Slope Of Calibration Curve Research Articles

Electrochemical detection of fentanyl with screen-printed carbon electrodes using square-wave adsorptive stripping voltammetry for forensic applications

Square-wave adsorptive stripping voltammetry (SWAdSV) is proposed as a fast, simple, and sensitive approach toward the detection, identification, and semi-quantitation of fentanyl in seized drug samples using screen-printed carbon electrodes. Electrochemical oxidation of fentanyl resulted in the formation of two anodic peaks, one at 0.75 V (peak I) and the second at 0.88 V (peak II) versus a Ag/AgCl pseudo reference electrode. Voltammetric measurements were conducted under optimized experimental conditions using fentanyl standards ranging from 0.076 μg/mL to 6.9 μg/mL, which resulted in a limit of detection of 0.037 μg/mL. Reproducibility was assessed as the average percent relative standard deviation of the slopes of calibration curves and was 2.6% for oxidation peak I and 7.4% for oxidation peak II in cell. Detection capabilities were assessed in a 5-mL cell and in a 100 microliter drop. Interference studies were conducted with cocaine, methamphetamine, quinine, caffeine, and acetaminophen. The mechanism for the electrochemical oxidation of fentanyl to norfentanyl is also described. Accuracy and suitability of the method for seized drug analysis was assessed using 11 simulated samples. Suitability of the method for future analysis of fentanyl in oral fluid was assessed.

Detection of L-Tyrosine by electrochemical method based on binary mixed CdO/SnO2 nanoparticles

Abstract Here, the nanoparticles (NPs) of CdO/SnO2 were prepared by co-precipitation method in alkaline phase at low temperature. The characterization of CdO/SnO2 NPs were analyzed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analysis. To fabricate the sensor, glassy carbon electrode (GCE) was coated by CdO/SnO2 NPs with 5% nafion suspension. The resulted sensor was applied to detect L-Tyrosine (L-Tyr) in buffer phase. A linear relation current versus concentration known as calibration curve was made. The sensor sensitivity (11.848 µA µM−1 cm−2) is calculated from the slope of calibration curve. Recognizing the maximum linear region in calibration curve (regression coefficient R2 = 0.99), the linear dynamic range (0.1 nM–0.01 mM) is used. Finally, the lower limit of detection (97.93 ± 4.89 pM) is estimated by applying the signal to noise ratio of 3 from the calibration curve. During the sensing performances, it was found as reliable, reproducible and long-term stable sensor and validated to detect the real biological samples by electrochemical approach in room conditions.

Determining the density of liquid using gamma scattering method

This study proposes an approach to determine the density of a liquid based on the gamma scattering method. The liquids used to determine density were poured in a cylindrical tube. This approach requires that the ratio R (the ratio of area under a single scattering peak for a liquid to that for water) increase linearly with an increase in the density of the liquid. In a certain range of density, a linear relationship was obtained between the ratio R and density, as described by a linear calibration curve with coefficients of slope and intercept, for the investigated tube diameters. In particular, the values of the slope and intercept could be expressed as mathematical functions of the diameter of the tube. For a given tube, the coefficients of slope and intercept of the linear calibration curve were obtained based on these functions, which helped determine the density of the liquid. The reliability of the proposed approach was evaluated by using it to calculate the densities of five liquids—n-hexane, diethyl ether, acetonitrile, toluene, and glycerol—using tubes with inner diameters of 1.8 cm, 2.25 cm, and 2.68 cm. The results show that the maximum relative deviation between the reference and the measured densities was 4.3%.

Selective and sensitive 4-Aminophenol chemical sensor development based on low-dimensional Ge-doped ZnO nanocomposites by electrochemical method

The present study aims to fabricate and investigate the germanium-doped zinc oxide (Ge/ZnO) composite nanoparticles (NPs) coated gassy carbon electrode (GCE) sensor by electrochemical method. The performances including sensitivity, stability, lower detection limit, reliability, and reproducibility were evaluated in details at room conditions. Electrochemical method was employed to deposit Ge/ZnO NPs on flat GCE in the presence of 5% nafion (conducting binders) for fabricating the sensor matrix, which exhibited the fast response towards hazardous 4-Aminophenol (4AP) chemical. UV/vis, FT-IR, EDS, XRD, FESEM, and XPS were used to characterize the prepared Ge/ZnO NPs. Electrochemical method is employed to investigate the current response in detecting 4AP chemical at room conditions. Results show that the current response of Ge/ZnO NPs coated GCE sensor precisely changes, which directly depended on the target concentration as well as the type of the target analyte existed in solution. The sensitivity and detection limit are calculated from the slope of calibration curve by considering the active surface area of fabricated electrode, which are found as 0.5063 µA cm−2 µM−1 and 0.5925 ± 0.02 nM respectively. The measured performances are found to be good and in some cases, better than those of other sensor materials reported in literatures. The developed chemical sensors could be efficiently applied to detect the phenolic derivatives for green environment by ensuring safety in broader scales.

Evaluation of matrix effect in one-dimensional and comprehensive two-dimensional liquid chromatography for the determination of the phenolic fraction in extra virgin olive oils.

Olea europaea, meaning "European olive," is asmalltreebelonging to thefamilyOleaceae, occurring in theMediterranean Basin. Olive oil is an essential component of a balanced diet because of its nutritional value. Among micronutrients, phenolic compounds did show important beneficial effects for human health. The majority of the research studies on the phenol content are carried out by liquid chromatography combined to photodiode array and/or mass spectrometry detection; however, because of matrix complexity, one-dimensional liquid chromatography cannot be sometimes sufficient to obtain rewarding separations, requiring more advanced analytical techniques. In this work, comprehensive two-dimensional liquid chromatography, incorporating RP-Amide and C18 stationary phases, in the first and second dimension, respectively, both under reversed phase conditions, was investigated for the determination of the phenolic fraction in extra virgin olive oil samples. As far as detection is concerned, triple quadrupole mass spectrometry was employed under multi reaction monitoring mode offering superior selectivity and sensitivity. The reduction of matrix effects, when using comprehensive two-dimensional liquid chromatography with respect to conventional one-dimensional liquid chromatography, was assessed by comparing the slopes of calibration curves built from standard solutions and spiked olive oil samples.

Evaluation of a carbon ink chemically modified electrode incorporating a copper-neocuproine complex for the quantification of antioxidants

A feasibility study on the use of a carbon ink chemically modified electrode to quantify antioxidants, containing [Cu(Nc)2](NO3)2. First, [Cu(Nc)2](NO3)2 was prepared and characterized, to demonstrate similarity with electrochemical response of CUPRAC solution. Then, the Chemically Modified Electrode (CME) was prepared with [Cu(Nc)2](NO3)2 and it was used to determine the total antioxidant content (TAC), employing Trolox, as a variation of the CUPRAC methodology in order to provide an alternative to the original methodology, which requires the preparation of several precursor solutions. CME also demonstrated reproducible results in the quantification of TAC for different antioxidants, where the anodic peak current of the cyclic voltammograms of the adsorbed [Cu(Nc)2]2+ showed a linear correlation with the antioxidant concentration. Those results resemble results obtained in CUPRAC solution, the characteristic calibration curve slopes can also be employed to determine the relative number of exchanged electrons. Analytical performance of the prepared CME referred to Trolox as probe lead to the following parameters: quantification limit of 2.10 × 10−4 mol L-1; detection limit of 6.29 × 10-5 mol L-1; and a linear range of 2.10–77.4 (x 10−4) mol L-1. Finally, analytical performance of this CME was also evaluated with Ascorbic Acid and Catechin as sample antioxidants. TAC determinations were performed in tea samples and the results were comparable to those obtained using the conventional spectrophotometric CUPRAC method. Obtained results suggest that this CME can be reused in consecutive determinations, as long as a previous calibration curve is prepared for the electrode on a regular basis.

Hybrid poly(ether-arylidene-ether-sulphone)s derivatives for divalent cobalt ion detection

A new set of hybrid poly(ether-arylidene-ether-sulphone)s containing diarylidenecycloalkanone moieties in the polymers main chains has been synthesized in good yields by solution poly-condensation well known polymerization method. The chemical structures of all precursors, monomers and model compound were confirmed by both elemental and spectral data. More particularly, a modified electrode of Co+2 cationic sensor was prepared by the coating of a glassy carbon electrode with synthesized copolymer 8e as a thin layer. The fabricated cationic sensor was displayed long-term stability, enhanced electrochemical activity, good sensitivity, shorter response time, broad linear dynamic range and lower detection limit. A calibration curve is plotted as current versus concentration of Co+2 ions. The cationic sensor sensitivity is calculated from the slope of calibration curve as 12.8165 µA nM−1 cm−2. The detection limit (0.74 ± 0.04 nM) is also estimated from the signal to noise ratio of 3. Therefore, the development of Co+2 cationic sensor might be a novel effort with hybrid sulphone polymers by electrochemical method to ensure the sustainability in health care sector.

Insight into the Origin of Pyrocatechol Inhibition on Oscillating Bray-Liebhafsky Reaction: Combined Experimental and Theoretical Study

Abstract The pyrocatechol inhibitory effect on the oscillatory Bray-Liebhafsky (BL) reaction is reported. Obtained results are compared with those available in the literature (R. Cervellati et al, Helvetica Chimica Acta 2001) for Briggs-Rauscher (BR) reaction with pyrocatechol addition. The two orders of magnitude larger calibration curve slope obtained in BR in comparison to BL reaction, suggests that different reactions are responsible for inhibitory effects in these systems. The potential explanation of pyrocatechol behavior is given by employing the ultraviolet-visible (UV/VIS) spectroscopy, density functional theory, and coupled cluster computational methods. The last two were employed for the first time to discover potential candidates among unstable chemical species HIO, HIO2, I2O, HOO•, HO•, IO•, IO2•, and I• of the BL (and BR) system for reaction with pyrocatechol. The calculated reaction rate constants for the hydrogen atom transfer reactions between pyrocatechol and free radical intermediates indicate the following order of reactivity: HO• > IO• > HOO• > IO2•. The same order of reactivity is also observed in the case of a thermodynamic investigation. In addition, kinetic insight indicates that the inhibitory behavior of pyrocatechol could not be explained with one particular chemical reaction in the BL (or in the BR) oscillatory system.

An Innovative in Situ Monitoring of Sulfate Reduction within a Wastewater Biofilm by H2S and SO42- Microsensors.

Microelectrodes can be used to obtain chemical profiles within biofilm microenvironments. For example, sulfate (SO42−) and hydrogen sulfide (H2S) microelectrodes can be used to study sulfate reduction activity in this context. However, there is no SO42− microelectrode available for studying sulfate reduction in biofilms. In this study, SO42− and H2S microelectrodes were fabricated and applied in the measurement of a wastewater membrane-aerated biofilm (MAB) to investigate the in situ sulfate reduction activity. Both the SO42− and H2S microelectrodes with a tip diameter of around 20 micrometers were successfully developed and displayed satisfying selectivity to SO42− and H2S, respectively. The Nernstian slopes of calibration curves of the fabricated SO42− electrodes were close to −28.1 mV/decade, and the R2 values were greater than 98%. Within the selected concentration range from 10−5 M (0.96 mg/L) to 10−2 M (960 mg/L), the response of the SO42− microelectrode was log-linearly related to its concentration. The successfully fabricated SO42− microelectrode was combined with the existing H2S microelectrode and applied on an environmental wastewater biofilm sample to investigate the sulfate reduction activity within it. The H2S and SO42− microelectrodes showed stable responses and good performance, and the decrease of SO42− with an accompanying increased of H2S within the biofilm indicated the in situ sulfate reduction activity. The application of combined SO42− and H2S microelectrodes in wastewater biofilms could amend the current understanding of sulfate reduction and sulfur oxidation within environmental biofilms based on only H2S microelectrodes.

Coupling of Anodic Stripping Voltammetry with Sampled-Current Voltammetry on an Electrode Array: Application to Lead Detection

Electrochemical detection systems are very promising for pollution monitoring owing to their easy miniaturization and low cost. For this purpose, we have recently developed a new concept of device based on Electrodes Array for Sampled-Current Voltammetry (EASCV), which is compatible with miniaturization and portability. In this work, to improve the sensitivity of the analytical method, we added a preconcentration step before EASCV analysis, combining sampled-current voltammetry with anodic stripping voltammetry. Lead was chosen as analyte for this probe of concept owing to its high toxicity. The conditions for electrodeposition of lead on gold were optimized by means of under potential deposition. Current intensities 300 times higher than with linear sweep anodic stripping voltammetry were obtained, showing the interest in the method. The value of the sampling time directly affected the sensitivity of the sensor given by the slope of the linear calibration curve. The sensor exhibited a limit of detection of 1.16 mg L−1, similar to those obtained with linear sweep anodic stripping voltammetry.

Fabrication of phenylhydrazine sensor with V2O5 doped ZnO nanocomposites

Herein, the V2O5 doped ZnO nanocomposites (NCs) were prepared by applying the wet-chemically (co-precipitation) technique in alkaline phase. The synthesized NCs were characterized in details by applying FESEM, XPS, EDS, TEM and XRD analysis. The doped V2O5 doped ZnO NCs were used to deposit in the form of thin layer on the glassy carbon electrode (GCE) by nafion binding agent (5% in ethanol) to result the desire electrochemical sensor selective to phenylhydrazine (PHyd). Plotting current versus concentration, a linear relation was established known as the calibration curve of PHyd sensor. Applying the regression-coefficient (R2 = 0.9936) on the calibration curve, the detection range of PHyd categorized by linear dynamic range (0.01 mM–0.1 nM) is evaluated. The sensor sensitivity (12.389 μAμM−1cm−2) using the calibration curve slope and GCE (0.0316 cm2) cross-sectional area is recognized. Finally, the lower limit for the detection (96.31 ± 4.82 pM) is calculated from signal-to-noise ratio at 3. From the detail investigation, the sensor was found as proficient in the term of reproducibility, long-term performing ability and response time. Furthermore, the collected samples from the various sources of environment and extracted were assessed for the practical validity of the sensor and found as satisfactory.

Fabrication of a 3,4‐Diaminotoluene Sensor Based on a TiO2 ‐Al2O3Nanocomposite Synthesized by a Fast and Facile Microwave Irradiation Method

AbstractA fast and facile synthesis of TiO2‐ Al2O3 nanocomposite based on Microwave (MW) irradiation is presented. The nanocomposite development were corroborated by X‐ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy‐dispersive X‐ray (EDX),and Fourier transform infrared spectroscopy (FT‐IR)analysis. The XPS analyzed results affirmed that elements on the nanocomposite surface were Al and O. Electrochemical properties of the as prepared TiO2‐Al2O3 nanocomposites were studied thoroughly to determine the sensing activity of the nanocomposites towards 3,4‐Diaminotoluene (3,4‐DAT) which is a harmful or hazardous chemical using I−V method. Selective electrochemical sensor using TiO2‐Al2O3 nanocomposite onto glassy carbon electrode (GCE) was assembled and the details electrochemical investigation of 3,4‐Diaminotoluene (3,4‐DAT) was developed. It was calibrated using in range of 3,4‐DAT concentration and data were plotted as current versus concentration. Considering the highest linearity (r2=0.99)of calibrated range, the linear dynamic range (1.0 pM∼ 1.0 μM) was found. Employing the slope of calibration curve, the sensitivity (0.5024×103 μAμM−1cm−3) and detection limit (0.19 ± 0.01 pM) were estimated. Besides this, the selective 3,4‐DAT chemical sensor was shown long‐term stability and precious reproducibility with very short response time without any interference effect.

Determination of lovastatin, mevastatin, rosuvastatin and simvastatin with HPLC by means of gradient elution.

A novel HPLC method with UV detection was developed and validated in skin penetration (in vitro) studies to identify and quantify lovastatin, mevastatin, rosuvastatin and simvastatin. A Venusil XBP C18 (2), 150 x 4.6 mm, 5 μm column (Agela Technologies, Newark, DE) was used with gradient elution (start at 45 % acetonitrile and increase linearly to 90 % after 1 min; hold at 90 % until 6 min and then re-equilibrate at start conditions) and the mobile phase consisted of (A) Milli-Q ® water and 0.1% orthophosphoric acid, and (B) HPLC grade acetonitrile. The flow rate was set at 1 ml/min, 240 nm UV detection and an injection volume of 10 μl. Linearity was obtained over a range of 0.50-200.00 μg/ml and correlation coefficients ranging from 0.998-1.000 were obtained. Average recovery ranged from 95.9-100.6 %. The LOD and LOQ values obtained from the slope of a calibration curve and the standard deviation of the response ranged from 0.0138-0.0860 μg/ml and 0.0419-0.2615 μg/ml, respectively, where lovastatin and simvastatin could be detected at a concentration similar to the other statins, but could only be quantified at a higher concentration than the remaining statins. The specificity of the method was proved as accurate and quantification of statins was found, even within the incorporation of other compounds.

Quantification of the inherent radiopacity of glass microspheres for precision dosimetry in yttrium-90 radioembolization

Introduction:Transarterial radioembolization is a treatment for nonresectable, hypervascular liver tumours where yttrium-90-infused microspheres are administered through the arterial vasculature of the liver to selectively target liver tumours. Compared to conventional PET and SPECT imaging, post-procedural CT imaging has the potential to provide superior spatial resolution imaging of microsphere distributions and improve dosimetry estimates. In this paper, we describe a methodology to quantify the inherent radiopacity of glass microspheres using CT. This methodology produces a calibration curve that relates microsphere concentration within a CT voxel to the corresponding change of Hounsfield unit for that voxel. Methods: The radiopaque microspheres under investigation are composed of proprietery blends of yttrium-strontium-gallium-silicate oxide glass similar in size and density to TheraSphere® microspheres. Tissue-equivalent phantoms were designed to determine CT voxel enhancement from uniformly distributed microspheres. Phantoms were imaged with a 128-slice CT scanner to determine the average Hounsfield unit value and with brightfield microscopy to determine the corresponding microsphere concentrations. Results: Hounsfield units (HU) and microsphere concentration (MS/mL) are positively correlated (r2 ≥ 0.930) over a range of CT acquisition parameters. Calibration curve slopes (sensitivities) range from 2.22 × 10−4 to 3.12 × 10−4 HU/MS/ml. Minimum detectable limits are between 1.83 × 105 and 2.54 × 105 MS mL−1. The application of this proposed methodology to recently developed microsphere formulations shows an improvement in correlation (r2 ≥ 0.995), sensitivity (7.53 × 10−4 HU/MS/ml), and minimum detectability (5.39 × 104 MS ml−1). Conclusion: CT has the potential to quantify the radiation dose from the infusion of microspheres for more accurate dosimetry in radioembolization. This finding may improve our understanding of the relationship between absorbed dose and tumour response, which could ultimately translate into improved patient outcomes. Optimization of the prototype microsphere composition to maximize its inherent radiopacity will be an important step in realizing this goal.

Evaluation of the impact of matrix effects in LC/MS measurement on the accurate quantification of neonicotinoid pesticides in food by isotope-dilution mass spectrometry

The use of isotope-labeled internal standards is the most widely accepted approach to overcome the matrix effects on quantification of pesticides in food by LC/MS. We evaluated the impact of the matrix effects on quantification of six neonicotinoid pesticides, acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam, in food by using deuterated internal standards. The calibration curves for each pesticide were obtained by using matrix-free and matrix-matched calibration solutions with blank brown rice, carrot, and green onion extracts. For brown rice and carrot, the matrix effects were not observed. In contrast, the slopes of calibration curves for each pesticide were influenced by presence of green onion extracts in calibration solutions (variability of the slopes was 4–9%), because the ratios of peak area for native pesticide to those for internal standards were influenced by matrix. The spike-and-recovery test with green onion was also performed. The analytical values obtained by using matrix-free calibration solution were biased from the spiked concentration, whereas those obtained by using matrix-matched calibration solution were comparable to the spiked concentration. These results indicate that matrix-matched calibration solution should be used for accurate quantification of neonicotinoid pesticides in food by LC/MS using deuterated internal standards.

Sensitive and selective m-tolyl hydrazine chemical sensor development based on CdO nanomaterial decorated multi-walled carbon nanotubes

In this approach, the wet-chemical (co-precipitation) technique was used to prepare the cadmium oxide (CdO) nanoparticles (NPs) decorated with multi-walled carbon nanotubes (CNT) at low temperature. The powder XDR, UV–vis, TEM, XPS, and FTIR spectroscopy were used for detail characterization of the synthesized CdO/CNT nanocomposite (NCs). A thin layer of CdO/CNT NCs was deposited onto a glassy carbon electrode (GCE) with conducting coating binder to obtain a chemical sensor which was subsequently used to detect m-tolyl hydrazine hydrochloride (m-THyd) in buffer medium by electrochemical approach for environmental safety. The proposed m-THyd chemical sensor exhibited long-term stability, good selectivity, broad linear dynamic range, lower detection limit, and enhanced electrochemical response. The calibration curve of the current vs concentration of m-THyd was found to be linear (r2 = 0.9903) over the linear dynamic range (LDR) of 0.01 nM to 0.1 mM. The sensitivity (25.7911 μA μM cm−2) of chemical sensor was calculated from the slope of calibration curve and surface area of GCE (0.0316 cm2) and the detection limit (4.0 ± 0.2 pM) was estimated from the signal to noise ratio at 3. These preliminary results suggest that the newly developed CdO/CNT NCs nanocomposite could be promising electrochemical sensors for the detection of hazardous toxins to clean the environment in broad scales.

Development of a Wireless Surface Acoustic Wave Methane Sensor Using a Metal-Organic Framework As a Sensing Layer for Natural Gas Pipelines

Methane emission from the processing and transportation of fossil fuels can create serious environmental and safety issues as well as a financial burden. The need to monitor the energy infrastructure creates an opportunity for developing low-cost and robust sensors with wireless options. Wireless surface acoustic wave (SAW) devices, which are highly sensitive, cost-efficient, and passive, are a potential candidate for these applications. Nanoporous metal-organic frameworks (MOFs), which can selectively adsorb large amounts of gases in engineered pores at ambient conditions, are potential sensing layers. Here, we present on the development of a wireless and passive SAW sensor using the MOF zeolitic imidazolate framework-8 (ZIF-8) as the sensing layer for methane detection at ambient conditions. The SAW delay lines (nominal operating frequency = 436 MHz) were custom fabricated on Y-Z LiNbO3 piezoelectric substrates and coated with a 500 nm thick ZIF-8 layer using a dip coating method. The devices were excited by 428 MHz RF pulses to test for various concentrations of CO2 and CH4 in N2 background at a constant gas flow rate. Wireless measurements were performed via dipole antennas of nominal resonant frequency 433 MHz. When the sensor was exposed to the gases, surface acoustic wave phase shifted in a negative direction relative to the N2 baseline. This shift was attributed to the decrease in SAW velocity due to the increased mass of the MOF film upon gas adsorption. The CO2 and CH4 sensitivities extracted as the slopes of the respective calibration curves were 1.26 deg/vol-% and 0.03 deg/vol-%, respectively. It is important to note that currently tested minimum concentrations of CO2 and CH4 were 1% and 20%, respectively. Also, the wireless measurements were highly affected by the housing and metal reflectors around it. The demonstration on wireless methane sensing is of great importance for remote monitoring of methane emission sites and transmission pipelines. Our current investigations are focused in advancing the detection limit for leak detection and addressing the electromagnetic interferences in wireless measurement caused by the housing.

A Modified QuEChERS Method for Determination of Pyrethroid Residues in Traditional Chinese Medicine Oral Liquids by High-Performance Liquid Chromatography.

Pyrethroid residues in traditional Chinese medicines have been a serious threat to the health and treatment of patients. However, because of the matrix complexity of traditional Chinese medicine, the detection of pyrethroid residues remains a challenge. Therefore, we developed a QuEChERS method coupled with high-performance liquid chromatography and ultraviolet detection (HPLC-UV) for the determination of pyrethroid pesticides in three kinds of traditional Chinese medicine oral liquid preparations, and we investigated and optimized the extraction conditions. The matrix effect was estimated in the organic solvent and the actual samples by comparing the slopes of calibration curves, and the results showed that the matrix effect is not significant when using the modified QuEChERS method. The pyrethroid pesticides could be completely separated in 30 min. The linear correlation coefficients were more than 0.999, and the recoveries of all the pyrethroid pesticides ranged from 87.2% to 104.8%. The intra-day precisions (n = 5) were 2.44–4.62%, and the inter-day precisions (n = 5) were 1.06–3.02%. Moreover, the limits of detection were in the range of 0.007–0.018 ng mL−1, while the limits of quantitation were in the range of 0.022–0.057 ng mL−1. This simple, low-cost, and highly sensitive analytical method can be a potential tool for the analysis of pyrethroid residues in traditional Chinese medicine oral liquid preparations.

Detection of multiclass explosives and related compounds in soil and water by liquid chromatography-dielectric barrier discharge ionization-mass spectrometry.

In this work, the multiclass detection of explosives and related compounds has been studied by liquid chromatography-high-resolution mass spectrometry by means of a time-of-flight mass spectrometer (TOFMS) operated in the negative ion mode, using dielectric barrier discharge ionization (DBDI). Reversed-phase high-performance liquid chromatography (HPLC) separation was performed using water-methanol mobile phase without any modifier, although the effect of ammonium acetate was studied. DBD plasma was generated by applying a square wave voltage of 2.5kV to a 100-mLmin-1 He flow. The DBDI probe was adjusted to fit the commercial API source housing so that the HPLC eluent was nebulized and vaporized in the same manner as for atmospheric-pressure chemical ionization (APCI). The ionization process was affected by the temperature of the two nitrogen streams used to vaporize the solvent and the analytes, particularly for RDX and HMX, which are thermolabile compounds. The best approach in terms of sensitivity for all the studied compounds was the use of a gradient of temperatures in the ionization source, starting at 225/200°C (vaporizer/drying gas temp) for nitramines and ending at 350/325°C for nitroaromatic compounds. High-resolution full-scan spectra of individual selected compounds were recorded by LC-DBDI-TOFMS, and the results were compared to LC-APCI-TOFMS. A better sensitivity (slope of calibration curve) was obtained by DBDI for more than 70% of the studied compounds in both wastewater and soil extracts. Graphical abstract ᅟ.

Internal Standardization in Dispersion Systems: an Efficient Application to Determine Mg in Crude Vegetable Oils by FS-FAAS

This study established two sample preparation procedures based on dispersion systems for the determination of Mg in crude vegetable oil by IS-FS-FAAS. The emulsions were obtained with 0.10 g of samples [0.5% (m/v)] + 200 μL HNO3 [1.0% (v/v)] + 200 μL Triton X-100 [1.0% (v/v)] in 16 mL of anhydrous ethanol [80% (v/v)] and 3.50 mL of aqueous phase [17.5% (v/v)], whereas the microemulsions were obtained with 0.10 g of samples [0.5% (m/v)] + 200 μL HNO3 [1.0% (v/v)] + 200 μL Triton X-100 [1.0% (v/v)] in 18 mL of 1-butanol [90% (v/v)] and 1.50 mL of aqueous phase [7.5% (v/v)]. To overcome non-spectral interference, Cd, Co, and Cu were used as internal standards, and the slopes of calibration curves for Mg in 1.0% (v/v) HNO3 aqueous solution, anhydrous ethanol + 1.0% (v/v) Triton X-100, and 1-butanol + 1.0% (v/v) Triton X-100 showed no significant difference at the 95% confidence level using Co and Cu. Calibration curves were obtained by plotting AMg/ACo and AMg/ACu vs Mg concentration with linear correlation coefficients better than 0.9972 and 0.9986, respectively. The accuracy was evaluated using recovery tests, and recoveries of 98.4–106.6% (IS-Co) and 93.9–106.9% (IS-Cu) were obtained. The RSD (n = 5) were 0.4–3.6% (IS-Co) and 0.3–3.6% (IS-Cu), and LOD were 0.1 μg g−1 (IS-Co) and 0.2 μg g−1 (IS-Cu). The content of Mg in four crude vegetable oil varied in the range of 8.91 ± 0.30 to 163.88 ± 0.48 μg g−1 for both dispersion systems with RSD < 4.22%.