Showing papers on "Calibration curve published in 2017"

Sensing system for salinity testing using laser-induced graphene sensors

Abstract: The paper presents the development and implementation of a low-cost salinity sensing system. Commercial polymer films were laser ablated at specific conditions to form graphene-based sensors on flexible Kapton substrates. Sodium chloride was considered as the primary constituent for testing due to its prominent presence in water bodies. The sensor was characterized by testing different concentrations of sodium chloride. A standard curve was developed to perform real-time testing with a sample taken from sea water of unknown concentration. The sensitivity and resolution of these graphene sensors for the experimental solutions were 1.07 Ω/ppm and 1 ppm respectively. The developed system was validated by testing it with a real sample and cross checking it on the calibration curve. The signal conditioning circuit was further enhanced by embedding a microcontroller to the designed system. The obtained results did provide a platform for implementation of a low-cost salinity sensing system that could be used in marine applications.

Spectral Interference Elimination in Soil Analysis Using Laser-Induced Breakdown Spectroscopy Assisted by Laser-Induced Fluorescence

Abstract: The complex and serious spectral interference makes it difficult to detect trace elements in soil using laser-induced breakdown spectroscopy (LIBS). To address it, LIBS-assisted by laser-induced fluorescence (LIBS-LIF) was applied to selectively enhance the spectral intensities of the interfered lines. Utilizing this selective enhancement effect, all the interference lines could be eliminated. As an example, the Pb I 405.78 nm line was enhanced selectively. The results showed that the determination coefficient (R2) of calibration curve (Pb concentration range = 14–94 ppm), the relative standard deviation (RSD) of spectral intensities, and the limit of detection (LOD) for Pb element were improved from 0.6235 to 0.9802, 10.18% to 4.77%, and 24 ppm to 0.6 ppm using LIBS-LIF, respectively. These demonstrate that LIBS-LIF can eliminate spectral interference effectively and improve the ability of LIBS to detect trace heavy metals in soil.

Standardized Procedure for the Simultaneous Determination of the Matrix Effect, Recovery, Process Efficiency, and Internal Standard Association

Abstract: The matrix effects (MEs) on the quantification of an analyte can be significant and should not be neglected during development and validation of an analytical method. According to this premise, we developed a standardized procedure based on a set of six tests performed on six different sample matrices to detect and characterize the effects of the matrix for single and multiple analytes methods. The link between the matrix effect, recovery, process efficiency, accuracy, precision, and calibration curve was underscored by calculations performed with peak areas, ratios of standard/internal standard peak area, and concentrations. The terms instrumental ME and global ME were introduced, and the term recovery was subdivided for clarity. The test accounts for the presence of ubiquitous and endogenous analytes through background subtraction. The results showed the necessity for using samples with an original concentration in the same range and that the concentration selected for the addition had a definite impact...

Trivalent Y 3+ ionic sensor development based on ( E )-Methyl- N ′-nitrobenzylidene-benzenesulfonohydrazide (MNBBSH) derivatives modified with nafion matrix

Abstract: (E)-Methyl-N'-nitrobenzylidene-benzenesulfonohydrazide (MNBBSH) compounds were synthesized using a condensation procedure from the derivatives of nitrobenzaldehyde and 4-Methyl-benzenesulfonylhydrazine, which crystallized in ethanol and methanol as well as characterized by FTIR, UV-Vis, 1H-NMR, and 13C-NMR. MNBBSH structure was confirmed using a single crystal X-ray diffraction technique and used for the detection of selective yttrium ion (Y3+) by I-V system. A thin layer of MNBBSH was deposited onto a glassy carbon electrode (GCE) with 5% nafion for the sensitive and selective Y3+ sensor. The modified MNBBSH/GCE sensor is exhibited the better electrochemical performances such as sensitivity, limit of detection (LOD), linear dynamic range (LDR), limit of quantification (LOQ), short response time, and long term storage ability towards the selective metal ion (Y3+). The calibration curve of 2-MNBBSH/GCE sensor was plotted at +1.1 V over a broad range of Y3+ concentration. Sensitivity, LOD, LDR and LOQ of the fabricated sensor towards Y3+ were calculated from the calibration curve and found as 1.90 pAμM-1 cm-2, 10.0 pM, 1.0 nM~1.0 mM and 338.33 mM respectively. The 2-MNBBSH/Nafion/GCE sensor was applied to the selective determination of Y3+ in spiked samples such as industrial effluent and real water samples from different sources, and found acceptable and reasonable results.

Frequency-tuned contactless conductivity detector for the electrophoretic separation of clinical samples in capillaries with very small internal dimensions.

Abstract: An axial design of a capacitively coupled contactless conductivity detector was tested in combination with fused silica capillaries with internal diameters of 10, 15 and 25 μm, which are used for high-efficiency electrophoretic separation. The transmission of the signal in the detection probe dependent on the specific conductivity of the solution in the capillary in the range 0–278 mS.m−1 has a complex character and a minimum appears on the curve at very low conductivities. The position of the minimum of the calibration dependence gradually shifts with decreasing frequency of the exciting signal from 1.0 to 0.25 MHz towards lower specific conductivity values. The presence of a minimum on the calibration curves is a natural property of the axial design of contactless conductivity detector, demonstrated by solution of the equivalent electrical circuit of the detection probe, and is specifically caused by the use of shielding foil. The behavior of contactless conductivity detector in the vicinity of the minimum was documented for practical separations of amino acids in solutions of 3.2 M acetic acid with addition of 0–50% v/v methanol. This article is protected by copyright. All rights reserved

Magnetic dispersive solid phase extraction based on polythiophene modified magnetic graphene oxide for mercury determination in seafood followed by flow-injection cold vapor atomic absorption spectrometry

Abstract: A new and efficient sorbent was introduced for magnetic dispersive solid phase extraction via oxidative polymerization of thiophene on the surface of magnetic graphene oxide. The sorbent was used for the extraction of mercury at trace levels in different seafood samples. Mineralization of the samples was carried out by microwave assisted digestion. Flow-injection cold vapor atomic absorption spectrometry was used for analysis of extracts. Scanning electron microscopy (SEM), energy-dispersive X-ray analyzer (EDX) and Fourier transform-infrared (FT-IR) were applied to characterize the prepared nanoparticles. Central composite design was applied to find the optimum values of adsorption and desorption parameters affecting the extraction efficiency. The optimum conditions were obtained as extraction time of 21 min; 20.0 mg sorbent in 50 mL of the sample solution with pH of 6.5, and elution with 2.5 mL of HCl 1.7 mol L−1 under fierce vortex for 2.0 min. Under the optimal conditions, the preconcentration factor of 17 and extraction recovery of 85% were obtained. The limits of detection and quantification were found to be 0.025 ng mL−1 and 1.0 ng mL−1, respectively. The calibration curve was in the range of 1.0–85 ng mL−1 with the coefficient of determination (R2) of 0.9997. The relative standard deviations (RSD%) for intra- and inter-day precisions were 4.0% and 9.98%, respectively. Finally, the proposed method was successfully applied to determine mercury in seafood samples.

Application of a mobile laser-induced breakdown spectroscopy system to detect heavy metal elements in soil

Abstract: In this work, a mobile laser-induced breakdown spectroscopy (LIBS) system has been successfully applied to in situ analysis of heavy metals in soil samples. The LIBS system had two working methods, which were a fixed measuring method and a handheld method. For the fixed measuring method, a simple sample pretreatment was needed to reduce the soil matrix effect generated by moisture and porosity. Experiments proved that this method could be used to semi-quantitatively detect heavy metals when combined with the traditional calibration curve method. The limits of detection for copper, lead, and zinc were all below 10 mg/kg, which satisfied the need of heavy metal detection in soil. Principal component analysis was used for soil classification, which helped to build appropriate calibration curves. On the basis of soil classification, accurate and rapid detection of heavy metals in soil is feasible. For the handheld method, spectrum intensity and stability decreased significantly compared with the fixed measuring method. However, by using the internal standard method, the stability of LIBS data was improved significantly to 6%. For soil samples with serious heavy-metal pollution, the measurement errors were less than 12%, which indicated that handheld LIBS was effective to monitor heavy-metal pollution in soil. The research results provide application support for rapid and on-site monitoring of heavy metals in soil.

Microwave-Induced Plasma Optical Emission Spectrometry (MIP OES) and Standard Dilution Analysis to Determine Trace Elements in Pharmaceutical Samples.

Abstract: In this work, we evaluate the application of microwave-induced plasma optical emission spectrometry (MIP OES) to determine of Al, Cr, Co, Cu, Fe, Mn, Ni and Zn in children's cough syrup, eye drops, and oral antiseptic using standard dilution analysis (SDA). The SDA method is simple, with only two calibration solutions prepared per sample. The first solution (S1), composed of 50% sample +50% of a standard solution, is introduced into the plasma and the analytical signals are monitored in a time-resolved fashion. Then, the second solution (S2), composed of 50% sample +50% blank, is poured into the vial containing S1. As the solutions mix, the analytical signals gradually drop to a stable baseline. The calibration curve is computed by plotting the ratio of the analyte signal (SA) over the internal standard signal (which is also part of S1) (SIS) on the y-axis, versus the inverse of the IS concentration on the x-axis (i.e., SA/SIS versus 1/CIS). In this study, SDA results were compared with values obtained with the traditional methods of external calibration (EC), internal standardization (IS), and standard additions (SA) in MIP OES determinations. The precision (represented as percent RSD) for SDA showed values in the range of 2.50-8.00% for all samples, while conventional calibration methods showed RSDs in the range of 6.40-32.50% for EC, 8.30-21.80% for IS, and 5.20-17.40% for SA. The LODs calculated for SDA are below the maximum limits allowed by the major pharmaceutical regulatory agencies, and presents superior precision and accuracy compared to the traditional calibration methods. Considering its simplicity and efficiency, SDA is an important new tool for accurate analyses of pharmaceuticals.

A novel chemiluminescence sensor for the determination of indomethacin based on sulfur and nitrogen co-doped carbon quantum dot–KMnO4 reaction

Abstract: We report on a simple and sensitive sulfur and nitrogen co-doped carbon quantum dot (S,N-CQD)-based chemiluminescence (CL) sensor for the determination of indomethacin. S,N-CQDs were prepared by a hydrothermal method and characterized by fluorescence spectra, Fourier transform infrared spectroscopy and transmission electron microscopy. To obtain the best CL system for determination of indomethacin, the reaction of S,N-CQDs with some common oxidants was studied. Among the tested systems, the S,N-CQD–KMnO4 reaction showed the highest sensitivity for the detection of indomethacin. Under optimum conditions, the calibration plot was linear over a concentration range of 0.1–1.5 mg L−1, with a limit of detection (3σ) of 65 μg L−1. The method was applied to the determination of indomethacin in environmental and biological samples with satisfactory results.

A hydrogel-based solidification method for the direct analysis of liquid samples by laser-induced breakdown spectroscopy

Abstract: Laser-induced breakdown spectroscopy (LIBS) is a simple, fast, and direct technique for the elemental analysis of various samples. However, the practical application of this method in direct liquid analysis is limited due to its inherent disadvantages including surface ripples and extinction of emitted intensity. Applicable treatments of liquids always involve complicated procedures or additional instruments, which is disadvantageous to its analytical performance. In this study, we proposed a novel method for the LIBS analysis of liquid samples via a hydrogel-based solidification technique. In this new method, aqueous solution is directly poured into sodium polyacrylate resins. Owing to the high hydroscopicity of sodium polyacrylate resins, the resins quickly form a hydrogel and immediately solidify the liquid samples. After this, the LIBS analysis is directly performed. To estimate the analytical performance of this proposed method, calibration curves were established and limits of detection for Al, Cu, and Cr were obtained. The limits of detection (LODs) for the emission lines of Al(I) 308.21 nm, Cu(I) 324.75 nm, and Cr(I) 425.43 nm were 0.460 μg mL−1, 4.69 μg mL−1, and 4.44 μg mL−1, respectively. According to the obtained results, this proposed method demonstrates its better analytical performance in terms of LODs at the ppm level and requires shorter processing time as compared to other analytical methods based on the LIBS technique for liquid sample analysis. Especially, the short pretreatment of samples and simple auxiliary equipment make this hydrogel-based solidification method bring LIBS out of the laboratory for the direct analysis of environmental liquid samples. The feasibility and potential of this novel method have also been discussed for special analytical applications in slurry samples.

Amperometric paper sensor based on Cu nanoparticles for the determination of carbohydrates

Abstract: In the present article the development of a paper-based amperometric sensor for the determination of glucose and of the total carbohydrates is described. The motivation of the study lies in the necessity of novel low cost and fast methods for the determination of sugars in foodstuff; the commonly used procedures, in fact, often suffer from inaccuracy. To this aim, paper-based electrodes have been fabricated through the deposition of an electrically conductive ink based on Cu nanoparticles, graphite and polystyrene. In order to gain highest oxidation currents for glucose, i.e. to increase the sensitivity of the sensor, the composition of the ink has been optimised through a suitable experimental design. The performance of the paper-based system has been estimated in glucose, 0.1 M KOH solution. The estimated concentration value calculated from the calibration curve is ca. 10.4 mM (0.6 mM standard deviation) when a probe solution containing 10.1 mM glucose is used. In addition, the effectiveness of the system has been verified in real matrices, i.e. soft drinks: calibration curves lead to accurate estimation of the total carbohydrates concentration. On the basis of a suitable t -test, the probability of being wrong in rejecting the proper null hypothesis is lower than 1%.