A Compact,High Speed Ion Beam Chopper

Abstract

A simple, compact pulse circuit was designed for use as an ion beam chopper with both synchronous and asynchronous triggering. The rise and fall times of the beam-on pulse are 60 ns and 320 ns, respectively, with a beam suppression potential of 180 V. The beam chopper was interfaced to a spark-source mass spectrometer for which the precision of analyses can be improved by reducing effects of sample or spark inhomogeneities. Additionally, the synchronous mode of chopping provides a means for temporal analysis of the spark.     

Estimation of Performance Characteristics of an Analytical Method Using the Data Set Of The Calibration Experiment

Abstract

A model to calculate the analytical sensitivity, limit of detection, limit of determination and precision of a method of instrumental analysis through a data set obtained by calibration experiment using the statistical analysis of linear regression, is proposed. This model has been applied to spectrophotometric, spectrofluorimetric and chromatographic methods. The values obtained are independent of the instrument used and can be applied as a criterion of comparison between different methods proposed for the same analyte. Also, these characteristics have been calculated using the IUPAC suggested model and both results have been compared.     

Evidence of Molecular Fragmentation inside the Charged Droplets Produced by Electrospray Process

The behavior of the analyte molecules inside the neutral core of the charged droplet produced by the electrospray (ES) process is not unambiguously known to date. We have identified interesting molecular transformations of two suitably chosen analytes inside the ES droplets. The highly stable Ni(II) complex of 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane (1) that consists of a positive charge at the metal center, and the allyl pendant armed tertiary amine containing macrocycle 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetraallyl-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-diene (M _4p ) have been studied by ESI mass spectrometry as the model analytes. We have shown that these two molecules are not representatively transferred from solution to gas phase by ESI; rather, they undergo fragmentation inside the charged droplets. The results indicated that a charged analyte such as 1 was possibly unstable inside the neutral core of the ES droplet and undergoes fragmentation due to the Coulombic repulsion imparted by the surface protons. Brownian motion of the neutral analyte such as M _4p inside the droplet, on the other hand, may lead to proton attachment on interaction with the charged surface causing destabilization that leads to fragmentation of M _4p and release of resonance stabilized allyl cations from the core of the droplet. Detailed solvent dependence and collision-induced dissociation (CID) studies provided compelling evidences that the fragmentation of the analytes indeed occurs inside the charged ES droplets. A viable model of molecular transformations inside the ES droplet was proposed based on these results to rationalize the behavior of the analyte molecules inside the charged ES droplets.     

Spark Source Mass Spectrographic Analysis of Gallium Arsenide for Trace Oxygen and Carbon Using Liquid Helium Cryopumping

Abstract

A spark source mass spectrometric system has been developed for trace levels of oxygen and carbon in gallium arsenide using liquid helium cryopumping of the source chamber. Following bake-out, a collector positioned inside the source chamber is cooled using a controlled flow of liquid helium. Residual back-ground gases are more effectively removed than with liquid nitrogen and detectabilities of 0.02 ppma for oxygen and 0.05 ppma for carbon have been obtained. Routine analyses are carried out with a moderate consumption of liquid helium.     

Analysis of Frozen Aqueous Solutions by Spark Source Mass Spectroscopy

Abstract

Aqueous solutions can be analyzed directly in a spark source mass spectrograph by sparking to frozen drops of the sample solution. The minimum detection limit obtained from a 10^?8 coulomb exposure is about 5 × 10^?7 M solution concentration. Analytical precision of 8 to 30% relative is achieved through use of an internal standard added to the sample solution.     

Fortschritte bei der emissionsspektrometrischen Stahlanalyse

Zusammenfassung Eine Verbesserung der Reproduzierbarkeit der Ergebnisse der emissionsspektrometrischen Analyse bei Fertigproduktproben aus Roheisen und Stahl, sowie gewalztem Stahl oder Blech kann mit Hilfe des Mehrfleckanfunkens in Kombination mit einer beschriebenen Kalibriertechnik unter Festlegung der Eichkurve im Koordinatensprung und dem Anfunken durch eine Bornitrid-Blende bewirkt werden.Durch eine geringe Änderung im Meßkreis des verwendeten Spektrometers kann erreicht werden, daß die Meßkondensatoren nicht nach jedem Anfunkprozeß entladen werden und die bei wiederholtem Anfunken resultierenden Spannungen zusätzlich auf diesen integriert werden können. Vier verschiedene Anfunkungen in dieser Weise mit je 5 sec Integration ergeben eine bessere Reproduzierbarkeit und Richtigkeit gegenüber der gebräuchlichen einmaligen Anfunkung mit 20 sec Integration.Mit Hilfe dieser Methodik ist auch die schnelle spektrometrische Analyse von gewalztem Stahl mit nicht erfaßbarer Seigerung möglich. Die Ergebnisse an Spanpreßlingen werden ebenfalls verbessert.

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Improvements in vacuum-spectrometric analysis of steelIII. A more-spot-sparking method in analysis of end-products

An increase of precision in emission-spectrometric analysis of samples from finished pig iron and steel charges or rolled steel and sheet-iron is effected by a combination of the method of more-spot sparking, the described technique of calibration with electronic fixation of zero of the calibration curves and sparking through a bornitride disc.By making a simple change in the switch in the measuring circuit of the spectrometer in application, it can be effected that after a single spark the recording by the measuring condensers does not get discharged when the next sparking process takes place. On account of this the intensities of the various successive sparks add together and then integrate on the charged condensers. Thus when sparked each 5 sec for four times it accounts to a considerable increase in the precision and accuracy when compared with the usual method to spark for 20 sec only once.Due to the appearance of a insignificant amount of segregation in rolled steel the application of emission-spectrometry to its analysis is possible and better results are obtained from sparking briquetted chips.

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II.Mitt.: Ohls, K., Koch, K. H., Becker, G.: diese Z. 241, 155 (1968).     

An electronic, adjustable-waveform spark source for basic and applied emission spectrometry

A conceptually new type of electronic spark source is described. A parallel combination of a hydrogen thyratron and a diode is used as the switch element. The switch operates by providing parallel paths for current oscillating from capacitors discharging through inductive loads. The same principle is used to route current through the analytical spark gap. Either the switch current or the spark current can be adjusted in waveform from fully oscillatory to fully unidirectional simply by changing the value of a single inductor, without changing capacitance, resistance, or the voltage at which the source operates.The electrical circuitry is singularly simple, thus producing a source that is characterized by reliable, long term operation, precise ignition with low time jitter (ca. 5 nsec) and low conducted or radiated radio-frequency interference. Because of the latter, modern electronic devices (such as microprocessors and minicomputers) can be used in conjunction with and in direct control of the spark source, i.e., while the spark is conducting current. The source functions equally well for industrial spectrochemical analysis and for basic research on optical emission phenomena.A partial circuit analysis is included here. The current commutation between the hydrogen thyratron and shunt diode is characterized. Electronic circuitry appropriate for source operation at variable repetition rate is described. The types of spark current waveforms that can be obtained under electronic control are illustrated.     

Determination of Fluorine in NBS Coal and Coal Fly Ash by Proton Induced Gamma Ray Emission and Spark Source Mass Spectrometry

Abstract

Fluorine concentrations in US National Bureau of Standards standard reference materials 1632a (coal) and 1633a (coal fly ash) have been determined by proton induced gamma ray emission (PIGME) and spark source mass spectrometry (SSMS) using the method of standard additions. Good agreement was obtained between the two techniques with no significant bias. The mean values for 1632a and 1633a were ± 18 mg kg^?1 and 109 ± 11 mg kg^?1 respectively.     

Determination Of Mexacarbate And Five Of Its Derivatives By High-Performance Liquid Chromatography

Abstract

A simple, sensitive and reliable analytical method has been developed and reported for mexacarbate (4-ditnethylamino-3,5-xylyl N-methylcarbamate) and five of its possible degradation products likely to be found in environmental samples using reversed-phase high-performance liquid chromatography with isocratic and gradient solvent systems. All chromatogram peaks were Identified through comparison to standards. The method has been used to identify and separate the six compounds from a mixture of the standards. It has been evaluated under different column conditions and with different mobile phases. Best resolution of the analytes was obtained by using a gradient solvent system consisting of CH₃CN and H₃O detecting at 200 nm and 30°C using a HP-RP8, 10 μ m, 20 cm 4.6 mm column.     

Identification Of Oxygen Derivatives Of Polycyclic Aromatic Hydrocarbons In Airborne Participate Matter Of Upper Silesia (Poland)

Abstract

Organic material extracted from airborne participate matter collected in various places of Upper Silesia has been separated by column liquid adsorption chromatography. Six fractions of different polarity have been eluted. These fractions have undergone careful spectral analysis, thin layer chromatography and gas chromatography-mass spectrometry. Several PAH oxygen derivatives which have not been found in air from our Region so far were identified. Their biological activity is higher than activity of basic PAH structures. These compounds can be responsible to a high degree for interference in living organism functions in this highly polluted region.     

Synthesis Of Ligands Related To The O-Specific Antigen Of Shigella Dysenteriae Type 1.

Abstract

Stereoselective α-D-galactosylation at the position 3 of 4,6-O-substituted derivatives of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside is described. Glycosyl chlorides derived from 3,4,6-tri-O-acetyl-2-O-benzyl- and 2-O-(4-methoxybenzyl)-D-galactopyranose have been used as glycosyl donors. Methyl 2-acetamido-4,6-di-O-acetyl-2-deoxy-3-O-(3,4,6-tri-O-acetyl-α-D-galactopyranosyl)-α-D-glucopyranoside (27) and methyl 2-acetamido-4,6-di-O-benzyl-2-deoxy-3-O-(3,4,6-tri-O-acetyl-α-D-galactopyranosyl)-α-D-glucopyranoside (31) have been prepared.     

Application Of Fluorescamine Xiv1. Determination Of Optical Purity Of A Small Amount Of Amino Acids By The Fluorescamine Method

Abstract

A new simple and fast micro method has been established to determine the optical purity of a small amount of amino acids (0.1–1 μg/ml). The amino acids react readily with fluorescamine to form pyrrolinone-type chromophores, which show strong CD bands at 400–300 nm and much larger optical rotation than the free amino acids in the visible spectral range.     

Comparison Of Analytical Techniques For The Determination Of Trace Elements In Rain Water

Abstract

Summary-Two methods for the determination of cadmium, copper and lead in EPA reference precipitation sample, corresponding to 1987, 1988, 1989 and 1990 BAPMoN Intercomparison Program, have been compared: graphite furnace atomic absorption spectroscopy (GFAAS) and anodic stripping voltametry (ASV). A relatively good agreement was found between the two techniques and with the reference values. The results for the analysis of Cl and F by spectrophotometry, Ca, Mg, Na, K and Zn by AAS, and Fe, Mn, Cu, Ni, Pb and Cd by GFAAS in the same sample, corresponding to 1988 and 1989, showed good agreement with the stated values. The results of Easter Island rain waters for the years 1990 and 1991 are presented.     

Of protons or proteins

Mass analyses have been carried out on ions produced by an Electrospray (ES) source from dilute solutions of protein molecules with molecular weights (M) in the range from 5000 to nearly 40000. Each spectrum comprises a sequence of peaks corresponding to multiply charged intact parent species. The ions of each peak differ from those of their adjacent neighbors by one unit charge, H⁺ in these experiments. The maximum number of charges per ion generally increases with the molecular weight of the parent molecule, reaching a value of 45 in the case of alcohol dehydrogenase, atM=39830 the largest species in this study. Thus the resulting values ofm/z are within reach of a simple quadrupole mass filter whose nominal upper mass limit is 1500 daltons! The immediate application for the ES source is in mass spectrometric analysis of large fragile molecules of biochemical importance. But the multiply charged ions it produces are newcomers to the laboratory scene that constitute interesting subjects for study.     

Cadmium Determination in Soil Extracts by Furnace Atomic Absorption

Abstract

A method for the direct determination of Cd in soil extracts by graphite furnace atomic absorption spectrosopy (GFAAS) has been developed. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. Characteristic amounts are 0.34pg for siliceous samples and 0.45 pg for calcareous soils. The precision has been based on ten replicate readings in standards, and was 1.6%. Cd has been determined by the proposed methods and the results have been compared with those obtained by ICP technique.     

Properties of low power spark ablation in aqueous solution for dissolution of precious metals and alloys

Spark ablation or electric dispersion of metal samples in aqueous solution can be a useful approach for sample preparation. The ablated metal forms a stable suspension that has been described as colloidal, which is easily dissolved with a small amount of concentrated (16 M) HNO₃. In this study, we have examined some of the properties of the spark ablation process for a variety of metals (Rh and Au) and alloys (stainless steel) using a low power spark (100–300 W). Particle size distributions and conductivity measurements were carried out on selected metals to characterize the stable suspensions. A LASER diffraction particle size analyzer was useful for showing that ablated particles varied in size from 1 to 30 μm for both the silver and the nickel alloy, Inconel. In terms of weight percent most of the particles were between 10 and 30 μm. Conductivity of the spark ablation solution was found to increase linearly for approximately 3 min before leveling off at approximately 300 S cm³. These measurements suggest that a significant portion of the ablated metal is also ionic in nature. Scanning electron microscope measurements revealed that a low power spark is much less damaging to the metal surface than a high power spark. Crater formation of the low power spark was found in a wider area than expected with the highest concentration where the spark was directed. The feasibility of using spark ablation for metal dissolution of a valuable artifact such as gold was also performed. Determinations of Ag (4–12%) and Cu (1–3%) in Bullion Reference Material (BRM) gave results that were in very good agreement with the certified values. The precision was ± 0.27% for Ag at 4.15% (RSD = 6.5%) and ± 0.09% for Cu at 1% (RSD = 9.0%).     

Analysis Of Contaminants On The Inner Surfaces Of Copper Tubing

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have been determined by GC/MS to be present on the inner surfaces of copper tubing as supplied by the manufactures. The PAHs presumably exist as byproducts of the manufacturing process. Concentrations of PAHs found ranged from 0.00021 to 0.17 mg/m of tubing.     

High Voltage Spark Excitation of Some Organic Molecules in Nitrogen and Argon Atmospheres

Abstract

A simple high voltage ac spark produced between tungsten electrodes in both nitrogen and argon atmospheres is investigated as an emissive detector for certain organic molecules. Volatile vapours entering the electrode gap lower the resistance and an increased current flows in the spark. The energy available, particularly using nitrogen as a carrier gas, is sufficient to excite UV/visible spectra for various organic compounds; carbon species may be detected at 389 nm (CN), sulphur compounds at 257 nm (CS), halogenated compounds at various tungsten atomic lines and iodine at 206.2 nm (iodine atomic).     

Recent Advances in Aqueous Gel Permeation Chromatography

Abstract

The recent literature on aqueous gel permeation chromatography is reviewed. The chromatography of charged and uncharged solutes has been considered. A major emphasis has been to document the newer types of column packings for use in aqueous systems and their typical applications.     

Complexes Of Thiophosphoryl Compounds with AgNO3

Abstract

Under conditions of interphase catalysis complexiDg agenta L¹, L² and L³ have been synthesized^l. Using spectral and X-ray methods complex fomation of thises ligands with AgNO₃ has been studied