Inter-day Repeatability Research Articles

An investigation of the sex-related differences in the stiffness of the Achilles tendon and gastrocnemius muscle: Inter-observer reliability and inter-day repeatability and the effect of ankle joint motion

PurposeThe purpose of the present study was to investigate sex-related differences in the stiffness of the Achilles tendon and gastrocnemius muscle at rest and tensioned state. Another purpose of the study was to investigate the inter-observer reliability and inter-day repeatability of MyotonPRO, a portable myotonometer, in measuring tendon and muscle stiffness. MethodsThe study included 73 healthy participants (19 males for the reliability and repeatability study; 24 males and 30 females for the experimental study) with an age range of 19–27 years. The stiffness of the Achilles tendon and medial gastrocnemius muscle was measured with a portable myotonometer (MyotonPRO). The stiffness measurements of the Achilles tendon and medial gastrocnemius muscle were performed at 0° and 10° of ankle joint dorsiflexion. The stiffness measurements were performed by two physiotherapists to determine the inter-observer reliability of the device. For the inter-day repeatability (or between-day precision), the same individuals were reassessed by the same examiner after a 3-day interval. ResultsIt was found that MyotonPRO has excellent inter-observer reliability and inter-day repeatability in measuring the stiffness of the Achilles tendon and medial gastrocnemius muscle (ICC=0.83-0.98). The stiffness of the Achilles tendon and gastrocnemius muscle at neutral and 10° joint dorsiflexion was higher in males compared to females (p<0.05); however, the stiffness value of difference between neutral and 10° joint dorsiflexion for the Achilles tendon and gastrocnemius muscle was similar in both groups (p>0.05). DiscussionThe obtained results suggest that MyotonPRO is a reliable and repeatable device in measuring the stiffness of the Achilles tendon and gastrocnemius muscle. Furthermore, males have stiffer Achilles tendon and gastrocnemius muscle, compared to females; however, the change in the stiffness of the assessed tissues caused by joint motion was similar in both sexes.

Targeted Clinical Metabolite Profiling Platform for the Stratification of Diabetic Patients.

Several small molecule biomarkers have been reported in the literature for prediction and diagnosis of (pre)diabetes, its co-morbidities, and complications. Here, we report the development and validation of a novel, quantitative method for the determination of a selected panel of 34 metabolite biomarkers from human plasma. We selected a panel of metabolites indicative of various clinically-relevant pathogenic stages of diabetes. We combined these candidate biomarkers into a single ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method and optimized it, prioritizing simplicity of sample preparation and time needed for analysis, enabling high-throughput analysis in clinical laboratory settings. We validated the method in terms of limits of detection (LOD) and quantitation (LOQ), linearity (R2), and intra- and inter-day repeatability of each metabolite. The method’s performance was demonstrated in the analysis of selected samples from a diabetes cohort study. Metabolite levels were associated with clinical measurements and kidney complications in type 1 diabetes (T1D) patients. Specifically, both amino acids and amino acid-related analytes, as well as specific bile acids, were associated with macro-albuminuria. Additionally, specific bile acids were associated with glycemic control, anti-hypertensive medication, statin medication, and clinical lipid measurements. The developed analytical method is suitable for robust determination of selected plasma metabolites in the diabetes clinic.

Multivariate optimization of ultrasound-assisted extraction for the determination of phenolic compounds in plums (Prunus salicina Lindl.) by high-performance liquid chromatography (HPLC)

A high-performance liquid chromatographic (HPLC) method with a diode array detector (DAD) and ultrasound-assisted extraction (UAE) was established to obtain the maximum response for the extraction of phenolic compounds in plums (Prunus salicina Lindl). The effects of solvent relationship (methanol/water) (0 to 100%, v/v) and ultrasound extraction time (5 to 30 min) using a multivariate design and response surface methodology were studied. All of the studied extracted condition models established showed significant effects (p < 0.05). Nevertheless, the determination of common optimum combination for all compounds was complex and a weighted desirability function was applied to maximize the extraction for each analyte. The optimum conditions of extraction were for a period of 30 min. For the solvent optimized conditions (84/16 methanol/water, v/v), the important phenolic compounds selected in the design model according to the concentration range and insignificant lack of fit p-value were extracted, detected, and quantified with a probability of 84% including hydroxycinnamic acids (chlorogenic and neochlorogenic acids), flavonols (quercetin-3-O-rutinoside, kaempferol-3-O-rutinoside, isoharmentin-3-O-rutinoside), and anthocyanins (cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside). The validity and adequacy of the predictive extraction model was checked in plums and no significant differences were detected between the predicted and the actual phenolic contents. The intra-day and inter-day assay repeatabilities for the analysis of real samples were less than 11.5% and 11.7%, respectively. Recovery values between 72.0 and 112% were obtained for all compounds. For all these reasons, the methodology is appropriate for the routine determination of the majority of phenolic compounds in Prunus salicina Lindl.

Determination of theobromine and caffeine in fermented and unfermented Amazonian cocoa (Theobromacacao L.) beans using square wave voltammetry after chromatographic separation

The concentrations of theobromine (TB) and caffeine (CF) together with other substances such as phenolic compounds, contribute to the perception of the bitter taste characteristic of fermented and unfermented Amazonian cocoa samples and their edible derivatives, such as chocolates. Thus, an analytical method based on square wave voltammetry (SWV) with a boron doped diamond electrode (BDD) was proposed to determine them. The supporting electrolyte, pH buffer solutions and parameters of the SWV technique were studied, and after determining the optimal conditions, analytical curves were constructed and the limits of detection and quantification calculated as 0.027 μmol L−1 and 0.093 μmol L−1 for CF and 0.025 and 0.085 μmol L−1 for TB. Intra-day and inter-day repeatability tests were carried out and the relative standard deviation values were below 2.51% and 6.50%, respectively. Interference studies were carried out and no potential interferents were found, except for high levels of TB in the presence of low CF concentrations, and vice-versa. To overcome this drawback, a preparative chromatographic procedure was used and the isolated aliquots of TB and CF quantified using SWV and high performance liquid chromatography (HPLC) with photodiode array detectors (PAD) as the reference method. Due to the low concentration of CF in the Amazonian cocoa sample, a miniaturized electrochemical cell produced in a 3D printer was developed. Based on the results, the relative errors were lower than 10% and the critical values for the F and t tests were lower than those tabulated at the 95% confidence level, with n = 3. The recoveries ranged from 80% to 115%. According to the results one can determine the TB and CF contents with acceptable precision and accuracy in fermented and unfermented Amazonian cocoa samples with a reduced amount of residues, representing good analytical tools for the quality control of fermented cocoa and chocolate.

Development of an in vivo magnetic resonance imaging and computer modelling platform to investigate the physiological optics of the crystalline lens.

We have developed and validated in vivo magnetic resonance imaging (MRI) protocols to extract parameters (T2 and geometry) of the human lens that, combined with biometric measures of the eye and optical modelling, enable us to investigate the relative contributions made by the gradient of refractive index (GRIN) and the shape of the lens to the refractive properties of each subject tested. Seven young and healthy participants (mean age: 25.6 ± 3.6 years) underwent an ophthalmic examination, and two sessions of MRI scans using a 3 T clinical magnet. Our MRI protocols for studying lens physiological optics and geometrical measurements were repeatable and reliable, using both 1D (95% confidence interval (CI) for mean differences for exponents = [-2.1, 2.6]) and 2D analysis (anterior T2 CI for differences [-6.4, 8.1] ms; posterior T2 CI for differences [-6.4, 8.3] ms). The lens thickness measured from MRI showed good correlation with that measured with clinical 'gold standard' LenStar (mean differences = [-0.18, 0.2] mm). The predicted refractive errors from ZEMAX had reasonable agreements with participants' clinic records (mean differences = [-1.7, 1.2] D). Quantitative measurements of lens geometry and GRIN with our MRI technique showed high inter-day repeatability. Our clinical MRI technique also provides reliable measures of lens geometry that are comparable to optical biometry. Finally, our ZEMAX optical models produced accurate refractive error and lens power estimations.

Phthalate sum determination in farmland soils using high-performance liquid chromatography with tandem mass spectrometry.

A selective and low organic-solvent-consuming method of sample preparation combined with high-performance liquid chromatography and tandem mass spectrometry is introduced for phthalate sum analysis in farmland soil. Sample treatment involves a one-step hydrolysis of phthalates using methanol and alkaline and tetrabutylammonium bromide for 20min at 80℃. Then, the resulting phthalic acid in the acidified hydrolysate is extracted using an octanol-based supramolecular solvent without purification. Under optimized conditions, the correlation coefficients were 0.992-0.999 and standard errors (Sy/x ) were 0.018-0.138 for calibration curves within the range of 50-2000ng/mL. No obvious matrix effect occurred between the pure supramolecular solvent and soil extract. The recovery rates ranged from 91 to 107% with the relative standard deviation ranging from 0.5-7.3%. Intra- and interday repeatability, expressed as relative standard deviation, was less than 8.0 and 11.0%, respectively. The detected limit was 2.49nmol/g, and the quantification limit was 3.64nmol/g. Fifteen soil samples were analysed, and the background corrected phthalate sum ranged from 1.44 to 120nmol/g.

Development and Validation of a CE Method for the Determination of Tetracyclines with Capacitively Coupled Contactless Conductivity Detection

In this study, a simple and robust capillary electrophoresis method with capacitively coupled contactless conductivity detection (C4D) is developed for the determination of the tetracycline antibiotics (1) tetracycline, (2) chlortetracycline and (3) oxytetracycline. An uncoated, fused silica capillary (60.2 cm long, 75 µm i.d.) and a solution of 50 mM tris(hydroxymethyl) aminomethane, 50 mM l-histidine and 5 mM methyl-β-cyclodextrin, without pH adjustment (pH 8.76), was used as background electrolyte. Electrophoresis at + 25 kV showed a rapid analysis with sufficient resolution among the three antibiotics in the order of tetracycline, chlortetracycline and oxytetracycline. Successive inter-injection rinsing (20 psi) of the capillary ensured intra- and inter-day repeatability (0.9–2.2% RSD and 2.0–4.5% RSD, respectively, for relative peak areas). The method showed satisfactory performance in terms of selectivity, accuracy (99.3–101.4%) and linearity (R2 = 0.999). Finally, the method was applied to commercial samples of tetracycline, oxytetracycline and chlortetracycline. This method can be applied for rapid quality control in developing countries in particular, and across the globe in general.

An optimized analysis of 2‐acetyl‐1‐pyrroline content diversity in the core collection of aromatic rice germplasm (Oryza sativa L.)

AbstractBackground and objectivesAromatic rice constitutes a small but a special group of rice varieties, considered as the best in quality. A headspace solid‐phase micro‐extraction (HS‐SPME) method, combined with a gas chromatography–mass spectrometry (GC‐MS) assay, was developed to enable the rapid, simple, and reliable quantification of 2‐acetyl‐1‐pyrroline (2AP) in rice.FindingsThe most effective release of 2AP was obtained using a divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber and extracting brown flour or single whole brown grain at 80°C for 30 min. By the optimized protocol, the limit of detection (LOD) and limit of quantification (LOQ) for 2AP was 1.0 µg/kg of 2AP and 4.0 µg/kg of brown rice flour, respectively. The reproducibility and interday repeatability were &lt;5.00% RSD (n = 10) and 12.5% RSD (n = 27), respectively. A good linearity was observed from 5 to 80 ng with a good correlation coefficient (R2) value of 0.9892. When the method was applied to a collection of aromatic rice germplasm, the 2AP content in 34 entries appeared to be below the limit of detection. The mean 2AP content in the set was 0.45 mg/kg, and the range was from undetectable to 2.73 mg/kg. Most entries contained 0.09–0.46 mg/kg 2AP.ConclusionsA rapid 2AP assay of brown flour or single brown whole grain, based on HS‐SPME combined with GC‐MS, was shown to generate reproducible and reliable outputs. When applied to a set of 228 aromatic rice entries, it was able to reveal the existence of substantial variation for 2AP content.Significance and noveltyThe results of this study produced an accurate, rapid, and highly reproducible assay, which are suitable for the screening of large numbers of samples and the helping of aromatic rice breeding.

Exploring the exocellular fungal biopolymer botryosphaeran for laccase-biosensor architecture and application to determine dopamine and spironolactone

Laccase was immobilized on a glassy carbon electrode layered with multi-walled carbon nanotubes using a film of botryosphaeran, a fungal (1 → 3)(1 → 6)-β-D-glucan. This novel biosensing platform was characterized by electrochemical impedance spectroscopy and scanning electron microscopy, and applied for the determination of dopamine. Experimental variables such as enzyme concentration, pH value and operational parameters of the electroanalytical technique were optimized. Using square-wave voltammetry, there was a linear dependence of peak current and dopamine concentration within the range of 2.99–38.5 μmol L−1 with a limit of detection of 0.127 μmol L−1. The biosensor was successfully applied in the determination of dopamine in pharmaceutical injection and synthetic biological samples, and presented good selectivity even in the presence of uric acid and ascorbic acid, as well as other phenolic compounds. The different aspects regarding the operational stability of the laccase biosensor were evaluated, demonstrating good intra-day and inter-day repeatability, and long-storage stability. Furthermore, this biosensor was evaluated in the indirect determination of spironolactone by using the analytical signal of dopamine, presenting a limit of detection of 0.94 μmol L−1. The results obtained in the analysis of spironolactone in commercial pharmaceutical samples were satisfactory.

Nickel oxide/chitosan nano-composite as a magnetic adsorbent for pre-concentration of Zn(II) ions

Abstract In this work, a magnetic nickel oxide/chitosan nanocomposite was fabricated by a facile precipitation approach. The structure and morphological properties of the prepared nano-material were characterized via X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The prepared nanocomposite was used as a nano-sorbent for the magnetic solid-phase extraction (MSPE) of the trace amounts of zinc (Zn(II)) ions from aqueous solutions followed by flame atomic absorption spectrometric (FAAS) detection. Several factors influencing the extraction efficiency of Zn(II) ions such as pH, extraction time, amount of the nano-sorbent, elution conditions and sample volume were investigated and optimized. Under optimized conditions, the calibration curve with a liner dynamic range of 0.35–15 ng mL−1 was attained. The preconcentration factor and limit of detection were 100 and 0.12 ng mL−1, respectively. The method precision was evaluated with seven replicates at the concentration level of 5 ng mL−1 and the relative standard deviations of 2.8% and 3.1% were obtained for intra-day and inter-day repeatability, respectively. The applicability of the developed MSPE-FAAS method for the measurement of Zn(II) ions was validated by analyzing the certified reference material NIST SRM 1549. Zinc(II) ion concentration was measured in various real samples including tap water, river water, well water, milk and powder milk using the method, and satisfactory relative recovery values were acquired for the spiked samples.

Determination of major components from Radix Achyranthes bidentate using ultra high performance liquid chromatography with triple quadrupole tandem mass spectrometry and an evaluation of their anti-osteoporosis effect in vitro.

Ecdysterone and saponins are the most characteristic components of Radix Achyranthes bidentate, which acts on the human body to promote collagen synthesis and stimulates cell growth. However, the relationship between these components and the differentiation of MC3T3-E1 osteoblastic cells is unknown. We developed a rapid ultra high performance liquid chromatography with triple quadrupole tandem mass spectrometry method for direct determination of one ecdysterone and four saponins in crude and salt-processed Radix Achyranthes bidentate. The method was interrogated in terms of linearity, intra- and inter-day precision, repeatability, stability and recovery. The method was linear within the concentration ranges of 0.003-336 μg/mL for β-ecdysterone, 0.0035-130 μg/mL for 25S-inokosterone, 0.004-423 μg/mL for ginsenoside Ro, 0.0036-66 μg/mL for chikusetsusaponin IV and 0.0044-111 μg/mL for chikusetsusaponin IVa. The intra- and inter-day precisions were all within 2.7%. The standard addition method determined recovery rates for each component (98.7-102.5%). The method was successfully applied to simultaneously quantify five components in ten batches of crude and salt-processed Radix Achyranthes bidentate. Subsequently, the examination of these extracts on the differentiation of MC3T3-E1 osteoblastic cells were carried out. Finally, the relationships between the contents of five components and their anti-osteoporosis effect were investigated by using canonical correlation analysis.

Laccase stabilized on β-D-glucan films on the surface of carbon black/gold nanoparticles: A new platform for electrochemical biosensing

In this study, (1→3)(1→6)-β-D-glucan (botryosphaeran) from Botryosphaeria rhodina MAMB-05 was used, for the first time, to immobilize laccase on a carbon black paste electrode modified with gold nanoparticles. The physicochemical characterization of the proposed laccase-biosensor was performed using transmission electron microscopy and electrochemical impedance spectroscopy. The performance of this novel bio-device was evaluated by choosing hydroquinone as a typical model of a phenolic compound. For hydroquinone determination, experimental variables such as enzyme concentration, pH and operational parameters of the electroanalytical technique were optimized. From square-wave voltammograms, a linear dependence between the cathodic current peak and the hydroquinone concentration was observed within the range 2.00–56.5μmolL−1, with a theoretical detection limit of 0.474μmolL−1. The proposed method was successfully applied to determine hydroquinone in dermatological cream, and samples from biological and environmental niches. The proposed biosensor device presented good selectivity in the presence of uric acid, various inorganic ions, as well as other phenolic compounds, demonstrating the potential application of this biosensing platform in complex matrices. Operational and analytical stability of the laccase biosensor were evaluated, and demonstrated good intra-day (SD=0.3%) and inter-day (SD=3.4%) repeatability and long storage stability (SD=4.9%).

Multiresidue Pesticides Analysis of Vegetables in Vietnam by Ultrahigh-Performance Liquid Chromatography in Combination with High-Resolution Mass Spectrometry (UPLC-Orbitrap MS).

An ultrahigh-performance liquid chromatography in combination with high-resolution mass spectrometry Thermo Q-Extractive Focus Orbitrap MS has been introduced for analysis of multiclass pesticides in vegetable samples collected in Hanoi, Vietnam. Multiclass pesticides were separated on the Thermo Hypersil Gold PFP column utilizing a gradient of the mobile phase consisting of 5 mM ammonium formate, 0.1% formic acid in deionized water, and methanol. The target analytes were detected in the full-scan mode on Thermo Scientific Q-Exactive Focus Orbitrap MS for quantitation at the optimum operating conditions. These conditions included, but not limit to, the resolution of 70000 at the full width at half maximum in both positive and negative mode, mass range from 80 to 1000 m/z, and optimized parameters for the heated electrospray ionization source. The identification of the analytes in real samples was based on retention times, mass to charge ratios, mass accuracies, and MS/MS spectra at the confirmation mode with the inclusion list of target analytes. The mass accuracies of target analytes were from −4.14 ppm (dinotefuran) to 1.42 ppm (cinosulfuron) in the neat solvent and from −3.91 ppm (spinosad D) to 1.29 ppm (cinosulfuron) in the matrix-matched solution. Target analytes in the vegetable-based matrix were extracted by the QuEChERS method. Some critical parameters of the analytical method such as linearity, repeatability, limit of detection, and limit of quantitation have been evaluated and implemented. Excellent LOD and LOQ of the developed method were achieved at the range of 0.04–0.85 and 0.13–2.9 μg·kg−1, respectively. Intraday and interday repeatability of the analytical signal (peak area, n=6) of the developed method were below 3% and 10%, correspondingly. The matrix effect, extraction recovery, and overall recovery were fully investigated by spiking experiments. Experimental results demonstrated that the ionization suppression or enhancement was the main contribution on the overall recoveries of target analytes. Finally, the in-house validated method was applied to pesticides screening in vegetables samples in local villages in Hanoi, Vietnam. The concentrations of all target analytes were below limit of quantitation and lower than US-FDA or EU maximum residue levels.

Voltammetric sensor based on cobalt-poly(methionine)-modified glassy carbon electrode for determination of estriol hormone in pharmaceuticals and urine

A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine) (Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse voltammetry (DPV) for the first time. The electrochemical properties of the Co-poly(Met)/GCE were analysed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the polymers on the GCE surface. The deposition of the Co-poly(Met) film on the GCE surface enhanced the sensor electronic transfer. CV studies revealed that estriol exhibits an irreversible oxidation peak at +0.58 V for the Co-poly(Met)/GCE (vs. Ag/AgCl reference electrode) in 0.10 mol/L Britton-Robinson buffer solution (pH = 7.0). Different voltammetric scan rates (10–200 mV/s) suggested that the estriol oxidation on the Co-poly(Met)/GCE surface is controlled by adsorption and diffusion processes. Based on the optimized DPV conditions, the linear responses for estriol quantification were from 0.596 μmol/L to 4.76 μmol/L (R2 = 0.996) and from 5.66 μmol/L to 9.90 μmol/L (R2 = 0.994) with a limit of detection (LOD) of 0.0340 μmol/L and a limit of quantification (LOQ) of 0.113 μmol/L. The DPV-Co-poly(Met)/GCE method provided good intra-day and inter-day repeatability with RSD values lower than 5%. Also, no interference of real sample matrices was observed on the estriol voltammetric response, making the DPV-Co-poly(Met)/GCE highly selective for estriol. The accuracy test showed that the estriol recovery was in the ranges 96.7%–103% and 98.7%–102% for pharmaceutical tablets and human urine, respectively. The estriol quantification in pharmaceutical tablets performed by the Co-poly(Met)/GCE-assisted DPV method was comparable to the official analytical protocols.

Repeatability of spinal reflexes of lower limb muscles evoked by transcutaneous spinal cord stimulation.

Transcutaneous electrical stimulation is a relatively new technique to evoke spinal reflexes in lower limb muscles. The advantage of this technique is that the spinal reflex responses can be obtained from multiple lower limb muscles simultaneously. However, repeatability of spinal reflexes evoked by transcutaneous spinal cord stimulation between days has not been evaluated. We aimed to examine repeatability of recruitment properties of the spinal reflexes evoked by transcutaneous spinal cord stimulation. Recruitment curves of the spinal reflexes evoked by transcutaneous spinal cord stimulation of 8 lower limb muscles (i.e., foot, lower leg, and thigh muscles) of 20 males were measured on two consecutive days. To confirm that responses were caused by activation of the sensory fiber, a double-pulse stimulation with 50 ms inter-pulse interval was delivered. Peak-to-peak amplitude of the first response was calculated for each muscle when no response was observed in the second response owing to post-activation depression. For comparison with the spinal reflexes evoked by transcutaneous spinal cord stimulation, the recruitment curves of the H-reflex amplitude of the soleus of 9 males were measured. Threshold intensity and maximal slope of the recruitment curves were calculated, and inter-day repeatability of the properties was quantified using intraclass correlation coefficients. For the spinal reflexes evoked by transcutaneous spinal cord stimulation, the intraclass correlation coefficient values of threshold intensity and maximal slope for each muscle ranged from 0.487 to 0.874 and from 0.471 to 0.964, respectively. Regarding the soleus H-reflex, the intraclass correlation coefficients of threshold intensity and maximal slope were 0.936 and 0.751, respectively. The present data showed that repeatability of the recruitment properties of the spinal reflexes evoked by transcutaneous spinal cord stimulation in the lower limb was moderate to high. Measurement of the spinal reflexes evoked by transcutaneous spinal cord stimulation would be useful for longitudinal neurophysiological studies.

A Novel Method to Characterise Levels of Pharmaceutical Pollution in Large-Scale Aquatic Monitoring Campaigns

Much of the current understanding of pharmaceutical pollution in the aquatic environment is based on research conducted in Europe, North America and other select high-income nations. One reason for this geographic disparity of data globally is the high cost and analytical intensity of the research, limiting accessibility to necessary equipment. To reduce the impact of such disparities, we present a novel method to support large-scale monitoring campaigns of pharmaceuticals at different geographical scales. The approach employs the use of a miniaturised sampling and shipping approach with a high throughput and fully validated direct-injection High-Performance Liquid Chromatography-Tandem Mass Spectrometry method for the quantification of 61 active pharmaceutical ingredients (APIs) and their metabolites in tap, surface, wastewater treatment plant (WWTP) influent and WWTP effluent water collected globally. A 7-day simulated shipping and sample stability assessment was undertaken demonstrating no significant degradation over the 1–3 days which is typical for global express shipping. Linearity (r2) was consistently ≥0.93 (median = 0.99 ± 0.02), relative standard deviation of intra- and inter-day repeatability and precision was &lt;20% for 75% and 68% of the determinations made at three concentrations, respectively, and recovery from Liquid Chromatography Mass Spectrometry grade water, tap water, surface water and WWTP effluent were within an acceptable range of 60–130% for 87%, 76%, 77% and 63% of determination made at three concentrations respectively. Limits of detection and quantification were determined in all validated matrices and were consistently in the ng/L level needed for environmentally relevant API research. Independent validation of method results was obtained via an interlaboratory comparison of three surface-water samples and one WWTP effluent sample collected in North Liberty, Iowa (USA). Samples used for the interlaboratory validation were analysed at the University of York Centre of Excellence in Mass Spectrometry (York, UK) and the U.S. Geological Survey National Water Quality Laboratory in Denver (Colorado, USA). These results document the robustness of using this method on a global scale. Such application of this method would essentially eliminate the interlaboratory analytical variability typical of such large-scale datasets where multiple methods were used.

Novel electrochemical strategy for determination of 6-mercaptopurine using anodically pretreated boron-doped diamond electrode

A novel electrochemical approach for 6-mercaptopurine (6-MP) determination employing an anodically pretreated boron-doped diamond electrode (AP-BDDE) is presented herein. The electrode reaction of 6-MP on AP-BDDE (AP achieved by application of +3V for 180s in 1M H2SO4) was represented by three well distinguished oxidation peaks at +0.25V, +1.19V and+1.63V (P1-P3) and one reduction peak at +0.11V (vs. Ag/AgCl/3M KCl) in Britton-Robinson buffer with pH2. More detailed study revealed a mixed adsorption and diffusion-controlled reaction mechanism of the analyte. Differential pulse voltammetry (DPV), adapting favorable working conditions found by cyclic voltammetry, was developed for the sensitive determination of 6-MP. A possibility to analyze three baseline separated peaks provided valuable selectivity enhancement of the method. The overall best analytical performance was achieved for the third oxidation peak (P3), which offered the highest sensitivity (30.4nA/μM) and the widest linear concentration range (1–450μM with two independent linear segments, R2=0.997). Submicromolar detection limit (0.51μM) and intra-day and inter-day repeatability (RSD=0.38 and 1.91%, respectively) underlined favorable performance of the developed method. The applicability of the proposed method was illustrated by the analysis of pharmaceutical dosages containing 6-MP and spiked human urine, with an excellent average recovery of 101.8% and 95.9%, respectively. Clearly, the combination of an innovative electrode material (BDD) and sensitive voltammetric technique (DPV) established a simple and highly reliable alternative to chemically modified electrodes that might be advantageous in routine pharmaceutical and clinical analysis.

Clothianidin residues in green bean, pepper and watermelon crops and dietary exposure evaluation based on dispersive liquid-liquid microextraction and LC–MS/MS

We developed an analytical method for quantifying clothianidin residues in green bean, pepper and watermelon crops using dispersive liquid-liquid microextraction (DLLME) and liquid chromatography-tandem mass spectrometry; this method was more rapid, sensitive and simple than QuEChERS sample preparation. Method validation indicated that the recovery for clothianidin was 80.8–93.1%, intra-day and inter-day repeatability ranged from 3.32 to 6.11% and 7.77 to 14.74%, respectively, limits of detection ranged from 0.64 to 0.74 µg/kg, and limits of quantification were 2.13–2.47 µg/kg. Matrix-matched calibration was used to compensate for matrix effects. Following application of the recommended dose in field trials, clothianidin dissipation followed first-order kinetics with half-lives of 1.9, 2.07, and 1.87 days in green bean, pepper, and watermelon crops; respective waiting periods of 5.76, 6.18, and 7.87 days after application are suggested for safe consumption. This study indicates the application of clothianidin presents no significant health risk to Egyptian consumers.

Simple and rapid method to analyse squalene in olive oils and extra virgin olive oils

Olive oil is one of the main vegetable sources of squalene, substance with several interesting properties and applications. This work aims to present and validate a rapid method to quantify squalene in olive oil by gas chromatography (GC) coupled with flame ionization detector and to apply the method to extra virgin olive oils (EVOOs) and olive oils (OOs) from large scale distribution retail, and to some EVOOs from little companies productions (Italian monovarietal Leccino and Frantoio EVOOs, and niche blend Italian EVOOs). A transmethylation of the oil sample is exploited to allow the direct GC analysis avoiding the separation from saponifiable fraction. The optimized conditions provide high sensitivity, short time (total GC run time is 5 min and about 10 min are needed for sample preparation) and require instruments and materials usually available in most of the laboratories. The method was validated by determining linearity, intraday and interday repeatability, recovery, limit of detection and limit of quantification. Within EVOOs investigated, the niche blend EVOO contained significantly higher amount (P < 0.05) of squalene (0.81–1.02 g/100 g) as compared to each of the other EVOOs groups investigated (monovarietal Leccino and Frantoio EVOOs and EVOOs from large scale distribution retail) containing a squalene concentration in the range 0.31–0.65 g/100 g; in OOs, the content, 0.17–0.27 g/100 g, was significantly lower (P < 0.05) as compared to EVOOs.

Sub-1 mL sample requirement for simultaneous determination of 17 organic and inorganic anions and cations in Antarctic ice core samples by dual capillary ion chromatography

The significant advance of delivering high value multi-species data from sub-1 mL ice core sample volumes allows higher temporal resolution in deposition records of inorganic and low molecular weight organic anions and cations. The determination of these species is a fundamental strategic requirement in modern paleoclimate studies. Herein, for the first time, a dual capillary ion chromatography (Cap-IC) based method for the simultaneous separation of 17 organic and inorganic anions and cations in low volume Antarctic ice core samples is presented. The total amount of sample required for direct injection has been reduced to 190 μL, which is 35 times lower than the amount of sample required by standard ion chromatography methods. A dual Cap-IC system configured for the simultaneous determination of cations and anions was used throughout. A range of chromatographic parameters was optimised for both anion and cation systems to obtain baseline separations of all target analytes in a suitable run time and to minimise the amount of sample required. Baseline separation of matrix and trace ‘marker’ ions were achieved in less than 35 min, after injecting only 40 μL of sample in each IC system. Limits of detection (LODs) for all analytes determined were within a range similar to that achieved by previously published standard bore IC-based methods. Intra- and inter-day repeatability were evaluated, with both parameters being typically below 3% for peak area. In further validation of the method, a comparative analysis of a set of 420 ice core samples from Aurora Basin North site, Antarctica, previously analysed by standard IC, established that the proposed low sample volume technique was applicable as a routine measurement approach in ice core analysis projects.