Non-dispersive atomic-fluorescence spectrometric determination of lead by the hydride-generation technique

Non-dispersive atomic-fluorescence spectrometry combined with hydride-generation has been developed for lead determination. A radiofrequency-excited electrodeless discharge lamp was used as light-source and a small argon-hydrogen flame as atomizer. The detection limit was 0.06ng/ml and the linear calibration graph was linear up 300ng/ml, with a precision of 5-6% over the dynamic range. Interference studies and optimization of the experimental parameters are reported. Severe suppression of the lead signal was observed in presence of Cu, Se or Te. An empirical equation was obtained for predicting the effect of copper on the lead signal at various concentration ratios. The strong effect of complexing agents such as EDTA was removed by addition of zinc salts.     

A simultaneous multielement non-dispersive atomic-fluorescence spectrometer using modulated sources and frequency discrimination of fluorescence signals

Commercial radiofrequency-excited electrodeless discharge lamps can be run from a square-wave modulated power supply so as to give a low level of continuous emission when modulated in the frequency range 3–10 kHz. Use of a different modulation frequency and lock-in amplifier for each lamp allows multielement non-dispersive atomic-fluorescence spectrometry to be performed. Very low detection limits have been obtained for arsenic, selenium, tin and mercury. The use of low-cost electronic components in the system largely offsets the high cost of the individual excitation power supplies and tuned a.c. detectors.     

On the determination of total dissolved tin in natural waters by direct hydride generation and non-dispersive atomic-fluorescence spectrometry

The analytical response of inorganic tin and of eleven organotin compounds of the type R(n)SnX(4-)(n) (with n = 1, 2, 3 and R = methyl, ethyl, butyl and phenyl) was compared for direct hydride generation with non-dispersive atomic fluorescence detection. Most of these compounds showed behaviour resembling that of inorganic tin, with the exception of tributyltin and the phenyltin compounds. A simple pretreatment with 10(-3)M bromine and 0.033M nitric acid at 70 degrees for 60 niin prevents any risk of underestimation and the total dissolved tin in natural waters can be determined with recoveries better than 90%, with inorganic tin as calibration standard.     

Application of a simple photoionization detector for non-dispersive atomic spectrometry in the vacuum ultraviolet region

The construction and operation of a simple, solar-blind photoionization detector which responds to incident radiation between 125 and 140 nm is described. The detector, the response characteristics of which are controlled by the ionization potential of the ethylamine filler gas and the calcium fluoride window employed, is shown to provide for efficient detection of atomic line emission from carbon, oxygen and chlorine in this wavelength region. The spectral sources employed for non-dispersive work with this detector are a microwave-excited argon plasma and a demountable hollow-cathode lamp.     

Determination of some phosphorus-containing compounds by flow injection with a molecular emission cavity detector

The use of molecular emission cavity analysis combined with a flow-injection system for the determination of nanogram amounts of some organophosphorus compounds and phosphorus oxo-anions is described. Sensitivit, calibration linearity, precision and detection limits were measured for each compound. Simultaneous determinations of some ternary mixtures of these compounds are also described. Sample throughput is 20 h^?1.     

Quantitative gas chromatographic analysis of perhalogenated compounds using a flame lonization detector

Summary In the determination of several perhalogenated compounds after gas chromatographic separation on an Apiezon L column, using a flame ionization detector, all the compounds tested gave linear area-mass plots although the coefficients observed do not lead to extrapolations which would permit quantitation of perhalogenated compounds for which no standard is available. Of the compounds tested, dibromodichloromethane, tetrachloroethene and tetrabromoethene gave good linear correlations of area ratio-mass ratio (using n-decane as the internal standard). Bromotrichloromethane and tetrabromomethane gave continuously curving area ratio-mass ratio plots which were very reproducible and could be used for graphical interpolation.     

Rapid estimation of the sensitivity of some non-dispersive X-ray methods of analysis

A way of graphical estimation of sensitivity is presented for the following methods:

1. X-ray fluorescent analysis without the elimination of matrix effects,
2. fluorescence-Compton-scattering method,
3. dilution method.

The influence of several parameters on the sensitivity has been considered, such as the concentration of the element to be determined, chemical composition of the sample, the ratio of the energy of primary radiation to the energy of fluorescent radiation, geometry of the measurement, chemical composition of the diluent, and the degree of dilution.     

RP-HPLC analysis of phenolic compounds and flavonoids in beverages and plant extracts using a CoulArray detector

Methods were developed for the analysis of natural antioxidants including phenolic compounds and flavonoids in beverages and plant extracts using gradient HPLC with multi-channel electrochemical coulometric detection. Suitability of various reversed-phase columns for this purpose was compared; pH and mobile phase gradients were optimized with respect to the separation selectivity and sensitivity of detection. Because of different target compounds in various sample types, the overlapping resolution maps and the normalized resolution product approaches described earlier were used to select optimum columns and gradients to suit the analysis of the individual sample types. The methods were applied to the analysis of phenolic compounds and flavonoids in beer, wine, tea, and yacon extracts. 32 phenolic compounds were identified and determined, including derivatives of benzoic and cinnamic acids, flavones, and a few related glycosides. Eight-channel CoulArray detection offers high selectivity and sensitivity with limits of detection in the low microg L(-1) range, at least an order of magnitude lower than single-channel coulometric detection using the Coulochem detector. No special sample pretreatment is necessary and, because of the compatibility of the CoulArray detector with gradient elution, phenolic antioxidants of different polarities can be determined in a single run. In addition to the retention times, the ratios of the areas of the pre-dominant and post-dominant peaks to the area of the dominant peak can be used for improved identification of natural antioxidants.     

Determination of UV-transparent compounds by liquid chromatography using the UV detector

An indirect UV photometric detection technique is described in which a low concentration of a UV-absorbing compound (UVAC) is added to the mobile phase in reversed phase liquid chromatography, thereby making it possible for non UV-absorbing compounds such as the lower alcohols to be detected by the UV detector. This happens because the injected analyte may extract a portion of the UV absorbing compound from the mobile and/or stationary phase and the complex is co-eluted as a positive peak at the retention time of the analyte. Alternatively, the injected analyte may appear as a negative peak if the UV-absorbing compound is transferred to the mobile and stationary phases. In any case, the injected compound appears either as a positive or negative peak depending on the relative polarities and concentrations of all the compounds in the system. In addition, the resulting excess or deficiency of detection agent in the stationary phase is eluted separately as a positive or negative peak, indicating that the system has returned to equilibrium. In the work described herein, the chromatographic conditions and variables of the indirect photometric technique were studied to develop a quantitative HPLC method for UV-transparent compounds. It was found that under optimal conditions it is possible to determine some analytes quantitatively at concentrations as low as 0.05%.     

Optimisation of gradient HPLC analysis of phenolic compounds and flavonoids in beer using a coularray detector

A method was developed for simultaneous analysis of natural antioxidants in beer using multichannel electrochemical detection with a CoulArray detector, which enables selective and sensitive antioxidant detection in gradient HPLC and facilitates the identification of analytes based on the ratios of signals recorded at different potentials applied to the detection cells arranged in series. The separation conditions were optimised for 27 phenolic compounds including derivatives of benzoic and cinnamic acids, flavones, and a few related glycosides identified in beer samples. Separation selectivities of 11 columns with different stationary phase chemistries were compared, and the pH and gradient programs were optimised for the individual columns to provide best resolution and high number of resolved peaks, using the window-diagram approach. The effects of pH on the sensitivity of electrochemical coulometric detection were considered in the optimisation approach. The optimised conditions were applied to the analysis of real beer samples.     

Studies in atomic-fluorescence spectroscopy-IV The atomic-fluorescence spectroscopic determination of selenium and tellurium

Selenium and tellurium are determined down to 0.25 and 0.12 p pm respectively by measuring the atomic-fluorescence signals at 2040 A and 2143 A respectively. Other possible wavelengths of measurement are considered in detail and the effects of some extraneous ions are examined. Microwave-excited electrodeless discharge tubes are used as spectral sources and intensity measurements are made with a Unicam SP 900A atomic-absorption/flame-emission spectrophotometer. Atomic-absorption measurements are also made with the same sources and spectrophotometer. The advantages of atomic-fluorescence methods and the use of electrodeless discharge tubes are discussed.     

Use of a filter in atomic-fluorescence spectroscopy

A detecting system incorporating an interference filter is described for use in atomic-fluorescence spectroscopy analysis in the 200.0-300.0 nm spectral region. Results obtained by using this system are compared with those from a detecting system incorporating either a monochromator or a solar-blind photomultiplier. Improvements of approximately 700-fold and 10-fold respectively in the limits of detection for zinc and mercury result from replacing the monochromator with the filter, while results with the filter are similar to those from a solar-blind photomultiplier. Limits of detection of 10(-5) ppm for zinc and 2.5 x 10(-4) ppm for mercury, both in aqueous solutions aspirated into an air-town-gas flame, are an improvement on other published results for these elements, obtained by atomic-fluorescence flame spectroscopy.     

Screening procedure for benzodiazepines in biological fluids by high-performance liquid chromatography using a rapid-scanning multichannel detector

A sensitive and specific determination of benzodiazepines in biological fluids is described, based on reversed-phase high-performance liquid chromatography. The compounds are extracted with a C2 AASP cartridge within 5 min. The recovery ranges from 92 to 104% and is independent of the concentration. Using a suitable gradient elution, complete separation of nineteen benzodiazepines is achieved in 50 min with detection limits of less than 3 ng/ml in urine and 5 ng/ml in other biological fluids. Using a rapid-scanning multichannel detector, the identities of the benzodiazepines can be confirmed. Prazepam is employed as internal standard. The precision and accuracy of the described method are suitable for monitoring benzodiazepine levels in clinical studies and an example is given.     

Simple and precise detection of lipid compounds present within liposomal formulations using a charged aerosol detector

In recent decades the use of liposomal preparations as drug delivery systems has become very attractive in pharmaceutical development. Therefore, thorough characterization and quantification of the lipids which form liposomes is wished from both investigators and regulatory authorities when the application in humans is being considered. In this study a new HPLC method for the detection of lipids in liposomal formulations was established using corona charged aerosol detection (CAD) which has the advantage to be independent of the chemical properties of the analytes. The superiority of this method over UV detection was demonstrated. Compared to UV detection no absorption effects of the organic solvent in the mobile phase interfering with the lipid signals were observed with CAD. CAD showed good linearity (R² > 0.990) for all liposomal compounds. The acceptance criteria for precision including repeatability were met. The average recovery for each of the excipients of the liposomal formulation was in the range of 90.0–110%.     

Asymmetric epoxidation of some arylalkenyl sulfones using a modified Juliá-Colonna procedure

A modified procedure for performing the Juliá-Colonna epoxidation reaction effects the oxidation of some vinyl sulfones to generate the corresponding epoxides 5-8 in good to excellent optical purity.     

Analysis of phenolic compounds in spruce needle extracts using an UV-VIS-diode array detector

Summary High-performance liquid chromatography (HPLC) coupled with ultraviolet-visible spectroscopy, using a photodiode-array detector, was applied to the investigation of plant extracts for polyphenolic compounds. Simultaneous detection at different wavelengths and measurement of the UV spectrum of each separated compound during the elution allows an easy and rapid identification of the derivatives of benzoic acid, o-coumaric acid, p-hydroxyacetophenone, stilbenes and flavonoide compounds as well as several catechins. However, as some of these compounds have closely related structures, a characterization by their UV-spectra is insufficient. Hydrolysis with hydrochloric acid and enzymes results in the formation of their monomeric non glycosidated compounds as well as in an increase of the peak area assigned to the monomeric compounds. This technique was applied for the phenol analysis of purified spruce needle extracts of picea abies species.

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Analyse phenolischer Fichtennadelinhaltsstoffe unter Verwendung eines UV-VIS-Dioden-Array-Detektors

     

Validation of a quantitative procedure for the extraction of sterols from edible oils using radiolabelled compounds

The work described in this paper is integrated in an analytical programme organised by the Community Bureau of Reference with the aim of developing reference materials certified for sterol content. Preliminary inter-comparison of methods showed that the level of agreement of the results was insufficient for certification purposes. Errors could occur in the different steps before the final determination by gas-liquid chromatography. It was, therefore, decided to validate a quantitative procedure for the isolation of sterols. A well defined saponification-extraction method was tested using labelled sterols ([3H]cholesterol and [3H]cholesteryl oleate) and radiochemical measurements. The study has shown that total cholesterol recovery reached 100.5 +/- 1.4%, that cholesteryl ester was saponified quantitatively and that there were no appreciable amounts of degradation products. The procedure has been used as the basis for the certification of three reference materials and it has been shown that the saponification and extraction procedure leads to the quantitative recovery of sterols regardless of the nature of the fatty material tested.