Calibration Curve Method Research Articles

LIBS coupled with ICP/OES for the spectral analysis of betel leaves

Laser-induced breakdown spectroscopy (LIBS) system was optimized and was applied for the elemental analysis and exposure of the heavy metals in betel leaves in air. Pulsed Nd:YAG (1064 nm) in conjunction with a suitable detector (LIBS 2000+, Ocean Optics, Inc) having the optical resolution of 0.06 nm was used to record the emission spectra from 200 to 720 nm. Elements like Al, Ba, Ca, Cr, Cu, P, Fe, K, Mg, Mn, Na, P, S, Sr, and Zn were found to be present in the samples. The abundances of observed elements were calculated through normalized calibration curve method, integrated intensity ratio method, and calibration free-LIBS approach. Quantitative analyses were accomplished under the assumption of local thermodynamic equilibrium (LTE) and optically thin plasma. LIBS findings were validated by comparing its results with the results obtained using a typical analytical technique of inductively coupled plasma-optical emission spectroscopy (ICP/OES). Limit of detection (LOD) of the LIBS system was also estimated for heavy metals.

Gold Nanoparticle-Aptamer-Based LSPR Sensing of Ochratoxin A at a Widened Detection Range by Double Calibration Curve Method

Ochratoxin A (OTA) is a type of mycotoxin generated from the metabolism of Aspergillus and Penicillium, and is extremely toxic to humans, livestock, and poultry. However, traditional assays for the detection of OTA are expensive and complicated. Other than OTA aptamer, OTA itself at high concentration can also adsorb on the surface of gold nanoparticles (AuNPs), and further inhibit AuNPs salt aggregation. We herein report a new OTA assay by applying the localized surface plasmon resonance effect of AuNPs and their aggregates. The result obtained from only one single linear calibration curve is not reliable, and so we developed a “double calibration curve” method to address this issue and widen the OTA detection range. A number of other analytes were also examined, and the structural properties of analytes that bind with the AuNPs were further discussed. We found that various considerations must be taken into account in the detection of these analytes when applying AuNP aggregation-based methods due to their different binding strengths.

Extended internal standard method for quantitative 1H NMR assisted by chromatography (EIC) for analyte overlapping impurity on 1H NMR spectra

We devised a novel extended internal standard method of quantitative 1H NMR (qNMR) assisted by chromatography (EIC) that accurately quantifies 1H signal areas of analytes, even when the chemical shifts of the impurity and analyte signals overlap completely. When impurity and analyte signals overlap in the 1H NMR spectrum but can be separated in a chromatogram, the response ratio of the impurity and an internal standard (IS) can be obtained from the chromatogram. If the response ratio can be converted into the 1H signal area ratio of the impurity and the IS, the 1H signal area of the analyte can be evaluated accurately by mathematically correcting the contributions of the 1H signal area of the impurity overlapping the analyte in the 1H NMR spectrum. In this study, gas chromatography and liquid chromatography were used. We used 2-chlorophenol and 4-chlorophenol containing phenol as an impurity as examples in which impurity and analyte signals overlap to validate and demonstrate the EIC, respectively. Because the 1H signals of 2-chlorophenol and phenol can be separated in specific alkaline solutions, 2-chlorophenol is suitable to validate the EIC by comparing analytical value obtained by the EIC with that by only qNMR under the alkaline condition. By the EIC, the purity of 2-chlorophenol was obtained with a relative expanded uncertainty (k = 2) of 0.24%. The purity matched that obtained under the alkaline condition. Furthermore, the EIC was also validated by evaluating the phenol content with the absolute calibration curve method by gas chromatography. Finally, we demonstrated that the EIC was possible to evaluate the purity of 4-chlorophenol, with a relative expanded uncertainty (k = 2) of 0.22%, which was not able to be separated from the 1H signal of phenol under any condition.

Screening and Determination of Pesticides from Various Classes in Natural Water without Sample Preparation by Ultra HPLC–High-Resolution Quadrupole Time-of-Flight Mass Spectrometry

A rapid screening and determination of 59 pesticides from various classes in natural water without sample preparation by high-resolution ultra HPLC–quadrupole time-of-flight mass spectrometry is proposed. The matrix effect is considered on an example of waters with a high (mineral) and low (artesian) salt concentration. It is demonstrated that pesticides can be determined in water using the calibration curve method with an insignificant matrix effect (neonicotinoids, carbamates, and derivatives of uracil, pyridine, and benzoic and aryloxycarboxylic acids) and the standard addition method with a significant matrix effect (triazines, triazinones, triazoles, imidazoles, pyridazinones, organophosphorus compounds, and urea derivatives). The limits of detection were 0.01–10 ng/mL; the analytical ranges for pesticides were 0.04–50 (100) ng/mL. The relative standard deviation of the results does not exceed 15%; the analysis time is 10–15 min.

Determination of lead content in drilling fueled soil using laser induced spectral analysis and its cross validation using ICP/OES method

A detection system based on Laser Induced Breakdown Spectroscopy (LIBS) was designed, optimized, and successfully employed for the estimation of lead (Pb) content in drilling fueled soil (DFS) collected from oil field drilling areas in Pakistan. The concentration of Pb was evaluated by the standard calibration curve method as well as by using an approach based on the integrated intensity of strongest emission of an element of interest. Remarkably, our investigation clearly demonstrated that the concentration of Pb in drilling fueled soil collected at the exact drilling site was greater than the safe permissible limits. Furthermore, the Pb concentration was observed to decline with increasing distance away from the specific drilling point. Analytical determinations were carried out under the assumptions that laser generated plasma was optically thin and in local thermodynamic equilibrium (LTE). In order to improve the sensitivity of our LIBS detection system, various parametric dependence studies were performed. To further validate the precision of our LIBS results, the concentration of Pb present in the acquired samples were also quantified via a standard analytical tool like inductively coupled plasma/optical emission spectroscopy (ICP/OES). Both results were in excellent agreement, implying remarkable reliability for the LIBS data. Furthermore, the Limit of detection (LOD) of our LIBS system for Pb was estimated to be 125.14 mg L−1.

Efficient extraction of perfluorocarboxylic acids in complex samples with a monolithic adsorbent combining fluorophilic and anion-exchange interactions

Efficient extraction of perfluorocarboxylic acids (PFCAs) is a key step for the accurate and sensitive determination of PFCAs due to their low concentration and the complexity of sample matrices. Herein, according to the chemical characteristics of PFCAs, a new adsorbent based on poly (2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate/(vinylbenzyl)trimethylammonium chloride-co-divinylbenzene/ethylenedimethacrylate) monolith was fabricated and utilized as the extraction medium of multiple monolithic fiber solid-phase microextraction (MMF-SPME). Results well indicted that the prepared monolithic adsorbent (MA) could efficient extract PFCAs through fluorophilic and anion-exchange interactions. Under the optimal conditions, the MA/MMF-SPME was combined with HPLC-MS/MS for the sensitive monitoring of ultra-trace PFCAs in water and milks samples. The limits of detection (S/N = 3) of the target PFCAs in water and milk samples were 0.40–4.40 ng/L and 0.9–12.1 ng/L, respectively. Furthermore, the proposed method also exhibited some merits including wide linear dynamic ranges, satisfactory sensitivity, good method precision and low consumption of sample and organic solvent. Isotope internal standard calibration curve method was used to quantify the concentration of PFCAs in real samples, and trace levels of PFCAs in tap water and milk samples had been successfully detected.

A Dissolved Oxygen Analyzer with an Optical Sensor

A serial analyzer of dissolved oxygen, Expert-009, based on the optical detection method is created. The sensitive element of the sensor is a polymer film with a dye—a metal complex of fluorine-substituted porphyrin—distributed in it. The method is based on the quenching of the phosphorescence of the dye by molecular oxygen, which the analyzer recounts to the concentration value by the calibration curve method. The metrological characteristics of the analyzer are determined.

Determination of metribuzin content in pesticide formulations using electroanalytical methodology

The work presents results of the determination of metribuzin content in commercial pesticide formulations by applying chronopotentiometry with thin film mercury electrode as an electrochemical sensor. In the analyzed pesticide formulations, a single well defined reduction peak of metribuzin is observed at the potential around -880 mV. The content of the herbicide in commercial formulations is determined using the calibration curve method, by applying the initial potential of -0.21 V, and the final potential of -1.10 V. Recovery values based on the declared and found content of the active ingredient are in the range from 100.67% to 101.68%, with the values of relative standard deviation lower than 1.00%, indicating high accuracy and precision of the presented method.

Photometric flow analysis system for biomedical investigations of iron/transferrin speciation in human serum

The Multicommutated Flow Analysis (MCFA) system for the estimation of clinical iron parameters: Serum Iron (SI), Unsaturated Iron Binding Capacity (UIBC) and Total Iron Binding Capacity (TIBC) has been proposed. The developed MCFA system based on simple photometric detection of iron with chromogenic agent (ferrozine) enables a speciation of transferrin (determination of free and Fe-bound protein) in human serum. The construction of manifold was adapted to the requirements of measurements under changing conditions. In the course of studies, a different effect of proteins on SI and UIBC determination has been proven. That was in turn the reason to perform two kinds of calibration methods. For measurements in acidic medium for SI/holotransferrin determination, the calibration curve method was applied, characterized by limit of determination and limit of quantitation on the level of 3.4 μmol L−1 and 9.1 μmol L−1, respectively. The determination method for UIBC parameter (related to apotransferrin level) in physiological medium of pH 7.4 forced the use of standard addition method due to the strong influence of proteins on obtaining analytical signals. These two different methodologies, performed in the presented system, enabled the estimation of all three clinical iron/transferrin parameters in human serum samples. TIBC corresponding to total transferrin level was calculated as a sum of SI and UIBC.

Separation, identification and quantification of carotenoids and chlorophylls in dietary supplements containing Chlorella vulgaris and Spirulina platensis using High Performance Thin Layer Chromatography

In this study, 14 commercial products (dietary supplements) containing alga Chlorella vulgaris and cyanobacteria Spirulina platensis, originated from China and Japan, were analysed. UV–vis spectrophotometric method was applied for rapid determination of chlorophylls, carotenoids and pheophytins; as degradation products of chlorophylls. High Performance Thin-Layer Chromatography (HPTLC) was used for effective separation of these compounds, and also Atomic Absorption Spectrometry for determination of heavy metals as indicator of environmental pollution. Based on the results obtained from UV–vis spectrophotometric determination of photosynthetic pigments (chlorophylls and carotenoids), it was confirmed that Chlorella vulgaris contains more of all these pigments compared to the cyanobacteria Spirulina platensis. The fastest mobility compound identified in Chlorella vulgaris and Spirulina platensis using HPTLC method was β-carotene. Spectral analysis and standard calibration curve method were used for identification and quantification of separated substances on Thin-Layer Chromatographic plate. Quantification of copper (Cu2+, at 324.7 nm) and zinc (Zn2+, at 213.9nm) was performed using Flame Atomic Absorption Spectrometry with air-acetylene flame atomization. Quantification of cadmium (Cd2+, at 228.8 nm), nickel (Ni2+, at 232.0nm) and lead (Pb2+, at 283.3nm) by Electrothermal Graphite Furnace Atomic Absorption Spectrometry; and quantification of mercury (Hg2+, at 254nm) by Cold Vapour Atomic Absorption Spectrometry.

A Quantitative Analysis of an Oil Component in an Emulsion by Multiphoton Ionization Mass Spectrometry.

The first quantitative analysis of an oil component in an emulsion was achieved by multiphoton ionization time-of-flight mass spectrometry (MPI-TOFMS). An oil-in-water (O/W) emulsion was prepared. Styrene (0 - 5000 ng μL-1) and Triton X-100 were used as the oil phase and the disperser, respectively. Toluene was employed as an internal standard. We obtained a series of mass spectra, and then constructed the time profiles for styrene and toluene. As a result, we found several spikes from both time profiles when measuring emulsions with higher concentrations of styrene. Moreover, the timing of spikes for toluene coincided with that of styrene. These results suggested the movement of toluene into styrene droplets in the prepared emulsion. Furthermore, we constructed calibration curves of styrene using both the absolute calibration curve method and an internal standard method. Linear calibration curves were obtained in the concentration range investigated in the present study; the coefficients of determination obtained by both methods were 0.9956 and 0.9986, respectively.

COMPARATIVE QUANTIFICATION OF ESCIN FROM DIFFERENT PRODUCTS

The paper aimed to quantify the saponins expressed in escin, the major bioactive constituent of Aesculus hippocastanum , from five different pharmaceutical formulations: two types of tablets, and one type of gel, tincture, and glycerol-hydroalcoholic extract. The products are part of over the counter drugs and dietary supplements categories. Two spectrophotometric methods were used to quantify the escin, after separation from the other active ingredients and excipients. The first method, calibration curve method, is based on the reaction between the oxidized triterpenoid saponins and vanillin and records the absorbance at 560 nm. The limit of detection, limit of quantification, and the RSD values were calculated. The second method is based on the molar absorptivity of escin. Both methods have proved to be suitable for the determination of escin in different products.

Determination of Metals Present in Textile Dyes Using Laser-Induced Breakdown Spectroscopy and Cross-Validation Using Inductively Coupled Plasma/Atomic Emission Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used for the quantitative analysis of elements present in textile dyes at ambient pressure via the fundamental mode (1064 nm) of a Nd:YAG pulsed laser. Three samples were collected for this purpose. Spectra of textile dyes were acquired using an HR spectrometer (LIBS2000+, Ocean Optics, Inc.) having an optical resolution of 0.06 nm in the spectral range of 200 to 720 nm. Toxic metals like Cr, Cu, Fe, Ni, and Zn along with other elements like Al, Mg, Ca, and Na were revealed to exist in the samples. The %-age concentrations of the detected elements were measured by means of standard calibration curve method, intensities of every emission from every species, and calibration-free (CF) LIBS approach. Only Sample 3 was found to contain heavy metals like Cr, Cu, and Ni above the prescribed limit. The results using LIBS were found to be in good agreement when compared to outcomes of inductively coupled plasma/atomic emission spectroscopy (ICP/AES).

Pressure-Thermal Kinetics of Furan Formation in Selected Fruit and Vegetable Juices

Furan, a potential carcinogenic compound, can be formed in array of processed foods. The objective of this study was to conduct kinetic studies in pineapple juice and assess the interactive effects of pressure (0.1 to 600 MPa) and temperature (30 to 120 °C) on furan formation. Additional experiments were carried out in tomato, watermelon, cantaloupe, kale, and carrot juice to understand the influence of matrix and juice pH. Furan was monitored in raw (control) and processed samples by automated headspace gas chromatography mass spectrometry, and quantified by calibration curve method with d4-furan as internal standard. The data were modeled using zero-, first-, and second-order equations. The zero-order rate constants (k T,P ), activation energy (E a ), and Gibbs free energy of activation (ΔG ‡) of furan formation in thermally processed (TP; 90–120 °C) pineapple juice were found to be 0.036–0.55 μg/kg/min, 98–114 kJ/mol, and 173.9–180.5 kJ/mol, respectively. Furan concentration was negligible and close to the detection limit (0.37 μg/kg) after pressure treatment (600 MPa at 30 °C) of juice samples. For similar process temperatures, the rate constants of pressure-assisted thermally processed (PATP; 600 MPa at 105 °C) pineapple juice were lower than that of TP samples. Furan formation was influenced by juice matrix and pH. On the other hand, PATP markedly suppressed furan (0.7 to 1.6 μg/kg) in these selected juices. In conclusion, furan formation increased with process temperature and treatment time, while pressure treatment at ambient temperature did not promote its production. Furan formation in TP fruit juices was also influenced by juice matrix and pH, but these were not the significant factors for PATP-treated juices.

The comparative verification of calibration curve and background fundamental parameter methods for impurity analysis in drug materials

The United States Pharmacopeia (USP) has established general analysis guidelines of X‐Ray fluorescence (XRF) methodology in chapter <735>, XRF spectrometry. Meanwhile, the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH Q3D) guideline, presenting a policy for limiting 24 elements such as Cd, Pb, and As in drug products and pharmaceutical ingredients, has now reached Step 5 (Implementation). The limit values of ICH Q3D are strict, for example, near or less than 1 μg/g for Cd and Pb. Moreover, there are other difficulties for accurate analysis, such as different types of matrices and the very small sample volumes in the synthesis research process for new product development in the pharmaceutical industries. Energy dispersive XRF can correct the influence of various matrices and volumes and also has the advantages of nonchemical pretreatment and nondestructive analysis. Advancements in the quantitation by fundamental parameters (FP) method using theoretical calculations, background (BG)‐FP method, leads to reduction in the number of standard samples and effectiveness on the practical elemental impurity control in pharmaceutical researches and inspections. In order to show the applicability of using the BG‐FP method, in this study, the quantitative values of some hazardous inorganic impurities for Cd, Pb, As, V, Co, and Ni in a cellulose matrix were compared by calibration curve method and BG‐FP method through the verification of USP <735>. Both methods can meet the acceptance criteria for accuracy and precision in USP <735>. Copyright © 2017 John Wiley & Sons, Ltd.

Monolithic capillary column with an integrated electrochemical detector

The carbon fiber and silver microwire were used as working and pseudoreference electrode, respectively, and inserted into the ending of capillary to prepare monolithic capillary column with an integrated electrochemical detector. Prepared capillary devices offered stable and robust results with relative standard deviations of retention, resolution, and detection signal lower than 1.5, 5.5, and 5.0%, respectively. To further increase sensitivity of developed electrochemical microdetector, multiple pulse amperometry detection mode has been used. Optimized integrated device provided reliable chromatographic separation of mixture of neurotransmitters with calibration curve for dopamine linear from 0.5 to 20.0mgL−1 and an instrumental limit of detection as low as 24pg of injected dopamine. Finally, developed capillary column was applied to successful determination of dopamine in a human urine. By using both calibration curve and standard addition method, the dopamine level was determined to be 0.74±0.03mgL−1 and 0.71±0.02mgL−1, respectively. Triplicates of dopamine analysis provided relative standard deviations lower than 2.7% for intraday analyses, while interday relative standard deviations were lower than 3.6% for five consecutive days.

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

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.

Chemically modified carbon paste ion-selective electrodes for determination of atorvastatin calcium in pharmaceutical preparations

A simple, rapid and sensitive method for the determination of atorvastatin calcium in pharmaceutical preparations using two modified carbon paste electrodes was developed. One electrode (sensor A) is based on ion-pair of atorvastatin with 5,6-diaminouracil hydrochloride (ATS-DAUH) and the other (sensor B) is based on atorvastatin with picric acid (ATS-PC). Among three different solvent mediators tested, dioctylphthalate (DOPH) exhibited a proper behavior including Nernstian slopes of the calibration curve at 58.76 ± 0.8 and 57.48±1 mV per decade for sensors A and B. The response times were 10 and 12 s, detection limits 1.3 × 10−6 and 2.2 × 10−6 M; the concentration range 2.5 × 10−6-7.9 × 10−2 M and 3.0 × 10−6 to 7.9 × 10−2 M respectively. The present electrodes show good discrimination of atorvastatin calcium from several inorganic, organic ions, sugars and some common excipients. The sensors were applied for the determination of atorvastatin calcium in pharmaceutical preparations using standard addition and the calibration curve methods. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay. The proposed potentiometric methods offer the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions.

Quantification of cystatin-C in human serum by stable isotope dilution liquid chromatography electrospray ionization tandem mass spectrometry.

Cystatin C (CysC)-based estimated glomerular filtration rate is an excellent marker for early diagnosis of Chronic Kidney Disease (CKD). Particle-enhanced nephelometric immunoassay (PENIA) and particle-enhanced turbidimetric immunoassay (PETIA) are commonly used methods for CysC quantification in clinical testing. However, both of them lack of specificity which mass spectrometry offers. In this paper, an isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) method was established for quantification of CysC in human serum. After CysC denaturation, reduction and alkylation of cysteine residues, trypsin was added for proteolytic digestion of CysC. Specific peptide ALDFAVGEYNK was selected as surrogates for intact CysC protein, then quantified CysC by stable isotope-labelled internal standard peptide A[13C615N]LDFAVGEYNK based on calibration curve method. The calibration curves were y=0.1565x-1.6715 (R2=0.988) and y=1.8785x-2.2497 (R2=0.991) for y9 and y6, respectively. The linear range was 0.1-10mg/L and 0.5-15mg/L for y9 and y6, respectively. The limit of quantification (LOQ) was 0.052mg/L. At different concentrations of CysC, the recoveries were in the range of 80.5%-93.7%, the intraday precisions were in the range of 0.3%-2.2%, and the inter-day precisions were in the range of 0.2%-2.8%. The results show that ID-LC-MS/MS and PETIA methods have higher consistency (y=0.8021x+0.6611, p=0.14), and the mean difference of the two methods was -0.29mg/L, and 95% of the individual difference values were in the range of -0.91mg/L-0.33mg/L.

Real-Time Composition Monitoring Using Support Vector Regression of Laser-Induced Plasma for Laser Additive Manufacturing

Laser additive manufacturing has gained widespread adoption in recent years. However, process diagnosis and process control lag behind the progresses of other key technologies, which make the product quality control a challenging problem. This work proposes an operating parameter conditioned support vector regression (SVR) method that uses processing parameter conditioned kernel function to achieve a processing parameter independent in-situ composition prediction. Two different features of laser-induced plasma, spectral line-intensity-ratio, and both spectral line-intensity-ratio and spectral integrated intensity were used to train the SVR. Composition measurements using a calibration curve method, partial least square regression, and artificial neural networks are also performed for comparison. The results show that the SVR with both spectral line-intensity-ratio and spectral integrated intensity as inputs has the best performance due to linearly separable point clusters in the high-dimensional space. Laser power independent composition prediction is achieved and real-time composition predictions are validated. It is proved that the operating parameter conditioned SVR provides a more accurate, a more universal, and an operating parameter independent prediction. Moreover, operating parameter conditioned SVR provides a potential data-driven-based approach for real-time composition monitoring of the laser additive manufacturing process.