Determination of Tangeretin in Rat Plasma by LC-Electrospray-Ion Trap MS

A selective, sensitive, and accurate method has been developed and validated for the quantification of tangeretin in rat plasma. The application of LC-electrospray-ion trap mass spectrometry in full scan and multiple reactions monitoring modes were investigated. Following solid phase extraction using a hydrophilic–lipophilic balance cartridge, the analytes were separated on a C₁₈ column using an isocratic mobile phase composed of acetonitrile/water (50:50, v/v) containing 0.3% formic acid. In full scan mode, the LOQ was 2 ng mL^?1. The standard calibration curve was linear (R ² = 0.9999) over the concentration range 2–200 ng mL^?1. The precision over the concentration range was within 15% (RSD) and the accuracy was ranged from 86 to 115%. In multiple reaction monitoring mode, the LOQ was 1 ng mL^?1 and the standard calibration curve was linear (R ² = 0.9976) over the concentration range 1–100 ng mL^?1 with a precision of 12% and accuracy rangeing from 91 to 113%.     

Simultaneous Determination of Amoxicillin and Clavulanic Acid in Dog Plasma by High-Performance Liquid Chromatography Tandem Mass Spectrometry

A rapid, sensitive, and specific high-performance liquid chromatography tandem mass spectrometric method was developed for the simultaneous determination and confirmation of amoxicillin and clavulanic acid in plasma. Plasma sample was subjected to a simple deproteinization with acetonitrile, and then the supernatant was directly diluted by water. Analysis was performed on a Phenomenex Luna C₈ reversed-phase column by detection with mass spectrometry in negative ions multiple reaction monitoring mode. A gradient elution program with 0.1% formic acid and acetonitrile was performed at a flow of 0.25 mL min^?1. There is good linearity in the range of 0.5–500 ng mL^?1 for both amoxicillin and clavulanic acid. The decision limits of amoxicillin and clavulanic acid were 0.06 ng mL^?1 and 0.08 ng mL^?1 in plasma, respectively, and the detection capabilities of two analytes were below 0.5 ng mL^?1. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The extraction recoveries of amoxicillin and clavulanic acid were between 102% and 115% in plasma at three spiked levels of 0.5, 50, and 500 ng mL^?1, with the relative standard deviations less than 15% for each analyte. The developed method was applied to pharmacokinetic studies of amoxicillin and clavulanic acid tablets in healthy beagles.     

Development of molecularly imprinted-solid phase extraction combined with dispersive liquid–liquid microextraction for selective extraction and preconcentration of triazine herbicides from aqueous samples

In this study, a sensitive and developed method based on the use of molecularly imprinted-solid phase extraction along with dispersive liquid–liquid microextraction has been reported for selective extraction and pre-concentration of triazine pesticides from aqueous samples. Molecularly imprinted microspheres (template, atrazine) were synthesized using precipitation polymerization and used as sorbent in SPE procedure. A model solution containing the studied pesticides was slowly passed through the atrazine-MIP cartridge. The adsorbed analytes were eluted with methanol, mixed with carbon tetrachloride (as extraction solvent) and rapidly injected into deionized water. In this process, the analytes were extracted into fine droplets of carbon tetrachloride and the fine droplets were sedimented in bottom of the conical test tube by centrifugation. Finally, GC-FID was used for the separation and determination of analytes in the sedimented phase. Some important parameters affecting the performance of developed method were completely investigated. The linear ranges of calibration curves were wide and limits of detection and limits of quantification were between 0.2–7 and 0.5–20 ng mL^?1, respectively. The relative standard deviation obtained for six repeated experiments of atrazine (10 ng mL^?1) was 3.1 %. The relative recoveries obtained for the atrazine in the spiked samples were within in the range of 92–98 %.     

Colorimetric Determination of Lead Using Gold Nanoparticles

A combined homogeneous assay and colorimetric determination method using gold nanoparticles was developed for rapid determination of lead(II) in contaminated natural waters. The presence of lead(II) in the colloidal gold suspension causes a change in the absorbance of the suspension. An increase in the absorption property at 595 nm is accompanied by a change in the size of the gold nanoparticles. High concentrations of lead cause aggregation of the gold colloids. Colloidal gold nanoparticles were synthesized using tannic acid as the reducing agent; this reagent allowed selective determination of lead in 10 µL of water, with a detection limit of 310 ng mL^?1 with an analysis time of 5 min. The coefficient of variation for lead(II) within the working range of the assay (520 ng mL^?1–13 µg mL^?1) varied from 1.3% to 9.2%. The limit of detection using this method with a sample volume of 50 µL was 60 ng mL^?1. The coefficient of variation for lead over the working range of the determined concentrations (80 ng mL^?1–25 µg mL^?1) varied from 0.2% to 9.3%, while the values for the inter-day assay (n = 8) were less than 10%. The method was employed for the analysis of river, lake, marsh, and spring water; the recovery of lead was determined to be 72.5%–130% for 10 µL of water and 93.6%–114.7% for 50 µL.     

Development of Immunoaffinity Sample-Purification for GC–MS Analysis of Ractopamine in Swine Tissue

A method combining immunoaffinity chromatography with gas chromatography–mass spectrometry (GC–MS) has been established for determination of ractopamine residues in swine liver and urine. After clean-up on an immunoaffinity chromatography column, GC–MS analysis revealed recovery from blank swine liver and urine fortified at 2.5–20 ng g^?1 (ng mL^?1 for urine), respectively, was 68.2–78.6 and 76.2–83.1%. The limits of detection and quantification were 0.5 ng g^?1 (or ng mL^?1) and 2.0 ng g^?1 (or ng mL^?1), respectively. The procedure was used for analysis of ractopamine residues in samples of swine liver and urine in which the levels were unknown. The amounts detected were 9–216 ng g^?1 (ng mL^?1).     

LC–MS/MS Determination of Catecholamines in Urine Using FMOC-Cl Derivatization on Solid-Phase Extraction Cartridge

A method for the determination of catecholamine derivatives in human urine is proposed that includes the derivatization of target compounds on a solid-phase extraction cartridge and determination of the analytes by a UHPLC method with tandem mass-spectrometric detection. 9-Fluorenyl-methoxycarbonyl chloride was used as the derivatization agent. The limits of detection for the analytes were 2.5 ng mL^?1 for 9-fluorenyl-methoxycarbonyl-adrenaline, 5 ng mL^?1 for 9-fluorenyl-methoxycarbonyl-octopamine, and 25 ng mL^?1 for 9-fluorenyl-methoxycarbonyl-dopamine. The proposed procedure was tested on real samples obtained from volunteers.     

Determination of Pantoprazole, Rabeprazole, Esomeprazole, Domperidone and Itopride in Pharmaceutical Products by Reversed Phase Liquid Chromatography Using Single Mobile Phase

A simple, sensitive, and precise high performance liquid chromatographic method for the analysis of pantoprazole, rabeprazole, esomeprazole, domperidone and itopride, with ultraviolet detection at 210 nm, has been developed, validated, and used for the determination of compounds in commercial pharmaceutical products. The compounds were well separated on a Hypersil BDS C18 reversed-phase column by use of a mobile phase consisting of 0.05 M, 4.70 pH, potassium dihydrogen phosphate buffer - acetonitrile (720:280 v/v) at a flow rate of 1.0 mL min^?1. The linearity ranges were 400–4,000 ng mL^?1 for pantoprazole, 200–2,000 ng mL^?1 for rabeprazole, 400–4,000 ng mL^?1 for esomeprazole, 300–3,000 ng mL^?1 for domperidone and 500–5,000 ng mL^?1 for itopride. Limits of detection (LOD) obtained were: pantoprazole 147.51 ng mL^?1, rabeprazole 65.65 ng mL^?1, esomeprazole 131.27 ng mL^?1, domperidone 98.33 ng mL^?1 and itopride 162.35 ng mL^?1. The study showed that reversed-phase liquid chromatography is sensitive and selective for the determination of pantoprazole, rabeprazole, esomeprazole, domperidone and itopride using single mobile phase.     

Quantification of Thiram in Honeybees: Development of a Chemiluminescent ELISA

Abstract

A Chemiluminescence Enzyme‐Linked Immuno‐Sorbent Assay (CL‐ELISA) for determination and quantification of the fungicide thiram in honeybees was developed in an indirect competitive format. The assay was optimized by determining: the optimal coating conjugate concentration and anti‐thiram antiserum dilution, the effect of the incubation time on the competitive step, the tolerance to organic solvents. The IC₅₀ and the limit of detection (LOD) values were 60 ng mL^?1 and 9 ng mL^?1, respectively, similar to those of colorimetric ELISA with a calibration range of 9–15,000 ng mL^?1. Cross reactivity of some related compounds such as some dithiocarbamates, a thiocarbamate, the ethylenethiourea and the tetramethylthiourea were tested. The assay was then applied to honeybees sample extracts obtained by using the liquid‐liquid extraction or the graphitized carbon‐based solid phase extraction.

The calibration curves in honeybee extracts from liquid‐liquid procedure gave an IC₅₀ of 141 ng mL^?1 and a LOD of 17 ng mL^?1. In case of extracts obtained by SPE these values were 139 ng mL^?1 and 15 ng mL^?1, respectively. The average recovery value from honeybee extracts spiked with 75 ng mL^?1 of thiram was 72% for SPE, higher than for liquid‐liquid extraction (60%). On the opposite, when the honeybees were directly spiked with 2 and 10 ppm the average recovery was higher for liquid‐liquid extraction (54%), than for SPE (31%). Finally, the assay was applied to honeybee samples collected during monitoring activities in Italy and Russia.     

Simultaneous Determination of Ebastine and Its Active Metabolite (Carebastine) in Human Plasma Using LC–MS–MS

A sensitive and rapid LC–MS–MS method was developed for the simultaneous determination of ebastine and carebastine in human plasma. Solid-phase extraction was used to isolate the compounds from the biological matrix followed by separation on a Symmetry C18 column under isocratic conditions. The mobile phase was 10 mM ammonium formate in water/acetonitrile (40:60, v/v). Detection was carried out using a triple-quadrupole mass spectrometer in positive electrospray ionization and multiple reaction monitoring mode. The method was fully validated over the concentration range of 0.1–10 ng mL^?1 for ebastine and 0.2–200 ng mL^?1 for carebastine in human plasma, respectively. The lower limit of quantification (LLOQ) was 0.1 ng mL^?1 for ebastine and 0.2 ng mL^?1 for carebastine. For ebastine and carebastine inter- and intra-day precision (CV%) and accuracy values were all within ±15% and 85–115%, respectively. The extraction recovery was on average 60.0% for ebastine and 60.3% for carebastine.     

Determination of Alkylphenols in Water by Dispersive Liquid–Liquid Microextraction Based on Solid Formation without a Disperser

Dispersive liquid–liquid microextraction based on solid formation without a disperser combined with high-performance liquid chromatography has been developed for the determination of 4-tert-butylphenol, 4-n-nonylphenol, and 4-tert-octylphenol. This method is rapid, easy, and uses only 10 µL of a low toxicity organic solvent (1-hexadecanethiol) for the extraction solvent and no disperser solvent. The extraction time and centrifugation time require less than 10 min. The linear range was 1–500 ng mL^?1 for 4-tert-butylphenol, 2–1000 ng mL^?1 for 4-tert-octylphenol, and 5–500 ng mL^?1 for 4-n-nonylphenol with r² ≥ 0.9986. The detection limits were between 0.2 and 1.5 ng mL^?1. The recoveries of lake and river water samples were in the range of 79% to 108%, and the relative standard deviations were 5% to 10%.     

Simultaneous Analysis of Carbamate and Organophosphorus Pesticides in Water by Single-Drop Microextraction Coupled with GC–MS

Single-drop microextraction (SDME) has been coupled with gas chromatography–mass spectrometry to enable rapid and simple simultaneous analysis of carbamate and organophosphorus pesticides (OPP). The significant conditions affecting SDME performance (microextraction solvent, extraction time, solvent volume, sample pH, stirring speed, and ionic strength) were studied and optimized. Extraction was achieved by suspending a 1.5-μL drop of toluene from the tip of a microsyringe directly immersed in 5-mL aqueous donor solution at pH 5 stirred at 800 rpm. The dynamic linear range and detection limits of the method were evaluated by analysis of water samples spiked with carbamate pesticides and OPP. Under selected ion-storage mode, very low detection limits (0.02–0.50 ng mL^?1) and good linearity (0.5–200 ng mL^?1) were achieved. When SDME was applied to analysis of pesticides in natural water samples good recoveries (89.4–102.1%) were obtained. Inter-day and intra-day RSD of most results were below 5.4 and 6.1%, respectively. The method proved to be a rapid and simple tool for extraction and analysis of these pesticides in water samples.     

Quantification of Imidacloprid in Honeybees: Development of a Chemiluminescent ELISA

A Chemiluminescent Enzyme-Linked Immuno-Sorbent Assay (CL-ELISA) for determination and quantification of the fungicide imidacloprid in honeybees was developed in an indirect competitive format. The assay was optimized by determining: the optimal coating conjugate concentration and anti-imidacloprid antiserum dilution, the effect of the incubation time on the competitive step, and the tolerance to organic solvents. The IC₅₀ and the limit of detection (LOD) values were 14.8 ng mL^?1 and 0.11 ng mL^?1, respectively, similar to those of colorimetric ELISA with a calibration range of 0.1–2600 ng mL^?1. Cross reactivity of some related compounds such as three imidacloprid metabolites, 6-chloro nicotinic acid, 5-hydroxy-imidacloprid, and imidacloprid olefin, and one other chloronicotinoid insecticide, acetamiprid, were tested. The assay was then applied to honeybee extracts obtained by using the liquid-liquid extraction. The calibration curves in honeybee extracts from the liquid-liquid procedure gave an IC₅₀ of 23.7 ng mL^?1 and a LOD 1.6 ng mL^?1. The average recovery value from honeybee extracts spiked with 100 and 1000 ng mL^?1 of imidacloprid were 73% and 76%, respectively. Finally, the assay was applied to honeybee samples collected during monitoring activities in Italy; it was found that only five of the 27 samples were positives, with low concentrations of imidacloprid ranging between 1.2 and 15.4 ng g^?1.     

Simultaneous Determination of Berberine and Palmatine in Rabbit Plasma by LC-MS–MS and Its Application in Pharmacokinetic Study After Oral Administration of Coptidis and Coptidis–Gardeniae Couple Extract

A valid and sensitive LC-MS–MS method is adopted for pharmacokinetics study of berberine and palmatine in rabbit plasma. After mixing with internal standard tetrahydroberberine, plasma samples were pretreated with 1.5 mL acetonitrile. Chromatographic separation was on a C₁₈ column using a mixture of water (containing 10 mmol L^?1 ammonium acetate, pH 3.5) and acetonitrile (50∶50, v/v) as mobile phase. The detection was performed by selected ion monitoring mode via electrospray ionization source operating in the positive ionization mode. The method was linear over the concentration range of 2.0–200.0 ng mL^?1 for berberine and 1.0–100.0 ng mL^?1 for palmatine. The lowest limits of quantitation (LLOQ) were 2.0 ng mL^?1 for berberine and 1.0 ng mL^?1 for palmatine. The intra- and inter-day precision values were less than 14.3% and the deviations were within ±11.0%. The fully validated LC-MS–MS method has been successfully applied to a pharmacokinetic study of berberine, palmatine in rabbit plasma after oral administration of Coptidis and coptidis–gardeniae couple extract. The results indicated that the plasma profiles of the two compounds in rabbit confirmed to one-compartment open model and the combinational utilization with Gardeniae could increase the bioavailability of berberine and palmatine, the two major active components of Coptidis.     

Development and Validation of Atorvastatin by LC–ESI–MS and Application in Bioequivalence Research in Healthy Chinese Volunteers

The aim of this research was to develop a sensitive liquid chromatographic–electrospray ionization–mass spectrometric (LC–MS) method for direct measurement of the concentration of Atorvastatin in human plasma. Plasma samples (1 mL) were extracted with 3 mL ethyl acetate, and by a simple reversed-phase chromatography. Pitavastatin was used as internal standard (IS). The LOQ was 0.25 ng mL^?1 (RSD 4.24%). The assay was linear from 0.25–20 ng mL^?1. And the correlation coefficient for the calibration regression line was 0.9996 or better. Intra-day and inter-day accuracy were better than 15%. The method has been successfully used for a pharmacokinetic study with human subjects. A two-period crossover designed bioequivalence research was also progressed in healthy Chinese volunteers. Among the pharmacokinetic data obtained, T _max was 1.36 ± 0.68 h for reference formulation and 0.81 ± 0.54 h for test formulation. C _max was 8.54 ± 5.06 ng mL^?1 for reference formulation and 9.54 ± 3.68 ng mL^?1 for test formulation. t _1/2 was 8.50 ± 2.74 h for reference formulation and 9.24 ± 3.17 h for test formulation. AUC _0?48h was 54.77 ± 21.82 h ng mL^?1 for reference formulation and 55.66 ± 20.91 h ng mL^?1 for test formulation. The method was successfully applied to the study of pharmacokinetics of Atorvastatin in healthy Chinese volunteers.     

Determination of Lead at Trace Level Through Cloud Point Extraction and Atomic Absorption Spectrometry with Electrothermal Atomization: An Environmentally Benign Methodology

The quantification of lead in water samples is presented at the sub-ppb level through preconcentration with cloud point extraction (using Triton x-100 and eriochrome black T) and atomic absorption spectrometry with electrothermal atomization. In order to study the influence of several variables, experimental design analyses were carried out. Linearity was observed between 0.15 to 1.20 ng mL^?1 (r = 0.98), with a detection limit of 0.04 ng mL^?1 and a quantification limit of 0.15 ng mL^?1. A mean recovery of 90 ± 9% (n = 6, P = 0.05) was found; at the precision was 9% expressed as the coefficient of variation. Anions and cations that were studied did not affect the recovery of lead. Water samples of different sources were analyzed directly as well as by the standard addition method; no statistical differences were found between the two procedures. Finally, the present methodology was compared with liquid–liquid extraction of the lead-ditizone complex, using green analytical indicators proposed for this purpose.     

Determination of Estrone and 17β-Estradiol in Water Samples Using Dispersive Liquid–Liquid Microextraction Followed by LC

A new method, termed dispersive liquid–liquid microextraction (DLLME), was developed for the extraction and pre-concentration of estrone (E1) and 17β-estradiol (E2) in water samples. The samples were extracted by 0.50 mL methanol (disperser solvent) containing 25.0 μL tetrachloroethane (extraction solvent). Important factors such as the volume and type of extraction and disperser solvent, extraction time and salt effect were studied. Under optimum conditions, the enrichment factors and the limits of detection were 347 and 0.2 ng mL^?1 for E1, and 203 and 0.1 ng mL^?1 for E2, respectively. The linear range was 0.5–5,000 ng mL^?1. Compared to other methods, DLLME–LC–VWD has advantages for E1 and E2 analysis in water: high enrichment factor, low cost, simplicity, quick and easy operation.     

A Validated Method for the Determination of Neonicotinoid,Pyrethroid and Organochlorine Residues in Human Milk

Exposure to pesticides in the environment is sensitively indicated by the concentration of these chemicals in human milk. However, to the best of our knowledge, detection methods in human milk for the relatively new class of pesticides, neonicotinoids, are yet to be validated. We developed a method of detection of neonicotinoids in human milk, together with two other classes of pesticides, pyrethroids and organochlorines. Neonicotinoids and pyrethroids are emerging pesticides that are replacing older and more persistent chemicals such as organochlorines. We optimized a procedure for extraction of these chemicals from whole milk and report our solutions to the problems of interference by co-extracted substances. The clean-up method was optimized using a minimum amount of PSA (50 mg) and MgSO₄ (150 mg). This was followed by GC–MS/MS analysis (for organochlorines and pyrethroids) and LC–MS/MS (for neonicotinoids). The method was validated following SANTE/11945/2015 guidelines at concentrations 10, 20 and 100 ng g^?1. Limits of quantification were obtained at ≤ 2 ng g^?1 for all pesticides and lowest validated level were 10 ng g^?1, with measurement uncertainty between 0.47 and 2.6 ng g^?1. Average recovery ranged from 84 to 102% and for most compounds was found to be more satisfactory than the original QuEChERS, AOAC 2007.01 acetate buffer method and modified QuEChERS methods. The relative standard deviation was less than 16%. The method was successfully utilized for the analysis of human milk samples from Nadia, West Bengal and was found positive for organochlorines and negative for neonicotinoids and pyrethroids.     

Rabbit Monoclonal Antibody-Based Lateral Flow Immunoassay Platform for Sensitive Quantitation of Four Sulfonamide Residues in Milk and Swine Urine

Based on the available rabbit monoclonal antibody (RabMAb), a rapid and sensitive lateral flow immunoassay (LFA) platform has been developed for quantitative detection of four sulfonamide residues(SRs) of sulfadiazine (SD), sulfathiazole (STZ), sulfapyridine (SP), and sulfamethoxazole (SMX).Within the designed LFA competitive format assay, which was based on antigen-antibody properties, the hapten conjugate N¹-[4-(carboxymethyl)-2-thiazolyl] sulfanilamide linked to protein ovalbumin (TS-OVA) and goat anti-rabbit antibody were sprayed as capture and control reagents, respectively, and then the antibody was conjugated to colloidal gold particles as the detection reagent. With quantitative assessment aided by a colorimetric strip reader, the sensitivities of the established LFA method for SD, STZ, SP, and SMX were 0.91 ng mL^?1, 0.10ng mL^?1,0.12ng mL^?1, and 2.13ng mL^?1, and the half-maximum inhibition concentrations (IC₅₀) were 5.19 ng mL^?1, 1.25 ng mL^?1, 0.66 ng mL^?1, and 24.14 ng mL^?1, respectively. The recoveries at three spiked levels (5, 20, 50 ng mL^?1for SD, STZ, and SP; 20, 50, 100 ng mL^?1 for SMX) were in the range of 78.02–135.10% and 76.40–137.16% for milk and swine urine, respectively. More importantly, the detection performance of the established platform was consistent with that of in-parallel LC-MS/MS analysis. In conclusion, the proposed LFA platform has showed the potential for fast, sensitive and relatively accurate quantification of four sulfonamide residues in practical uses.     

Chemiluminometric Determination of the Pesticide Pirimicarb by a Flow Injection Analysis Assembly

Abstract

A flow injection (FI) method is described for the determination of pirimicarb. It was found that an enhanced chemiluminescence (CL) signal is obtained when employing the luminol–H₂O₂–horseradish peroxidase (HRP) system. Under the optimum experimental conditions, the enhanced CL intensity was linear with the concentration 4.25–30.75 ng mL^?1 (r = 0.997, n = 8) with a relative standard deviation of 0.99%, containing 12.75 ng mL^?1 (n = 8). The limit of detection of the investigated compound was 0.12 ng mL^?1. The method shows a moderate selectivity against other pesticides (Amitrole, Atrazine, 2,4,5-T, Dichlorprop, and Metamidophos).The proposed method was sensitive, simple, rapid, and successfully applied to the determination of pirimicarb when it is applied in freshwater; the mean recoveries were 98.3–118.5%.     

Diol sep-pak cartridges for enrichment of polychlorobiphenyls and chlorinated pesticides from water samples; determination by GC-ECD

Summary Gas chromatography of polychlorinated biphenyls and chlorinated pesticides in water samples has been performed after adsorption from a 20–200-mL sample on to a cartridge containing 100 mg diol-bonded porous silica. The PCBs are desorbed with 500 μL ethyl acetate, which is concentrated and analysed by gas chromatography with electron-capture detection (GC-ECD). The average recovery of 0.1 ng mL⁻¹ PCB congeners from distilled water and from Aniene river water is≥95% (standard deviation≤2.8). Average recoveries of 25 ng mL⁻¹ Aroclor 1254 from distilled water and from Aniene river water were, respectively, 94.4% and 92.5% (standard deviation 5.8). In the separation of PCB congeners from the chlorinated pesticides only the aldrin (40%) was eluted with the PCBs from the diol Sep-Pak cartridge by aqueous methanol. The method described is simple and reproducible.