Andrzej Pelc

Inter-laboratory calibration of new silver orthophosphate comparison materials for the stable oxygen isotope analysis of phosphates

Stable oxygen isotope compositions (δ(18)O values) of two commercial and one synthesized silver orthophosphate reagents have been determined on the VSMOW scale. The analyses were carried out in three different laboratories: lab (1) applying off-line oxygen extraction in the form of CO(2) which was analyzed on a dual inlet and triple collector isotope ratio mass spectrometer, while labs (2) and (3) employed an isotope ratio mass spectrometer coupled to a high-temperature conversion/elemental analyzer (TC/EA) where Ag(3)PO(4) samples were analyzed as CO in continuous flow mode. The δ(18)O values for the proposed new comparison materials were linked to the generally accepted δ(18)O values for Vennemanns TU-1 and TU-2 standards as well as for Ag(3)PO(4) extracted from NBS120c. The weighted average δ(18)O(VSMOW) values for the new comparison materials UMCS-1, UMCS-2 and AGPO-SCRI were determined to be + 32.60 (± 0.12), + 19.40 (± 0.12) and + 14.58 (± 0.13)‰, respectively.

Generation of negative ions from SF6 gas by means of hot surface ionization

RATIONALE Sulfur hexafluoride (SF(6)) is a man-made compound with many industrial applications. This compound is also one of the most powerful greenhouse gases with a relatively long atmospheric lifetime. Therefore, it is important to investigate processes leading to SF(6) decomposition. METHODS A magnetic sector mass spectrometer with a thermoemission gaseous ion source was used in this study. The filament temperature was changed and monitored pyrometrically during the course of the studies. In the hot surface ionization process, negative ions may be generated both by free electron attachment to a molecule and by thermal dissociation followed by electron capture to the one of the fragments formed. RESULTS Eight ion species: SF(5)(-), F(-), SF(6)(-), SF(4)(-), SF(3)(-), SF(2)(-), SF(-) and F(2)(-), with ion current intensities ratios of 1000:200:100:10:5:0.5:0.5:0.05, respectively, were detected. The filament temperature dependencies of the SF(5)(-), F(-), SF(6)(-), SF(4)(-) ion current intensities were measured. The optimal temperatures at which the maximum of the ion current intensity is observed were estimated in the 1830-2000 ± 10 °C range. The formation of F(2)(-) ions is probably disturbed by a dissociation process at high temperatures. CONCLUSIONS Negative surface ionization on the hot filament is a relatively simple and effective method for carrying out negative ion formation studies. Eight SF(6) decomposition channels leading to the formation of negative ions have been detected and analyzed using this technique.

New isotope ratio mass spectrometric method of precise δ37Cl determinations

The most precise method of chlorine isotope analysis described to date is based on the isotope ratio mass spectrometry (IRMS) of chlorine quantitatively converted into chloromethane, CH(3)Cl. This gas can be produced from several chlorine-containing compounds and analyzed by IRMS. However, the mass spectrum of chloromethane is rather complicated and the ratio of the most abundant ions (mass-52/mass-50) differs from the (37)Cl/(35)Cl isotope ratio. This difference becomes significant when the delta37 Cl exceeds 10 per thousand. Moreover, the electron ionization source yields approximately 80% of all the ionic species at the useful masses 50 and 52. To overcome these drawbacks, we have devised a negative ion mass spectrometer which retains all the best features of IRMS, including a dual-inlet system with changeover valve, dual collector assembly and CH(3)Cl gas as analyte. In the modified ion source we have replaced the ionization chamber with an electron beam by a metal tube with a hot metal filament inside it. Within this tube the (35)Cl(-) and (37)Cl(-) ions are produced with an efficiency dependent on the filament material and its temperature. No other ionic species were found in the mass spectrum except of traces at masses 26 and 28 at ppm levels, probably due to the formation of CN(-) and CO(-). The minimal amount of Cl used in our method is of the order of 5 micromol (3 mg AgCl) and the precision is better than 0.005 per thousand (1sigma).

Negative ion source for chlorine isotope ratio measurements

A negative chlorine ion source has been designed and constructed. The source utilizes direct surface ionization of chloromethane gas on a hot metal filament. Four different alloys for the filament material were tested: W99Th1, W75Re25, Hf97.5Zr2.5 and Mo52.5Re47.5. We conclude that the best filament material is the MoRe alloy, for which the signal-to-noise ratio is optimal. The ion source is used for chlorine isotope ratio measurements with higher precision and sensitivity than the positive ionization source used previously. Inasmuch as only negative ions of the two isotopes of interest are observed, no corrections to the measured isotope ratio are necessary, and less rigously purified samples may be analyzed. The negative ion currents are considerably larger than positive ion currents obtained with an electron ionization source. This implies higher analytical precision (typically 0.005 permil) and sensitivity.

Electron impact study of carbon disulphide micro-clusters

Abstract The production of carbon disulphide micro-clusters (CS 2 ) n , n ⩽11, by adiabatic gas expansion of mixture of CS 2 vapour and Ar is studied by using an electron impact ion source and a double focusing sector field mass spectrometer. The appearance potentials for clusters n ⩽9 decreased as n increased but was not a simple function of 1/ n . The appearance pressures of observed clusters showed a slowly increasing dependence on cluster size. Results of measurements of appearance potentials and appearance pressures of selected clusters are described for a range of operating conditions.

Electron ionization study of ammonia micro-clusters

An electron impact ion source on a double focusing sector field mass spectrometer was used to investigate ammonia micro-clusters produced by the adiabatic free jet expansion of ammonia gas. The appearance energies for [NH(3)](n)(+), n </= 9, ions have been determined. Results of measurements of appearance pressures of selected clusters are described for a range of operating conditions. An empirical formula describing the ammonia clusters production is proposed. Copyright 2000 John Wiley & Sons, Ltd.

Production of carbon disulphide dimers by an adiabatic gas expansion method

Abstract The production of carbon disulphide dimers by adiabatic gas expansion of a mixture comprised of CS2 vapour and Ar is studied by using an electron impact ion source and a double focusing sector field mass spectrometer. Results of measurements of the generation of (CS2)2+ cluster ions versus the stagnation pressure (0–160 kPa) at several stagnation temperatures (267–300 K) are described. An empirical formula describing the carbon disulphide dimer production is proposed.

In vacuo reduction of silver orthophosphate with graphite for high-precision oxygen isotope analysis

The reduction of silver phosphate with graphite under vacuum conditions was studied at final reaction temperatures varying from 430 to 915°C to determine: (i) the CO(2) extraction yield, and (ii) the oxygen isotopic composition of CO(2). The CO(2) yield and oxygen isotopic composition were determined on a calibrated dual inlet and triple collector isotope ratio mass spectrometer. We observed the following three stages of the reduction process. (1) At temperatures below 590°C only CO(2) is formed, while silver orthophosphate decays to pyrophosphate. (2) At higher temperatures, 590-830°C, predominantly CO is formed from silver pyrophosphate which decays to metaphosphate; this CO was always converted into CO(2) by the glow discharge method. (3) At temperatures above 830°C the noticeable sublimation of silver orthophosphate occurs. This observation was accompanied by the oxygen isotope analysis of the obtained CO(2). The measured δ(18)O value varied from -11.93‰ (at the lowest temperature) to -20.32‰ (at the highest temperature). The optimum reduction temperature range was found to be 780-830°C. In this temperature range the oxygen isotopic composition of CO(2) is nearly constant and the reaction efficiency is relatively high. The determined difference between the δ(18)O value of oxygen in silver phosphate and that in CO(2) extracted from this phosphate is +0.70‰.

Homologous micro-clusters of carbon disulphide

Abstract Mass spectrometric investigations of homologous micro-clusters ( n ⩽6) of carbon disulphide are studied by using an electron impact ion source and a double focusing sector field mass spectrometer. Clusters are produced by adiabatic gas expansion of mixture of CS 2 vapour and Ar. The appearance potentials for ions (CS 2 ) n S + , (CS 2 ) n CS + , (CS 2 ) n S + 2 ( n =1 and 2), CS 2 C + and (CS 2 ) 3 S + are determined. The temperature dependences of selected clusters are also presented.

Oxygen isotope analysis of shark teeth phosphates from Bartonian (Eocene) deposits in Mangyshlak peninsula, Kazakhstan

Oxygen isotope analysis of shark teeth phosphates from Bartonian (Eocene) deposits in Mangyshlak peninsula, Kazakhstan We report the results of high-precision (±0.05‰) oxygen isotope analysis of phosphates in 6 teeth of fossil sharks from the Mangyshlak peninsula. This precision was achieved by the offline preparation of CO2 which was then analyzed on a dual-inlet and triple-collector IRMS. The teeth samples were separated from Middle- and Late Bartonian sediments cropping out in two locations, Usak and Kuilus. Seawater temperatures calculated from the δ18O data vary from 23-41°C. However, these temperatures are probably overestimated due to freshwater inflow. The data point at higher temperature in the Late Bartonian than in the Middle Bartonian and suggest differences in the depth habitats of the shark species studied.