Construction Of Calibration Curve Research Articles

The utility of ultra‐performance liquid chromatography/electrospray ionisation time‐of‐flight mass spectrometry for multi‐residue determination of pesticides in strawberry

The utility of ultra-performance liquid chromatography/orthogonal-acceleration time-of flight mass spectrometry (UPLC/TOFMS) for the rapid qualitative and quantitative analysis of 100 pesticides targeted in strawberry was assessed by comparing results with those obtained using a validated in-house UPLC tandem mass spectrometry (MS/MS) multi-residue method. Crude extracts from retail strawberry samples received as part of the 2007 annual UK pesticide residues in food surveillance programme were screened for the presence of pesticide residues using UPLC/TOFMS. Accurate mass measurement of positive and negative ions allowed their extraction following 'full mass range data acquisition' with negligible interference from background or co-eluting species observed during UPLC gradient separation (in a cycle time of just 6.5 min per run). Extracted ion data was used to construct calibration curves and to detect and identify any incurred residues (i.e. pesticides incorporated in or on the test material following application during cultivation, harvest and storage). Calibration using matrix-matched standards was performed over a narrow concentration range of 0.005-0.04 mg kg(-1) with determination coefficients (r2) > or =0.99 for all analytes with the exception of malathion/fenarimol/fludioxanil (r2 = 0.98), quassia/pymetrazine (r2 = 0.97) and fenthion sulfone (r2 = 0.95). Residues found in selected samples ranged from 0.025-0.28 mg kg(-1) and were in excellent agreement with results obtained using UPLC/MS/MS. Mass measurement accuracies of < or =5 ppm were achieved consistently throughout the separation, mass range and concentration range of interest thus providing the opportunity to obtain discrete elemental compositions of target ions.

Determination of trace elements in bone by two-jet plasma atomic emission spectrometry

This paper describes an analytical method for trace element determination in bone tissues. The study of the influence of the bone matrix showed that the addition of 25% ground bone to graphite powder with introduced impurities did not affect the analytical signal of elements in the spectral excitation in a two-jet plasma. On basis of these investigations a method for direct multielement analysis of bone tissues was suggested. The sample preparation procedure consisted in mixing powdered bone (particle size 30μm or less) with a spectroscopic buffer (graphite powder plus NaCl) in ratio 1:3 or to a greater extent depending on the analyte concentration. Reference samples based on graphite powder were used for construction of calibration curves. The NaCl concentration in analyzed and calibration samples was 15 wt%. The effect of particle size was revealed from the determination of Ba, Sr, and Mg. To eliminate this effect, treatment of the samples with nitric acid was proposed. The validation of the technique was confirmed by comparison of the analysis results of a bone sample with those obtained by inductively coupled plasma atomic emission spectrometry after wet acid digestion. The limits of detection estimated for 20 elements were the following (μg g(-1)): 0.1 (Ag), 1.0 (Al), 1.0 (Ba), 0.1 (Be), 1.2 (Bi), 0.4 (Cd), 1.0 (Co), 0.2 (Cu), 0.6 (Cr), 1.9 (In), 2 (Fe), 0.3 (Ga), 0.4 (Mn), 0.4 (Mo), 0.7 (Ni), 1.0 (Pb), 0.7 (Sn), 0.8 (Tl), 5 (Sr), 1.0 (Zn).

Detection and quantification of root-knot nematode (Meloidogyne javanica), lesion nematode (Pratylenchus zeae) and dagger nematode (Xiphinema elongatum) parasites of sugarcane using real-time PCR

A number of different plant parasitic nematode species are found associated with sugarcane in South Africa. Of these, the root-knot nematode (Meloidogyne javanica), the lesion nematode (Pratylenchus zeae) and the dagger nematode (Xiphinema elongatum) are potentially the most damaging pests. Identification and enumeration of the number of these nematodes are necessary for providing advice to farmers as well as studying the effects of various treatments in field and glasshouse trials. We report on the development, use, and extent of specificity of three sets of primers, for M. javanica, P. zeae and X. elongatum, and on tests to detect and quantify the number of these nematodes in soil samples using SYBR Green I dye and real-time PCR technology. Amplicons from the three target species (obtained with their respective primer sets) are discernible in size by gel electrophoresis (380bp for M. javanica, 250bp for P. zeae and 500bp for X. elongatum). Also, these amplicons have characteristic melting temperatures of 83.8 degrees C (M. javanica), 86.6 degrees C (P. zeae) and 86.1 degrees C (X. elongatum). Investigations into multiplex reactions found competition between species with M. javanica competing with P. zeae and X. elongatum. Subsequent single tube (simplex) assays, enabled the construction of calibration curves for each of the three species. These were then used for quantification of the numbers of each of these species in nematode samples extracted from the field, with a high (R2=0.83) and significant positive correlation between real-time PCR and counts performed with microscopy.

Development of Rapid Real-Time PCR and Most-Probable-Number Real-Time PCR Assays To Quantify Enterotoxigenic Strains of the Species in the Bacillus cereus Group

Members of the Bacillus cereus group may produce diarrheal enterotoxins and could be potential hazards if they enter the food chain. Therefore, a method capable of detecting all the species in the B. cereus group rather than B. cereus alone is important. We selected nhe as the target and developed a real-time PCR assay to quantify enterotoxigenic strains of the B. cereus group. The real-time PCR assay was evaluated with 60 B. cereus group strains and 28 others. The assay was also used to construct calibration curves for different food matrices and feces. The assay has an excellent quantification capacity, as proved by its linearity (R2 > 0.993), wide dynamic quantification range (102 to 107 CFU/g for cooked rice and chicken, 103 to 107 CFU/ml for milk, and 104 to 107 CFU/g for feces), and adequate relative accuracy (85.5 to 101.1%). For the low-level contaminations, a most-probable-number real-time PCR assay was developed that could detect as low as 100 CFU/ml. Both assays were tested with real food samples and shown to be considerably appropriate for B. cereus group detection and quantification.

Solubility and Size Separation of Large Fullerenes in Concentrated Sulfuric Acids

We show that large fullerenes (LFs) are soluble in concentrated sulfuric acids. We employ a centrifugation technique in conjunction with ultraviolet−visible and near-infrared (UV−vis−nIR) spectroscopy to quantify solubility. The Beer's Law dependence of UV−vis−nIR absorbance of LFs in concentrated sulfuric acids between 400 and 1400 nm facilitates the construction of linear calibration curves for measuring LF concentration in acids. Centrifugation of concentrated dispersions of LFs in concentrated sulfuric acids results in a clear phase separation. UV−vis-nIR absorbance measurements on the less concentrated phase yield the solubility of LFs. Large fullerenes exhibit an unusually high solubility in sulfuric acids concentrated in the range of 88−96%. The solubility of LFs in 96% sulfuric acid is higher than the solubility of the smallest fullerene (C60) in many organic solvents. We find that the solubility of LFs grows with acid strength, as is expected for solubilization by a protonation mechanism. Moreove...

Quantitation of Humalog Insulin by Reversed-Phase High-Performance Liquid Chromatography

The methodology for in vitro testing of insulin delivery systems for long-term infusion of lispro insulin requires insulin flow studies over time, with the measurement of lispro concentrations in wells or other laboratory fluid collection systems. We postulated that the efficiency of the insulin assay could be improved if the insulin collected in the wells could be measured without having to perform dilutions of insulin samples. The manufacturer's method for the identification of Humalog(R) insulin by high-performance liquid chromatography (HPLC) does not provide a detailed method for the quantitation of the clinical formulation. No reports could be found in the literature describing a method to quantitate lispro insulin's entire concentration range, nor could we find detailed information on pH effects. The purpose of this study was to investigate the use of a reversed-phase HPLC method to quantitate Humalog insulin at three levels of pH. Serial dilutions of Humalog insulin stock solution were prepared at pH levels of 2.6 and 7.4 (concentrations 0.20-100 IU/ml) to construct calibration curves. Samples were also prepared at lower concentrations (0.23-15.0 IU/ml) at pH levels of 4.0 and 7.4. Areas under curve data were plotted against known concentrations, and the limit of quantitation and precision of the assay were determined. Calibration curves for the 0.20-100 IU/ml concentration (pH 7.4 and 2.6) revealed no significant differences (p < 0.01) between those curves. pH and concentration did not have an effect on the overall precision of the method. Linearity was not conserved past the 15-IU/ml concentration. Coefficient of variation (CV) values were generally <15% except at the lower concentrations where the largest CVs were observed. Mean known concentrations plotted on a logarithmic scale demonstrated linearity from 12.5 to 100 IU/ml. Humalog insulin clinical formulation can be quantitated over the entire concentration range by a reversed-phase HPLC method using nonlinear regression analysis. The method is reproducible at lower (<15 IU/ml) and higher insulin concentrations. Linear regression analysis may be used when the concentrations of interest are in the 0- to 15-IU range. Preparation of insulin solutions at pH 2.6, 4.0, and 7.4 did not significantly affect the reproducibility of the assay.

Mass Spectral Behavior of the Hydrolysis Products of Sesqui- and Oxy-Mustard Type Chemical Warfare Agents in Atmospheric Pressure Chemical Ionization

Bis(2-hydroxyethylthio)alkanes and bis(2-hydroxyethylthioalkyl)ethers are important biological and environmental degradation products of sulfur mustard analogs known as sesqui- and oxy-mustards. We used atmospheric pressure chemical ionization mass spectrometry (APCI MS) to acquire characteristic spectra of these compounds in positive and negative ionization modes. Positive APCI mass spectra exhibited [M + H](+); negative APCI MS generated [M + O(2)](-), [M - H](-), and [M - 3H](-); and both positive and negative APCI mass spectra contained fragment ions due to in-source collision-induced dissociation. Product ion scans confirmed the origin of fragment ions observed in single-stage MS. Although the spectra of these compounds were very similar, positive and negative APCI mass spectra of the oxy-mustard hydrolysis product, bis(2-hydroxyethylthiomethyl)ether, differed from the spectra of the other compounds in a manner that suggested a rearrangement to the sesqui-mustard hydrolysis product, bis(2-hydroxyethylthio)methane. We evaluated the [M + O(2)](-) adduct ion for quantification via liquid chromatography-MS/MS in the multiple-reaction monitoring (MRM) mode by constructing calibration curves from three precursor/product ion transitions for all the analytes. Analytical figures of merit generated from the calibration curves indicated the stability and suitability of these transitions for quantification at concentrations in the low ng/mL range. Thus, we are the first to propose a quantitative method predicated on the measurement of product ions generated from the superoxide adduct anion of the sesqui-and oxy-mustard hydrolysis products.

Radiocarbon Analysis of Tree Rings from a 15.5-Cal kyr BP Pyroclastically Buried Forest: A Pilot Study

We have determined the radiocarbon ages for 40-yr-interval tree rings in 2 fossil trees of the Towada Hachinohe buried forest, northeastern Honshu Island, Japan. The 14C ages range from 13.0 to 13.3 kyr BP (about 15.5 cal kyr BP). The weighted average of the 14C age of the outermost 5 rings is 13,133 ± 33 BP, which can be calibrated to 15,363–15,679 cal BP by using the IntCal04 standard curve (Reimer et al. 2004). The estimated δ14C values range between 265 and 300% and show approximately sinusoidal fluctuation of an indicated ∼200-yr cycle, perhaps reflecting contemporary solar activity change. Comparison between the tree 14C profile and the Cariaco Basin 14C record provides further information on the accurate date of the Towada Hachinohe buried forest and the eruption that produced it. 14C analysis of tree rings from the buried forest may contribute to the construction of a better 14C calibration curve and the elucidation of solar activity change during the last glacial period, as well as possible global and regional impacts of the huge eruption from Towada Volcano.

Radiolytic studies on some organic dyes in aqueous solutions

Radiolytic studies on four aqueous dye solutions were carried out. Colour bleaching of the dye solutions upon irradiation was followed by quantitative TLC. Spot comparison methods were used to determine the dependence of the Spot Area Weight (SAW) of the chromatographic spots on the spot content. A good linear relationship was obtained. The percentage changes of SAW values of the analysed dye samples, after being subjected to different known γ-irradiation doses, were used to construct calibration curves. The straight sections of the calibration curves were used to determine the irradiation doses given to some test samples. The results obtained showed that the applied method could be used to determine γ-irradiation doses using aqueous dye solutions.

Comparative analysis of lamivudine in two commercially available brands using HPLC and UV-VIS spectroscopy

One of the components of care for people living with HIV/AIDS is the use of antiretroviral drugs (ART) and the successful outcome of these drugs requires proven quality, safety and efficacy. The quality of these drugs can be assessed by qualitative and quantitative analysis using different analytical techniques. The objective of this study is to compare the analytical results of two brands of ART drug, Lamivox-150 and Lamidine using high pressure liquid chromatography (HPLC) and UV spectroscopy in order to select a validated, simple, cost-effective and affordable analytical technique. The two brands of a lamivudine tablets were quantified against a reference standard, lamivudine with HPLC and UV spectroscopy and the results were compared. The HPLC method involves the use of methanol:acetonitrile (5:95) as a mobile phase, and octadecylsilane (C18) as a stationary phase. For UV spectroscopic analysis, complete release of the active ingredient from the tablets was achieved with 0.01N HCl using ultrasonic bath for 10 min. This is followed by subsequent quantitative determination of the released drug at maximum absorbance wavelength of 280 nm. Concentrations of lamivudine ranging from 0.2-2 mg/ml and 1.6-16 µg/m were used to construct calibration curves for HPLC and UV spectroscopic analyses, respectively. The content of lamivudine per tablet in Lamivox-150 and Lamidine was found to be in agreement with the labelled amount when analysed by both techniques (p

On-line sample preconcentration by sweeping with dodecyltrimethylammonium bromide in capillary zone electrophoresis

On-line sample preconcentration of oligonucleotides with a new sweeping carrier was developed by using dodecyltrimethylammonium bromide (DTAB) below the critical micelle concentration (CMC). The sweeping results with DTAB below and above the CMC were compared. The use of DTAB below the CMC benefits the preconcentration of the oligonucleotides, while the use of DTAB above the CMC is good for hydrophobic small molecules. The factors affecting the sweeping results were optimized and this method was evaluated by constructing calibration curves for thrombin aptamers. The sweeping scheme produced a 112-fold sensitivity enhancement for the oligonucleotides relative to that run in a running buffer without DTAB. The sweeping method developed here can be a good reinforcement of the preconcentration scheme by sweeping when less-hydrophobic analytes or large negatively-charged molecules need to be preconcentrated.

The statistics of the fractional moments: Is there any chance to “read quantitatively” any randomness?

The statistical meaning of higher Δ N ( p ) ( p = 1 , 2 , … ) and fractional Δ N ( p ) ( 0 < p < ∞ ) moments for an arbitrary random sequence of the length N has been found. The higher moments help to reduce the sequence analyzed to a finite set of k statistically stable parameters, keeping invariant the values of the first kth moments Δ k ( p ) ( p = 1 , 2 , … , k ) . The conditions of statistical stability and proximity expressed in terms of higher moments Δ N ( p ) = Δ N + k ( p ) ( p = 1 , 2 , … , k ) help to find k unknown stable points and predict possible future behavior of the random sequence analyzed. The generalized mean value (GMV)-function defined as G N ( p ) = ( Δ N ( p ) ) 1 / p is turned to be very effective in analysis of statistically close random sequences or containing large numbers of measured points ( N ⪢ 1 ) . The approximate analytical expression for an arbitrary p value from the range ( - ∞ < p < ∞ ) entering into G N ( p ) has been found. It gives a possibility to transform any random sequence to the determined GMV curve and express quantitatively the reduced characteristics of any random sequence in terms of a ‘universal’ set of the fitting parameters defined by the determined GMV-function. Statistical proximity factor can be used for construction of calibration curves, when it is necessary to compare one random sequence with another one to respect of variations of some given external factor (small signal). The higher moments are easily generalized for the fractional and even complex moments. In turn, the GMV-function can be also generalized and then calculated for 2D and 3D random sequences. The approach developed in this paper is free from any model assumption and can be extremely helpful in comparison of different random sequences using for these purposes the ‘unified’ quantitative language based on introduction of the given set of fractional moments. The relationship between the value of the fractional moment and nonextensive parameter q entering into the definition of the nonextensive Tsallis entropy has been found. A possible model of statistical protection of plastic cards and other valuable documents demonstrating the effectiveness of the statistics of fractional moments has been considered. Some instructive examples in detection of superweak signals embedded into the basic random sequence ( S / N = 10 - 2 , 10 - 3 ) based on model and real data confirm the effectiveness of new approach and can serve a new basis for numerous practical applications. Analysis of dielectric spectroscopy data by means of fractional moments gives unique possibility to compare quantitatively each measurement with each other and express the influence of a neutral additive in terms of calibration curve without concrete knowledge of the corresponding fitting function.

Determination of the Substrate Specificity of Tripeptidyl-peptidase I Using Combinatorial Peptide Libraries and Development of Improved Fluorogenic Substrates

Classical late-infantile neuronal ceroid lipofuscinosis is a fatal neurodegenerative disease caused by mutations in CLN2, the gene encoding the lysosomal protease tripeptidyl-peptidase I (TPP I). The natural substrates for TPP I and the pathophysiological processes associated with lysosomal storage and disease progression are not well understood. Detailed characterization of TPP I substrate specificity should provide insights into these issues and also aid in the development of improved clinical and biochemical assays. To this end, we constructed fluorogenic and standard combinatorial peptide libraries and analyzed them using fluorescence and mass spectrometry-based activity assays. The fluorogenic group 7-amino-4-carbamoylmethylcoumarin was incorporated into a series of 7-amino-4-carbamoylmethylcoumarin tripeptide libraries using a design strategy that allowed systematic evaluation of the P1, P2, and P3 positions. TPP I digestion of these substrates liberates the fluorescence group and results in a large increase in fluorescence that can be used to calculate kinetic parameters and to derive the substrate specificity constant kcat/KM. In addition, we implemented a mass spectrometry-based assay to measure the hydrolysis of individual peptides in peptide pools and thus expand the scope of the analysis. Nonfluorogenic tetrapeptide and pentapeptide libraries were synthesized and analyzed to evaluate P1' and P2' residues. Together, this analysis allowed us to predict the relative specificity of TPP I toward a wide range of potential biological substrates. In addition, we evaluated a variety of new fluorogenic peptides with a P3 Arg residue, and we demonstrated their superiority compared with the widely used substrate Ala-Ala-Phe-AMC for selectively measuring TPP I activity in biological specimens.

High-performance liquid chromatographic method for simple and rapid determination of linezolid in human plasma

A simple high-performance liquid chromatographic (HPLC) method was developed and validated for rapid quantification of linezolid in human plasma. Protein precipitation using a mixture of 5% trichloroacetic acid and methanol (3:1, v/v) provided a straightforward method of sample preparation and the internal standard eperezolid was employed. A concentration range from 0.20 to 40.0 mg/L was utilized to construct calibration curves, and analysis of low- (0.40 mg/L), medium- (7.50 mg/L) and high-quality (25.0 mg/L) control samples revealed excellent reproducibility (<or=3.88%) and accuracy (<or=4.20%). The recovery of both linezolid and eperezolid was approximately 100%. No interference was observed at the retention times of linezolid and eperezolid from blank plasma or eight commonly used antibiotics. Tests confirmed the stability of linezolid in plasma during three freeze-thaw cycles, on the bench during 24 h and during long-term storage of frozen plasma for up to 12 weeks; in extracts it was stable in the HPLC autosampler over 12 h. Overall, this assay offers a highly simplistic approach to quantifying linezolid in plasma, and would be well suited to clinical pharmacokinetic, pharmacodynamic and toxicodynamic analyses.

Determination of Pesticides in Soy-Based Infant Formula Using Liquid Chromatography with Electrospray Ionization Tandem Mass Spectrometry

A sensitive method using liquid chromatography with electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) was developed and validated to quantify and confirm 13 pesticides, including aldicarb sulfoxide, aldicarb sulfone, oxamyl, methomyl, formetanate, 3-hydroxycarbofuran, carbendazim, thiabendazole, aldicarb, propoxur, carbofuran, carbaryl, and methiocarb, in soy-based infant formula. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring of 2 fragment ion transitions to provide a high degree of sensitivity and selectivity for both quantitation and confirmation. Different approaches to constructing calibration curves were compared and discussed to address issues of the extraction efficiency or recovery, and matrix effects. Matrix-matched standard calibration curves with the use of isoprocarb as an internal standard were finally used to achieve the best accuracy of the method. Under most circumstances, recoveries of 13 pesticides, spiked at 5.0, 25.0, and 45.0 microg/kg, were close to 100%. The method detection limits (signal-to-noise ratio > or =3:1; microg/kg) of 13 pesticides were 0.2 for thiabendazole and methiocarb, 0.6 for aldicarb, and 0.1 for the others.

Calorimetric determination of amorphous content in lactose: A note on the preparation of calibration curves

Calorimetric methods (isothermal or solution calorimetry) offer the ability to detect amorphous contents to 0.5% (w/w) or better in processed pharmaceuticals and calorimetric data are becoming more widely accepted in regulatory submissions. However, both methods require the construction of calibration curves, prepared using quantitative physical mixtures of entirely amorphous and entirely crystalline material. If the sample under investigation exists in two or more isomers or polymorphs, and the enthalpy of solution (solution calorimetry) or the enthalpy of crystallisation (isothermal calorimetry) are different for the isomers or polymorphs, then it must be ensured that the batch of material used to prepare the calibration samples has the same isomeric or polymorphic composition as the (processed) material to be tested. Here, we demonstrate the problems that may arise using lactose as a pharmaceutically important model substance. Calibration curves were prepared from solution calorimetry and isothermal gas perfusion calorimetry data using two batches of lactose (one predominantly anhydrous α-lactose and one predominantly β-lactose). The calibration curves are shown to be significantly different for the two batches, and it is shown that quantification of the amorphous content of a processed sample of unknown isomeric composition is impossible, unless the calibration curve is prepared from the same batch of material as the processed sample. In addition, some of the other problems inherent in using isothermal gas perfusion calorimetry for amorphous content determination, such as wetting issues and the preparation of calibration standards that mimic processes samples, are discussed.

Mesoscopic Concentration Variations Analyzed by Secondary Ion Mass Spectrometry

ABSTRACT Secondary ion mass spectrometry (SIMS) was used to identify concentration gradients of polyacrylate samples. Applying discriminant function analysis (DFA) on the SIMS spectra resulted in visualized separations between different sample concentrations. We identified and separated concentrations of polyacrylate blends; from the separation we can construct calibration curves. The visual identification was followed in depth of a poly(fluoro-acrylate) film covered by poly(iso-bornylmethacrylate), which served as model sample of a photo-induced phase separated device. The combination of SIMS and DFA offers new possibilities to study the phase separation processes. Furthermore, it can predict how the phase separation creates mesoscopic layered electro-optical devices.

Aluminum alloy analysis using microchip-laser induced breakdown spectroscopy

A laser induced breakdown spectroscopy-based apparatus for the analysis of aluminum alloys which employs a microchip laser and a handheld spectrometer with an ungated, non-intensified CCD array has been built and tested. The microchip laser, which emits low energy pulses (4–15 μJ) at high repetition rates (1–10 kHz) at 1064 nm, produces, when focused, an ablation crater with a radius on the order of only 10 μm. The resulting emission is focused onto an optical fiber connected to 0.10 m focal length spectrometer with a spectral range of 275–413 nm. The apparatus was tested using 30 different aluminum alloy reference samples. Two techniques for constructing calibration curves from the data, peak integration and partial least squares regression, were quantitatively evaluated. Results for Fe, Mg, Mn, Ni, Si, and Zn indicated limits of detection (LOD) that ranged from 0.05 to 0.14 wt.% and overall measurement errors which varied from 0.06 to 0.18 wt.%. Higher limits of detection and overall error for Cu (> 0.3 wt.%) were attributed to analysis problems associated with the presence of optically thick lines and a spectral interference from Zn. Improvements in design and component sensitivity should increase overall performance by at least a factor of 2, allowing for dependable aluminum alloy classification.

A correlated method for quantifying mixed and dispersed carbon nanotubes: analysis of the Raman band intensities and evidence of wavenumber shift

AbstractWe present an experimental investigation of a correlated quantitative analytical method based on advanced Raman spectroscopy. This method was developed for the intensity weight distribution analysis of mixed and dispersed carbon nanotube (CNT) mixtures. For Raman spectroscopy, mixtures of single‐walled CNTs (SWNTs) and multi‐walled CNTs (MWNTs) were prepared and dispersed on a coverslip. Mixtures were made in the range from 1 to 100 mg (wt%) of SWNTs in 100 to 1 mg (wt%) of MWNTs. The ratios of the relative intensities of the Raman bands corresponding to pure SWNTs and pure MWNTs were used for the construction of calibration curves used for quantitative analysis. The relative intensity of the deconvoluted spectral bands shows a characteristic feature at 1350 and 1592 cm−1 which was found to be proportional to the relative amounts of SWNTs and MWNTs in the mixtures. A correlation between the atomic force microscopy images and the tangential mode Raman intensity ratio was used without the need for other analytical techniques. With this feature, it is possible to quantify the different components in the mixed, dispersed or unknown bulk of the CNTs investigated. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Application of probability circles analysis to the construction of calibration curves for infra red spectroscopy

A new method, based on the presentation of initial data in the form of probability circles (PC), has been developed for constructing a calibration curve, which shows a monotonic dependence with respect to the given concentration. The centre of the reference probability circle is defined by its mean value and the radius of the circle is calculated as the value of the standard deviation of the sampling considered. The comparative probability circle is defined by the same corresponding parameters but rotated, relative to the initial reference circle, by an angle, which is related to the Pearson's correlation coefficient (PCC). The two parameters of the PCC and the statistical proximity factor (PCF), which defines the positions of the centres of the circles relative to each other, can be chosen as statistical parameters for the construction of the desired calibration curve. Experiments realized with the mixture of two liquids (chloroform serves as the basic matrix) and acetone (serves as an additive) confirm the efficiency of this new analytical method and demonstrate a possible increase sensitivity for the detection of lower concentration limit by approximately one order of magnitude. This new approach, which is free from model assumptions, and having very clear geometrical meaning, can be applied for different types of spectra and has many potential applications in the construction of calibration curves for different additives embedded within different matrices.