Limits Of Qualification Research Articles

Two-dimensional Ni/Co bimetal pyrophosphate nanosheets for sensitive electrochemical detection of phenol

As a priority pollutant in many regions, phenol in environment may cause severe damage to human health and ecosystem. For the simultaneous detection of phenol in environment, a novel electrochemical sensor has been constructed in this work based on the 2D nickel cobalt pyrophosphate (denoted as NCppi) nanosheets modified glass carbon electrode (GCE). The nickel cobalt pyrophosphate was prepared by a facile hydrothermal method. The prepared 2D nickel cobalt pyrophosphate nanosheet was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The bimetal nickel cobalt pyrophosphate exhibited favorable catalytic activity in phenol detection. The excellent sensing performance of nickel cobalt pyrophosphate was attributed to its charge transfer mobility and abundant catalytic sites. The nickel cobalt bimetal pyrophosphate was applied to modify glass carbon electrode (denoted as NCppi/GCE) and the obtained sensor processed satisfactory analytic performance in practical detection of phenol. Cyclic voltammetry (CV) was employed to characterize electrochemical behavior of modified GCE and bare GCE in 100 μM phenol solution. Electrochemical impedance spectroscopy (EIS) and CV were employed to characterize the charge transfer process and redox nature of different electrodes in 4 mM Fe(CN)63-/4- containing 0.1 M KCl. Square wave voltammetry (SWV) was employed to detect phenol in 0.2 M phosphate buffer solution (pH=7.0). The fabricated electrochemical sensor with optimized Ni/Co ratio also exhibited a limit of detection (LOD) of 0.25 μM, a limit of qualification (LOQ) of 0.45 μM and a linear range of 0.5–100 μM with a sensitivity of 0.0269 μA/μM using square wave voltammetry (SWV) toward phenol. Besides, the electrochemical sensor showed desirable selectivity. In standard addition test of tap water sample from Longwangzui Water Plant and river water from Xunsi River, the sensor displayed reliable recoveries. The electrochemical sensor still maintained 87.5% current response after 3-week storage. The GCE was 50 $ and the cost of catalytic ink could be ignored. The active surface area of NCppi/GCE was 0.12 cm2.

Mulberry Juice-Derived Carbon Quantum Dots as a Cu2+ Ion Sensor: Investigating the Influence of Fruit Ripeness on the Optical Properties

This study synthesized carbon quantum dots (CQDs) with green photoluminescence through a hydrothermal method that utilized mulberry juice as the carbon source. The influence of fruit ripeness on the physical and chemical properties, focusing on the fluorescence spectra, has been explored. Fourier-transform infrared spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX) showed that there were oxygen-containing groups, and X-ray diffraction (XRD) showed that the carbon quantum dots (CQDs) were graphitic. The results revealed that the CQDs had an average size of around 7.4 nm and 9.7 nm for unripe and ripe mulberry juice, respectively. These CQDs emitted green light at 500 nm and 510 nm in unripe and ripe mulberry juice, respectively, when excited at a wavelength of 400 nm. The prepared CQDs exhibited excitation-dependent photoluminescence (PL) emission behavior, demonstrating their dependence on the excitation light. The impact of fruit ripeness on optical properties was explored by examining fluorescent spectra from different fruits (including tomato and blackberry), demonstrating comparable behaviors observed in mulberry fruit. In addition, the prepared CQDs were utilized as a fluorescent sensor with high specificity to detect Cu2+ ions. The detection limit (DL) for this sensor was determined to be 0.2687 µM, and the limit of qualification (LOQ) is 0.814 µM. The linear range for detection lies between 0.1 and 1 µM. The selectivity of the CQDs towards Cu2+ ions was confirmed by recording the PL response for Cu2+ ions compared to the weak response of other metal ions. According to these results, the CQDs can be applied in various cellular imaging and biology applications, bio-sensing, optoelectronics, and sensors.

Construction of a magnetic solid-phase extraction method for the analysis of azole pesticides residue in medicinal plants

In this work, a sensitive and cost-effective method for the quantitative analysis of azole pesticides residues in six medicinal plants was established based on magnetic cyclodextrin crosslinked with tetrafluoroterephthalonitrile (Fe3O4@TFN-CDPs) coupled with high-performance liquid chromatography (HPLC). Through characterization analysis, the outer shell of Fe3O4@TFN-CDPs has observed coating with a network of the polymer and forming a core–shell structure. Under the optimum conditions, the limits of detection (LODs) and limits of qualification (LOQs) of target pesticides were ranged from 0.011 to 0.106 µg Kg−1 and from 0.036 to 0.354 µg Kg−1, respectively. Finally, the achieved recoveries of pesticides in six medicinal samples fluctuated from 60.1% to 102.3%. Altogether, this method based on Fe3O4@TFN-CDPs composites provided a new idea for the analysis of trace pesticides in complicated matrices.

Electrospun Polyacrylonitrile as a New Coating for Mechanical Stir Bar Sorptive Extraction of Polycyclic Aromatic Hydrocarbons from Water Samples

A polyacrylonitrile (PAN) coating was fabricated by electrospinning technique for using as a new extraction phase in mechanical stir bar sorptive extraction (MSBSE). The setup coupled with gas chromatography (GC) was proposed and applied for the extraction and determination of some low molecular weight polycyclic aromatic hydrocarbons (PAHs) in water samples. The effective parameters on the extraction process were optimized by the response surface methodology (RSM) based on the central composite design (CCD). Under the optimum conditions, the limits of detection (LOD) and limits of qualification (LOQ) were 0.008–0.4 ng mL−1 and 0.02–1.3 ng mL−1, respectively. The relative standard deviations (RSDs) for the analytes, including acenaphthene (Ace), anthracene (Ant), naphthalene (Nap) and phenanthrene (Phe), was less than 12.7%. The relative recoveries (RRs) were above 94%. The extraction of the analytes by the MSBSE coated with PAN consumed about 256 kWh m−3 of electric energy. The coating can be used 200 times without significant changes in its performance because of hydrophobicity and the high mechanical strength of PAN. The proposed approach to improve SBSE for extracting PAHs from water samples is cost-effective and time-efficient because the introduced coating can be fabricated in a short time and by inexpensive raw materials.

Neutral polyfluoroalkyl and perfluoroalkyl substances in surface water and sediment from the Haihe River and Dagu Drainage Canal deserve more attention.

Neutral polyfluoroalkyl and perfluoroalkyl substances (nPFASs) were detected in the surface water and sediment from the Haihe River (HR) and Dagu Drainage Canal (DDC), Tianjin, China. N-methyl perfluorooctane sulfonamide ethanol (MeFOSE) and N-ethyl perfluorooctane sulfonamide ethanol (EtFOSE) were the predominant nPFASs in surface water and sediment, which was different from the composition in air. The concentrations of ΣnPFASs in water from the HR (1.88-8.21 ng/L) were lower than those from the DDC (3.72-11.32 ng/L). Concentrations of ΣnPFASs were higher in the middle of the HR in the Dongli District due to industrial activity, whereas at lower reaches of the DDC, high ΣnPFAS concentrations might be due to effluent from wastewater treatment plants (WWTPs). The detection frequency in sediment (13.5%) was less than that in water (83%). The concentrations in sediment from the DDC (below limit of qualification (LOQ) to 5.58 ng/g) were higher than those from the HR (below LOQ to 2.46 ng/g). The distribution coefficient (log KD) between water and sediment was calculated, and they were highly related to the compound structures. The contribution of nPFASs to nPFASs+PFAAs was up to 52% in sediment in the DDC, suggesting the importance of nPFASs in aquatic systems.

Quantification of Dopamine in Brain Microdialysates with High-Performance Liquid Chromatography-Tandem Mass Spectrometry.

The dopamine level in the brain and the mesolimbick dopaminergic system are responsible for nicotine addiction. In the present study, extracellular dopamine in nucleus accumbens was collected by a brain microdialysis technique. Also a sensitive high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method with a gradient elution procedure was developed for a precise determination of dopamine in brain dialysate. The retention time of dopamine was about 11.32 min. The linear range was 20 - 1000 pg/mL. The limit of detection (LOD) and the limit of qualification (LOQ) were 5 and 20 pg/mL, respectively. The recovery ranged from 98.2 to 109.0%, and both the intra-RSD and inter-RSD were below <9%, respectively. The probe recovery for dopamine in this brain microdialysis experiment was about 25%. Finally, the dopamine concentrations in the rat brain microdialysates were determined, and the pharmacokinetics of extracellular dopamine in the brain nucleus accumbens after an intravenous injection of nicotine was successfully evaluated.

Simultaneous determination of biotoxins DSP and AZAs in bivalve molluscs and fish by liquid chromatography/tandem mass spectrometry.

A method has been developed for simultaneous determination of the toxins OA, DTX-1, AZA-1, AZA-2 and AZA-3 in various aquatic products as these can cause diarrhoetic shellfish poisoning (DSP) in humans, an intoxication characterized by vomiting and diarrhea. Separation of the toxins was achieved on a C18 column (150 mm × 2.1 mm, 3.5 µm) using an acetonitrile/water gradient with formic acid as an eluent modifier. Electrospray ionisation (ESI) in negative mode was used to generate the molecule related ion [M-H](-), for OA and DTX-1, while ESI in positive mode was used to generate the molecule related ion [M+H](+) for AZAs. Samples were extracted with 80% methanol, followed by partitioning with ethyl acetate, purified on a Poly-Sery MAX cartridge and finally analyzed by LC/ESI-MS/MS in the multiple reaction monitoring (MRM) mode. The limit of detection (LOD) and limit of qualification (LOQ) of the method were in the range of 0.02-0.79 µg/kg and 0.07-2.64 µg/kg in Scomberomorus niphonius, blood clam and oyster, respectively, recoveries of the toxins at three fortification levels ranged from 71.3% to 104.8% with relative standard deviation from 1.0% to 12.5%. The calibration curves were well linear between the LC peak area of the selected ion pair and the concentration of the toxins, with the correlation coefficient over 0.99. The method was sufficiently sensitive to permit the determination of the toxins DSP and AZA in sea food.

Simultaneous Determination of 23 Prohibited Drugs in Swine Urine by Liquid Chromatography Tandem Mass Spectrometry

A liquid chromatography-electrospray ionization tandem mass spectrometric(LC-ESI-MS/MS) method was developed for the simultaneous determination of 23 forbidden drugs including β-agonists,steriods,nitroimidazoles,sedatives etc.in swine urine.The samples were freeze-dried under vacuum and then dissolved with 10% methanol in water containing 0.1% formic acid,followed by cleanup and enrichment using Anpel MCX solid phase extraction cartridge.Qualitative and quantitative analysis was achieved for the analytes under the multiple reaction monitoring(MRM) mode after the chromatographic separation on a CNW Athena C18(150 mm × 2.1 mm i.d.,5 μm) column.Matrix-matched calibration curves with good correlation coefficients(r0.99) were obtained in the concentration range of 0.5-100 μg/L.The limits of detection(LODs) and the limits of qualification(LOQs) for the 23 compounds were in the range of 0.5-4.0 μg/L(S/N3) and 1.0-10 μg/L(S/N10),respectively.The mean recoveries at the four spiked levels of 1.0-50 μg/L were between 50.2% and 97.9% with the intra-day relative standard deviation(RSD) less than 10% and inter-day RSD less than 18%.The proposed method was successfully used to detect 23 banned drugs in 200 swine urine samples,two of them contained clenbuterol,with the concentrations of 4.45 and 2.16 μg/L,respectively.

Simultaneous determination of ferulic acid, hesperidin, 6-gingerol and glycyrrhizin in Insampaedok-san by HPLC coupled with diode array detection

For the simultaneous determination of ferulic acid, hesperidin, 6-gingerol and glycyrrhizin in Insampaedok-san, one of traditional oriental medicine prescription, a high performance liquid chromatography (HPLC) analytical method was developed. The separation was achieved on a SHISEIDO C18 column (S-5 μm, 4.6 mm I.D. × 250 mm). The mobile phase consisted of water with 0.1% trifluoroacetic acid and methanol in gradient elution at a flow rate of 1.0 mL/min. The UV wavelength was set at 250, 280 and 320 nm. The method was validated for linearity, precision and recovery. All calibration curves showed good linear regression (r 2 > 0.9994) over the wide test ranges. LOD (limit of detection) and LOQ (limit of qualification) ranged from 0.02 to 0.14 μg/mL and 0.05 to 0.42 μg/mL, respectively. The relative standard deviation (RSD) of the intra- and inter-day test, precision test were within 2.26 and 2.45%, respectively, with accuracy from 95.95 to 108.22%. The recoveries of the four compounds were obtained between 94.30 and 106.34% with RSD less than 1.96%. The verified method was successfully applied to quality control of Insampaedok-san.