Mean RSD Research Articles

Interplatform comparison between three ion mobility techniques for human plasma lipid collision cross sections

The implementation of ion mobility spectrometry (IMS) in liquid chromatography-high-resolution mass spectrometry (LC-HRMS) workflows has become a valuable tool for improving compound annotation in metabolomics analyses by increasing peak capacity and by adding a new molecular descriptor, the collision cross section (CCS). Although some studies reported high repeatability and reproducibility of CCS determination and only few studies reported good interplatform agreement for small molecules, standardized protocols are still missing due to the lack of reference CCS values and reference materials.We present a comparison of CCS values of approximatively one hundred lipid species either commercially available or extracted from human plasma. We used three different commercial ion mobility technologies from different laboratories, drift tube IMS (DTIMS), travelling wave IMS (TWIMS) and trapped IMS (TIMS), to evaluate both instrument repeatability and interlaboratory reproducibility. We showed that CCS discrepancies of 0.3% (average) could occur depending on the data processing software tools. Moreover, eleven CCS calibrants were evaluated yielding mean RSD below 2% for eight calibrants, ESI Low concentration tuning mix (Tune Mix) showing the lowest RSD (< 0.5%) in both ion modes. Tune Mix calibrated CCS from the three different IMS instruments proved to be well correlated and highly reproducible (R2 > 0.995 and mean RSD ≤ 1%). More than 90% of the lipid CCS had deviations of less than 1%, demonstrating high comparability between techniques, and the possibility to use the CCS as molecular descriptor. We highlighted the need of standardized procedures for calibration, data acquisition, and data processing. This work demonstrates that using harmonized analytical conditions are required for interplatform reproducibility for CCS determination of human plasma lipids.

LC–MS/MS method for the quantitation of decitabine and venetoclax in rat plasma after SPE: Application to pharmacokinetic study

This study developed a novel, sensitive and selective LC-MS/MS method for the concurrent determination of DCB and VTX in rat plasma using encorafenib as internal standard (IS). To identify DCB, VTX, and IS, the positive multiple reaction monitoring (MRM) mode was used. Chromatographic separation was carried out using a reversed-phase Agilent Eclipse plus C18 column (100 mm × 2.1 mm, 3.5 µm) and an isocratic mobile phase made up of water with 0.1% formic acid and acetonitrile (50:50, v/v, pH 3.2) at a flow rate of 0.30 mL/min for 3.0 min. Prior to analysis, the DCB and VTX with the IS were extracted from plasma using the solid-phase extraction (SPE) method. High recovery rates for DCB, VTX and IS were achieved using the C18 cartridge without interference from plasma endogenous. The developed method was validated as per the FDA guidelines over a linear concentration range in rat plasma from 5–3000 and 5–1000 ng/mL for DCB and VTX, respectively with r2 ≥ 0.998. For both drugs, the lower limits of detection (LLOD) were 2.0 ng/mL. After the HLOQ sample was injected, less than 20% of the LLOQ of DCB, VTX, and less than 5% of the IS carry-over in the blank sample was attained. The overall recoveries of DCB and VTX from rat plasma were in the range of 90.68–97.56%, and the mean RSD of accuracy and precision results was ≤6.84%. For the first time, the newly developed approach was effectively used in a pharmacokinetic study on the simultaneous oral administration of DCB and VTX in rats that received 15.0 mg/kg of DCB and 100.0 mg/kg of VTX.

Surface-Enhanced Raman scattering (SERS) filter paper substrates decorated with silver nanoparticles for the detection of molecular vibrations of Acyclovir drug

Acyclovir (ACV) drug, a common antiviral agent, is frequently used as the primary clinical treatment method for treating hepatitis B, herpes simplex, and varicella zoster viruses due to its potent therapeutic effect. In patients with compromised immune systems, this medication can stop cytomegalovirus infections, and high doses of this drug are required; however, such prescription leads to kidney toxicity. Therefore, timely and accurate detection of ACV is crucial in many areas. Surface-Enhanced Raman Scattering (SERS) is a reliable, rapid, and precise approach for the identification of trace biomaterials and chemicals. Filter paper substrates decorated with silver nanoparticles (AgNPs) were applied as SERS biosensors to detect ACV and control its adverse effects. Initially, a chemical reduction procedure was utilized to produce AgNPs. Afterward, UV–Vis, FE-SEM, XRD, TEM, DLS, and AFM were employed to examine the properties of prepared AgNPs. In order to prepare SERS-active filter paper substrates (SERS-FPS) to detect Molecular vibrations of ACV, AgNPs prepared by immersion method were coated on filter paper substrates. Moreover, the UV–Vis DRS analysis was carried out to assess the stability of filter paper substrates and SERS-FPS. The AgNPs reacted with ACV after being coated on SERS-active plasmonic substrates and could sensitively detect ACV in small concentrations. It was discovered that the limit of detection of SERS plasmonic substrates was 10-12 M. Moreover, the mean RSD for ten repeated tests was calculated as 4.19%. The enhancement factor for detecting ACV using the developed biosensors was calculated to be 3.024 × 105 and 3.058 × 105 experimentally and via simulation, respectively. According to the Raman results, SERS-FPS for the detection of ACV, fabricated by the present methods, showed promising results for SERS-based investigations. Furthermore, these substrates showed significant disposablity, reproducibility, and chemical stability. Therefore, the fabricated substrates are capable to be employed as potential SERS biosensors to detect trace substances.

Development of ternary H-point standard addition method for simultaneous analysis of curcuminoids by differential pulse voltammetry

Turmeric (Curcuma longa L.) rhizome is one of the most famous plants that has been widely used in food, medicine, and industry. Its quality deeply depends on the presence of curcuminoids and their ratios. As their structures are very similar to each other, this work reported simple, accurate, fast, and sensitive method based on developed ternary H-point standard for differential pulse voltammetry (t-HPSAM-DPV). For electrochemical determination of three analytes in the sample, three standards were added simultaneously. This method was developed for detection of three curcuminoids including curcumin (CU), desmethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC) in real samples. The precision of method has RSD% < 5.5 % and the accuracy of proposed method has relative error lower than 7.0 %. Also, intra and inter-day precisions have provided the mean RSD% < 4.50. The LOD values were obtained for CU, DMC and BDMC are 0.6 × 10-6, 0.57 × 10-6 and 0.42 × 10-6, respectively. Compared with other reported HPLC methods, the results revealed a reasonable accurate precision for proposed method. Under optimized experimental conditions, t-HPSMA significantly resolved overlapping of DPV peaks of CU, DMC, and BDMC. This method can be successfully used for ternary analysis of analytes using one standard addition to the real samples.

Simultaneous Determination of Multi-Class Pesticide Residues and PAHs in Plant Material and Soil Samples Using the Optimized QuEChERS Method and Tandem Mass Spectrometry Analysis.

New analytical approaches to the simultaneous identification and quantification of 94 pesticides and 13 polycyclic aromatic hydrocarbons (PAHs) in five representative matrices (pepper, apple, lettuce, wheat, and soil) were developed. The analyses were based on gas chromatography coupled with triple quadrupole tandem mass spectrometry (GC-MS/MS). The procedure was optimized by changing the solvent used during the extraction, from acetonitrile to the acetone: n-hexane mixture at a volume ratio of 1:4 (v/v), as well as the use of a reduced amount of water during the extraction of compounds from cereals. An additional modification was the use of florisil instead of GCB in the sample cleanup step. A full method validation study was performed, at two concentration levels (LOQ and 1000 × LOQ), which showed satisfactory results for all analytes from the PAHs group, with recoveries ranging from 70.7–115.1%, and an average RSD of 3.9%. Linearity was tested in the range of 0.001–1.000 mg/kg and showed coefficients of determination (R2) ≥ 0.99 for all PAHs. Satisfactory recovery and precision parameters (LOQ and 100 × LOQ) were achieved for almost all analytes from the pesticide group in the range of 70.1–119.3% with the mean RSD equal to 5.9%. The observed linearity for all analytes in the concentration range of 0.005–1.44 mg/kg was R2 ≥ 0.99, with the exception of famoxadone, chizalofop-p-ethyl, prothioconazole, spirodiclofen, tefluthrin, and zoxamid. The extended uncertainties were estimated, using a top-down approach of 9.9% (average) and 15.3% (average) for PAHs and pesticides samples, respectively (the coverage factor k = 2, the 95% confidence level). Ultimately, the method was successfully applied to determine pesticide residues in commercial samples of fruit, vegetables and grain, and soil samples for PAHs, which were collected from selected places in the Podkarpacie region. A total of 38 real samples were tested, in which 10 pesticides and 13 PAHs were determined. Proposed changes allow us to shorten the sample preparation time (by 20%) and to reduce the consumption of organic solvents (by 17%). The use of florisil for sample cleanup, instead of GCB, improves the recovery of compounds with flat particles.

Synthesis and identification of meta-(4-bromobenzyloxy) benzaldehyde thiosemicarbazone (MBBOTSC) as novel ligand for cadmium extraction by ultrasound assisted-dispersive-ionic liquid-liquid micro extraction method

In this research, meta-(4-bromobenzyloxy) benzaldehyde thiosemicarbazone (MBBOTSC) as a novel ligand was synthesized from the reaction between meta-(4-bromobenzyloxy) benzaldehyde and thiosemicarbazide under basic condition in water and ethanol as solvents. Ligand has the ability to chelate ions and therefore, it was used to form a complex and extract ions. Then, the cadmium ions in water and wastewater samples were separated based on MBBOTSC by ultrasound assisted-dispersive-ionic liquid-liquid microextraction method (USA-D-ILLME) before determination by AT-F-AAS. The MBBOTSC ligand was added to the mixture of the ionic liquid/acetone (IL/AC, [OMIM][PF6]) and then injected by syringe to 50 mL of water samples at pH 6-7. The sample was put into the ultrasonic accessory for 5 minutes, after complexation (Ligand-Cd; RS…Cd….RS), the water sample was centrifuged for 3 min for phase separation. Due to complexation and back-extraction of Cd in liquid phase, the amount of Cd ions in the water samples was determined by AT-F-AAS . In optimized conditions, the Linear ranges and LOD for 50 mL of water samples were obtained 1-36 μg L-1 and 0.3 μg L-1, respectively (Mean RSD= 1.26%). The validation results were successfully achieved by spiking real samples and using ET-AAS.

Thallium extraction in urine and water samples by nanomagnetic 4-Aminothieno[2,3-d] pyrimidine-2-thiol functionalized on graphene oxide

Thallium is a water-soluble metal and extra dosage has toxicological effect in human body. Thallium is readily absorbed by inhalation, ingestion and skin contact. The symptomatology of thallium toxicity was seen in patients with hemorrhage, bone/gastrointestinal problems, delirium, convulsions and coma. So, accurate determination of thallium in water and human urine is necessary. In this research, a novel and applied method based on 25 mg of nanomagnetic 4-Aminothieno[2,3-d] pyrimidine-2-thiol functionalized on graphene oxide (Fe3O4-ATPyHS@GO) was used for thallium extraction in 50 mL of water, wastewater and urine samples by dispersive magnetic micro solid-phase extraction (DM-μ-SPE). After extraction and back-extraction of solid phase by 1 mL of nitric acid solution, the concentration of thallium ions determined by flame atomic absorption spectrometry (F-AAS). The working/linear range, the limit of detection (LOD), and preconcentration factor (PF) were achieved (4-1400 μg L−1; 4-300 μg L−1), 0.9 µg L−1, and 50, respectively (Mean RSD%=1.8 water; 2.1 urine). The absorption capacity of Go and Fe3O4-ATPyHS@GO adsorbent were achieved 7.2 and 137.5 mg g-1 for 5 mg L-1 of thallium, respectively. The procedure was validated by ICP-MS analyzer.

Spray drift deposition comparison of fluorimetry and analytical confirmation techniques.

Tracer dyes are often used as surrogates to characterize pesticide spray drift and it is assumed that they accurately reflect analytical measurement of active ingredients; however, the validity of this assumption remains inconclusive. Consequently, the influence of measurement technique on the magnitude of deposition of spray drift was investigated using spray drift samples evaluated by traditional analytical techniques (HPLC-MS/MS) and fluorimetry (1,3,6,8-pyrene-tetra sulfonic acid tetrasodium salt dye tracer). The experiment was conducted in a low-speed wind tunnel under controlled meteorological conditions. The herbicide mesotrione was sprayed through three spray air induction nozzles (anvil deflector flat fan TTI11004; flat fan AI11004; flat fan AIXR11003). Spray drift deposition samples were collected using stainless steel discs pairs placed side by side in the center of the wind tunnel at distances of 5, 10, 20, 30, and 40 ft (1.5, 3.1, 6.1, 9.1, and 12.2m) from the spray nozzle. The analytical technique determined pesticide concentration on one disc per pair, and the other was evaluated by fluorimetry. The experimental results, analyzed using the linear split-split plot model, revealed that median deposition concentrations were 15% higher using the tracer dye fluorescence method relative to the analytical method, potentially due in part to procedural recovery inefficiencies of the analytical method (the mean overall procedural recovery result and RSD was 87% ± 6.4% (n=12). This relationship was consistent and held true for the three nozzle types at all distances within the wind tunnel. © 2021 Society of Chemical Industry.

Investigation of the Conditions for Preconcentration of Cadmium Ions by Solid Phase Extraction Method Using Modified Juglans regia L. Shells.

Juglans regia L. shells as agricultural waste can be considered as alternative sorbents to minimize the problems associated with heavy metal pollution. In this study, J. regia shells (JRS) and JRS modified with hydrazine hydrate (JRS-HH) were used as sorbents and compared for the preconcentration of Cd(II) ions from aqueous solution. For the characterization of sorbents, scanning electron microscopy and energy dispersive X-ray (SEM/EDX) analysis and Fourier transform infrared (FTIR) spectroscopy were used. For preconcentration, the solid phase extraction (SPE) technique was used. Preconcentration studies were performed by column method and pH, eluent type and concentration, sample volume, flow rate, and interfering ions effect were studied to determine the optimum column parameters. The limit of detection (LOD) of the sorbents (JRS and JRS-HH) are 0.31 and 0.18 µg/L, respectively. According to the Langmuir isotherm model for both sorbents, for JRS KL = 0.030 L/mg, R2 = 0.992, 0.016 L/mg, and for JRS-HH KL = 0.016 L/mg, R2 = 0.998 and maximum adsorption capacities of the sorbents were found to be as 29.6 and 65.7 mg/g, respectively. The mean recoveries and RSD values at a 95% confidence level (N = 6) for Cd(II) were 100.9% and 3.42, and 100.6% and 3.79, for the JRS and JRS-HH sorbents, respectively. Using this method good results were obtained when compared with those in the literature and the proposed method was successfully applied to the analysis of the certificated reference material (NIST 1640). JRS are an effective and inexpensive sorbent for the preconcentration of metal ions when modified. Thus, low-cost agricultural wastes are both recovered and have an economic value.

A Validated Volumetric Absorptive Microsampling-Liquid Chromatography Tandem Mass Spectrometry Method to Quantify Doxycycline Levels in Urine: An Application to Monitor the Malaria Chemoprophylaxis Compliance.

Because of logistics and cost constraints, monitoring of the compliance to antimalarial chemoprophylaxis by the quantitation of drugs in biological samples is not a simple operation on the field. Indeed, analytical devices are fragile to transport and must be used in a perfectly controlled environment. This is also the case for reagents and supplies, and the waste management is constraining. Thus, samples should be repatriated. They should be frozen after collection and transported with no rupture in the cold chain. This is crucial to generate available and interpretable data but often without any difficulties. Hence, to propose an alternative solution easier to implement, a quantitation method of determining doxycycline in urine has been validated using a volumetric absorptive microsampling (VAMS®) device. As blotting paper, the device is dried after collection and transferred at room temperature, but contrarily to dried spot, the collection volume is perfectly repeatable. Analysis of VAMS® was performed with a high-performance liquid chromatography coupled to a mass spectrometer. The chromatographic separation was achieved on a core-shell C18 column. The mean extraction recovery was 109% (mean RSD, 5.4%, n = 6) for doxycycline and 102% (mean RSD, 7.0%) for the internal standard. No matrix effect has been shown. Within-run as within-day precision and accuracy were, respectively, below 14% and ranged from 96 to 106%. The signal/concentration ratio was studied in the 0.25–50 µg/mL range, and recoveries from back-calculated concentrations were in the 96–105% range (RSD < 11.0%). The RSD on slope was 10%. To achieve the validation, this new quantitation method was applied to real samples. In parallel, samples were analyzed directly after a simple dilution. No statistical difference was observed, confirming that the use of VAMS® is an excellent alternative device to monitor the doxycycline compliance.

RP-HPLC method development and validation for bedaquiline fumarate to evaluate its forced degradation behaviour and stability in official dissolution media

BackgroundA simple, rapid and accurate reverse phase RP-HPLC method for the validation of antitubercular drug bedaquiline fumarate (BQF) was developed. The stability and forced degradation behaviour of bedaquiline fumarate (BQF) in official dissolution media (0.01 N HCl) and methanol were assessed.ResultsThe method provided linear responses within the concentration range which varies from 10 to 100 μg/mL with LOD values of 2.6 μg/mL and LOQ of 7.9 μg/mL. Mean percent recovery varied between 97.46 and 103.82% and precise mean RSD of 0.31% (repeatability) and 0.48% (intermediate precision). The method was validated for other parameters like specificity, system suitability and robustness. Potential degradation of the BQF when exposed to direct sunlight in official dissolution media was 90.75% and in methanolic stock solution was 91.98%. Acid-alkali degradation study showed 86.59% loss of BQF in 0.5 N NaOH, and in acidic environment (0.5 N HCl), there was 6.15% loss. Thermal degradation of BQF was 70.11% loss in official dissolution media at 80 °C. No significant change in drug concentrations was noted when exposed and protected from normal daylight at room temperature and at 2–8 °C temperature.ConclusionThe developed method has significant applicability for the qualitative and quantitative determination of BQF in different pharmaceutical formulations in the official dissolution media in routine quality control analysis.

Quantification of persistent organic pollutants in dietary supplements using stir bar sorptive extraction coupled with GC-MS/MS and isotope dilution mass spectrometry

ABSTRACT In this work, we describe a method developed to quantify persistent organic pollutants (POPs) including polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in dietary supplement samples using stir-bar sorptive extraction (SBSE)-GC-MS/MS-isotope dilution mass spectrometry (IDMS). This method enables accurate, precise, and sensitive quantification of POPs in plant-extract based dietary supplement products commercially available in the United States. When compared with calibration curves, IDMS provided more accurate and precise measurements. The mean error of measurements using this method was 7.24% with a mean RSD of 8.26%. The application of GC-MS/MS enabled approximately two-order-of-magnitude lower limit of quantifications compared with GC-MS. 12 commercially available plant-extract based dietary supplement samples were analysed using this method. PAHs including naphthalene, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, and benzo[a]pyrene were detected in most of the products and had average concentrations over 1 ng/g. OCPs were detected less frequently than PAHs in these products, and none of the OCPs had mean concentrations over 1 ng/g. The mean toxin concentration of each product was calculated, and the highest value was 3.20 ng/g. These results were compared with existing guidelines and none of the analytes in the samples were found to be above the daily allowable limits.

Identification and quantification of selected plastics in biosolids by pressurized liquid extraction combined with double-shot pyrolysis gas chromatography-mass spectrometry.

The identification and quantification of selected plastics (polystyrene (PS), polycarbonate (PC), poly-(methyl methacrylate) (PMMA), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE) and polyvinyl chloride (PVC)) in biosolids (treated sewage sludge) was performed by pressurized liquid extraction (PLE) combined with double-shot pyrolysis gas chromatography-mass spectrometry. Validation of the method yielded recoveries of between 85 and 128% (mean RSD 11%) at a linear range of between 0.01 and 2μg. The distribution of plastics within 25 biosolid samples from a single wastewater treatment plant in Australia was assessed. The mass concentration of PE, PVC, PP, PS and PMMA was between 0.1 and 4.1mg/g dry weight (dw) across all samples, with a total plastic concentration ƩPlastics of between 2.8 and 6.6mg/g dw (median=4.1mg/g dw). PE was the predominant plastic detected (mean concentration of 2.2mg/g dw), contributing to 50% of the total of all plastics. Overall, this study demonstrates that pressurized liquid extraction (PLE) combined with double-shot pyrolysis gas chromatography-mass spectrometry can be used to identify and quantify PE, PP, PVC, PS, and PMMA in biosolids.

Studies on Preparation and UHPLC Analysis of the Usnea Barbata (L) F.H.Wigg Dry acetone extract

In the category of medicinal plants with remarkable therapeutic properties, lichens are also included. An important representative of this group is the Usnea Adans. genus, with over 650 species spread throughout the globe. Representative species of this genus were also found in Romania, so the studies were conducted on Usnea barbata (L.) F.H.Wigg., harvested from the Calimani Mountains, Suceava County. The objectives of this research are: obtaining the dry extract of the Usneae lichen followed by the identification and determination of the usnic acid content by ultra-high performance liquid chromatography (UHPLC) method. Usnic acid content determined in dry extract of Usnea barbata (L.) F.H.Wigg. was significant, of 16.53 � 6.53% (mean � RSD), which supports the continuation of the research with the evaluation of biological effects (antibacterial, antioxidant and antitumoral).

Studies on Preparation and UHPLC Analysis of the Usnea Barbata (L) F.H.Wigg Dry acetone extract

In the category of medicinal plants with remarkable therapeutic properties, lichens are also included. An important representative of this group is the Usnea Adans. genus, with over 650 species spread throughout the globe. Representative species of this genus were also found in Romania, so the studies were conducted on Usnea barbata (L.) F.H.Wigg., harvested from the Calimani Mountains, Suceava County. The objectives of this research are: obtaining the dry extract of the Usneae lichen followed by the identification and determination of the usnic acid content by ultra-high performance liquid chromatography (UHPLC) method. Usnic acid content determined in dry extract of Usnea barbata (L.) F.H.Wigg. was significant, of 16.53 � 6.53% (mean � RSD), which supports the continuation of the research with the evaluation of biological effects (antibacterial, antioxidant and antitumoral).

Development of analytical methods GC-MS vs LC-UV for the serum monitoring of an inflammatory glycotoxin (methylglyoxal): A new biomarker of bovine hepatobiliary distomatosis

Two analytical methods; high performance liquid chromatography and gas chromatography were used to determine the content of 2-methylquinoxaline, a methylglyoxal-derived agent in sera from cattle with fascioliasis. Methylglyoxal is a highly mutagenic and cytotoxic reactive dicarbonyl compound formed by non-enzymatic fragmentation of triose phosphate GAP and DHAP during glycolysis which regularly contributes to repositioning the energetic balance between physiological and pathological situations. The aim of this study was to propose the MGO as a new biomarker in the bovine fasciolosis.Strongly infected animals showed a correlation between the relatively high levels of Fasciola hepatica anti-f2 antibody and methylglyoxal compared to unharmed animals. Also, an acute hyperglycemia was recorded and closely related to hepatic parenchyma hyperplasia, inflammation, bile ducts obstruction and scléro-fibrous foci formation.Unlike HPLC, which has shown analytical flaws and irregularities, GC-MS remains an excellent diagnostic tool for detecting and quantifying methylglyoxal in biological fluids. The developed method has been validated under FDA guidelines. A full scan-range was set from m/z 39 to 144/999 and the molecular weight of the 2-methylquinoxaline was identified according to NIST Database and ES. Methylglyoxal was the only analyte successfully quantified in a relatively short run time. It was linear over a concentration range of 0.057–5.7 μg.ml-1with mean recoveries and RSD of 118% and 3.63% respectively. The intra and inter-day assays were satisfying and not exceed 3.00%. Results reflect the degree of precision of our method and indicate that MGO was an important contributor to understand the hepatic failure independently of other serum markers.

Electrochemically initiated co-polymerization of monomers of different oxidation potentials for molecular imprinting of electroactive analyte

Herein, we report an electrochemically initiated co-polymerization of two electroactive monomers of different oxidation potentials. The molar ratio of low oxidation potential monomer in the solution for electropolymerization was optimized to find condition suitable for co-polymerization of high-oxidation potential monomer effectively at lower oxidation potential. The XPS analysis confirmed successful co-polymerization. This co-polymerization condition was further used in imprinting of melatonin, an electroactive compound. Entrapment of melatonin in the polymer matrix was confirmed by measuring electroactivity of melatonin in the 0.1 M KCl−HCl solution (pH 1.6). This MIP based electrochemical sensor determined melatonin in the linear dynamic concentration range 10–80 μM. Detectability of proposed chemosensor was 0.14 μM (S/N = 3). The mean RSD for the concentration range studied was ∼20%. Selectivity of the chemosensor was satisfactory towards common structural analogues and biomolecules. Furthermore, the chemosensor was successfully used to determine melatonin in real samples. The sensitivity in the presence of matrix components and that for the KCl−HCl solution were quite similar. The results obtained indicate the suitability of the devised chemosensor for practical applications.

Molecularly Imprinted Stir Bar Sorptive Extraction Coupled with High‑Performance Liquid Chromatography for Trace Analysis of Diclofenac in Different Real Samples

A novel molecularly imprinted polymer-coated stir bar has been used to selectively extract diclofenac (DFC) directly from real samples. DFC was used as template molecule for preparation of MIP coating. The effect of different parameters on the extraction efficiency were studied and the optimum conditions were established as: the absorption and desorption times were fixed at 10 min, stirring speed was 600 rpm, pH was adjusted to 5.1, the amount of NaCl was 0.35 mol/L and extraction process was performed at a temperature of 45 °C. Under the optimum conditions, the linear range of method was 0.5- 500.0 µg/L for DFC and the detection limit was calculated to be 0.15 µg/L with an enrichment factor of 242 folds. The technique was successfully applied for the analysis of trace amounts of DFC in seawater and commercial tablet samples. The mean recoveries of spiking real samples with DFC at 10.0 µg/L level were between 94.2-100.0 % with a mean RSD of 0.7-4.6%.

Application of Box-Behnken design in response surface methodology for the molecularly imprinted polymer pipette-tip solid phase extraction of methyl red from seawater samples and its determination by spectrophotometery

In this paper, a rapid, selective and effective technique, pipette-tip solid phase extraction based on molecularly imprinted polymer, was used for extraction and pre-concentration of methyl red (MR) prior to its determination by spectrophotometer. Variables influencing extraction efficiency including type and volume of eluent solvent, sample volume, number of cycles of extraction and elution, amount of sorbent and pH of the sample solution were optimized with two methods of one-variable-at-a-time and response surface methodology (RSM). For RSM optimization, seven factors in three-levels were utilized for Box-Behnken experimental design. Under optimum conditions, a linear calibration graph in the range of 3.0–300.0 μg L−1 for MR was resulted. The limit of detection of proposed method was 0.50 μg L−1 for MR. Finally, the investigated method was used for the determination of MR in seawater and the mean recoveries were calculated to be 84.0–98.0% with mean RSD of 2.5–6.7%.

N2O flux measurements over an irrigated maize crop: A comparison of three methods

This paper presents the NitroCOSMES campaign, aimed at testing and evaluating the performance of three methods for monitoring N2O fluxes over an agricultural field. The experiment was conducted from May to August 2012 at a site located in the south-west of France. N2O fluxes from a 24 ha irrigated maize field were measured using eddy covariance (EC), automated chamber (AC) and static chamber (SC) methodologies. Uncertainties were calculated according to the specificities of each set-up. Measurements were performed over a large range of water-filled pore spaces (WFPS), soil temperatures, and mineral nitrogen availability, and offered the opportunity to compare methodologies over a wide range of N2O emission intensities. The average N2O fluxes were compared among the three methodologies during the same periods of measurement and for different intensities of emissions (low, moderate and high). Periods of comparison were determined according to the AC results. On average, the three methods gave comparable results for the low (SC: 14.7 ± 2.2, EC: 15.7 ± 10.1, AC: 17.5 ± 1.6 ng N2O-N m−² s−1) and the high (SC: 131.7 ± 22.1, EC: 125.3 ± 8, AC: 125.1 ± 8.9 ng N2O-N m−² s−1) N2O emission ranges. For the moderate N2O emission range, AC measurements gave higher emissions (57.2 ± 3.9 ng N2O-N m−² s−1) on average than both the SC (41.6 ± 6.6 ng N2O-N m−² s−1) and EC (33.8 ± 3.9 ng N2O-N m−² s−1) methods, which agreed better with each other. The relative standard deviation coefficient (RSD) indicated that EC methodology gave highly variable values during periods of low N2O emissions, from -52.2 ± 88.1 to 62.2 ± 50.7 ng N2O-N m−² s−1, with a mean RSD of 151%. Water vapour effects (dilution and spectroscopic cross-sensitivity) were discussed in an attempt to explain the high variability in low N2O emission measurements. Even after applying the Webb term correction, there could still be a spectroscopic cross-sensitivity effect of water vapour on the N2O trace gas signal because of the layout of the analysers, which was not determined during the experiment. This study underlined that EC methodology is a promising way to estimate and refine N2O budgets at the field scale and to analyse the effects of different agricultural practices more finely with continuous flux monitoring. It also highlighted the need to continue the effort to assess and develop chambers and EC methodologies, especially for the low N2O emission measurement range, for which values and systematic uncertainties remain high and highly variable.