Slope Of Calibration Line Research Articles

Multi-well plate as headspaces for paper-based colorimetric detection of sulfur dioxide gas: An alternative method of sulfite titration for determination of formaldehyde

This work describes the analysis of formaldehyde using a 96-well microplate as multiple headspaces for the separation of sulfur dioxide gas generated from the sulfite remaining after its reaction with the formaldehyde in the sample. The quantitation of the gas is by colorimetric detection of an indicator paper placed over the microplate. The samples are aqueous extracts of various foods that are possibly adulterated with formaldehyde. A known excess amount of sulfite is added to the extract solution aliquoted in the well. The remaining sulfite is acidified with hydrochloric acid to generate sulfur dioxide gas which diffuses through the headspace above the solution to be absorbed at the moist strip of the indicator paper placed over the mouth of the wells. Anthocyanins extracted from the butterfly pea flower is used as the pH indicator giving a color change from the increase of hydrogen ions by hydrolysis of the absorbed sulfur dioxide gas. The exposed paper strip is scanned, and the digital images of the colored region analyzed using ImageJ software. The optimized method has a linear range of 200–1000 mg L−1 formaldehyde with limit of detection ((2.57*SD of intercept)/(slope of calibration line)) of the aqueous extract of 40 mg L−1 and coefficient of determination (r2) > 0.9979. Samples of fresh produce, such as seafood, meat, and vegetables, and various processed food were analyzed for their possible formaldehyde content. The results obtained from the headspace paper-based colorimetric detection are not statistically different from the values obtained from the titration method by paired t-tests.

A New Technique of Eliminating the Actual Plasma Background When Calibrating Emission Spectrometers with a CCD Recording System

This research focuses on the development of a new technique of emission spectral analysis designed to accurately account for the background radiation. The technique enables the evaluation of background radiation while being unaffected by its spectral shape. This is possible through the use of standard data obtained in an analytical-line-recording process performed by light-intensity-to-electric-signal converters such as CCDs, PMTs, photodiodes, etc. This technique, when applied at a set RMS deviation of the analytical-line-radiation intensity, reduces the random error of a determined low impure-element concentration due to the optimal calibration-line slope. In areas of high concentrations, an accurate accounting of the background does little to affect the emission spectrometer’s measurement accuracy. This technique also allows the replication of calibration curves in spectrometers of the same type by a linear-intensity conversion with only two standard samples required. The technique was tested on SPAS-02 and SPAS-05 commercial spark spectrometers. The testing fully confirmed the aforementioned advantages of the developed technique. The authors also determined the applicability conditions of the conventional emission-spectrometer-recalibration method by a linear conversion of the analytical-line intensity.

Validated contemporary risk model of acute kidney injury in patients undergoing percutaneous coronary interventions: insights from the National Cardiovascular Data Registry Cath-PCI Registry.

BackgroundWe developed risk models for predicting acute kidney injury (AKI) and AKI requiring dialysis (AKI‐D) after percutaneous coronary intervention (PCI) to support quality assessment and the use of preventative strategies.Methods and ResultsAKI was defined as an absolute increase of ≥0.3 mg/dL or a relative increase of 50% in serum creatinine (AKIN Stage 1 or greater) and AKI‐D was a new requirement for dialysis following PCI. Data from 947 012 consecutive PCI patients and 1253 sites participating in the NCDR Cath/PCI registry between 6/09 and 7/11 were used to develop the model, with 70% randomly assigned to a derivation cohort and 30% for validation. AKI occurred in 7.33% of the derivation and validation cohorts. Eleven variables were associated with AKI: older age, baseline renal impairment (categorized as mild, moderate, and severe), prior cerebrovascular disease, prior heart failure, prior PCI, presentation (non‐ACS versus NSTEMI versus STEMI), diabetes, chronic lung disease, hypertension, cardiac arrest, anemia, heart failure on presentation, balloon pump use, and cardiogenic shock. STEMI presentation, cardiogenic shock, and severe baseline CKD were the strongest predictors for AKI. The full model showed good discrimination in the derivation and validation cohorts (c‐statistic of 0.72 and 0.71, respectively) and identical calibration (slope of calibration line=1.01). The AKI‐D model had even better discrimination (c‐statistic=0.89) and good calibration (slope of calibration line=0.99).ConclusionThe NCDR AKI prediction models can successfully risk‐stratify patients undergoing PCI. The potential for this tool to aid clinicians in counseling patients regarding the risk of PCI, identify patients for preventative strategies, and support local quality improvement efforts should be prospectively tested.

Determination of total sterols in brown algae by Fourier transform infrared spectroscopy

A procedure is proposed for the determination of the total amount of sterols in brown algae Bifurcaria bifurcata, Cladostephus hirsitus, Dictyota dichotoma and Cystoseira sedoides, globally determined as fucosterol, which is the major sterol contained in these algae. The method involves the use of cholesterol as reference standard and a correction factor of 1.259 ± 0.003, which represents the ratio between the slopes of calibration lines obtained from fucosterol and cholesterol. The method provides precise and accurate results for the IR analysis of real samples.

New simple spectrophotometric assay of total carotenes in margarines

Direct and reliable spectrophotometric method for assaying total carotenes (TC) in margarines with the minimum of sample manipulation is proposed. For the first time saponification step used in determination of carotenes in margarines was omitted leading to a substantial cost saving and reduction of time needed to complete the analysis. The resulting analytical procedure is characterized in details in terms of the figures of merit. The method is sensitive, precise and accurate; for both, standard additions and calibration in soybean oil, recovery ranges between 98 and 102%. For the most accurate analyses the approach of standard additions is preferred but for quick routine analyses this latter can be replaced by the calibration in soybean oil. Limit of detection value (LOD = 3S.D. B/ a, where S.D. B is the standard deviation of the blank, “ a” is the slope of calibration line) as low as 12 μg TC/100 g was achieved in soybean oil enabling the sensitive detection. Concentration of TC in margarines declared as being coloured with β-carotene (carotene) ranges between 0.3 and 0.9 mg/100 g while in carrot extract-coloured margarine TC is 0.2 mg/100 g.

Selective spectrophotometric determination of TNT in soil and water with dicyclohexylamine extraction

Contaminated land and groundwater remediation in military waste dumping sites often necessitates the use of simple, cost-effective, and rapid tests for detecting trinitrotoluene (TNT) residues in the field along with their dinitro-analogues. A simple, rapid, low-cost, and field-adaptable (on-site) colorimetric method was developed for quantifying TNT in the presence of RDX, PETN, picric acid, 2,4-DNT (dinitrotoluene), dinitrophenol, and dinitroaniline. Most commercialized methods for TNT assay-with the exception of Cold Regions Research and Engineering Laboratory of the U.S. Army (CRREL) method-use proprietary chemicals, and the color stability and intensity are highly dependent on the composition of the organic solution comprised of acetone or methanol. The developed colorimetric method is based on the extraction of TNT from water–acetone solution into an organic solvent mixture of dicyclohexylamine (DCHA)–isobutyl methyl ketone (IBMK) (10:1, v/v), filtration through a filter paper into a stoppered optical cell containing anhydrous sodium sulfate, and measurement of the absorbance of the organic extract at 531 nm after 5 min. The red-violet color of the extract was due to intermolecular charge-transfer (CT) between the electron attracting TNT and electron-donating DCHA, and the molar absorptivity for TNT in final organic solution was (1.16 ± 0.02) × 10 4 L mol −1 cm −1.The R.S.D. of the slope of calibration line was 0.7%. The LOD of the method in the final organic phase was 0.38 μM TNT, and LOD values expressed on the basis of original soil TNT content were 0.5, 1.3, and 1.5 ppm (μg g −1) for clay, loamy clay, and sandy soils, respectively. Unlike other spectrophotometric methods, the developed assay was basically tolerant to common cations and anions found in soil and water at 100-fold weight ratios, and to soil humic acids. Among a number of compounds that may be encountered in polynitro-explosive storage and waste reclaimation sites such as picric acid, dinitrophenol, 2,4-dinitrotoluene, dinitroaniline, RDX, PETN, and tetryl, only tetryl interfered with the developed TNT assay. Water tolerance and exploitability over a wide pH range were other superiorities over the CRREL method. The CT-complex was relatively stable, as the absorbance of the organic extract was not significantly influenced from the dilution of the water–acetone phase. Aside from the extractive-photometric procedure established for aqueous solutions, a simulated field colorimetric assay for TNT directly applicable to soil was also devised, based on direct color development in a 4:1 (v/v) acetone–dicyclohexylamine organic extract of soil at a liquid-to-solid ratio of 5 mL g −1.

Phase Studies by Diffusive Interfacial Transport Using Near-Infrared Analysis for Water (DIT-NIR)

The Diffusive Interfacial Transport (DIT) method for performing phase studies (in which all the phases that exist along an isotherm are produced by isothermal swelling and their compositions determined by using refractive index data) was introduced in 1987.1 While this method represented a significant qualitative advance in phase studies methodology, its quantitative accuracy has since been found to be unsatisfactory. We describe herein the DIT-NIR method in which execution of the study is the same as before, but peak-area data on the bend−stretch combination band of water are used to determine composition. Peak-area data are obtained by using Fourier transform near-infrared (FT-NIR) microspectroscopy. Calibration studies with octyldimethylphosphine oxide−water mixtures demonstrated that peak areas vary linearly with composition over the entire composition range. The slopes of calibration lines follow a power-law dependence upon temperature. Phase studies of the C12E3−water system, using both DIT-NIR and ...

Effect of plasma pooling on the International Sensitivity Index of prothrombin time systems.

Guidelines set by the World Health Organization (WHO) state that in order to calibrate a prothrombin time system for International Sensitivity Index (ISI), freshly prepared specimens from 20 normal individuals and 60 patients receiving coumarin are required. These numbers are required to obtain a precise value of the calibration line slope when there is considerable scatter of individual data about the regression line. The scatter can be reduced by pooling individual plasma samples. In the present study, four pooled plasmas were prepared, one from 20 normal individuals and three from three groups of 30 patients receiving treatment with long-term oral anticoagulants. Prothrombin times were determined with four thromboplastins, HepatoQuick (rabbit thromboplastin combined with adsorbed plasma), Recombiplastin (recombinant human thromboplastin), Thromborel-S (human placenta), and Thromboplastin-C Plus (rabbit brain). Calibration line slopes were calculated for the six possible combinations of thromboplastins using the set of all individual plasma samples and the set of four pooled plasmas. In most comparisons, the WHO calibration model was appropriate, i.e. the line calculated for the patients' samples passed through the mean of the normals. The calibration line slopes obtained with the set of four pooled plasmas did not differ by more than 5% from the corresponding slopes calculated with the original individual plasmas. For some combinations of thromboplastins non-linear relations were observed both with the individual plasmas and with the pooled plasmas. We conclude that pooling individual plasmas does not significantly change the calibration relation between prothrombin times determined with the original individual plasmas. Freshly pooled plasmas can be used to determine the ISI of prothrombin time systems with an acceptable degree of precision.

A Room Temperature Procedure for the Manual Determination of Urea in Seawater

Several earlier studies underpin the important role of dissolved organic matter and more particularly urea in phytoplanktonic nitrogen uptake fluxes. Generally, the determination of urea concentrations relies on the formation of an imidazolone-thiosemicarbizide complex, a complexation which requires very accurate temperature control when carried out at high temperature. It is also possible, however, to obtain reliable results with a room temperature procedure. The measured abundances for both complexation at high temperature (85°C, 20min) and at ambient temperature (22°C, 72h) are closely comparable. Lower values are observed for temperatures <10°C though. Moreover, a comparison of both techniques reveals similar precision (coefficient of variation: 2%), sensitivity (slope of calibration line: 0·2) and detection limit (0·14mM). The room temperature alternative to the earlier described method is therefore a handy tool for urea analyses, when a strict temperature control is difficult or impossible.

TDR calibration of organic forest floor media

We carried out a time domain reflectometry (TDR) calibration for 25 forest floor samples of five different forest stands. Linear regression was used to estimate the volumetric water content from the refraction index. Due to the presence of bound water, it was impossible to predict the calibration line parameters from theoretical values with a refractive mixing model. However, when the apparent dielectric constant of the water was considered, it was possible to predict the offset parameter because the low forest floor bulk density caused the calibration line slope and offset to be almost reversely proportional. Calibration parameters for different forest floor materials are presented. Allowing a somewhat higher margin of error we could also establish general calibration curves which were in close agreement with a published calibration curve (Malicki et al., 1994). An error analysis showed that decomposition of organic matter, residual water and temperature effects have negligible effects on the calibration parameters. Shrinkage of the organic material significantly influenced both the volumetric water content and the TDR reflection times. If not corrected, both effects yielded systematic errors of approximately 0.02 cm 3 cm −3 for a strongly shrinking H horizon.

Determination of slopes of calibration lines in multi element XRF analysis of thin films using polychromatic excitation from Mo, Au, W, and Cr anodes and one standard.

An algorithm is described for the theoretical calculation of the slopes of calibration lines for the elements of the K-series in multi element X-ray fluorescence analysis of thin films using polychromatic excitation with X-ray tubes producing widely differing primary radiation intensity profiles. The mathematical equations used to calculate slopes as a function of atomic number are based on the fundamental relationship between fluorescent intensity and atomic number, fluorescent yield, concentration and mass absorption coefficients of the analyte for primary radiation. A normalisation procedure based on a single known slope in the series ensured that the calculated slopes were correct for the particular measuring conditions.

An improved micromethod for vancomycin determination by high-performance liquid chromatography.

A micromethod using reversed-phase high-performance liquid chromatography for the analysis of vancomycin in human serum or plasma was developed. Ristocetin was used as the internal standard. Chromatographic conditions included an amino propyl column, a mobile phase with 62% acetonitrile and 38% sodium phosphate buffer (pH 7.0), a total run time of 10 min, and ultraviolet absorbance detection at 225 nm. Multilevel calibration was found to be linear between 1.0 and 100 micrograms/ml with correlation coefficients of the calibration line slope consistently > 0.999. Recovery of vancomycin from serum was nearly complete, and no interference from commonly used drugs was observed. This procedure is simple, sensitive, rapid, precise, selective, and requires only 50 microliters of serum or plasma for completion.

A new procedure for stable quantification of endotoxin in dialysate fluid using Limulus reagent.

For reliable determination of endotoxin, the activation of enzymes in lysate before measurement should be prevented, and the authors have designed a new procedure to effect this by dissolving the enzymes in lysate in a buffer solution of low pH. A given amount of the enzymes in lysate was dissolved in a lower pH buffer solution (pH 6.1-6.3) and the substrate was dissolved in a higher pH buffer solution (pH 8.0). After standing for 0-24 hr, both solutions were mixed with the sample solution. Data on blank absorbance and calibration line slope obtained by the new procedure were compared with those obtained by the conventional procedure. In the conventional procedure, blank absorbance increased with standing time, reaching approximately seven times the initial value in 24 hr, whereas in the improved procedure, it increased by 1.5 times at a standing time of 3 hr, after which it was independent of standing time. The change in slope of the calibration line with standing time was more gradual in the improved procedure than in the conventional procedure. The authors conclude that the activation of enzymes in lysate can be prevented by dissolving the enzymes in a buffer solution of low pH, and that this procedure is effective for long-term monitoring of endotoxin concentration.

Mono-standard calibration approach to multi-element XRF analysis of thin films using polychromatic excitation

A reliable method is described for the calculation of slopes of calibration lines for thin-film samples using polychromatic excitation. Theoretically calculated slopes for elements within one series, e.g. the K-series, are normalized using one or two known slopes for elements in the series. The mathematical equations used to interpolate slopes as a function of atomic number are based on the fundamental relationship between fluorescent intensity and atomic number, fluorescent yield, detector efficiency, concentration and mass absorption coefficients. Kramer's formula is used to approximate the shape of the primary radiation spectrum. The method was applied to the analysis of thin films.

Multi-Center Study of Replacement of the International Reference Preparation for Thromboplastin, Rabbit, Plain

A multi-center study of the three W.H.O. international reference preparations (IRP) for thromboplastin has been performed. The main purpose of the study was the determination of the mean international sensitivity index (ISI) of a proposed replacement IRP for thromboplastin, rabbit, plain. Twenty laboratories in Europe, North America, and Australasia participated in the study. All clotting times were determined with the manual technique. The inter-laboratory variation of the ISI was considered as the relevant parameter for assessment of ISI precision. Low interlaboratory variation was observed in the calibration of rabbit thromboplastin against rabbit thromboplastin (2.9-3.0% coefficient of variation of calibration line slope). Relatively high interlaboratory variation was observed in the calibration of rabbit against human thromboplastin (3.7-7.2 CV). Intermediary interlaboratory variation was obtained in the comparison of rabbit or human plain thromboplastin with bovine combined thromboplastin (3.5-4.0% CV). These findings confirm the principle of like-to-like calibration in biological standardization. The mean ISI values based on the IRP for rabbit thromboplastin (RBT/79) are in excellent agreement with those obtained with the IRP for bovine thromboplastin (OBT/79). In contrast, the mean ISI values determined with the IRP for human thromboplastin (BCT/253) were 6% lower than those with RBT/79. This bias may be caused by a difference in design of the two historical calibration studies. The mean ISI of the proposed replacement IRP for thromboplastin, rabbit, plain obtained by calibration against RBT/79 was 1.035 (standard error: 0.027). It is recommended to round the mean ISI off to 1.0. Opportunity was also taken to compare a lyophilized normal pooled plasma with fresh individual normal plasmas.(ABSTRACT TRUNCATED AT 250 WORDS)

Multi-element X-ray fluorescence analysis of thin films using a mono-standard calibration procedure

A semi-fundamental approach to calibration for multi-element X-ray fluorescence analysis of thin films is described. The curve, calibration line slope vs. atomic number, is calculated using known values for mass absorption coefficients, fluorescent yields and detector efficiency. This curve is then standardised for a particular matrix by determining the slope of at least one matched standard or via a standard addition procedure for one element. The technique is applied to the analysis of industrial waste water.

Oxide bond energies for the calibration of matrix effects in secondary ion mass spectrometry

Analyses of trace and major elements in Group III-V compound matrices by secondary ion mass spectrometry (SIMS) have shown that practical ion yields are related linearly to the matrix composition. The affinity of the matrix to oxygen appears to be the critical factor in this relationship. A direct relationship between the slopes of calibration lines, determined for elements in the same column of the periodic table, and the first ionization potential of the respective elements has also been shown.

Untersuchungen zur Anwendung ternärer Komplexe in der Photometrie—II Die Bestimmung des Titanium(IV) mit Tiron in Gegenwart von Iminodiessigsäure, Nitrilotriessigsäure bzw. Diethylentriaminpentaessigsäure

As part of a study to evaluate the use of ternary complexes in photometric methods of analysis, three model systems involving titanium(IV) and tiron plus iminodiacetic acid, nitrilotriacetic acid or diethylenetriaminepenta-acetic acid have been investigated. The methods were compared in terms of working range, molar absorptivity, standard deviation, coefficient of variation, slope of calibration line, limit of detection and limit of determination. The extent of interference from 20 other ions was also examined. The nitrilotriacetic acid system was shown to have better selectivity than the other two.