Diode-array Spectrophotometric Detection Research Articles

A new functional food ingredient enriched by Phytoecdisteroids and Polyphenols from quinoa grains (Chenopodium quinoa Willd.)

Objective: Quinoa grains (Chenopodium quinoa Willd.) contain a large number of secondary metabolites. Phytoecdysteroids and polyphenols, secondary metabolites, are of great interest for research today. The aim of the study is a method development for the extraction of biologically active substances (BAS) from quinoa grains to obtain a functional food ingredient (FFI) enriched with phytoecdysteroids and polyphenols. Materials and methods: The content of phytoecdysteroids at each stage of quinoa extract production was determined by two methods: HPLC with a spectrophotometric detector and HPLC with a mass spectrometer. The content of total polyphenols was determined by the Folin-Ciocalteu method. The flavonoid profile was determined using a liquid chromatography system with a diode array spectrophotometric detector and a triple quadrupole mass spectrometric detector. Results: The chosen technological scheme for the production of FFI can concentrate more than 200 times the major phytoecdysteroid 20-hydroxyecdysone major in quinoa in the final product relative to the raw material. The maximum yield of flavonoids in the final product was observed in cases of 20 and 40% ethanol extraction. Conclusion: These results lead to the conclusion that highly enriched sources of BAS can be obtained using fairly simple technological approaches and commercially available reagents from quinoa grains.

Simple and fast method for simultaneous determination of propionate and sorbate in bread by capillary electrophoresis with UV spectrophotometric detection

A novel method for simultaneous determination of the preservatives propionate and sorbate in bread samples using capillary electrophoresis with diode array spectrophotometric detection is proposed. This method requires a simple and fast sample preparation using aqueous extraction with sonication aid. A background electrolyte (BGE) composed of 10 mmol L−1 benzoic acid, 15 mmol L−1l-histidine and 0.2 mmol L−1 of cetyltrimethylammonium bromide (CTAB) allowed the separation of the preservatives with good resolution in less than 5 min. Propionate was indirectly detected at 235 nm, and the sorbate was directly detected at 250 nm. The limits of quantification (LOQ) were 4.3 and 1.5 mg kg−1 for propionate and sorbate, respectively. The proposed method was successfully applied for analysis of commercial samples of sliced white bread.

Modeling of second-order spectrophotometric data generated by a pH-gradient flow injection technique for the determination of doxorubicin in human plasma

In this paper, the development of a pH-gradient flow-injection method with diode-array spectrophotometric detection combined with extended multivariate curve resolution–alternating least-squares (MCR–ALS) to quantitate doxorubicin in the presence of rifampicin in plasma samples is presented.Quantitation of doxorubicin was based on acid–base and spectral differences between its species and those for the interference. Overlapped profiles among the analyte and the interference were mathematically solved by data modeling with the well-known extended MCR–ALS algorithm.The method, which involves a simple sample pretreatment consisting in the addition of trichloroacetic acid followed by centrifugation, was applied to resolve validation mixtures composed of human plasma spiked with doxorubicin. Acceptable analytical figures of merit were obtained, i.e. recoveries from 96 to 107%, coefficients of variation between 0.2% and 7.8%, and limits of detection and quantification of 0.77 and 2.32μgL−1, respectively.

Determination of alkyl methylphosphonates and methylphosphonic acid by capillary electrophoresis with a diode-array spectrophotometric detector

Method of capillary electrophoresis with a diode-array detector was used to study the conditions of the separation of three alkyl methylphosphonates and methylphosphonic acid, hydrolysis products of nerve agents. The optimal conditions providing their separation and determination are reported (background electrolyte based on 100 mM boric acid with the addition of 10 mM of phenylphosphonic acid (pH 6.0); voltage +30 kV, detection wavelength 210 nm, electrokinetic introduction of the sample (10 kV, 10 sec), separation time below 10 min). Calibration curve for all the compounds was linear in the concentration range 0.05–1.0 mg/mL, the correlation coefficient was 0.999 in all cases. The procedure was tested for river and ground waters containing a mixture of isopropyl, isobutyl, pinacolyl methylphosphonates and methylphosphonic acid. Relative standard deviations of the migration times under the conditions of the repeatability of the results lie in the range 1.9–2.7% (n = 5), the relative standard deviation of the reduced peak areas vary from 1.2 to 7.0%.

Monitoring imatinib plasma concentrations in chronic myeloid leukemia

Imatinib has proved to be effective in the treatment of chronic myeloid leukemia, but plasma levels above 1,000 ng/mL must be achieved to optimize activity. Therapeutic drug monitoring of imatinib is useful for patients that do not present clinical response. There are several analytical methods to measure imatinib in biosamples, which are mainly based on liquid chromatography with mass spectrometric or diode array spectrophotometric detection. The former is preferred due to its lower cost and wider availability. The present manuscript presents a review of the clinical and analytical aspects of the therapeutic drug monitoring of imatinib in the treatment of chronic myeloid leukemia. The review includes references published over the last 10 years. There is evidence that the monitoring of plasmatic levels of imatinib is an useful alternative, especially considering the wide pharmacokinetic variability of this drug.

Sequential injection titration method using second-order signals: Determination of acidity in plant oils and biodiesel samples

A new concept of flow titration is proposed and demonstrated for the determination of total acidity in plant oils and biodiesel. We use sequential injection analysis (SIA) with a diode array spectrophotometric detector linked to chemometric tools such as multivariate curve resolution-alternating least squares (MCR-ALS). This system is based on the evolution of the basic specie of an acid-base indicator, alizarine, when it comes into contact with a sample that contains free fatty acids. The gradual pH change in the reactor coil due to diffusion and reaction phenomenona allows the sequential appearance of both species of the indicator in the detector coil, recording a data matrix for each sample. The SIA-MCR-ALS method helps to reduce the amounts of sample, the reagents and the time consumed. Each determination consumes 0.413ml of sample, 0.250ml of indicator and 3ml of carrier (ethanol) and generates 3.333ml of waste. The frequency of the analysis is high (12 samples h(-1) including all steps, i.e., cleaning, preparing and analysing). The utilized reagents are of common use in the laboratory and it is not necessary to use the reagents of perfect known concentration. The method was applied to determine acidity in plant oil and biodiesel samples. Results obtained by the proposed method compare well with those obtained by the official European Community method that is time consuming and uses large amounts of organic solvents.

Simultaneous determination of β-lactamic antibiotics by a new high-performance low-pressure chromatographic system using a multisyringe burette coupled to a monolithic column (MSC)

A technique based on multisyringe chromatography (MSC) was developed to determine three beta-lactamic antibiotics. Amoxicillin (AMOXI), ampicillin (AMPI) and cephalexin (CEPHA) were analyzed using a system with a very simple design and very low-cost equipment consisting of a multisyringe module, three low-pressure solenoid valves, a monolithic Chromolith Flash RP-18e column and a diode array spectrophotometric detector monitoring at 250 nm. Mobile phases containing methanol:acetic acid (0.1 M)-sodium acetate (0.1 M), pH 6.2, were tested for various ratios of methanol:acetic acid-sodium acetate, but a ratio of 10:90 gave optimum results with a flow rate of 2 ml min(-1). Validation parameters were evaluated for amoxicillin. The response to amoxicillin was linear over the range 0.04-0.4 mg/mL, with a correlation coefficient of 0.9996; precisions, evaluated as the repeatability for 0.04, 0.16 and 0.4 mg/mL amoxicillin, were 0.6%, 0.1% and 0.6%, respectively. Recovery from a generic formulation of amoxicillin was evaluated. The method showed selectivity in the presence of excipients commonly used in capsules, and satisfactory specificity was observed for amoxicillin and hydrolytic degradation products. The linearity was also evaluated for cephalexin and ampicillin. The conditions selected for MSC separation were compared with those for a HPLC system, and similar results were obtained in terms of chromatographic parameters but a difference in retention times was observed.

Fractional factorial design and simplex algorithm for optimizing sequential injection analysis (SIA) and second order calibration

In this study, we report a method for finding an analytical sequence that allows to simultaneously determine two analytes with very similar physical and chemical characteristics, such as amoxicillin and clavulanic acid, using sequential injection analysis (SIA) with a diode-array spectrophotometric detector and multivariate curve resolution with alternating least squares (MCR-ALS). This method comprises two stages. In the first stage, a fractional factorial design (2 6–2) is carried out in order to address the responses, reduce later experimentation and study how the factors, though confounded, interact with each other. In the second stage, optimization is carried out using the simplex algorithm. This method has advantages over response surface modelling, for example, when the number of significant factors is high. If simplex is begun in a suitable zone, the number of experiments may be considerably reduced.

Sequential Injection Analysis for the Simultaneous Determination of Clavulanic Acid and Amoxicillin in Pharmaceuticals Using Second-order Calibration

In this paper, we report on a method for quantifying clavulanic acid and amoxicillin simultaneously in pharmaceuticals using sequential injection analysis (SIA) with a diode-array spectrophotometric detector and multivariate curve resolution with alternating least squares (MCR-ALS). We optimized the experimental parameters so that the analytical sequence could distinguish the concentrations and spectrum profiles of the species of interest with optimum resolution quality. After establishing the optimum conditions, we quantified clavulanic acid and amoxicillin in four pharmaceuticals. In most cases our results were slightly higher than those in the prospectus of the pharmaceutical. The relative standard deviations were below 5% for amoxicillin and below 7% for clavulanic acid. These results are acceptable because, to prevent degradation due to bacteriostatic activity, the concentration of the main reactant is usually higher.

Use of multivariate curve resolution for determination of chromium in tanning samples using sequential injection analysis

We report a method for determining total chromium in tanning samples using sequential injection analysis (SIA) with a diode-array spectrophotometric detector. With a suitable analytical sequence CrO4(2-) is converted to Cr2O7(2-) inside the tubes of the SIA system, after total oxidation of chromium(III). A data matrix is obtained and analysed by several chemometric techniques based on multivariate analysis: principal components analysis, simple-to-use interactive self-modelling mixture analysis, and multivariate curve resolution-alternating least-squares. We studied several samples from different stages of a tanning process. Two of these samples were easily oxidized but the others needed more extreme conditions. The analytical sequence prepared, which was based on obtaining a pH gradient and used H2SO4 as reagent, is valid and independent of the level of oxidation needed for the sample. We established a calibration model and evaluated the figures of merit. In some samples we found interferents. With this method the amounts of chromium in each sample were quantified and the results were statistically similar to those obtained by use of the reference method, atomic absorption spectrometry.

Use of polyoxyethylene-6-lauryl ether and microwave-assisted extraction for the determination of chlorophenols in marine sediments

Microwave-assisted micellar extraction was optimised and applied to the extraction, prior to analysis by liquid chromatography with diode array spectrophotometric detection, of chlorophenols in marine sediment samples. This study was carried out using a non-ionic surfactant polyoxyethylene-6-lauryl ether as extractant. Parameters studied included surfactant concentration, pH of the solution, extraction time and power. Once the method was optimised, it was applied to different spiked marine sediments from coasts of the Canary Islands (Spain). The results obtained indicate that irradiation of 500 W for 2 min achieved the best extraction efficiency (100% recovery) and standard deviation values <10%. Detection limits were obtained in the range 1.2–12.7 μg g −1 for the chlorophenols studied. The proposed method provides a simple, fast and organic solvent-free procedure to analyse for chlorophenols in marine sediment samples.

Determination of amoxicillin in pharmaceuticals using sequential injection analysis and multivariate curve resolution

In this study, we report a method for quantifying amoxicillin in pharmaceuticals in the presence of interferents using sequential injection analysis (SIA) with a diode-array spectrophotometric detector and multivariate curve resolution with alternating least squares (MCR–ALS). With a suitable analytical sequence, we can use SIA to generate a pH gradient and, for each sample, obtain a data matrix. We used augmented matrices to resolve the system and obtain the spectra and concentration profiles of the components in the sample. We studied what are the effects of imposing trilinearity at the resolution stage, how to choose the species that will be used for quantification (acid, basic or the sum of the two), and which is the most suitable concentration of the reference standard. Once the optimum conditions were established, we performed the quantification in three amoxicillin-containing pharmaceuticals (flubiotic, augmentine, and clamoxyl). With this method, determination is quick, the reactants and instrumentation are inexpensive, and pretreatment of the sample is unnecessary.

Determination of amoxicillin in pharmaceuticals using sequential injection analysis (SIA): Evaluation of the presence of interferents using multivariate curve resolution

In this study, we report a method for determining amoxicillin in pharmaceuticals using sequential injection analysis (SIA) with a diode-array spectrophotometric detector. Before determining the amoxicillin, we use multivariate curve resolution with alternating least squares (MCR-ALS) to investigate whether any interferents are present. With a suitable analytical sequence, we can use SIA to generate a pH gradient and, for each sample, obtain a matrix of data that have been analysed by several chemometric techniques based on multivariate analysis: principal components analysis (PCA), simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) and MCR-ALS. In this way we obtain the concentration profiles and spectra of the species in the sample. We studied six pharmaceuticals containing amoxicillin. Two of these pharmaceuticals contained no interferents, one contained an interferent but amoxicillin had a selective spectral area with respect to it, and the other three contained interferents. For the first three samples, we set up a system of univariate calibration, which determines amoxicillin quickly (it can analyse 20 samples/h) using inexpensive instrumentation and reactives.

Union of capillary high-performance liquid chromatography and microcoil nuclear magnetic resonance spectroscopy applied to the separation and identification of terpenoids

This paper describes the first coupling of a commercial capillary HPLC system with a diode array spectrophotometric detector and a custom-built nuclear magnetic resonance (NMR) flow microprobe. The eluent from a 3-μm diameter C 18 HPLC column is linked to a 500 MHz 1H-NMR microcoil probe with an observe volume of 1.1 μl. The separation and structurally-rich detection of a mixture of terpenoids under both isocratic and gradient solvent elution conditions is presented. The lowest limits of detection yet reported for capillary HPLC on-line measurement (i.e., 37 ng for α-pinene) are achieved with this system. The complementary nature of diode array and NMR detection allows stopped-flow data collection from analytes which would otherwise go unnoticed in continuous-flow NMR. Moreover, stopped-flow NMR data is presented for the detection of a trace (sub-nmol) impurity in the sample mixture. Since NMR signals degrade and shift during solvent gradients, flow injection analysis studies are conducted with injected solvent plugs differing in mobile phase composition. The NMR signal degradation accompanying these injections is largely due to the variance in chemical shift with the solvent composition rather than to changes in magnetic susceptibility of the solvent. Characterization of such effects enables the development of improved NMR probes for the coupling of capillary HPLC and NMR.

Microwave synthesis of fullerenes from chloroform

Fullerenes C60 and C70 were synthesized continuously via microwave plasma from chloroform at low pressure argon atmosphere, and identified in toluene extracts of soot, using high-performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry and diode-array spectrophotometric detection. Yield of C60 (0.3%–1.3%) and C70 (0.1%–0.3%) and their ratio depend on the temperature gradient and the collision probability. Besides fullerenes, a series of perchlorinated carbon clusters were found in the synthesis products. Since frameworks of the products are fragments of fullerenes, the further investigation of this process may lead to a better knowledge of the formation mechanisms of fullerenes.

Ion paired chromatography of iron (II,III), nickel (II) and copper (II) as their 4,7-Diphenyl-1,10-phenanthroline chelates

A reversed phase ion-paired chromatographic method that can be used to determine trace amounts of iron (II,III), nickel (II) and copper (II) was developed and applied to the determination of iron (II) and iron (III) levels in natural water. The separation of these metal ions as their 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline) chelates on an Inertsil ODS column was investigated by using acetonitrile-water (80/20, v/v) containing 0.06 M perchloric acid as mobile phase and diode array spectrophotometric detection at 250–650 nm. Chromatographic parameters such as composition of mobile phase and concentration of perchloric acid in mobile phase were optimized. The calibration graphs of iron (II), nickel (II) and copper (II) ions were linear ( r > 0.991) in the concentration range 0–0.5, 0–2.0 and 0–4.0 μg ml −1, respectively. The detection limit of iron (II), nickel (II) and copper (II) were 2.67, 5.42 and 18.2 ng ml −1 with relative standard deviation ( n = 5) of 3.11, 5.81 and 7.16% at a concentration level of 10 ng ml −1 for iron (II) and nickel (II) and 25 ng ml −1 for copper (II), respectively. The proposed method was applied to the determination of iron(II) and iron(III) in tap water and sea water samples without any interference from other common metal ions.

Determination of triazines in surface waters by membrane separation coupled on-line to a flow-injection system and partial least squares regression

A flow-injection analysis method is described intended for the determination of triazine herbicides in natural waters. The proposed flow-injection manifold incorporates a membrane separation module inserted in the sample loop of the injection valve. This module works as an extraction-preconcentration cell. Analytes are extracted from the aqueous matrix to an organic solution and are carried to the flow cell of a diode array spectrophotometric detector. A partial least squares regression method enables the simultaneous determination of both chloro- and methylthiotriazine families in mixtures without chromatographic separation. The method can therefore be used as a screening method of these classes of compounds. Optimization of the method involves study of the extraction-preconcentration process (composition of the acceptor solution, preconcentration time) as well as all the variables affecting the calibration procedure. The determination of both classes of triazines added to surface waters was satisfactory; detection limits of 4–5 μg 1−1 were achieved for the determination of binary mixtures of chloro- and methylthiotriazines added to river water samples, the relative standard deviations being < 6%.

On-line multicomponent determination of organic compounds in water following gel permeation chromatographic separation

Gel permeation chromatography with on-line multicomponent determination of analytes in the column effluent is described. The system includes simultaneous measurement of organic carbon, organic nitrogen and organic halogens based on segmented flow analysis and on-line UV oxidation. Quantitative recoveries of various organic model compounds were obtained. Additionally the diode-array spectrophotometric detection applied gives UV-visible absorption spectra providing fingerprints for the specific components present in water samples. The system was applied for characterization of wastewater from chemical industry.

Kinetic determination of methotrimeprazine, thioridazine and their mixture by use of a modular stopped-flow/diode-array detection system

The oxidation reactions of methotrimeprazine and thioridazine by iron(III) were used to develop kinetic methods based on measurements of the formation rate of the corresponding coloured phenothiazinyl free radicals. The calibration graphs were linear over the range 0.8–60 μg/ml for methotrimeprazine and 1.1–60 μg/ml for thioridazine. The relative standard deviation was 1.1–3.4%. The method was used to determine the analytes in commercially available pharmaceutical preparations. The different absorption maxima of the oxidation products formed and also the different, high initial rates of the reactions for both analytes allow their simultaneous determination by using a stopped-flow module coupled to a diode-array spectrophotometric detector. Reaction rate and absorbance increment measurements of the kinetic curves obtained were used to resolve mixtures of both phenothiazines by using the proportional-equation method and establishing three different equation systems that allowed the results obtained in each case to be compared. Mixtures of methotrimeprazine and thioridazine in ratios between 8:1 and 1:8 were satisfactorily resolved.

Automatic simultaneous determination of Ca and Mg in natural waters with no interference separation

In this study a methodology is reported for the automatic, simultaneous determination of Ca and Mg in natural waters which is not affected by the presence of species that may interfere with other methods. A flow system based on the sinusoidal injection analysis (SIA) methodology with diode array spectrophotometric detection of the complex formed by both analytes with the Arsenazo III has been used. The technique of multivariate calibration used, PLS1, enables Ca to be determined in the concentration range 45–85 mg l −1 and Mg to be determined in the range 2–70 mg l −1, with no need for the samples to be previously diluted. The accuracy of the method has been tested by comparing the results obtained with the standard atomic absorption spectrometry method. With an analysis speed of 20–30 samples per hour, the RMSE in terms of standard deviation of the original variables was 6.1 for Mg and 6.4 for Ca.