Improved three-filament thermal ionization mass spectrometry ion source for isotope ratio determination of two samples.

RATIONALE: In order to make a single-filament thermal ionization mass spectrometry (TIMS) instrument more versatile and efficient in element isotope analysis, a multifilament ion source has to be employed. In the currently used three-filament ion sources, the same sample must be loaded on all the evaporator filaments, because of the possibility of cross-contamination. METHODS: The elimination of cross-contamination in a TIMS three-filament ion source was achieved by installation of a wide ionizer filament (ribbon shape) perpendicular to the extracting slit plane between two parallel evaporators. In such a configuration, the ionizer filament serves also as a screen separating two evaporator filaments on which two different samples can be loaded. RESULTS: The lack of cross-contamination (on a measurement uncertainty 1σ level of 0.3‰) has been demonstrated by measurements of the isotope ratios of a potassium chloride sample (39 K/41 K = 13.7801 ± 0.0023) versus a spike (39 K/41 K = 1.5670 ± 0.0003). The reproducibility of the isotope ratios for potassium 41 K/39 K and lithium 7 Li/6 Li is about 600 ppm (1σ). CONCLUSIONS: The small change of the ionizer filament configuration significantly improves the functionality of the ion source. The proposed modification enables us to perform alternating isotope analyses under the same working conditions for two different samples (e.g. studied sample and standard).

Oxygen isotope fractionation between bird bone phosphate and drinking water.

Oxygen isotope compositions of bone phosphate (δ18Op) were measured in broiler chickens reared in 21 farms worldwide characterized by contrasted latitudes and local climates. These sedentary birds were raised during an approximately 3 to 4-month period, and local precipitation was the ultimate source of their drinking water. This sampling strategy allowed the relationship to be determined between the bone phosphate δ18Op values (from 9.8 to 22.5‰ V-SMOW) and the local rainfall δ18Ow values estimated from nearby IAEA/WMO stations (from -16.0 to -1.0‰ V-SMOW). Linear least square fitting of data provided the following isotopic fractionation equation: δ18Ow = 1.119 (±0.040) δ18Op - 24.222 (±0.644); R 2 = 0.98. The δ18Op-δ18Ow couples of five extant mallard ducks, a common buzzard, a European herring gull, a common ostrich, and a greater rhea fall within the predicted range of the equation, indicating that the relationship established for extant chickens can also be applied to birds of various ecologies and body masses. Applied to published oxygen isotope compositions of Miocene and Pliocene penguins from Peru, this new equation computes estimates of local seawater similar to those previously calculated. Applied to the basal bird Confuciusornis from the Early Cretaceous of Northeastern China, our equation gives a slightly higher δ18Ow value compared to the previously estimated one, possibly as a result of lower body temperature. These data indicate that caution should be exercised when the relationship estimated for modern birds is applied to their basal counterparts that likely had a metabolism intermediate between that of their theropod dinosaur ancestors and that of advanced ornithurines.

A new negative and positive gas ion source for isotope ratio mass spectrometry.

RATIONALE: The goal of this research was to construct an effective gas ion source for isotope ratio mass spectrometry, which generates sufficiently strong and stable ion beams for multiple isotope ratio analysis of sulfur and oxygen from readily available gases such as SO2 , CO2 , CO, O2 and chlorine from CH3 Cl gas. METHODS: By means of a 60° sector mass spectrometer equipped with a new type of sensitive ion source and with a dual-inlet system and triple collector assembly, we have measured 34 S/32 S and challenging 36 S/32 S isotope ratios using positive sulfur ions generated from SO2 gas. The new ion source differs from the Nier-type ones by the electron beam being replaced with a tungsten filament. The obtained isotope signals of 32 S+ , 34 S+ and 36 S+ were from 1 to 5 V (depending on the pressure of admitted gas) on high-ohm resistors of 200 MΩ, 5 GΩ and 500 GΩ, respectively. The variable 33 S peak was not recorded as useful due to interference from H32 S+ ions. RESULTS: Although the ionizing electrons in the new ion source have significant energy dispersion the obtained peak profiles are flat-topped and they lead to good resolving power for the mass spectrometer (M/∆M ≈ 100). The achieved precision of δ34 S and δ36 S determination was better than ±0.01 and ±0.1‰, respectively. The determination of 37 Cl/35 Cl in a volatile organic compound CH2 Cl2 was easily achieved on Cl- negative ions with a precision of ±0.005‰. CONCLUSIONS: The new ion source has great potential in the quantitative analysis of gases on positive ion mass spectra as well as, in the case of gases with high electron affinity such as CH3 Cl, CH3 Br, SF6 , SiF4 , on negative ones. It usefulness was demonstrated on an example of multiple sulfur isotope analysis and 37 Cl/35 Cl ratio determination with great precision. A negative ion source of this type will probably be useful in a more complicated instruments used in SIMS or AMS. Copyright © 2017 John Wiley & Sons, Ltd.

Direct matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis of lysozyme contained in hen egg white.

As a natural antibacterial peptide, lysozyme (LZ) is widely used in medicine and the food industry. Despite many years of research on this compound, its new antibacterial properties are still to be determined. The primary aim of this work is to demonstrate the application of the matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometric analysis of LZ directly in hen egg white samples without extraction thereof. The egg white samples were kept over 10 weeks at room temperature and measured every week. The resulting positive and negative ion mass spectra were then compared to determine the intensity of the LZ mass peak. Storage of the egg white for over 10 weeks did not influence the LZ mass peak intensity (both positive and negative). It can be concluded that the LZ concentration in the egg white samples did not vary with time. The effect of the matrix/sample ratio on LZ detection was also examined, and it was found to be different in the case of positive and negative ionization. The mass peaks of LZ oligomeric forms were observed in all mass spectra, so the MALDI method could be used in subsequent studies.

Quantification of the PR-39 cathelicidin compound in porcine blood by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RATIONALE: The PR-39 porcine cathelicidin occurs naturally in animal neutrophils. Its main function is antimicrobial activity, which potentially can be used in antibiotic treatments in veterinary medicine. Investigations concerning such a use require the detection and quantification of PR-39 in a given sample. The aim of this work is to determine the concentration of PR-39 contained in porcine blood. METHODS: Prior to matrix-assisted laser desorption/ionization (MALDI) analysis, the porcine blood sample was subjected to crude extraction in order to release the active form of PR-39 from the neutrophil granules. Next, gel filtration chromatography was performed to separate PR-39 from other cathelicidins present in porcine blood. Positive ion MALDI time-of-flight (TOF) mass spectra of the resulting portion of lyophilisate with unknown PR-39 content were acquired in linear mode. To quantify PR-39 in the lyophilisate sample, the standard addition method was applied. The PR-39 concentration obtained in the lyophilisate sample was then converted into the peptide concentration in porcine blood. RESULTS: The linear fit function of the constructed calibration curve indicates an excellent correlation between the PR-39 peak intensity and the added quantity of synthetic PR-39 (R(2) = 0.994) and a low relative standard deviation of the slope = 1.98%. From the x-intercept of the straight line, we estimated the PR-39 concentration in porcine blood to be 20.5 ± 4.6 ng/mL. CONCLUSIONS: The MALDI method was successfully applied for the quantitative analysis of PR-39 found in porcine blood. Compared with other available methods, it is relatively easy, inexpensive and not time-consuming. Despite the method having lower accuracy than the enzyme-linked immunosorbent assay (ELISA), the results obtained here, by a much simpler method, are in good agreement with the literature data.

Isotope fractionation in aqua-gas systems: Cl(2)-HCl-Cl(-), Br(2)-HBr-Br(-) and H(2)S-S(2-).

We report calculated values of isotope fractionation factors between chlorine, bromine and sulphide hydrated anions and respective gaseous compounds: hydrogen chloride, hydrogen bromide, molecular chlorine and bromine and hydrogen sulphide. For the calculation of the reduced partition function ratios (ß-factors) of hydrated Cl(-), Br(-) and S(2-) anions, we used a model of a cluster composed of the considered ion surrounded by two shells of H(2)O molecules. Only the electrostatic interaction between ion and water molecules treated as electric dipoles was taken into account. The ß-factors for the gaseous compounds (HCl, Cl(2), HBr, Br(2) and H(2)S) were calculated from vibrational frequencies reported by Urey and Greiff [Isotopic Exchange Equilibria, J. Am. Chem. Soc. 57, 321 (1935)] and Schauble et al. [Theoretical Estimates Equilibrium Chlorine-Isotope Fractionation, Geochim. Cosmochim. Acta 67, 3267 (2003)]. Low-temperature isotope fractionation between chlorine-hydrated anion and hydrogen chloride attains 1.55-1.68‰ (this work), which is in good agreement with experimental data (1.4-1.8‰) [Z.D. Sharp, J.D. Barnes, T.P. Fischer and M. Halick, An Experimental Determination of Chlorine Isotope Fractionation in Acid Systems and Applications to Volcanic Fumaroles, Geochim. Cosmochim. Acta 74, 264 (2010)]. The predicted isotope fractionations for hydrated bromine and HBr, Br(2) gases are very small, 1000 ln α, do not exceed 0.8‰; thus, the expected variations of bromine isotope composition in aqua-gas systems will require enhanced precision for their detection. In contrast, the sulphur isotope fractionation between H(2)S( gas ) and S(2-) attains 6.0‰ at room temperature and drops nearly linearly to 3.1‰ at 350°C.

A novel circuit for independent control of electron energy and emission current of a hot cathode electron source.

The implementation of a non-linear combination of two reference voltages to control the anode voltage in the previously described biasing system of an electron source with a hot cathode allows elimination of the correlation between the emission current and the accelerating voltage. The presented system is highly suitable for applications in electron-impact mass spectrometers, ionization gauges and other instruments (for example, electron microscopes).

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 Vennemann's 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.

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‰.

Isotope study of therapeutic waters from Horyniec Spa, SE Poland.

The curative waters of HCO3-SO4-Mg-Na+H2S chemical type and 0.6-0.8 g/dm³ total dissolved solids are exploited in Horyniec Spa located at the northern boundary of the Carpathian Foredeep, near the Polish-Ukrainian border. Although these waters occur at relatively shallow depths (their aquifer is encountered about 30 m below the ground surface), they are quite well protected from surface pollutants by a cover of clayey sands. This paper revises and discusses the origin of specific chemical components of these waters based on the following analyses of stable isotopes: (a) δ³4S in SO4²â», H2S, and CaSO4·2H2O, (b) δ¹8O in SO4²â», H2O, and CaSO4·2H2O, and (c) δ²H in H2O and CaSO4·2H2O. The most important process which takes place in the aquifer is the dissolution of gypsum present in the Miocene formation and subsequent bacterial reduction of sulphate ion to hydrogen sulphide in the presence of an organic matter. This process shifts both δ³4S and δ1¹8O of sulfate ions towards higher concentration of heavy isotopes by several per mil in comparison to that in the original Miocene gypsum. The hydrogen sulphide generated this way (up to a concentration of 45 mg/dm³) is highly depleted in a heavy isotope by about 41‰ with respect to a sulphate ion.

Stable sulphur isotope ratios in the moss species Hylocomium splendens (Hedw.) B.S.G. and Pleurozium schreberi (Brid.) Mitt. from the Kielce area (south-central Poland).

Stable sulphur isotope determinations were performed on 18 moss samples collected at nine sites in forested areas of the city of Kielce. The delta(34)S of Hylocomium splendens varied from 4.4 to 7.1 per thousand, whereas the delta(34)S of Pleurozium schreberi was in the range of 3.7-9.1 per thousand. The Holy Cross Mountains mosses display a positive delta(34)S signature of airborne SO(2) and sulphates of anthropogenic origin, which is characteristic for this part of Europe. Some spatial variations in the delta(34)S of mosses are due to the interactions that occur between coal combustion emissions with diverse isotopic imprints, variations in wind direction and topographic features combined with biological fractionation.

New isotope ratio mass spectrometric method of precise delta37Cl 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.

About isotope equilibrium between liquid and vapour phases.

A new semi-empirical formula was devised for liquid-vapour fractionation at thermodynamic equilibrium, which is valid for the whole temperature range, i.e. from the freezing to the critical temperature, Tc. The new formula contains three parameters (A, B and C) only: 10(3) ln alpha = ((A/T2) - (B/T))(1-x)+ C((Tc-T)/(T2))X, where X is the ratio of saturated vapour pressure at temperature T to the critical pressure. Physical reasons for the above formula are presented. The following numerical values of the parameters have been obtained by fitting the above expression to the experimental data from literature: A=1.3781x10(6), B=1.8876x10(3), C=3655.8 for 18O/16O, and A=18.993x10(6), B=40.798x10(3), C=18405 for D/H isotope fractionation. In both cases, X was calculated from the Van der Waals semi-empirical formula for vapour pressure, which has only one crude parameter: X=exp(-3.3(Tc-T/(T)).

Millimeter scale variations in the isotopic composition of vein sulphide minerals in the Kupferschiefer deposits, Lubin area, SW Poland.

A slice of black shale rock cut by various metal sulphide veins of different generations from the Kupferschiefer deposits of Lubin, Poland was subjected to bombardment in a Laser Microprobe Combustion Reactor to produce SO2 for S-isotope analyses. The delta34S values ranged from-22 to-29 per thousand consistent with previous findings using conventional IRMS and attributable to primary generation of H2S by bacterial sulphate reduction. Systematic trends in delta34S values of a few per mil over distances of the order of mm attest to low temperatures of mineralization with accompanying change in the isotope composition of the fluids due to kinetic or equilibrium isotope fractionation.

Stable carbon isotopic composition of tree rings from a pine tree from Augustów Wilderness, Poland, as a temperature and local environment conditions indicator.

Tree rings can be used as archives of climatic and environmental data with annual resolution. Tree rings widths, maximum late wood density and other parameters as stable composition in tree rings can be used for the reconstruction of past climatic and environmental changes. Stable carbon isotope ratios in tree rings may provide valuable information on past climatic conditions. 13C/12C ratios of plant organic matter can reflect corresponding 13C/12C ratio of atmospheric CO2 during formation of the rings. Investigations of isotopic carbon composition in tree rings from in the ecologically clean the Augustów Wilderness region in the north-eastern part of Poland (22 degrees 58'E, 53 degrees 51'N) (nowadays a sanctuary) were undertaken. Series of delta13C in alpha-cellulose and in wholewood were acquired. Those measurements constituted a part of more complex investigations of carbon isotope composition in tree rings including the measurements of radiocarbon concentration and tree ring widths. This article presents preliminary results. It is argued that contrary to the tree ring widths and delta13C in wholewood that do not reveal significant correlation with temperature, the variation of delta13C in the latewood alpha-cellulose is correlated with combined July and August temperatures.

Temperature controller for thermal ionization mass spectrometry.

We describe the use of a simple voltage stabilizer that controls the filament temperature (T(f)) in the ion source of a thermal ionization mass spectrometer. The filament voltage (V(f)) is measured by means of a separate pair of wires connected inside of the ion source in parallel to the wires supplying power. It has been demonstrated that V(f) is directly proportional to T(f) in a wide range of filament temperature. The T(f) value is solely controlled by the reference voltage (V(r)) that can be manually selected from a voltage divider or by means of a computer. Digital signals from the computer in the form of a series of pulses are transmitted opto-electronically and subsequently converted to analog signals. The temperature controller described here was successfully applied for analysis of potassium concentration by the isotope dilution method.