Inter-day Repeatability Research Articles

An environmentally friendly sample pre-treatment method based on magnetic ionic liquids for trace determination of nitrotoluene compounds in soil and water samples by gas chromatography–mass spectrometry using response surface methodology

In this study, a new sample preparation strategy termed ultrasonic-assisted dispersive magnetic ionic liquid/magnetic solid wire microextraction (UA-DMIL/MSW-ME) has been developed for simultaneous determination of fifteen nitrotoluene compounds (NTCs) in the soil and water samples. The extraction was performed by dispersing a magnetic ionic liquid (MIL) into the sample solution using ultrasonic irradiation. After completing the extraction, by stopping the sonication, a neodymium wire (NW) was placed inside the sample solution allowing the MIL containing the pre-concentrated analytes to cover the surface of NW with a thin layer due to the magnetic forces. Afterward, the MIL-coated NW was subjected to a homemade syringe and directly injected into a gas chromatography–mass spectrometry (GC–MS) instrument for thermal desorption of analytes; then, quantitative measurements were taken. The central composite design was applied to explore some parameters influencing the extraction efficiency. Ultimately, under the optimized conditions, the proposed method was successfully implemented to analyze NTCs in the real samples (coastal and forestal soils, river water, and industrial wastewater) and acceptable results were obtained. The resultant calibration curves were linear over the concentration range of 0.07–80 μg/L (R2 > 0.993). The estimated limits of detection and quantification were lower than 0.07 μg/L, and the enrichment factors were between 3538 and 3817. The wire-to-wire and single-wire reproducibility values were found to be lower than 5.8% (n = 6). The intra- and inter-day repeatability varied below 5.5% (n = 6), and the relative recoveries were calculated between 91–110 and 89–108% for soil and water samples, respectively.

Abstract B8: Multiplex quantification of immunomodulatory proteins in tissue and plasma using next-gen targeted MRM mass spectrometry

Abstract Quantifying the many immunomodulatory proteins in the “cancer-immunity cycle” is critical for both patient selection and development of novel immunotherapies. Conventional technologies to measure proteins (IHC, ELISA, Western blot, flow cytometry) are often semiquantitative, not multiplexable, feature poor specificity, and are difficult to develop. Due to these limitations, investigators have turned to mRNA-based measurements to infer protein expression of immunomodulatory factors. However, as has been unequivocally demonstrated for human breast, colorectal, and ovarian cancers (Pubmed IDs: 27251275, 25043054, 27372738), RNA levels can be poor predictors of protein levels or activity. Thus, direct quantification of proteins is desirable. As part of the National Cancer Institute’s Cancer Moonshot, we are developing >300 multiplex assays for quantifying immunomodulatory proteins in tissue and plasma using a next-gen technology for protein quantification, based on targeted multiple reaction monitoring mass spectrometry (MRM-MS). MRM-MS complements traditional immunoassays by enabling highly specific, precise, harmonizable quantification of proteins in biospecimens, even at high multiplex levels. As proof of concept, we will present a novel multiplex assay based on next-gen MRM-MS for quantification of 47 immunomodulatory proteins in plasma and/or tumor tissue. The technology uses immunoaffinity enrichment coupled with MRM-MS (immuno-MRM assay). Assay bioanalytical validation was conducted in accordance with industry standards for use in FFPE tissue and plasma matrices and included determination of limits of detection, linear range of response, intraday and interday repeatability, stability of analytes in sample processing, and characterization of reproducibility of endogenous analyte measurement. The mean linear range was over three orders of magnitude with median intra- and interday CVs less than 10%. The characterized assays are being applied to a panel of tumor specimens from a variety of cancer types to document detection and determine minimum sample requirements. Additional assay panels are under development to provide measurements of up to 350 immunomodulatory proteins. Citation Format: Jeffrey R. Whiteaker, Lei Zhao, Richard G. Ivey, Julia Voytovich, Regine M. Schoenherr, Dongqing Huang, Jacob J. Kennedy, Amanda G. Paulovich. Multiplex quantification of immunomodulatory proteins in tissue and plasma using next-gen targeted MRM mass spectrometry [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B8.

A needle trap device packed with MIL-100(Fe) metal organic frameworks for efficient headspace sampling and analysis of urinary BTEXs.

The aim of this study was to develop a new method for the determination of benzene, toluene, ethylbenzene and xylene isomers (BTEXs) in urine samples. In this method, MIL-100(Fe)@Fe3 O4 @SiO2 metal-organic framework was synthesized, characterized and packed inside a needle trap device (NTD) as a sorbent for headspace extraction of unmetabolized BTEXs from urine samples followed by gas chromatography (GC) analysis. The GC device was equipped with a flame ionization detector (FID). The results showed that the optimal extraction time, extraction temperature and salt content were 60 min, 30°C and 5%, respectively. Also, the optimal desorption time and temperature were determined to be 1 min and 250°C, respectively. The limits of detection and quantification of the analytes of interest were in the ranges 0.0001-0.0005 and 0.0003-0.0014 μg ml-1 , respectively. The intra- and inter-day repeatability were <7.6%. The accuracy of the measurements in urine samples was in the range 7.1-11.4%. The results also demonstrated that the proposed NTD offered various advantages such as having high sensitivity and being inexpensive, reusable, user friendly, environmentally friendly and compatible for use with the GC device. Therefore, it can be efficiently used as a MIL-NTD for the extraction and analysis of unmetabolized BTEXs from urine samples.

On-Line Electrokinetic Supercharging and Sweeping for the Preconcentration and Determination of Nucleosides and Related Compounds by Capillary Electrophoresis

Nucleosides and related compounds have vital physiological and pharmacological activities. In this study, on-line preconcentration using electrokinetic supercharging (EKS)-sweeping method was proposed to enhance the efficiency of the capillary electrophoresis separation of the nucleosides and related compounds. The separation conditions, including the pH of the borate buffer (terminating electrolyte), the concentration and pH of the phosphate buffer (leading electrolyte), the concentration of sodium dodecyl sulfate (SDS) and the electrokinetic injection (EKI) time, were investigated in detail. The optimum EKS-sweeping conditions were as follows: 40 mM sodium phosphate buffer at pH 2.0 containing 50 mM SDS as the BGE, 120 mM sodium phosphate buffer at pH 2.0 as the leading electrolyte, 30 mM borate buffer at pH 12.0 as the terminating electrolyte, and EKI of the sample at −10 kV for 30 s. The separation was performed by micellar electrokinetic chromatography at −5 kV. Under these conditions, the sensitivity values of five analytes were enhanced from 26 to 109-fold compared to a standard capillary zone electrophoresis (CZE) procedure. The intra- and inter-day repeatability values (as the relative standard deviation) were less than 1.1% and 5.2% for the migration time and lower than 4.4% and 4.8% for the peak areas. Finally, the developed method was successfully applied for the determination of nucleosides and related compounds in Chinese cordyceps samples.

Simultaneous determination of nine dinitroaniline herbicides in environmental samples using a validated vortex-assisted dispersive liquid–liquid microextraction procedure coupled with GC–MS/MS

A sensitive, rapid, cheap and ecologically safe analytical method has been developed for simultaneous quantification of nine dinitroaniline herbicides (ethalfluralin, trifluralin, benfluralin, profluralin, fluchloralin, isopropalin, pendimethalin, nitralin, prodiamine) in environmental samples, namely surface water, soil and food (tomato) matrices. Vortex-assisted dispersive liquid–liquid microextraction (VA-DLLME) sample preparation and gas chromatography coupled with tandem mass spectrometry (GC–MS/MS) enabled simultaneous quantification of the nine dinitroaniline herbicides in as little as 20 min. The effects of different variables on the DLLME procedure were evaluated, including the type and volume of disperser solvent, the volume of chloroform as the extractant solvent, and extraction time. An optimal analyte protectant mixture (0.5, 1, and 1 mg/mL D-sorbitol, shikimic acid, and δ-gluconolactone, respectively) was identified and employed to improve the detection sensitivity for the tested analytes; this mixture was added to the standards in solvent and used instead of matrix-matched calibration curves during quantification. The selectivity, linearity, precision and accuracy of the proposed methodology were validated: the correlation coefficients were > 0.99 and the limits of detection ranged from 0.3 to 3.3 µg/L for the tested analytes. The limits of quantification (LOQ) ranged from 0.4 to 2 µg/kg in surface water and 2 to 10 µg/kg in soil and tomato samples. Percentage recovery at the LOQ ranged from 64.1 to 87.9%, with inter-day repeatability of ≤ 15.1%. The proposed method was also used to monitor the target analytes in real samples.

Simultaneous Determination of Propylene Glycol, Glycerol and Lactic Acid in Rat Plasma and Serum by Gas Chromatography–mass Spectrometry

A simple and rapid gas chromatographic–mass spectrometric (GC–MS) method using selected ion monitoring mode was developed for simultaneous determination of propylene glycol, glycerol and lactic acid in rat plasma and serum. The method employed a single-step derivatization using bis(N,O-trimethylsilyl) trifluoroacetamide with trimethylchlorosilane and required only a small amount of plasma or serum (100 μL). The calibration curves showed linearity with the correlation coefficients of 0.996–0.999. To validate the method, the intra- and inter-day repeatability of the proposed method in rat plasma was evaluated. Recovery was assessed by the standard addition method. To test the applicability of the method, twenty plasma samples in two different time points were analyzed and levels of both propylene glycol and lactic acid in plasma were found to increase after exposure to the propylene glycol aerosol (500 mg/kg). With satisfactory repeatability and recovery the proposed GC–MS method can be successfully applied for analysis of plasma and serum samples.

Direct-immersion SPME in soy milk for pesticide analysis at trace levels by means of a matrix-compatible coating

This study demonstrates a newly developed PDMS/DVB/PDMS fiber's suitability for the determination of pesticides in soy milk via direct-immersion solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry, eliminating the need for extensive sample pre-treatment procedures. Fouling accumulation on the coating surface was further minimized by implementing rapid and effective pre- and post-desorption cleaning steps. Under optimum conditions, the fiber was used to perform over 120 extractions while maintaining RSD values of less than 24.5% for 10 extracted pesticides. By comparison, the RSD values ranged from 8.4% to 42.8% over 80 extractions using a commercial PDMS/DVB fiber. The optimized conditions were used to fully validate a quantitative method for the targeted analytes by matrix-matched calibration and isotopically labeled internal standard correction. Significantly, the proposed method was able to achieve limits of quantitation (1–2.5 μg/kg) for the targeted analytes that were below the Maximum Residue Levels mandated for soy-based products. Accuracy, intra- and inter-day repeatability were also satisfactory. The proposed PDMS/DVB/PDMS fiber dramatically improved repeatability and suitability for direct-immersion SPME in soy milk, and represents a good alternative to other extraction methods for high-throughput quantitative analysis of pesticide residues in soy-based products.

Determination of aqueous bisphenol A and tetrabromobisphenol A using molecular-complex-based liquid-liquid microextraction

A sample preparation method for the extraction of bisphenol A (BPA) and tetrabromobisphenol A (TBBPA), potential endocrine-disrupting chemicals common in manufacturing, from environmental water samples was established by means of molecular-complex-based liquid-liquid microextraction coupled to high-performance liquid chromatography with diode array and mass spectrometric detection. In this method, tributyl phosphate acts as an extractant of BPA and TBBPA via hydrogen bond interactions. Additionally, no dispersants are needed. Attenuated total reflection Fourier transform infrared spectroscopy provides robust evidence for the formation of hydrogen bonds between the extractant and phenols in the molecular complexes, which supports the experimental results. Under optimised conditions, calibration plots were linear in the range of 0.05–2 μg mL−1, and detection limits ranged from 0.16 to 0.23 ng mL−1. The relative standard deviations of intra-day and inter-day repeatability were in the ranges of 3.5–4.9% and 5.1–6.8%, respectively, and recoveries ranged from 84.5 to 105.6%. The method we developed has been successfully employed in the measurement of BPA and TBBPA in four aqueous environmental samples.

Development and validation of a GC-FID method for the analysis of short chain fatty acids in rat and human faeces and in fermentation fluids

Short-chain fatty acids (SCFAs) are gut microbiota metabolites recognized for their beneficial effects on the host organism. In this study, a simple and rapid sample preparation method combined to SCFAs analysis by direct injection and gas chromatography coupled with flame ionization detection (GC-FID), for the determination and quantification of eight SCFAs (acetic, propionic, i-butyric, butyric, i-valeric, valeric, i-caproic and caproic acids) in rat, mice and human faeces and in fermentation fluids samples, has been developed and validated. The method consists of extraction of the SCFAs by ethyl ether after acidification of the samples. The effect of the number of extractions has been assessed in order to optimize the procedure and to obtain a satisfactory yield for all the analyzed SCFAs. The increase of the extracted analytes quantity was significant passing from 1 to 2 and from 2 to 3 extractions (P < 0.05), while no significant differences were found performing 3, 4 or 5 extractions (P > 0.05). The SCFAs extracted are directly analyzed by GC-FID without derivatization and separated on a polyethylene glycol nitroterephthalic acid modified coated capillary column, with a chromatographic run time of 13 min. The proposed method showed good sensitivity, with limits of quantifications in the range 0.14–0.48 µM for SCFAs from propionic to caproic acids and 2.12 µM for acetic acid; recovery was between 80.8 and 108.8% and intraday and interday repeatability in the range 0.6–5.0% of precision (RSD, %) The optimized method is suitable for the quantitative analysis of SCFAs in real samples of rat, mouse and human faeces and in fermentation fluids, and it can be applied also to very small amount of faecal sample (20 mg).

Template-directed fabrication of zeolitic imidazolate framework-67-derived coating materials on nickel/titanium alloy fiber substrate for selective solid-phase microextraction

Novel solid-phase microextraction fibers were fabricated by electrochemical deposition of cobalt on the pretreated nickel/titanium alloy (NiTi) fiber substrate and subsequent in situ growth of zeolitic imidazolate framework-67 (ZIF-67) followed by annealing treatment. The Co@ZIF-67 coating was used as a precursor and template for controlled fabrication of the Co@ZIF-67-derived coatings including Co@ZIF-67-Co3O4 and carbonaceous composite coatings. . The extraction performance of the Co@ZIF-67-derived coatings was evaluated using typical aromatic compounds coupled to high-performance liquid chromatography with UV detection. The results clearly demonstrate that the extraction selectivity is subject to the surface elemental composition of the ZIF-67-derived coatings. In view of long-term stability and good extraction selectivity, the Co@ZIF-67-C coating was selected for the enrichment and determination of polycyclic aromatic hydrocarbons (PAHs). Under the optimized conditions, the calibration curves were linear in the range of 0.05–100 μg•L−1 with the correlation coefficients above 0.998. Limits of detection were 0.005–0.042 μg•L−1. Furthermore, the intra-day and inter-day repeatability of the proposed method with the single fiber varied from 2.3% to 5.8% and from 3.3% to 6.9%, respectively. The fiber-to-fiber reproducibility ranged from 4.1% to 8.5%. The proposed method was suitable for selective enrichment and determination of target PAHs from real water samples. Moreover, the fabricated fiber showed precisely controllable growth and 150 extraction and desorption cycles.

A Simple and Effective Liquid-Liquid-Liquid Microextraction Method with Ultraviolet Spectrophotometric Detection for the Determination of Bisphenol A in Aqueous Matrices and Plastic Leachates

This study shows the development and application of an analytical method for the determination of bisphenol A (BPA) in aqueous samples such as tap, river and mineral water and plastic leachates, based on an extensive literature search to understand the gaps for the determination of BPA in aqueous samples. We found that most of the methods in the literature employ some chromatographic strategy, and, to a much lesser extent, non-chromatographic instrumentation. In this scenario, we show an ultraviolet spectrophotometric-based method that can be used for routine analysis. Sample preparation was conducted by means of solvent extraction followed by back-extraction into an alkaline aqueous solution (liquid-liquid-liquid microextraction) and the detection was performed by UV spectrophotometry at 294 nm. Optimization of variables affecting both extraction and back-extraction was conducted, and the optimal extraction conditions were obtained: 85 mL aqueous sample buffered at pH 10, ionic strength adjusted with NaCl to a 2 mol L-1 final concentration, extraction with 6 mL of ethyl ether for 10 min and back-extraction into 0.5 mL of 2 mol L-1 aqueous NaOH. The following quality parameters were obtained: determination coefficient (R2) > 0.999, intra and inter-day repeatability better than 7.8% and 300 enhancement factor. The method was applied in different aqueous samples with excellent recovery and precision results, and no BPA was detected in natural water, even with the excellent limit of detection (3.5 μg L-1) and limit of quantification obtained. Limitations of this method involve analysis of samples with humic acid concentrations higher than 2 mg L-1 or high concentration of phenols and/or phthalate esters.

β-cyclodextrin modified quantum dots as pseudo-stationary phase for direct enantioseparation based on capillary electrophoresis with laser-induced fluorescence detection

In recent years, quantum dots (QDs) have attracted a tremendous amount of attention due to their compelling features. In this work, a kind of composite QDs based on β-cyclodextrin (β-CD) and its derivatives modification was prepared, and for the first time utilized to separate and determine enantiomers in the combined system of capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). By taking advantages of the inclusion complexation of β-CD and the fluorescence property of QD core, the composite QDs were added into the running buffer as pseudo-stationary phase. The resultant CE-LIF method accomplished enantioseparation for six groups of model analytes without need of capillary preparation and analyte derivatization. The effects of composite QDs concentration, the pH value and concentration of the running buffer on resolution have been investigated individually. The RSDs of interday and intraday repeatability were in the range of 2.7–8.1%, 0.7–3.9%, and 1.5–3.8% for the peak area, migration time and resolution, respectively. The theoretical calculation results of the binding energies and binding constant further validated the interaction mechanism of composite QDs and target analytes. Furthermore, this developed method was successfully applied to the analysis of the active components (catechin and epicatechin) in Chinese herb Catechu, and the recoveries were in the range of 92.2–108%. The experimental results suggested that the preparation strategy of the composite QDs is appropriate for enantioseparation of more enantiomers by adjusting the modifiers on the surface of QDs, which is particularly promising for electrophoretic enantioseparation based on fluorescence detection, especially for those analytes lacking proper derivative functional groups.

Thiacloprid Residues in Green Onion (Allium cepa) Using Micro Liquid–Liquid Extraction and Liquid Chromatography–Tandem Mass Spectrometry

Conventional sample preparation methods for liquid chromatography–mass spectrometry (LC–MS/MS) are time consuming, laborious, expensive, and require large volumes of solvent for extraction and cleanup. We developed and validated a micro liquid–liquid extraction (MLLE) sample preparation method for LC–MS/MS analysis of thiacloprid insecticide residues in green onion. MLLE is a simple, rapid, and cost-effective method that uses less extraction solvent and does not require adsorbents or the cleanup step. The samples are homogenized with dichloromethane, centrifuged, the solvent evaporated to dryness and the residue is reconstituted with fivefold of acetonitrile; thus, the method is ecologically safer and low cost. The limit of quantification was 0.01 mg/kg. Method efficiency for MLLE was compared with the conventional QuEChERS sample preparation. MLLE exhibited good linearity (correlation coefficient, > 0.99). The average recovery ranged from 97.2 to 101.5%. Intra- and inter-day repeatabilities were 9.7 and 13.8%, respectively. Matrix effects were nonsignificant (suppression, 2.2%). The MLLE method was used to quantify the residual levels and rate of dissipation of thiacloprid in field trial green onion. The dissipation of thiacloprid fitted first-order kinetics, with half-lives of 1.92 and 2 days after application of the recommended dose (48 g a.i/ha) and double the recommended dose (96 g a.i/ha). Thiacloprid residues were below the limit of detection in green onion samples analyzed 14 days after spraying with either dose. Based on the maximum residue limit, a waiting period of 9 days is recommended. From Egyptian consumers’ point of view, the consumption of onion seems quite safe.

A rapid method for on-line solid-phase extraction and determination of dioscin in human plasma using a homemade monolithic sorbent combined with high-performance liquid chromatography.

A phenyl-based polymer monolithic column was prepared via free radical polymerization in a stainless steel column with the size of 4.6 mm i.d. × 50 mm, using ethylene glycol phenyl ether acrylate as the monomer. The resulting monolithic column shows high porosity of 73.42% and relative uniform pore structure, as characterized by mercury porosimetry and scanning electron microscopy, respectively. The optimized polymer monolith column was used for on-line solid-phase extraction prior to the reversed phase mode HPLC-UV analysis for the determination of dioscin in human plasma, using a COSMOSIL C18 column (4.6 mm × 150 mm, 4.5 μm). Water was used to wash non-retained components from the SPE sorbent, and methanol water (80:20, V/V) was used as the mobile phase for isocratic elution of dioscin. The maximum adsorbed quantity of dioscin to the SPE column is 6.79 mg/g, which is high enough for the quantitative analysis of dioscin in plasma, due to the low content of dioscin in plasma. The method was validated by assessing the linearity, lower limit of quantification, intra- and inter-day precision, accuracy, and repeatability. The developed method was applied for the analysis of dioscin in plasma from a volunteer who had orally administered an aqueous extract of dioscorea nipponica rhizome, showing the method capable of detecting dioscin in the plasma. These results show that the developed method is a rapid method for on-line solid-phase extraction and determination of dioscin from plasma, exhibiting good selectivity with hydrogen bond interaction and hydrophobic interaction, good clean-up ability, cost-saving, and time-saving. Graphical abstract.

Stir membrane liquid phase microextraction of tetracyclines using switchable hydrophilicity solvents followed by high-performance liquid chromatography

A novel approach for stir membrane liquid phase microextraction of tetracyclines from biological fluids was developed. The microextraction procedure assumed in situ formation of microdroplets of a hydrophobic medium-chain fatty acid (extraction solvent) from homogeneous sample solution containing water-soluble medium-chain fatty acid salt by acidification and simultaneous analytes extraction and organic phase separation into pores of stir membrane disk. Obtained large surface area between the extraction solvent and aqueous phase and high porosity of the membrane provided fast extraction and phase separation (extraction time – 5 min) and reducing extraction solvent volume to the order of several µL. The developed approach was applied for the HPLC-UV determination of tetracycline, oxytetracycline and chlortetracycline in biological fluids samples. The calibration graphs were linear over the concentration ranges of 0.1–100 mg L−1 for oxytetracycline, tetracycline and chlortetracycline. Regression coefficients were in the range from 0.994 to 0.998. The LOD values, calculated from the blank tests based on 3σ, were 30 µg L−1 for tetracycline, oxytetracycline and chlortetracycline. The RSD values expressing intra-day and inter-day repeatability were lower than 5% and 8%, respectively.

Ammonium Fluoride as Suitable Additive for HILIC-Based LC-HRMS Metabolomics.

Hydrophilic Interaction Liquid Chromatography (HILIC) chromatography is widely applied in metabolomics as a complementary strategy to reverse phase chromatography. Nevertheless, it still faces several issues in terms of peak shape and compounds ionization, limiting the automatic de-convolution and data semi-quantification performed through dedicated software. A way to improve the chromatographic and ionization performance of a HILIC method is to modify the electrostatic interactions of the analytes with both mobile and stationary phases. In this study, using a ZIC-HILIC chromatographic phase, we evaluated the performance of ammonium fluoride (AF) as additive salt, comparing its performance to ammonium acetate (AA). Three comparative criteria were selected: (1) identification and peak quality of 34 standards following a metabolomics-specific evaluation approach, (2) an intraday repeatability test with real samples and (3) performing two real metabolomics fingerprints with the AF method to evaluate its inter-day repeatability. The AF method showed not only higher ionization efficiency and signal-to-noise ratio but also better repeatability and robustness than the AA approach. A tips and tricks section is then added, aiming at improving method replicability for further users. In conclusion, ammonium fluoride as additive salt presents several advantages and might be considered as a step forward in the application of robust HILIC methods in metabolomics.

Hydrophilic Interaction Chromatography Coupled with Charged Aerosol Detection for Simultaneous Quantitation of Carbohydrates, Polyols and Ions in Food and Beverages.

Here, we report an accurate and versatile method for the simultaneous determination of 17 sugars (arabinose, erythrose, fructose, galactose, glucose, isomaltulose, lactose, lyxose, maltose, maltotriose, mannose, raffinose, rhamnose, ribose, sucrose, sorbose and xylose), seven polyols (erythritol, inositol, lactitol, maltitol, mannitol, sorbitol and xylitol), five ions (K+, Br−, Cl−, NO3− and SO42−) and the pseudosaccharide acarbose. For compound separation, hydrophilic interaction chromatography (HILIC) coupled to a corona charged aerosol detector (CAD) was used. The method was validated for linearity, precision, reproducibility, retention factor and optimal injection volume. Standards were measured in the range of 1–1000 mg L−1 and showed good intraday and interday repeatability, as well as precision (relative standard deviation (RSD) < 5%). The LODs and LOQs for the 30 analytes were in the range of 0.032–2.675 mg L−1 and 0.107–8.918 mg L−1, respectively. This method exhibited correlation coefficients of at least R2 > 0.97 for all analytes. The method was tested in 24 food and beverage samples to validate the separation efficiency and sensitivity in natural food matrices and to show the practicability of its use for routine food analysis.

Determination of rare earth elements by inductively coupled plasma-mass spectrometry after dispersive solid phase extraction with novel oxidized graphene oxide and optimization with response surface methodology and central composite design

A novel oxidized graphene oxide (OGO) material was prepared and employed for the dispersive solid phase extraction (d-SPE) of rare earth elements (REEs) in drinking water and nuts followed by inductively coupled plasma mass spectrometry (ICP-MS) determination. The novel material was characterized by Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform-Infrared spectroscopy (FT-IR). Response Surface Methodology (RSM) with a Central Composite Design (CCD) and Derringer's type Desirability Function were employed for the optimization of factors that could possibly influence the extraction recovery. Response surfaces charts illustrated the effects of the examined parameters and their interactions. Under the optimum conditions, the detection limits ranged between 0.03 and 1.08 ng L−1 and the limits of quantification range between 0.09 and 3.26 ng L−1. The relative standard deviations for intra-day repeatability (concentration = 50 ng g−1, n = =5) and the inter-day repeatability (concentration = 50 ng g−1, n = =5 × 3) were 4.2–6.2% and 6.2–7.6%, respectively. The sample preparation procedure with the oxidized graphene oxide nanoparticles was simple and fast while it provided good enrichment factors and extraction recoveries. The method was successfully applied for the determination of trace REEs in almonds, peanuts and walnuts as well as tap and mineral water.

Separation and quantification of imidazoles in atmospheric particles using LC-Orbitrap-MS.

A method using ultra-high performance liquid chromatography coupled to a high resolution Orbitrap mass spectrometer was developed to identify and quantify imidazoles in aqueous extracts of aerosol particles. The aqueous particle extract was used without further enrichment or sample clean-up. Five columns were tested for efficient separation of ten imidazoles and the Acquity HSS T3 column was chosen for further optimization. Low limits of detection (<25nM) and good intraday and interday repeatability (<1.6 and<6%, respectively) were achieved. Investigation of matrix effects showed that external calibration is applicable when the loading of organic carbon in the sample is below 10µgm-3 . The developed method was applied to ten real samples, and six out of the ten test imidazoles were successfully quantified, while six further imidazoles were qualitatively identified, among them 4-imidazolecarboxaldehyde and 4-methyl-5-imidazolecarboxaldehyde. Advantages of the method are the minimal sample preparation, the short run time for each sample, and the low detection limits. These allow for a fast and reliable quantification of imidazoles even in a large number of aqueous particle extract samples.

A novel and sensitive HILIC-CAD method for glucosamine quantification in plasma and its application to a human pharmacokinetic study

The clinical effect of glucosamine, the most widely used supplement in patients with osteoarthritis, on joint pain and function improvement, is reported to be inconsistent. Inter-patient variability in the pharmacokinetics of glucosamine, especially its oral absorption, could contribute to the inconsistent clinical outcomes. To test this hypothesis, a novel but simple Hydrophilic Interaction Liquid Chromatography coupled with Charged Aerosol Detector method was developed and validated. The sample was prepared by simple protein precipitation and analysed using an amino column and acetonitrile:100 mM ammonium formate with gradient elution. The developed method was linear (12.5–800 ng/mL, r2 = 0.999) and the relative standard deviations for intra- and inter-day accuracy, precision and repeatability were all less than 6%. The sensitivity of the method (lower limit of quantitation; 12.5 ng/mL) allowed the quantification of endogenous and exogenous glucosamine levels in 12 patients with osteoarthritis, taking 1500 mg glucosamine daily. The analysis showed 120-fold variation (81.7% variance) in exogenous glucosamine levels among the patients, indicating that substantial variability in the extent of absorption and/or rate of elimination could be a possible cause for the reported inconsistent clinical outcomes. The newly-developed method was sensitive and can be used to study the pharmacokinetics of glucosamine.