Extraction of the contribution of kinetic profile for reaction of a chemical species in unknown matrices by standard addition method

A new and simple strategy is applied to resolve kinetic profile for the reaction of an analyte in unknown matrices, using standard addition method (SAM). The proposed method uses kinetic spectrophotometric data obtained by standard addition of analyte into unknown mixtures followed by the reaction of analyte with a proper reagent. The proposed method extracts kinetic profile for the reaction of an analyte by averaging the kinetic profiles obtained by subtraction of kinetic profiles after and before standard addition. The rate constant can be obtained using computational curve fitting. The performance of method was evaluated by using synthetic data as well as several experimental data sets. The proposed method can be applied to obtain kinetic profiles of the reactions in the presence of additive interference as well as multiplicative interferences. Hydroxylation reaction of diphenylcarbazide (DPCI) in the presence of diphenylcarbazone (DPCO) as a real system at various pHs was also studied by the present method. The rate constant and the order of the hydroxylation reaction were determined from extracted kinetic profiles.     

Study of ε-caprolactone polymerization by NIR spectroscopy

Near-infrared (NIR) spectroscopy is proposed for the in-line quantitative and kinetic study of the polymerization of ε-caprolactone and eventually to facilitate real-time control of the manufacturing process. Spectra were acquired with a fibre-optic probe operating in transflectance mode immersed in the reactor. The NIR data acquired were processed using a multivariate curve resolution alternating least squares (MCR-ALS) algorithm. The proposed method allows calculation of the concentration and spectral profiles of the species involved in the reaction. The key point of this method is the lack of reference concentrations needed to perform the MCR-ALS method. The use of an extended spectral matrix using both process and pure analyte spectra solves the rank deficiency. The concentration profiles obtained were used to calculate a kinetic fitting of the reaction, but the method was improved by applying kinetic constraints (hard modelling). The rate constants of batches at different temperatures and the energy of activation for this reaction were calculated. Whenever possible, the hard modelling combined with the MCR-ALS method improves the fit of the experimental data: the results show good correlation between the NIR and reference data and allow the collection of high-quality kinetic information on the reaction (rate constants and energy of activation).     

Pre-study and in-study validation of a SPE-LC-MS-MS method for the determination of 5-S-cysteinyldopa, a melanoma biomarker, in human plasma

The incidence of malignant melanona has increased over the past decades, particularly in Caucasian population. This disease presents defavourable prognosis in terms of survey, especially when detection occurs at the metastatic phase. Reliable analytical methods for biomarker determination are thus an interesting tool in pathology detection and follow-up. In this context, a method using SPE-LC-ESI-MS-MS for the determination of 5-S-cysteinyldopa (5-SCD) in human plasma was optimized. The presence of matrix effect was investigated in details while 5-SCD stability was studied according to FDA requirements for the validation of bioanalytical methods. Pre-study and in-study validations of the entire method were then successfully performed by applying the approach based on total measurement error and accuracy profiles over a concentration ranges from 1.6 to 200 ng/ml. Good results with respect to accuracy, trueness and precision were obtained. The maximum risk of observing future measurements falling outside the acceptance limits during routine analysis was also estimated.     

Curing reaction of glycidylthioether resins: Kinetic model study by near infrared spectroscopy and multivariate curve resolution

The reactivity of sulfur‐based epoxy monomers was studied by monitoring of a model system involving phenylglycidylthioether and aniline. The reaction was carried out under isothermal conditions and monitored in situ by near infrared spectroscopy. Using multivariate curve resolution‐alternating least squares made it possible to obtain the concentration and spectral profiles of each species throughout the reaction. To obtain the kinetic rate constants, the values of the recovered concentration profiles were fitted to a kinetic model proposed for the reaction. Reactivity was evaluated by comparing the concentration profiles and kinetic rate constants obtained with the same parameters obtained for phenylglycidylether/aniline as a reference system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4846–4856, 2006     

Development of a selective and sensitive spectrophotometric method for the trace determination of thallium(III) using 3-methyl-2-benzothiazolinone hydrazone hydrochloride and N-(1-naphthyl)-ethylenediamine dihydrochloride

A simple, selective, sensitive, and rapid spectrophotometric method has been developed for the determination of thallium(III) using 3-methyl-2-benzothiazolinone hydrazone hydrochloride and N-(1-naphthyl)-ethylenediamine dihydrochloride. The obtained product had an absorption maximum of 590 nm. Beer's law was valid over the concentration range of 0.15-8 microg/mL. The molar absorptivity and Sandell's sensitivity of the colored system were 2.93 x 10(4) L/mol x cm and 0.00723 microg/mL, respectively. The effect of different acids on the sensitivity of the method, interference by foreign substances, the optimum reaction conditions, and other analytical parameters were evaluated. The proposed method has been successfully applied in the analysis of T1(III) in standard reference materials, synthetic mixtures, and water and urine samples. The performance of the proposed method was evaluated in terms of Student's t-test and variance ratio F-test, which indicated the significance of the proposed method over reported methods.     

Development of a mass spectrometry method for the determination of a melanoma biomarker, 5-S-cysteinyldopa, in human plasma using solid phase extraction for sample clean-up

5-S-cysteinyldopa is a well-known pigment intermediate and analysis of its plasma concentration is interesting for the early diagnosis, as well as for evaluation of treatment and follow-up of malignant melanoma. A determination method of 5-SCD in human plasma was developed using solid phase extraction (SPE) on disposable cartridges and liquid chromatography electrospray mass spectrometry (LC-ESI-MS-MS). Compound's sensitivity to light and oxidation requires the addition of anti-oxidative agents (AO), to work in acidic media at 4 degrees C and to avoid light exposure of samples since blood collection. Different solid phases involving covalent binding to phenylboronic groups or dual retention mechanisms were evaluated and extraction cartridges containing both hydrophobic and strong cation exchange functionalities were finally selected. The LC separation of 5-SCD from endogenous catecholamines was achieved by gradient elution on a C18 stationary phase. 5-SCD was detected by multiple reaction monitoring (MRM) performed on ES(+) generated ions. Finally, the method was prevalidated in the lower ng/ml range. Good results with respect to accuracy, trueness and precision were obtained.     

Nonaqueous capillary electrophoresis method for the enantiomeric purity determination of S-timolol using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin: validation using the accuracy profile strategy and estimation of uncertainty

Nonaqueous capillary electrophoresis (NACE) was successfully applied to the enantiomeric purity determination of S-timolol maleate using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD) as chiral selector. With a background electrolyte made up of a methanolic solution of 0.75 M formic acid, 30 mM potassium camphorsulfonate and containing 30 mM HDMS-beta-CD, the determination of 0.1% of R-timolol in S-timolol could be performed with an enantiomeric resolution of 8.5. Pyridoxine was selected as internal standard. The NACE method was then fully validated by applying a novel strategy using accuracy profiles. It is based on beta-expectation tolerance intervals for the total measurement error which includes trueness and intermediate precision. The uncertainty of measurements derived from beta-expectation tolerance intervals was estimated at each concentration level of the validation standards. To confirm the suitability of the developed and validated method, several real samples of S-timolol maleate containing R-timolol maleate at different concentrations were analysed and the results were compared to those obtained by liquid chromatography.     

Development of a nano-liquid chromatography on chip tandem mass spectrometry method for high-sensitivity hepcidin quantitation

Microfluidic LC systems present undeniable advantages over classical LC in terms of sensitivity. Hepcidin, a peptide marker of clinical disorders linked to iron metabolism, was used as model to demonstrate peptide quantification potentialities of LC-chip coupled to a nanoelectrospray source ion trap mass spectrometer in an aqueous sample. First, stable isotope labelled hepcidin was chosen as internal standard and gradient as well as sample compositions were optimised using design of experiments as development tool. The method was then prevalidated using accuracy profiles in order to select the most appropriate response function and to confirm the ability of the technique to quantify low hepcidin concentration. A reliable and very sensitive quantitation method was finally obtained using this integrated microfluidic technology. Indeed, good results with respect to accuracy, trueness and precision were achieved, as well as a very low limit of quantitation (0.07 ng/ml). Method suitability of nano-LC on chip tandem mass spectrometry for hepcidin quantitation was also demonstrated in complex media such as human plasma.     

A simple method of target preparation for the bulk analysis of powder samples by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

A simple and rapid procedure using a glue technique has been developed for the preparation of stable targets from powder samples for bulk analysis by LA-ICP-MS. The procedure was evaluated for the analysis of trace elements in SiC, of rare-earth elements in different types of silicate (rocks, sediments, and soils), and of Au and platinum-group elements in geological silicates. The test analysis was conducted using an IR laser in combination with a quadrupole mass spectrometer. The recommended preparation procedure offers the possibility of different types of calibration, for example application of certified reference samples in combination with prepared spiked samples on a base of a natural or synthetic matrix, or addition calibration. The resulting calibration functions are linear over a range of several decades. The trueness of the results was evaluated by use of certified reference samples. Analytical concentration ranges, detection limits, and the relative standard deviations are reported.     

Spectrophotometric investigation of the effect of beta-cyclodextrin on the intramolecular cyclization reaction of catecholamines using rank annihilation factor analysis

The catalytic effect of β-cyclodextrin (β-CD) on the intramolecular cyclization reaction of catecholamines dopamine, methyldopa and levodopa after their oxidation with periodate was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The method was based on the effect of β-CD concentration on the intramolecular cyclization reaction of the investigated catecholamines after their oxidation with potassium periodate. In order to perform RAFA, concentration profiles were calculated by optimizing the value of formation constant. The rank of original data matrix can be reduced by one by annihilating the information of the cyclization reaction in the absence of β-CD. The rate constant for the reactions in the presence and absence of β-CD was also determined. The best estimation of rate constant in the presence of β-CD reduces the rank of the system to zero (noise level). The method was evaluated using synthetic data as well as experimental data and good results were obtained.     

Measurement uncertainty evaluation and in-house method validation of the herbicide iodosulfuron-methyl-sodium in water samples by using HPLC analysis

A method for separation and quantitative determination of the iodosulfuron-methyl-sodium in water samples by high-performance liquid chromatography (HPLC) was developed and in-house validated in order to demonstrate its performance for monitoring of heterogeneous photocatalytic elimination of the herbicide iodosulfuron-methyl-sodium from water. Surface and ground water samples were used to demonstrate its selectivity, detection and quantification limits, linearity, trueness and precision. In addition, stability of iodosulfuron-methyl-sodium was studied in function of temperature and time. Method accuracy was quantified through measurement uncertainty estimate based on method validation data. The paper gives practical and easy to follow guidance on how uncertainty estimates can be obtained from method validation experiments. It shows that, if properly planned and executed, key precision and trueness studies undertaken for validation purposes can also provide much of the data needed to produce an estimate of measurement uncertainty. Our analytical protocol allowed us to quantify iodosulfuron-methyl-sodium in ground water and surface water in concentration level between 2.50–50.0 μmol L⁻¹ with satisfactory recoveries (99–104%) and repeatability lower or equal than 0.3% for all the matrices. We also estimated within-laboratory reproducibility over 3-month period, which was 0.7%. We proved that the method was selective for determination of iodosulfuron-methyl-sodium in the relevant matrices. Measurement uncertainty of results was evaluated to be 4.0% with 95% confidence level. After validation and measurement uncertainty evaluation steps, results obtained showed that the method can be applied to efficiently monitor heterogenous photocatalytic degradation of the herbicide iodosulfuron-methyl-sodium.     

Investigation of the Effect of Inclusion of Eriochrome Black T with β-Cyclodextrin on Its Complexation Reaction with Ca2+ and Mg2+ Using Rank Annihilation Factor Analysis

Rank annihilation factor analysis (RAFA) was used to investigate the effects of inclusion of eriochrome black T (EBT) on its complexation reaction with Ca²⁺ and Mg²⁺ at different pH values. Addition of β-cyclodextrin (β-CD) to Ca-EBT or Mg-EBT caused decomposition of the 1:1 metal complex and increase in EBT concentration in solution due to the formation of EBT-β-CD inclusion complex. In order to perform RAFA, concentration profiles were calculated by optimizing the value of the conditional stability constant and inclusion constant. The rank of original data matrix reduces by one by removing the information from the complex form (Ca-EBT or Mg-EBT). The performance of the method was evaluated by using synthetic data as well as experimental data and good results were obtained. The proposed method is capable of the simultaneous spectrophotometric determination of formation constant of a complex and the equilibrium constant of the competing reaction in solution.     

A new fluorimetric method for the determination of formaldehyde in air based on the liquid droplet sampling technique

A new, simple, sensitive, selective and in-field fluorimetric method for the determination of formaldehyde is proposed. The reaction of formaldehyde with hydralazine in acidic medium, heating on a boiling water-bath for 25 min, produces s-triazolo[3,4-a]phthalazine (Tri-P). The fluorescence intensity of the product formed (Tri-P) was determined at lambda em = 389 nm with lambda ex = 236 nm. The fluorescence intensity is linear over a formaldehyde concentration range of 1.2-33.0 micrograms l-1. The proposed method was applied successfully to the determination of formaldehyde sampled from the atmosphere using the liquid droplet technique. Formaldehyde vapour in a wind tunnel was produced by a mean of permeater. A linear curve was obtained between the concentration in the wind tunnel and that in the droplet. The detection limit for formaldehyde was 2.0 micrograms l-1 with RSDs varying from 3 to 12% in ambient air, using a droplet correction solution (boric acid and hydralazine). The effect of interfering substances on the determination shows that most cations and anions did not interfere. The results obtained were satisfactory compared with a reference method.     

Evaluation of N-bromosuccinimide as a new analytical reagent for the spectrophotometric determination of fluoroquinolone antibiotics

Analytical studies were carried out, for the first time, to evaluate the use of N-bromosuccinimide (NBS) as an analytical reagent for the spectrophotometric determination of eleven therapeutically important fluoroquinolone antibiotics (FQA). The procedures involved the reaction of the FQA with NBS and subsequent measurement of the excess NBS by its reaction with p-phenylenediamine (PDA) to give a violet colored product that was measured at 530 nm. Different variables affecting the reaction (concentration of NBS, concentration of PDA, pH of reaction medium, reaction time, and the diluting solvents) were carefully studied and optimized. The molar ratio and mechanism of the reaction between each of the studied FQA with NBS were proposed using UV-vis, IR, and NMR techniques. Under the optimum reaction conditions, the analytical method was developed and validated. Beer's law was obeyed in the general concentration range of 3-25 microg/ml. The assay limits of detection and quantitation were 0.33-1.29 and 1.10-4.31 microg/ml, respectively. The precision of the method was satisfactory; the values of relative standard deviations did not exceed 2%. The proposed method was successfully applied to the analysis of the investigated FQA in their pure and pharmaceutical dosage forms without interference from the common excipients (label claim values were 99.85-100.17+/-0.13-0.59%). Interference from ascorbic acid, that is co-formulated as a stabilizer for the ampoule form, was avoided by its pre-oxidation with potassium bromate before applying the analytical procedure. The results obtained by the proposed method were comparable with those obtained by the official and reported methods.     

Determination of rhenium content in molybdenite by ICP-MS after separation of the major matrix by solvent extraction with N-benzoyl-N-phenylhydroxalamine

A simple and rapid analytical method for determining the concentration of rhenium in molybdenite for Re-Os dating was developed. The method used isotope dilution-inductively coupled plasma-mass spectrometry (ID-ICP-MS) after the removal of major matrix elements (e.g., Mo, Fe, and W) from Re by solvent extraction with N-benzoyl-N-phenylhydroxylamine (BPHA) in chloroform solution. The effect on extraction efficiency of parameters such as pH (HCl concentration), BPHA concentration, and extraction time were also assessed. Under the optimal experimental conditions, the validity of the separation method was accessed by measuring ¹⁸⁷Re/¹⁸⁵Re values for a molybdenite reference material (JDC). The obtained values were in good agreement with previously measured values of the Re standard. The proposed method was applied to replicate Re-Os dating of JDC and seven samples of molybdenite from the Yuanzhuding large Cu-Mo porphyry deposit. The results demonstrate good precision and accuracy for the proposed method. The advantages of the method (i.e., simplicity, efficiency, short analysis time, and low cost) make it suitable for routine analysis.     

Kinetic Spectrophotometric Determination of Ritodrine Hydrochloride in Dosage Forms

A simple and sensitive kinetic method was developed for the determination of ritodrine hydrochloride in pharmaceutical preparations. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permenganate at room temperature for a fixed 12.5 min; the absorbance of the colored permenganate ion was measured at 609 nm. The absorbance concentration plots were rectilinear over the range of 1.6–11.2 μg mL^?1 (r = 0.9992) with a minimum detectability of 0.096 μgmL^?1 (2.88 × 10^?7 M). The different experimental parameters affecting the development and stability of color were carefully studied and optimized. The determination of ritodrine hydrochloride by the fixed concentration and rate constant methods is also feasible with the calibration equations obtained, but the fixed time method has been found to be more applicable. The proposed method was applied successfully to the determination of ritodrine hydrochloride in tablets and ampoules with average recoveries of 100.37 ± 0.93% and 100.42 ± 0.87%, respectively. The results obtained were in good agreement with those obtained using a reference method for comparison. A proposal of the reaction pathway is also presented.     

Estimation of measurement uncertainty for the determination of nonylphenol in water using solid-phase extraction and solid-phase microextraction procedures

We describe an estimation of measurement uncertainty calculated by the “bottom-up” approach for the determination of the oestrogenic compound nonylphenol in treated water samples by solid-phase extraction (SPE) and solid-phase microextraction (SPME) procedures and GC/MS detection. The results were compared and the different contributions to the uncertainty were evaluated. A study of the linear range was established and validation was performed for both methods using statistical analysis of several indicative parameters. In terms of validation data, precision (R.S.D. values <20%) and trueness (relative error <11%) were obtained for both methods under day-to-day conditions. The results of the estimation of measurement uncertainty obtained for both methods for concentrations higher than 1 μg/l have demonstrated that the time-consuming SPE method has a lower relative uncertainty (32%) than the SPME method (42.8%). The chromatographic uncertainty value was the main factor in the SPME method whereas the recovery factor (used to calculate the concentration) was the main contribution to uncertainty in the SPE method.     

Kinetic spectrophotometric determination of ethamsylate in dosage forms

A simple and sensitive kinetic method has been developed for the determination of ethamsylate (ESL) in its pharmaceutical preparations. The method is based upon oxidation of ESL with 3-methyl-2-benzothiazolinone hydrazone hydrochloride in presence of cerium (IV) ammonium sulfate at room temperature for 20 min. The absorbance of the reaction product is measured at 514 nm. The absorbance-concentration plot was rectilinear over the range of 4-30 microg/mL (r = 0.9999). The lower detection limit was 0.267 microl/mL (9.110 x 10(-6) M) and the lower quantitation limit was 0.808 microg/mL. The different experimental parameters affecting the development and stability of the reaction product were studied and optimized. The proposed method was applied to the determination of ESL in formulations, and the results obtained were in good agreement with those obtained using a reference method. The proposed method was also used for the in vitro detection of ESL in spiked human plasma at its therapeutic concentration level.     

Assessing oral bioaccessibility of trace elements in soils under worst-case scenarios by automated in-line dynamic extraction as a front end to inductively coupled plasma atomic emission spectrometry

A novel biomimetic extraction procedure that allows for the in-line handing of ≥400 mg solid substrates is herein proposed for automatic ascertainment of trace element (TE) bioaccessibility in soils under worst-case conditions as per recommendations of ISO norms. A unified bioaccessibility/BARGE method (UBM)-like physiological-based extraction test is evaluated for the first time in a dynamic format for accurate assessment of in-vitro bioaccessibility of Cr, Cu, Ni, Pb and Zn in forest and residential-garden soils by on-line coupling of a hybrid flow set-up to inductively coupled plasma atomic emission spectrometry. Three biologically relevant operational extraction modes mimicking: (i) gastric juice extraction alone; (ii) saliva and gastric juice composite in unidirectional flow extraction format and (iii) saliva and gastric juice composite in a recirculation mode were thoroughly investigated. The extraction profiles of the three configurations using digestive fluids were proven to fit a first order reaction kinetic model for estimating the maximum TE bioaccessibility, that is, the actual worst-case scenario in human risk assessment protocols. A full factorial design, in which the sample amount (400–800 mg), the extractant flow rate (0.5–1.5 mL min⁻¹) and the extraction temperature (27–37 °C) were selected as variables for the multivariate optimization studies in order to obtain the maximum TE extractability. Two soils of varied physicochemical properties were analysed and no significant differences were found at the 0.05 significance level between the summation of leached concentrations of TE in gastric juice plus the residual fraction and the total concentration of the overall assayed metals determined by microwave digestion. These results showed the reliability and lack of bias (trueness) of the automatic biomimetic extraction approach using digestive juices.