Showing papers in "Analytical Chemistry in 1987"

Ion spray interface for combined liquid chromatography/atmospheric pressure ionization mass spectrometry

Abstract: Appareillage avec interface qui combine les principes d'evaporation ionique et d'electroprojection. Application a l'analyse de colorants et de steroides

On-line mass spectrometric detection for capillary zone electrophoresis

Abstract: The authors have developed a viable alternative to capillary zone electrophoresis (CZE) detection based on mass spectrometric interfacing. A capillary zone electrophoresis-mass spectrometry (CZE-MS) interface obviously requires a substantial departure from the conventional CZE arrangement; it is clear that the interface design and ionization method are crucial to success. The liquid flow rate in CZE (approx.1 ..mu..L/min) is highly compatible with conventional mass spectrometers even if the total column effluent was introduced directly. The direct liquid introduction interfaces developed for LC-MS suffer from orifice plugging at low flow rates and the thermal degradation of high mass-low volatility components. Thermospray ionization, though attractive, has not been shown to be effective for liquid flow rates below a few tenths of a mL/min. Therefore, the authors evaluation of the requirements for a mass spectrometer interface suggested an approach that incorporates the electrospray ionization technique developed by Dole et al. and the more recent work reported by Fenn and co-workers. In this communication, the authors report the successful development of CZE-MS instrumentation for the separation and analysis of ionic species in aqueous solutions.

Accuracy of selective extraction procedures for metal speciation in model aquatic sediments

Abstract: The interpretability of a selective extraction procedure for metals in aquatic sediments was tested by means of synthetic models. The major sedimentary geochemical phases were prepared and characterized by X-ray diffraction and scanning electron microscopy. A specific trace metal was doped into each phase by adsorption or coprecipitation, content being verified by atomic absorption (AA). The phases and metals were calcite (Pb), iron sulfides (zn), humic acid (Cu), and iron oxyhydroxides (Cu or Ni). Three different model sediments were prepared by combining phases and diluting with silica or illite. Measurements of extracts by AA and inductively coupled plasma (ICP) indicated that trace metals were not recovered in the appropriate fractions. This implies that selective extraction procedures as currently practiced may not be suitable for distinguishing the phase association of metals in real sediments.

Determination of oxygen concentrations by luminescence quenching of a polymer-immobilized transition-metal complex

Abstract: Oxygen quenching of the luminescence of the tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate immobilized in a silicone rubber is shown to be an accurate and precise method for measuring oxygen concentrations in solutions and in the gas phase. Quenching can be quantitated by either lifetime or intensity quenching measurements. Aqueous strong acids, bases, complexing agents, oxidants, and reductants do not penetrate the hydrophobic polymer and, therefore, do not affect the response. Gaseous interferents, such as H/sub 2/S, anesthetic gases (e.g., N/sub 2/O, halothane), and fluorocarbons do not affect the response. Chlorine and especially SO/sub 2/ are strong, but fully reversible, interferents. A system was developed with a response time of less than 0.2 s, which is adequate for the monitoring of breathing subjects.

Properties of an asymmetrical flow field-flow fractionation channel having one permeable wall.

Abstract: Description d'un tube a fractionnement flux-force ayant juste une simple paroi permeable, constitue d'une membrane frittee bicouche permeable a l'eluant mais pas a l'echantillon

Capillary zone electrophoresis with electrochemical detection.

Abstract: Ce systeme a permis d'obtenir une efficacite de separation (pour la separation du pyrocatechol et de catecholamines) de l'ordre de 180000 plateaux theoriques

Generation of chemiluminescence upon reaction of aliphatic amines with tris(2,2'-bipyridine)ruthenium(III)

Abstract: Tris(2,2'-bipyridine)ruthenium(III) (Ru(bpy)/sub 3//sup 3 +/) will undergo an electron-transfer reaction with an appropriate reducing agent to form Ru(bpy)/sub 3//sup 2 +/, which upon achieving an excited state can result in chemiluminescence. Aliphatic amines with an increasing number of carbon atoms were tested between a pH of 4 and 6 and found to act as chemiluminescent reducing agents. In addition, some diamines and phosphines were also found to react. Linear range and detection limit studies were done for the mono-, di-, and tri-n-propylamines as well as other selected compounds. Linear range values for these amines varied between approximately 3 and 5 orders of magnitude. The lowest detection limit of 0.28 pmol was found for tri-n-propylamine. Ionization potentials taken from photoelectron spectroscopy data for aliphatic amines were related linearly with the log of the chemiluminescent signal intensity. In addition, it appeared that assignment of the first ionization potential from a nonbonding orbital of the heteroatom was required for chemiluminscence.

Fluorescence Properties of Metal Complexes of 8-Hydroxyquinoline-5-sulfonic Acid and Chromatographic Applications

Abstract: Seventy-eight metal species are examined for fluorescence properties of their chelates with 8-hydroxyquinoline-5-sutfonic acid (HQS); 42 of these fluoresce, many intensely. The optimum pH, determined by ligand ionization vs. hydroxo compiex formation, iles between 5 and 8. Cadmlum forms the most fluorescent complex In a purely aqueous solution. Fluorescence Is enhanced for many metals in surfactant (hexadecyltrlmethyiammonlum ion, HTA') containing media and in a water:dimethytformamide solvent. A number of metal ions quench the fluorescence of other metal-HQS chelates, Fe(II1) being by far the most effective, and such quenching is accentuated in media contalnlng HTA'. The fluorescence propertles can be exploited by introducing the ligand through a postcolumn reactor or by Incorporating it in the eluent in a chromatographic system. Subpicomole detection limits are attainable for Cd, Mg, and Zn.

Electrokinetic resolution of amino acid enantiomers with copper(II)-aspartame support electrolyte

Abstract: Analyse de melanges racemiques de 14 aminoacides dansyles, pour des concentrations inferieures a la fentomole

Laser ablation of solids for elemental analysis by inductively coupled plasma mass spectrometry

Abstract: A technique for direct elemental analysis of solids is described. A focused Nd:YAG laser efficiently ablates many materials, including ceramics and polymers, that are difficult to prepare for solution analysis. Ablated particulate material is transported by gas flow into an inductively coupled plasma (ICP) and the resulting ions are detected by mass spectrometry. The laser may be used either in single-pulse mode to give a transient signal or at 10 Hz repetition rate, resulting in a continuous signal. The continuous signal may be maintained constant over long periods by translation of the sample, resulting in improved precision and duty cycle for data acquisition. Quantitative analysis is obtained by internal standardization on either a known analyte or the sample matrix signal. Analytical curves obtained for NBS microprobe steel standards are linear over 4 orders of magnitude and estimated detection limits are 0.2-2 ..sigma..=g g/sup -1/ in the solid. Precision and accuracy are approximately +/-5%.

Detection limits with specified assurance probabilities

Abstract: Definition, estimation empirique et theorique, methodologie des limites de detection en analyse chimique

Determination of the rare-earth elements in geological materials by inductively coupled plasma mass spectrometry

Abstract: A method of analysis of geological materials for the determination of the rare-earth elements using the inductively coupled plasma mass spectrometric technique (ICP-MS) has been developed. Instrumental parameters and factors affecting analytical results have been first studied and then optimized. Samples are analyzed directly following an acid digestion, without the need for separation or preconcentration with limits of detection of 2-11 ng/g, precision of +/-2.5% relative standard deviation, and accuracy comparable to inductively coupled plasma emission spectrometry and instrumental neutron activation analysis. A commercially available ICP-MS instrument is used with modifications to the sample introduction system, torch, and sampler orifice to reduce the effects of high salt content of sample solutions prepared from geologic materials. Corrections for isobaric interferences from oxide ions and other diatomic and triatomic ions are made mathematically. Special internal standard procedures are used to compensate for drift in metal:metal oxide ratios and sensitivity. Reference standard values are used to verify the accuracy and utility of the method.

Extraction and recovery of polycyclic aromatic hydrocarbons from environmental solids using supercritical fluids.

Abstract: The use of supercritical fluids for the extraction and recovery of polycyclic aromatic hydrocarbons (PAH) from environmental solids has been developed and tested by using urban dust, fly ash, and river sediment. Supercritical N/sub 2/O and 5% methanol modifier gave the best recoveries of PAH from all three samples when compared to supercritical CO/sub 2/ with 5% methanol, N/sub 2/O, CO/sub 2/, and ethane. Quantitative recovery of PAH from National Bureau of Standards SRM 1649 (urban dust) and of deuteriated PAH spikes (phenanthrene-d/sub 10/, pyrene-d/sub 10/, and perylene-d/sub 12/) from the river sediment was obtained with supercritical fluid extractions in as little as 30 min. In most cases, 30-60 min extractions of the river sediment and fly ash with supercritical N/sub 2/O/5% methanol gave better recovery of the deuteriated PAH spikes than the recoveries obtained by using 4 h of sonication or 8 h of Soxhlet extraction with either benzene or methylene chloride. Supercritical fluid extractions yield good PAH recoveries, require only small amounts of sample, minimize analyte concentration steps, and are simple and rapid to perform.

Measurement of diffusion coefficients in supercritical carbon dioxide and correlation with the equation of Wilke and Chang

Abstract: Diffusion coefficients of acetone, benzene, naphthalene, 1,3,5-trimethylbenzene, phenanthrene, pyrene, and chrysene have been measured by a chromatographic broadening technique in an open capillary tube (950 x 0.103 cm) filled with pure supercritical carbon dioxide or, in the case of benzene, with CO/sub 2/-methanol mixtures ranging from 0 to 100% in methanol. In pure supercritical CO/sub 2/, diffusion coefficients decrease when density increases; they increase linearly vs. the reciprocal of the viscosity; a linear relationship exists between the logarithms of the diffusion coefficients and the molar volumes with a slope of 0.6. Finally, in the range 0.6-0.9 g cm/sup -3/, the Wilke and Chang equation for the calculation of diffusion coefficients is valid for supercritical CO/sub 2/. For methanol-CO/sub 2/ mixtures there is no discontinuity of the diffusion coefficient of benzene when the methanol content varies from 0 to 100%. In the usual supercritical chromatographic conditions with a methanol content less than 10%, diffusion coefficients are at least 4 times higher than in pure methanol.

Detection of single molecules of phycoerythrin in hydrodynamically focused flows by laser-induced fluorescence.

Abstract: Single molecules of B-phycoerythrin were detected by laser-induced fluorescence in hydrodynamically focused flows as each molecule transited a focused laser beam. Phycoerythrin is a large protein molecule containing the equivalent of 25 rhodamine-6G chromophores. Single molecule detection is documented by the following: (1 )the number of counts per molecules is in agreement with the expected number, (2) the number of molecules per second is in agreement with the concentration and the flow rate, and (3) the time interval distribution between detected molecules is In agreement with the concentration and the flow rate. The molecular transit time through the 1.1-pL probe volume was 180 micros.

Application of polymer-coated glassy carbon electrodes in anodic stripping voltammetry

Abstract: For all cations, the magnitude of the inaccuracy is lower at higher sodium concentrations. Results presented in this paper clearly demonstrate sig- nificant inaccuracies in the response of the sodium glass membrane electrode when operated in a non-steady-state mode. The time-dependent selectivity of the glass membrane, caused by rapid activity steps of cations, appears to be re- sponsible for these inaccuracies. As a result, this electrode must be used with caution and optimal experimental condi- tions must be established for each particular application to minimize this time-dependent selectivity phenomenon. Several experimental parameters have been identified that can be used in such optimization studies. Even under optimal conditions, however, the use of “effective” selectivity coeffi- cients in the non-steady-state mode must be considered for glass membrane electrodes.

Comprehensive trace level determination of organotin compounds in environmental samples using high-resolution gas chromatography with flame photometric detection

Abstract: A comprehensive method for trace analysis of mono-, di-, tri-, and some tetrasubstituted organotin compounds is presented. The ionic compounds are extracted from diluted aqueous solutions as chlorides by using a Tropolon-C/sub 18/ silica cartridge and from sediment and sewage sludge by using an ethereal tropolon solution. The extracted organotin compounds are ethylated by a Grignard reagent and analyzed by using high-resolution gas chromatography with flame photometric detection (HRGC/FPD). Gas chromatography/mass spectrometry (GC/MS) was used for confirmation. The extraction behavior, gas chromatographic retention, and photometric response of a series of organotin compounds are described, and the identification via electron impact (EI) and chemical ionization (CI) mass spectrometry is discussed. The main organotin compounds detected in various samples are butyltins; cyclohexyl- and phenyltins were identified in some of the sediment and sewage sludge samples. Methylbutyltins and tetrabutyltin were not detected. Concentrations were found to range from low ng/L (part per trillion) in surface water to low mg/kg (parts per million) in sewage sludge.

Effect of phase length on column selectivity for the separation of polycyclic aromatic hydrocarbons by reversed-phase liquid chromatography

Abstract: A series of monomeric and polymeric alkyl phases of different phase lengths was prepared by reaction with appropriate mono- and trichlorosilanes. Selectivity changes with alkyl phase length were examined for phases ranging in length from C/sub 8/ to C/sub 30/. The retention behavior of polycyclic aromatic hydrocarbons (PAH) was observed to vary significantly with alkyl length. By use of PAH solute probes, phase selectivity of long-chain-length monomeric phases was found to approach that observed for C/sub 18/ polymeric phases. Retention behavior is discussed in terms of schematic representation of bonded phase behavior.

Liquid chromatography/electrochemical detection of carbohydrates at a cobalt phthalocyanine containing chemically modified electrode

Abstract: Les limites de detection des glucides sont repousses avec cette methode jusqu'a 100 p.mol pour le glucose et le maltose, et jusqu'a 500 p.mol pour le fructose et le necrose