Search results for "Internal standard"
showing 10 items of 14 documents
Development of the H-point standard additions method for analyte determinations in unknown matrix
1993
Abstract The development of the H-point standard additions method is proposed in order to obtain the unbiased analyte concentration when the matrix of the sample is completely unknown. A spectral region where the interferent behaviour can be considered linear at three wavelengths must be chosen. The method uses the analytical signal data at these three wavelengths, usually situated in the maxima region of the analyte. Two procedures are proposed in order to know and to locate this behaviour for the unknown interferent. Several binary and ternary mixtures of phenol, 4-chlorophenol and 4-chloro-3-methylphenol as representative examples have been assayed, with accurate (less than 3% relative e…
Generalised H-point standard addition method for the isolation of the analyte signal from the sample signal when coelution of unknown compounds occur…
1999
The generalised H-point standard addition method (GHPSAM) is proposed for isolating the analytical signal of an analyte from the signal of an unknown sample. Samples containing two and three coeluting compounds have been analysed. The accuracy of the predictions depends on the shape of the analyte and interferent spectra but not on the degree of chromatographic overlap. This methodology involves the location of linear intervals for the unknown interference spectrum from the spectrum of the sample. Once the linear interval has been found the selection of three wavelengths within the interval will allow the cancellation of the signal of the unknown interferent. The method has been applied to …
A mathematical model based on the limit dilution method to obtain linear calibration curves which eliminate the matrix effect in quantitative analysi…
1995
Abstract We propose a mathematical model from an analytical application viewpoint inspired in the limit dilution method. The theoretical development of the model and its results are given. The model shows that there is a linear relation between the inverse of fluorescence intensity and the inverse of the dilution factor; each analytic system (sample, diluent and analyte) is characterised by a general linear function which is easily obtained. The analytical applications arising from this linearity are of great importance in X-ray fluorescence analysis. The following immediate applications are proposed: direct procurement of the total correction factor Y/H, rapid calculation of the fluorescen…
Quantitative electron probe microanalysis of metallic oxide mixtures applying an empirical calibration technique
1997
Abstract An analytical procedure is proposed for the independent quantitative chemical analysis of each element in the presence of other elements in the matrix of a sample by Energy Dispersive Electron Probe Microanalysis. For this purpose, an empirical calibration technique (which we shall call here the JABO method), which studies the variation of the X-ray intensities in terms of the analyte concentration in a chemical system with a complex matrix, is established. The methodology consists of the modification of the unknown sample by addition of a diluent, an internal standard and the analyte itself (dilution-addition method). A mathematical model is proposed to calculate the K parameters …
Study of mycotoxin calibration approaches on the example of trichothecenes analysis from flour
2012
The aim of this study was to evaluate the applicability of different calibration approaches in trichothecenes analysis from wheat flour. Concretely eight trichothecenes (five type B trichothecenes and three type A trichothecenes) were analyzed by matrix solid-phase dispersion (MSPD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In the first set of experiments the presence of matrix effects was evaluated; values ranged between 59% and 79%. In the second set of experiments, solutions to compensate these signal suppressions were examined. Different calibration methods showed to tackle matrix effects obtaining values between 69% and 85% for external matrix matched calibration a…
Application of an HPLC-MS/MS method for mycotoxin analysis in commercial baby foods
2012
Abstract This article describes the validation of an analytical method for the detection of 21 mycotoxins in baby food. The analytical method is based on the simultaneous extraction of selected mycotoxins by matrix solid-phase dispersion (MSPD) followed by liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS) using a hybrid triple quadrupole-linear ion trap mass spectrometer (QTRAP®). Information Dependent Acquisition (IDA), an extra confirmation tool for samples that contain the selected mycotoxins, was used. The matrix effects were evaluated, and the corrections for the matrix effects were performed using two calibration approaches: external matrix-matched calibration and…
Substitution–dilution method to correct the matrix effect in multi-element quantitative analysis by X-ray fluorescence
2001
Abstract A mathematical model based on the dilution–addition method (DAM) for multi-elemental analysis using an X-ray fluorescence technique is proposed. The conditions for sample preparation do not require both the unknown and standard samples to be similar in composition and mineralogy, and the unknown sample is replaced quantitatively by the standard sample, hence the denomination substitution–dilution method (SDM). This method makes it possible to correct the matrix effect in multi-elemental quantitative analysis by X-ray fluorescence for each analyte. The proposed model presents hyperbolic behaviour of the experimental data when the X-ray fluorescence intensities are represented versus…
H-Point standard additions method for resolution of binary mixtures with simultaneous addition of both analytes
1995
Abstract The basis of the H-point standard additions method, HPSAM, with simultaneous addition of both analytes is proposed for the resolution of binary mixtures. It is a modification of the previously described H-point standard additions method that permits the resolution of both species from a unique calibration set by making the simultaneous addition of the two analytes. The method uses as analytical signals the absorbances at pairs of wavelengths where each species shows the same absorbance. The required data to apply the method are the absorbance values at the previously selected wavelengths for the sample alone and spiked with both species at known concentrations. Linear relations bet…
Determination of metabolite concentrations in human brain tumour biopsy samples using HR-MAS and ERETIC measurements.
2009
Accurate determination of the concentration of the metabolites contained in intact human biopsies of 10 glioblastoma multiforme samples was achieved using one-dimensional 1H high-resolution magic angle spinning (HR-MAS) NMR combined with ERETIC™ (electronic reference to in vivo concentrations) measurements. The amount of sample used ranged from 6.8 to 12.9 mg. Metabolite concentrations were measured in each sample using two methods: with DSS (2,2-dimethyl-2-silapentane-5-sulfonate sodium salt) as an internal reference and with ERETIC™ as an external electronically generated reference. The ERETIC™ signal was shown to be highly reproducible and did not affect the spectral quality. The concent…
Determination and separation of diarylheptanoids from alder growing in Latvia
2015
The composition of diarylhepatnoids fraction isolated from bark of two alder species (grey alder and black alder) was studied. The efficiency of three extraction methods used for isolation of diarylhepatnoids from alder bark was compared. Two diarylhepatnoids: 1,7-bis-(3,4-dihydroxyphenyl)-heptan- 3-one-5-O-β-D-xylopyronoside (oregonin) and 1,7-bis-(3,4-dihydroxyphenyl)-3-hydroxyheptane-5-O-β-D- xylopyranoside were isolated from the bark of grey alder. The phenolic components of the extracts were analyzed by high-performance liquid chromatography (HPLC). Quantitative determination of oregonin was performed using an internal standard method. The results obtained show that alder barks are ric…