Showing papers on "Calibration curve published in 2014"

Interlaboratory Agreement of Insulin-Like Growth Factor 1 Concentrations Measured by Mass Spectrometry

Abstract: BACKGROUND: Insulin-like growth factor 1 (IGF-1)[7][1] is a key mediator of growth hormone (GH) action and a well-characterized biomarker of GH abuse. Current immunoassays for IGF-1 suffer from poor concordance between platforms, which makes comparison of results between laboratories difficult. Although previous work has demonstrated good interlaboratory imprecision of LC-MS/MS methods when plasma is supplemented with purified proteins, the interlaboratory imprecision of an endogenous protein in the nanogram-per-milliliter concentration range has not been reported. METHODS: We deployed an LC-MS/MS method to quantify serum IGF-1 in 5 laboratories using 5 different instruments and analyzed 130 healthy human samples and 22 samples from patients with acromegaly. We determined measurement imprecision (CV) for differences due to instrumentation, calibration curve construction, method of calibration, and reference material. RESULTS: Instrument-dependent variation, exclusive of digestion, across 5 different instrument platforms was determined to be 5.6%. Interlaboratory variation was strongly dependent on calibration. Calibration materials from a single laboratory resulted in less variation than materials made in individual laboratories (CV 5.2% vs 12.8%, respectively). The mean imprecision for 152 samples between the 5 laboratories was 16.0% when a calibration curve was made in each laboratory and 11.1% when a single-point calibration approach was used. CONCLUSIONS: The interlaboratory imprecision of serum IGF-1 concentrations is acceptable for use of the assay in antidoping laboratories and in standardizing results across clinical laboratories. The primary source of variability is not derived from the sample preparation but from the method of calibration. [1]: #fn-10

Hot pepper and determining method for 96 pesticide residues in product of hot pepper

Abstract: The invention discloses hot pepper and a determining method for 96 pesticide residues in a product of the hot pepper. The determining method comprises the following steps: homogenously extracting residual pesticide in a sample with 1% acetic acid-acetonitrile solution, purifying the extracting solution with a Florisil solid phase extraction column, dispersing and purifying the extracting solution with ethylenediamine-N-propyl silane (PSA) and octadecyl silane bonded phase (C18) substrate, detecting 69 pesticide residuals in the purified concentrated liquid of the Florisil column by GC-MS (gaschromatographic mass spectrometry), detecting 27 pesticide residuals in the substrate dispersed purified liquid by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using the black substrate solution dilution standard to construct the updated calibration curves, adopting an internal standard method to quantify when using GC/MS to detect the residuals, and adopting an external standard method to quantify when using LC-MS/MS to detect the residuals. The average recovery rate of the method is 70.7-118.6%; the average relative standard deviation (RSD) is 3.2-11.4%; the detection limit is 0.13-28.2 ug/kg. The determining method has the advantages of simplicity and convenience in operation, high speed, accuracy, high sensitivity and good repeatability.

Comparison of single- and multivariate calibration for determination of Si, Mn, Cr and Ni in high-alloyed stainless steels by laser-induced breakdown spectrometry

Abstract: The quantitative analysis of high-alloyed steels by LIBS is usually complicated by overlap of the analytical lines with iron lines due to the complex structure of the emission spectra of each component. To overcome this problem, we compared two calibration strategies in the current research work. Univariate regression analysis was used for a number of analytical lines of Si, Mn, Ni, and Cr with and without strong spectral interference with other lines. Several methods of data pre-processing (for example, by normalization using an internal standard or baseline correction) to compensate for matrix effects or the pulse to pulse deviations of the analytical signal have been compared with the calibration curves constructed with the use of peak intensities. As an alternative to the univariate strategy, multivariate calibration based on principal component regression (PCR) was used in this work. We examined two criteria separately to select the most predictive model. The minimal values of the relative Root Mean Square Error of Cross Validation (RMSECV, %) provided the best prediction accuracy while the use of the well known F-criterion reduced the number of principal components up to 4 or 5 for each analyte without significant worsening of prediction capability. The measurements within four spectral windows (210–230 nm, 280–300 nm, 345–365 nm and 400–420 nm) were carried out on a set of 10 standard samples. Univariate calibration for Cr, Ni and Mn provided the best prediction (R2 = 0.996) if an appropriate reference line could be found and analytical lines were not overlapped with others. The best prediction for Si (R2 = 0.94) was obtained with the use of a peak signal of the Si 212.41 nm line without normalization. Otherwise, PCR provided good predictive capability (RMSECV, % = 3, 4, 5 and 9 of quantification of Mn, Cr, Ni and Si, respectively) in the spectral ranges where numerous matrix lines strongly interfered with analytical lines.

Effect of self-absorption correction on LIBS measurements by calibration curve and artificial neural network

Abstract: In this paper, laser-induced breakdown spectroscopy (LIBS) technique is used for concentration prediction of six elements of Mn, Si, Cu, Fe, Zn, and Mg in seven Al samples by two approaches of artificial neural network (ANN) and standard calibration curve. ANN is utilized as a new technique for determination and classification of various materials and elements in LIBS method. In this study, a few spectra of six aluminum standards with known concentrations are used for training of ANN. It should be noted that the mentioned network is not on trial and error basis, but it is a self-organized network. Calibration curve method, which is implemented in represented paper, determines certain relation between concentration and intensity. Then, the calibration curve and ANN methods obtained by six samples are used for prediction of the elements of the seventh standard sample in order to check the accuracy of these methods and make a comparison. In both approaches, a self-absorption correction is applied for high concentrations species and an improvement in prediction of two methods is seen. Results illustrate that at high concentrations except for Si, ANN shows a better prediction with a lower relative error compared to calibration curve approach after self-absorption correction. Primitive study without any self-absorption correction shows that ANN and calibration curve predictions with the best result are related to Fe with R 2 = 0.99 % having the minimum errors.

Practical considerations in the calibration of CT scanners for proton therapy.

Abstract: Treatment planning systems for proton therapy require a CT calibration curve relating Hounsfield units to proton stopping powers. An understanding of the accuracy of this curve, together with its limitations, is of utmost importance because the calibration underpins the calculated dose distribution of every patient preparing to undergo proton therapy, independent of delivery technique. The most common approach to the calibration is the stoichiometric method, which is well-defined and, in principle, straightforward to perform. Nevertheless, care must be taken when implementing it in the clinic in order to avoid introducing proton range uncertainties into treatment plans that are larger than the 3.5% that target margins are typically designed to account for. This work presents a variety of aspects related to the user-specific implementation of the stoichiometric calibration, from both a measurement setup and a data-handling point of view, and evaluates the potential impact of each for treatment planning purposes. We demonstrate that two alternative commercial vendors' tissue phantoms yield consistent results, that variable CT slice thickness is unimportant, and that, for a given cross-sectional size, all phantom data can, with today's state-of-the-art beam hardening-related artifact reduction software, be acquired quickly and easily with a single scan, such that the resulting curve describes the calibration well at different positions across the imaging plane. We also show that one should be cautious of using metals in the calibration procedure and of using a single curve for anatomical sites differing widely in size. Further, we suggest that the quality of the parametric fit to the measurement data can be improved by performing a constrained, weighted linear regression. These observations, based on the 40 separate curves that were calculated, should help the medical physicist at any new proton therapy facility in deciding which considerations are worth particular attention.

Potentiality of chemometric approaches for the determination of (+)-catechin in green tea leaves at the surface of multiwalled carbon nanotube paste electrode

Abstract: Differential pulse voltammetry technique assisted by chemometric methods such as multivariate curve resolution-alternating least squares (MCR-ALS) has been proposed as a valuable approach for (+)-catechin determination in the presence of gallic acid at the surface of multiwalled carbon nanotube paste electrode. Central composite design and response surface methodology were used to optimize the influencing parameters. To determine (+)-catechin in the presence of unexpected electroactive interference with a very high degree of overlapping, second-order electrochemical data were generated by changing the pulse height as an instrumental parameter. After potential shift correction, MCR-ALS results show that second-order calibration could be applied with great success for electroanalytical determination of highly overlapped electroactive species. The linear least-squares calibration curve based on the area under concentration profile was provided over the range of 0.10–2.69 μM for (+)-catechin, whereas detection limit was found to be 0.017 μM. Also in this study, the effect of rotational ambiguity associated with a particular MCR solution under a set of constraints was investigated.

Improving provenance studies in migratory birds when using feather hydrogen stable isotopes

Abstract: Hydrogen stable isotopes (δ2H) in feathers are used to determine the origin and migration strategy of birds. To identify the geographic location of the site of feather synthesis, calibration curves for the relation between feather δ2H and amount-weighted growing-season δ2H in precipitation are used to generate feather δ2H isoscapes. Factors like species, age and year might generate isotopic variation in calibration curves, but the extent to which accounting for variation may improve calibration curves and hence provenance determination of birds, is unknown. We compared three European calibration curves: 1) an existing multi-species curve, uncorrected for age and year variation, and two species-specific calibration curves, based on mallard Anas platyrhynchos feathers, of 2) varying age and year, and 3) juvenile natal origin, corrected for year variation. Calibration curves using ordinary least square linear regression (OLS) as opposed to standard major axis regression showed least bias in estimation. As expected, we found that a single species (mallard) OLS calibration curve corrected for age and year yielded the highest coefficient of determination, but was still surprisingly similar to the other two calibration curves. Nevertheless, when using feathers of known-origin to assess provenance accuracy, the calibration curve that accounted for species, age and year variation yielded the best prediction in as many as 59% of the cases. Our study is the first to demonstrate implications of isotopic variation on assessing the origin of individual birds, but also highlights the relatively small gain in precision that is achieved by generating species, age and year specific calibration curves rather than resorting to more general alternatives.

Cloud point extraction of some precious metals using Triton X-114 and a thioamide derivative with a salting-out effect

Abstract: A cloud point extraction procedure is proposed for preconcentration of trace amounts of palladium (II), silver (I) and gold (III) in aqueous medium. The metal ions in the initial aqueous solution were extracted using the non-ionic surfactant, Triton X-114 after complex formation with 4-( p -chlorophenyl)-1-(pyridin-2-yl)thiosemicarbazide at pH 6.0 in the presence of 0.3 mol L −1 sodium sulfate as a salting-out agent at 25 °C. Dilution of the surfactant-rich phase with acidified methanol was performed after phase separation, and the metal ions were determined by electrothermal atomic absorption spectrometry. The main factors affecting extraction procedure, such as pH, concentration of the ligand, and amount of Triton X-114 were studied in detail. Under the optimum experimental conditions, the calibration graphs were linear upto 125, 50 and 100 μg L −1 and the enrichment factors were 52, 46 and 56 for palladium, silver and gold, respectively. The limits of detection, based on three times of standard deviation of blank signal by 10 replicate measurements divided by the slope of calibration curves were 0.12, 0.08 and 0.30 μg L −1 for palladium, silver and gold, respectively. The accuracy of the results was verified by analyzing spiked water samples. The proposed method has been applied for the determination of the metal ions in soil and rock samples with satisfactory results.

Single point calibration for semi-quantitative screening based on an internal reference in thin layer chromatography-SERS: the case of Rhodamine B in chili oil

Abstract: Thin layer chromatography (TLC) has been used in combination with surface enhanced Raman spectroscopy (SERS) for onsite screening of various analytes. In this work, we propose a novel concept for future field semi-quantitative SERS screening applications, where calibration curves were pre-built in the lab but subjected to onsite single point known standard amendment. Rhodamine B (RhB) in chili oil, a case of food scandal reported in China, was chosen as our model sample. A standard calibration curve of RhB was built using melamine as an internal standard and used throughout the assay. Before the analysis of samples, one single known RhB standard mixed with melamine was tested and used to calibrate the previously built standard calibration curve. RhB in chili oil was separated through the TLC method. Then, it was extracted and mixed with melamine. The signal of the mixture was recorded and compared with the single point calibrated calibration curve, instead of building a new curve each time. A limit of quantification (LOQ) of RhB from chili oil by SERS, 1.00 × 10−7 M, was realized for the first time, and the recovery range was from 66.1% to 110%, despite the fact that the cheapest and non-uniform SERS substrate was used. We expect such a protocol could be used for future fast onsite food quality assurance inspection.

Quantification of 33 antidepressants by LC-MS/MS—comparative validation in whole blood, plasma, and serum

Abstract: In the present study, a liquid chromatography-mass spectrometry (LC-MS/MS) multi-analyte approach based on a simple liquid-liquid extraction was developed for fast target screening and quantification of 33 antidepressants in whole blood, plasma, and serum. The method was validated with respect to selectivity, matrix effects, recovery, process efficiency, accuracy and precision, stabilities, and limits. In addition, cross-calibration between the three biosamples was done to assess the impact of the different matrices on the calibration. Whole blood, plasma, and serum (500 μL each) were extracted twice at pH 7.4 and at pH 10 with ether-ethyl acetate (1:1). Separation, detection, and quantification were performed using LC-MS/MS with electrospray ionization in positive mode. For accuracy and precision, full calibration was performed with ranges from subtherapeutic to toxic concentrations. The approach was sensitive and selective for 33 analytes in whole blood and 31 analytes in plasma and serum and accurate and precise for 30 of the 33 tested drugs in whole blood, 31 in plasma, and 28 in serum. Cross-calibration was successful only for 13 analytes in whole blood and 16 analytes in serum calculated over a calibration curve made in plasma, 12 analytes in whole blood and 15 analytes in plasma calculated over a calibration curve made in serum, and 10 analytes in plasma and 15 analytes in serum calculated over a calibration curve made in whole blood.

Gaining improved chemical composition by exploitation of Compton-to-Rayleigh intensity ratio in XRF analysis.

Abstract: The high specificity of the coherent (Rayleigh), as well as incoherent (Compton) X-ray scattering to the mean atomic number of a specimen to be analyzed by X-ray fluorescence (XRF), is exploited to gain more information on the chemical composition. Concretely, the evaluation of the Compton-to-Rayleigh intensity ratio from XRF spectra and its relation to the average atomic number of reference materials via a calibration curve can reveal valuable information on the elemental composition complementary to that obtained from the reference-free XRF analysis. Particularly for matrices of lower mean atomic numbers, the sensitivity of the approach is so high that it can be easily distinguished between specimens of mean atomic numbers differing from each other by 0.1. Hence, the content of light elements which are “invisible” for XRF, particularly hydrogen, or of heavier impurities/additives in light materials can be calculated “by difference” from the scattering calibration curve. The excellent agreement between s...

Application of Dispersive Liquid–Liquid Micro-extraction Using Mean Centering of Ratio Spectra Method for Trace Determination of Mercury in Food and Environmental Samples

Abstract: In the present study, dispersive liquid–liquid micro-extraction has been applied for trace extraction and determination of mercury (Hg) ions in environmental samples. The mean centering of ratio spectra method was used to optimize the experimental parameters affecting the extraction of Hg. The factors influencing the extraction procedure such as type and volume of extracting and disperser solvent, concentration of chelating reagent, pH, salt effect, and centrifuge time were investigated and optimized. Under the optimized conditions, the limit of detection of the method was 0.15 μg l−1 and enrichment factor was 39. The calibration curve was linear in the range of 0.5–100 μg l−1 with a correlation of determination (R2) of 0.998. The relative standard deviation for determination of 40 μg l−1 of Hg(II) was 2.6 % (n = 5). The proposed method was applied for the determination of Hg in pine leaf, sea and river fish, sand, and water samples as indicators of environmental pollution and cigarette with satisfactory analytical results. In comparison with other methods, the proposed method is very simple, easy, rapid, and sensitive for determination of Hg at trace levels in complex matrices.

Quantitation of sugar content in pyrolysis liquids after acid hydrolysis using high-performance liquid chromatography without neutralization.

Abstract: A rapid method for the quantitation of total sugars in pyrolysis liquids using high-performance liquid chromatography (HPLC) was developed. The method avoids the tedious and time-consuming sample preparation required by current analytical methods. It is possible to directly analyze hydrolyzed pyrolysis liquids, bypassing the neutralization step usually required in determination of total sugars. A comparison with traditional methods was used to determine the validity of the results. The calibration curve coefficient of determination on all standard compounds was >0.999 using a refractive index detector. The relative standard deviation for the new method was 1.13%. The spiked sugar recoveries on the pyrolysis liquid samples were between 104 and 105%. The research demonstrates that it is possible to obtain excellent accuracy and efficiency using HPLC to quantitate glucose after acid hydrolysis of polymeric and oligomeric sugars found in fast pyrolysis bio-oils without neutralization.

Quantitative determination of manganese in aqueous solutions and seawater by laser-induced breakdown spectroscopy (LIBS) using paper substrates.

Abstract: The detection of manganese (Mn) in industrial wastewater and seawater plays an important role in pollution monitoring and the investigation of geochemical and biological processes in the ocean. An approach has been introduced in this work to improve the detection sensitivity of Mn in liquids by laser-induced breakdown spectroscopy with a filter paper as solid substrate. The calibration curves of Mn in aqueous solutions were obtained with the detection of a Czerny-Turner spectrometer and an echelle spectrometer, respectively. The results showed that the Czerny-Turner spectrometer equipped with an intensified charge-coupled device (ICCD) had a more sensitive detection of Mn in aqueous solution with this approach. The limit of detection (LOD) for Mn was down to 0.11 mg/L with laser pulse energy of 90 mJ. With the same approach, the compact echelle spectrometer equipped with an ICCD was used to verify the feasibility for rapid onsite detection. The calibration curves for Mn in simulated industrial wastewater and seawater were constructed to calculate relevant LODs. The LODs of Mn were 2.78 mg/L in mixed solutions and 2.73 mg/L in seawater by calculation. Both the calibration curves and LODs were affected slightly by the matrix effect in the experiment. In order to assess the accuracy, a mixed solution including Mn, Cr, Cd, and Cu with known concentrations was determined, and good agreement between the measured and real values were achieved. It demonstrated that this approach has significant potential for rapid onsite detection of Mn and other metal elements in industrial wastewater and seawater.

Exploration of a 3D nano-channel porous membrane material combined with laser-induced breakdown spectrometry for fast and sensitive heavy metal detection of solution samples

Abstract: In this paper, a nano-channel material was combined with laser induced breakdown spectroscopy (LIBS) to achieve sensitive and quick detection of metal ions in liquid samples. A 3D anodic aluminum oxide porous membrane (AAOPM) was selected as a novel substrate for the first time, which showed excellent potential for liquid analysis. It is worth mentioning that the LIBS signal of the target elements in aqueous solution dropped on the 3D AAOPM was increased by up to 19 times in comparison with that on the tablet sample made of aluminium oxide powder. The attractive results are mainly attributed to the peculiar structure of the 3D AAOPM. Firstly, an abundant strong coordination metal–oxygen bond between hydroxyl groups and metal ions existed on the surface of the novel substrate. Secondly, the extremely high aspect ratio of the 3D AAOPM could supply a much larger contact area between the matrix and analytes. Thirdly, the special nano-channel distribution could make efficient coupling of a laser beam with the materials. Finally, the sample pervasion and volatilization could be finished within a very short time because of the micrometer level thickness and porosity of the 3D AAOPM. The calibration curves with linearity ranges (1–100 μg mL−1) and good linearity (R squared better than 0.983 for all of the four target elements) were established, and the limits of detection (LODs) obtained were 0.18 μg mL−1, 0.12 μg mL−1, 0.081 μg mL−1, and 0.11 μg mL−1 for Cu2+, Ag+, Pb2+, and Cr3+, respectively. In real sample analyses, the recoveries of three elements at different concentration levels were all in the range of 92.5–107.4%, with the relative standard deviations of parallel samples around 10.0%. This novel method showed a fast, simple and super sensitive monitoring tool for liquid sample analysis compared with the traditional LIBS method.

Photon-counting detector calibration

Abstract: A method includes determining calibration factors for calibrating photon-counting detectors of a spectral imaging system by combining a heuristic calibration of the photon-counting detectors and an analytical calibration of the photon-counting detectors and generating a set of photon-counting calibration factors based on the combining of the a heuristic calibration and the analytical calibration. The photon-counting calibration factors, when applied to measured energy-resolved data from the photon-counting detectors of a spectral CT scan of a subject or object, mitigate spectral distortion caused by a radiation intensity profile shaper that filters a radiation beam of the spectral CT scan.

Advanced calibration for analyte sensors

Abstract: Systems and methods for processing sensor data and calibration of the sensors are provided. In some embodiments, the method for calibrating at least one sensor data point from an analyte sensor comprises receiving a priori calibration distribution information; receiving one or more real-time inputs that may influence calibration of the analyte sensor; forming a posteriori calibration distribution information based on the one or more real-time inputs; and converting, in real-time, at least one sensor data point calibrated sensor data based on the a posteriori calibration distribution information.

Development of a Simple and Fast Electrochemical Method for Screening and Stoichiometric Determination of Dimenhydrinate

Abstract: Dimenhydrinate (DIM) is a salt composed by the combination of two active pharmaceutical ingredients: diphenhydramine (DIP) and 8-chlorotheophylline (CTP). In this work, the use of batch injection analysis with multiple pulse amperometric detection (BIA-MPA) was proposed for the first time for fast stoichiometric determination of DIM. DIP (cation) and CTP (anion) were determined simultaneously in pharmaceutical samples with a simple and fast injection procedure (70 injections h−1). Additional strategies were also proposed for rapid screening of samples containing the DIM salt. By a simple injection of a sample into the BIA system (without using of calibration curve), reliable information about stoichiometry of the DIM salt (1 : 1; DIP:CTP) and presence or absence of interfering species (electroactive) can be achieved.

1:10 希釈合成試料ガラスビードを用いた蛍光x 線分析装置による岩石中の主成分元素の定量分析

Abstract: A high dilution ratio glass bead with a sample to flux ratio of 1:10 was prepared for a wide range of major element analyses using X-ray fluorescence spectrometer. Calibration curves were determined from 16 rock standards of the Geological Survey of Japan (GSJ) and 4 synthetic samples employing the software of the instrument. The precision of the calibration curves was sufficiently high, and the reproducibility was of adequate quality when compared to the 1:10 glass bead methods in other institutions laboratories. This method enables the measurement of igneous and metamorphic rocks that have extreme or anomalous bulk chemical compositions.

Reasons for calibration standard curve slope variation in LC-MS assays and how to address it.

Abstract: A consistent calibration curve slope is a positive indication of assay performance in a validated bioanalytical method using LC–MS/MS. It is one of the quality indicators utilized by bioanalytical scientists during the data review process. However, it is not uncommon that a calibration curve slope varies significantly across different analytical runs during sample analysis. The causes for such variation and their potential impacts on the assay ruggedness have been discussed on multiple occasions [1,2]. Although there is no specific requirements for the acceptability of calibration curve slope in regulatory guidelines, a scientific understanding of what is behind the observed deviation is valuable during method development, validation and sample analysis. Large variance in curve slope often indicates potential issues associated with a method. We advocate always assessing and understanding root cause for such variance and this paper tries to illustrate possible causes for the calibration curve slope variation (including the linearity change) and assess their impacts on the analysis results.