Multi-wavelength Detection Research Articles

In-line UV spectroscopy of YBa2Cu3O7 MOCVD precursors

Abstract Real-time UV absorbance of YBCO MOCVD precursors was monitored in-line at the bubbler effluent using a remote fiber-optic based dual-wavelength detection scheme. A S N of 50:1 was obtained by signal averaging detector response over a one second interval. This technique provided a chemical specific measurement of extremely dilute concentrations of MOCVD source materials. In addition, several concentration transients were observed. Multi-wavelength detection (PDA/spectrograph) provided full spectral information. Bubbler efficiency of Y(thd)3 was shown to improve as system pressure was increased.

Second order multivariate curve resolution applied to the flow injection analysis of mixtures of amino acids

A flow injection system with diode-array multi-wavelength spectrophotometric detection was used to generate second order data. The system was applied to monitoring the reaction between amino acids (lysine and proline) and l,2-naphthoquinone-4-sulfonate (NQS) to give the corresponding derivatives. The sample injection produced a pH gradient which allowed the discrimination of the time profiles of the different amino acid derivatives. Each amino acid gave a FIA response which was arranged in a data matrix whose chemical rank was higher than one (more than one spectrophotometrically active species was present in the reaction system). The method was applied to the simultaneous determination of Lys and Pro by second order multivariate curve resolution, obtaining a global quantification error of 0.36%. The analysis of one of these amino acids in presence of the other as interference by using a pure standard (without any information about the interference) was also studied. In this case, errors in the quantification were of 2.75 and 3.0% for Lys and Pro, respectively.

Capillary electrophoresis for drug analysis in body fluids.

Capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) represent attractive methods for the determination of drugs and metabolites in body fluids. In CZE, minute (nanoliter) quantities of samples are applied to the beginning of a fused-silica capillary filled with buffer. On application of a high-voltage DC field, charged solutes begin to separate and are swept through the capillary by the combined action of electrophoresis and electroosmotic bulk flow and are on-column detected toward the capillary end. In MECC, the buffer contains charged micelles (e.g., dodecyl sulfate micelles) and both uncharged and charged solutes separate based on differential partitioning between the micelles and the surrounding buffer and, if charged, also by differential charge effects, including electrophoresis. Based on validated MECC drug assays developed in our laboratory, key aspects of measuring drug levels by MECC, including sample preparation, solute detection and identification, quantitation, reproducibility, and quality assurance are discussed. Drug levels determined by MECC are shown to be in good agreement with those obtained by nonisotopic immunoassays and/or high-performance liquid chromatography (HPLC). Using on-column multi-wavelength detection, this technology is also well suited for toxicological drug screening and confirmation and for the exploration of drug metabolism. Compared with HPLC and gas chromatography, capillary electrophoresis has distinct advantages, including automation, small sample size, minimal sample preparation, use of very small amounts of organic solvents and inexpensive chemicals, ease of buffer change and method development, and low cost of capillary columns. Electrokinetic capillary assays are complementary to the widely employed immunoassays. The state of the art and the pros and cons of capillary electrophoresis for the determination of drugs in body fluids are discussed with the goal of encouraging newcomers to start using this emerging analytical methodology.

Multicomponent Analysis of Highly Overlapped Capillary Electrophoretic Peaks Using Multiwave-Length Charge-Coupled Devices Detection

Abstract A chemometric method, Kalman filtering, was applied to deal with three-dimensional electropherograms, obtained by capillary electrophoresis connected to a charge-coupled device multiwavelength fluorescence detector. The capillary electrophoretic peaks of a mixture, which were not effectively separated, were resolved into electrophoretic peaks of individual components to obtain qualitative and quantitative information. The approach has been applied to analyze a mixture of rhodamine fluorescent dyes with excellent results.

LC-MS and CZE of dianthrones fromCassia Angustifolia andAcutifolia

Capillary zone electrophoresis (CZE) with multiwavelength detection has been used for the separation of the main dianthrones fromCassia angustifolia. Onptimum separation has been achieved with a sufed silica capillary and 0.1 M borate-sodium hydroxide buffer (pH 8.4). KCl and 5% of isopropano has been added to the electrolyte. Applied voltyage was 25 kV and capillary temperature constant at 20 °C. LC separation of senna dianthrones was on reversed phase (RP 18) material with an acetonitrile-water solvent gradient containing 0.01% trifluoracetic acid. UV detection was at 205 nm, column temperature 44°C. LC-electrospray ionisation-MS was used for peak assignment and purity control. New alsoe-emodine dianthrone isomers could also be identified by this technique. The established HPLC and CZE methods are suitable for qualiitative characterization and quantitative determination of sennosides in curde senna extracts and phytopharmaceuticals.

Application of capillary zone electrophoresis to the analysis of betalains from Beta vulgaris

Capillary zone electrophoresis (CZE) with multi-wavelength detection was used for the separation of the main betacyanins, betanin and isobetanin, and the corresponding aglycones from extracts of Beta vulgaris. Optimum separation was achieved with a fused-silica capillary tube and a citric acid-Na 2HPO 4 buffer (10 m M). The applied voltage was −22 kV and the capillary thermostating temperature was kept constant at 15°C. The results of the quantitative CZE analyses were compared with those obtained by HPLC.

Multiwavelength fluorescence detection for purity analysis of fluorescence agents using capillary electrophoresis with a charge-coupled device

A capillary electrophoresis system with charge-coupled device multi-wavelength fluorescence detection was used for the separation and identification of fluorescence agents. Based on the differences between agents and impurities in fluorescence spectra and retention times shown in the three-dimensional electropherograms and by the use of a standard addition procedure, the fluorescence impurities in agents were identified. A novel method for the determination of the purity of fluorescence agents was proposed and applied to the purity analysis of three kinds of fluorescence agents.

Optical chemical sensors for environmental control and system management

Several fiber optic based chemical sensors have been developed for use in plant growth systems and enclosed life support systems. Optical chemical sensors offer several distinct advantages in terms of sensitivity, calibration stability, immunity to biofouling and electrical interference, and ease of multiplexing sensors for multipoint/multiparameter analysis. Also, the ability to locate fiber optic sensors in close proximity to plant roots or leaves should improve the measurement reliability by obviating the need for handling and transport which can compromise sample integrity. Polestar Technologies and GEO-CENTERS have developed and tested many types of optical chemical sensors which utilize novel glass and polymeric materials as the sensor substrate. Analytes are detected using immobilized colorimetric indication systems or molecular recognition elements. Typically transduction is via wavelength specific absorption changes with multiwavelength detection for drift compensation. Sensors have been developed for solution pH, NH 3, ethylene, CO 2, and dissolved metal ions. In addition, unique PC-compatible optoelectronic interfaces, as well as distributed measurement systems, so that integrated detection systems are now available. In this paper recent efforts to develop sensors for critical nutrient ions are presented.

Application of β-cyclodextrin for the analysis of the main alkaloids from Chelidonium majus by capillary electrophoresis

Capillary zone electrophoresis (CZE) with multi-wavelength detection was used for the separation of the main alkaloids from Chelidonium majus. Optimum separation was achieved with a fused-silica capillary tube (70 cm × 50 μm I.D.) and a running electrolyte at pH 5.5 prepared from 40 m M citric acid and 80 m M Na 2HPO 4 solutions. Addition of β-cyclodextrin (12.5 mmol/l) to the buffer system was found to be essential for the separation. The applied voltage was 25 kV and the capillary temperature was kept constant at 25°C.

Development and testing of a new computerized method for multicomponent kinetic determinations based on multiwavelength spectrophotometric detection

We developed a new kinetic multidetermination method based on multiwavelength spectrophotometric detection and used simulated processes to evaluate its performance. The method uses spectral differences between analytes and kinetic equations solved by means of a nonlinear regression procedure. It allows the simultaneous determination of rate constants and analyte concentrations, and takes account of potential matrix effects and changes in the rate constants arising from temperature oscillations. The results obtained by using simulated Gaussian spectra revealed that the method allows correct resolution of simultaneous kinetic processes, even if they involve strong spectral overlap and identical kinetic constants. The “standardized spectral difference”, concept introduced with this work, allows results to be extrapolated to non-Gaussian spectra.

Reversed-phase high-performance liquid chromatography--photodiode-array analysis of alkaloid drugs of forensic interest.

A reversed-phase high-performance liquid chromatography-photodiode-array method for the analysis of 23 drugs of forensic interest is presented. The separation method development was based on mobile-phase optimisation, temperature control and use of three ODS stationary phases. Multiwavelength detection and quantitation was performed at 225, 232, 239, 254, 275 and 289 nm. Absorbance rationing proved to be very helpful for the identification of these drugs. Recognition of the analysed compounds was achieved by means of correlation of retention time and absorbance ratios. The method was directly applied to the analysis of illicit heroin and cocaine samples and to the analysis of pharmaceutical preparations containing codeine.

Photolabeling of human serum albumin by 4-azido-2-([ 14C]-methylamino) trifluorobenzonitrile. A high-efficiency, long wavelength photolabel

N-alkyl derivatives of perfluoroarylazides are excellent candidates for photolabeling of proteins since they have absorption spectra in the 340–350 nm range permitting photolabel absorption without direct protein photolysis. The [ 14C]-N-methylamino derivative of 4-azido-tetrafluorobenzonitrile has been used to demonstrate that 80% of the photo-induced nitrene transient becomes covalently attached to HSA during photolysis. Multiwavelength detection of the photoprobe-protein separation by size exclusion chromatography is shown to be an effective tool for assessing the conjugation of the photoprobe to the protein.

A Hadamard transform UV absorption detection for high performance liquidchromatography. Part I. Preliminary experiments

The principles and design of a Hadamard transform UV absorbance detector for liquid chromatography are outlined, and some spectra of aromatic compounds passing through its flow cell are presented. This approach could be valuable in providing a low-cost multi-wavelength detection method for liquid chromatography.

Analysis of felodipine by packed column supercritical fluid chromatography with electron capture and ultraviolet absorbance detection

A reproducible and selective supercritical fluid chromatography (SFC) method was developed for the analysis of felodipine, a drug indicated for the treatment of hypertension. Methanol-modified carbon dioxide was employed as the SFC mobile phase with both electron capture detection (ECD) and multi-wavelength detection (MWD) being used simultaneously for analyte determination. Chromatography limit of detection (LOD) and limit of quantitation (LOQ), linear dynamic range (LDR) and injection precision were obtained in order to assess chromatographic and detector performance for both the SFC/MWD and SFC/ECD/MWD systems. The method was shown to be stability indicating since felodipine could be separated from its potential oxidative degradation product, H152/37, in under 6 min (felodipine k' = 2.44). Sample throughput was increased by 60% with the SFC assay vs LC. The optimized SFC method was shown to be equivalent to an existing LC/UV procedure for the analysis of a sustained-release tablet while realizing a 92% saving in disposable solvent waste. In order to achieve further solvent savings overall, supercritical fluid extraction (SFE) with 8% methanol-modified carbon dioxide as the extraction fluid was used to extract felodipine from a sustained-release tablet (as opposed to traditional solvent extraction). Comparable drug recoveries were obtained with SFE sample preparation technique when either SFC or LC extract analysis was utilized.

Measurements of temperature and seed atom density in high-speed MHD flows

Emission absorption measurements of temperature, potassium seed atom density, and electron conductivity have been demonstrated in the high-speed, turbulent coal-fired flow of a simulated MHD channel. A two-beam optical system provides coincident exposures of transmitted lamp and emission-only signals with a time resolution of one-half ms. Multiwavelength detection allows for optimization of the measurement wavelengths for a twowavelength analysis that eliminates error due to ash/slag particle extinction and emission. Previous measurements with single beam, 1 ms temporally separated measurements showed large standard deviations due to fluctuations in flow parameters between the two noncoincident exposures. Comparison of the two types of measurements for nominally the same flow conditions reveals the considerable improvement in measurement uncertainty with the two-beam optical system.

Retinol, alpha-tocopherol, lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, trans-beta-carotene, and four retinyl esters in serum determined simultaneously by reversed-phase HPLC with multiwavelength detection

We describe the use of HPLC with multiwavelength detection to measure retinol, alpha-tocopherol, lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, trans-beta-carotene, beta-carotene, and the linoleate, oleate, palmitate, and stearate esters of retinol in a single 200-microL serum sample. The method is sensitive enough to detect individual retinyl esters in fasting serum from a nonhyperlipidemic population and requires only 12 min for each sample. Serum concentration ranges and means are reported for retinol, alpha-tocopherol, lutein/zeaxanthin, beta-cryptoxanthin, lycopene, alpha-carotene, trans-beta-carotene, and the sum of the retinyl esters from serum analyses of 3480 participants from several different studies.

Advantages of multi-wavelength detection for the analysis of mineral anions with capillary electrophoresis

The advantages of multi-wavelength detection for the CE-analysis of mineral anions are pointed out: enhanced detection sensitivity and simplified peak identification.

Capillary Zone Electrophoretic Analysis of the Main Alkaloids fromEschscholtzia californica

Capillary zone electrophoresis (CZE) with multi-wavelength detection has been used for the separation of the main alkaloids fromEschscholtzia californica. Optimum separation has been achieved with a fused silica capillary tube and a running electrolyte at pH 2.8 prepared from a 40 mM solution of citric acid and a 80 mM solution of Na2HPO4. The applied voltage was 20 kV and the capillary thermostating temperature was kept constant at 10°C.

Capillary zone electrophoretic analysis of the main alkaloids fromEschscholtzia californica

Capillary zone electrophoresis (CZE) with multi-wavelength detection has been used for the separation of the main alkaloids fromEschscholtzia californica. Optimum separation has been achieved with a fused silica capillary tube and a running electrolyte at pH 2.8 prepared from a 40 mM solution of citric acid and a 80 mM solution of Na2HPO4. The applied voltage was 20 kV and the capillary thermostating temperature was kept constant at 10°C.

Comparative use of three electrokinetic capillary methods for the determination of drugs in body fluids: Prospects for rapid determination of intoxications

Three electrokinetic capillary methods, micellar electrokinetic capillary chromatography, capillary zone electrophoresis and capillary isotachophoresis, are shown to be well suited for the rapid screening and confirmation of drugs in serum and urine of patients with medical drug overdoses (intoxications), situations where rapid identification without precise quantification is needed. Patients' samples obtained from the emergency care unit were analysed in an instrument featuring on-column, fast forward-scanning multi-wavelength detection and the data were compared with those obtained by conventional methods. The drugs studied included salicylate, acetaminophen (paracetamol) and antiepileptics. In cases with high drug concentrations, body fluids can be injected directly or may have only to be diluted (urine) or ultrafiltered (serum) prior to analysis, providing results within about 30 min. Thus, electrokinetic capillary methods can be employed for rapid drug screening, provided that instrumentation with a database for peak identification is available.