role in the analyte stabilization. Citric acid in addition helps to remove most of interfering chloride at low temperature. The further addition of Li increased significantly the robustness of chemical modifier against strongly interfering ZnCl₂ matrix by binding free chlorine into a more stable LiCl molecule. In the presence of the proposed chemical modifier the temperature for the final step of pyrolysis was adjustable up to 1000 °C, without any noticeable loss of volatile Tl species and the interference of the rest chloride matrix was significantly reduced. The application of the modifier to direct determination of Tl in aqua regia extracts from rocks, soils and sediments has ensured the characteristic mass and LOD value for the original sample 13 pg and 0.043 μg g⁻¹, respectively (10-μL aliquots of sample) and has enabled the use of matrix-free standard solutions for attaining accurate analysis. The accuracy was verified by the analysis of certified reference samples and by the comparison of results with those found by an inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometer (ICP-oa-TOFMS) method.     

Integration of microfiltration and anion-exchange nanoparticles-based magnetic separation with MALDI mass spectrometry for bacterial analysis

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is powerful in characterizing and identifying bacterial isolates. However, sufficient quantities of bacterial cells are required for generating MALDI mass spectra and a procedure to isolate and enrich target bacteria from sample matrix prior to MALDI-MS analysis is often necessary. In this paper, anion-exchange superparamagnetic nanoparticles (NPs), i.e., fluidMAG-DEAE and fluidMAG-Q, were employed to capture Aeromonas, Salmonella, Pseudomonas, Enterococcus, Bacillus, Staphylococcus and Escherichia coli from aqueous solutions and fresh water. The magnetically isolated bacteria were then characterized by whole cell MALDI-MS. The capture efficiency was found to be dependent on bacterial species, medium pH, the functional group and concentration of the NPs. The experimental results demonstrated that fluidMAG-DEAE and fluidMAG-Q were broad spectrum probes for bacteria. Furthermore, both dead and live bacteria could be captured by the NPs, and the live bacteria captured remained viable. Membrane filtration prior to the magnetic isolation could increase enrichment factor and eliminate potential matrix interference. A detection limit of 1 × 10³ cfu/ml was achieved for the bacteria spiked in tap water and reservoir water, and the analytical time was around 2 h.