Ion Current Ratio Research Articles

Mass-spectrometric Measurement of Activities in Both Solid and Liquid Solutions of the KCl–NaCl System

Abstract The activities of the KCl–NaCl system were mass-spectrometrically determined by the ion-current-ratio method in the temperature range From 793 to 1083 K. As a result, the activities of KCl or NaCl in the solid solution showed greatly positive deviations from Raoult’s law while the liquid solution at 1083 K gave slightly negative values. The heats of mixing in the solid solution were calculated from the temperature dependence of the modified ion-current ratios, [(INa2Cl+/XNaCl2)/(IK2Cl2/XKCl2)]. The excess entropy of mixing in the solid solution was attributed to the change in the vibrational spectrum, and the vibrational contribution to the heat of mixing was evaluated.

Aerosol charging by bipolar ions of unequal current densities: experiments in low electric fields

Results of experimental measurements of the electrical charge acquired by aerosols exposed to unequal current densities of positive and negative ions are presented. Highly monodisperse polystyrene aerosols ranging in size from 0.3 to 1.1 μm in diameter are exposed to air ions in the presence of electric fields between 100 and 500 V/cm. Mean aerosol charge is determined by integral mobility analysis. Charge levels are found to depend on particle size, ion current density ratio, electric field strength, and the product of ion conductivity and charging time. Time-dependent behavior is characterized by the accumulation of a steady-state level of charge. Diffusion charge is obtained by extrapolation of data obtained in low fields to E = 0. Classical diffusion theory and experiment are in close agreement for the unipolar case and for steady-state bipolar conditions at low current density ratios, but differ slightly under bipolar transient conditions.

Conservation of axial momentum in intense ion beam systems

In a number of systems, interaction between electrons and ions results in acceleration of ions. Because of the large ion/electron mass ratio, the efficiency of intense ion beam sources can often be low. A macroscopic momentum conservation law is presented which allows the efficiency of collective accelerators and ion diodes to be evaluated. The application of the equation is straightforward and does not depend on the specific dynamical processes involved. A number of new relations are derived from the basic equation including the efficiency of a collective accelerator, the average ion velocity for collective acceleration in vacuum, the ratio of electron and ion currents in a pinched beam diode, and a relation for current enhancements in magnetically insulated diodes. These relations also serve to elucidate the role of magnetic pressure in intense ion beam systems.

An improved selected ion recording system for precise isotope ratio determination.

An improved analog four-channel selected ion recording system is described, in which major modifications permit a decrease in the dwell time to 33 ms per channel, thus minimizing the mass cycling error. Synchronization with a sinusoidal sweep voltage superimposed on the normal accelerating voltage (8 kV) enables two channels to be monitored simultaneously in real time and each mass to be recorded continuously. These improvements allow measurement of ion current ratios with a precision of 0.2% over a wide dynamic range, permitting accurate determination of isotopic enrichment in biomedical assays even when this enrichment is derived from a single label. Use of the system is illustrated by the analysis of palmitate turnover in dogs (using [1--13C] palmitic acid) with an average standard deviation corresponding to the detection of 0.04% excess of [1--13C] palmitate.

Capacitive integration to produce high precision isotope ratio measurements on methyl chloride and methyl bromide samples

A capacitive integration circuit for the measurement of ion current ratios in an isotope ratio mass spectrometer is described. Sources of error and their effect on measurement precision are discussed. Results from the isotopic analysis of methyl chloride and of methyl bromide gases are presented. The relative standard deviation of measured ratios for methyl chloride was 13 parts in 10/sup 6/ while that for methyl bromide was 7 parts in 10/sup 6/. 3 tables, 1 fig.

Thermodynamic properties of the liquid Sn−Ge and Sn−Au systems by mass spectrometry

The activities and partial molar heats of mixing have been determined for the liquid Ge-Cu system at 1525°C and the liquid Ge-Au system at 1400°C. The experimental technique consisted of analyzing Knudsen cell effusates with a TOF mass spectrometer. The ion current ratios for the monomeric vapor species were measured as a function of temperature and composition and the thermodynamic properties calculated using a modified form of the Gibbs-Duhem equations. Both systems exhibited negative deviations from ideal behavior. The results for the Raoultian activity coefficients can be partially represented by $$\begin{gathered} \log \gamma _{Ge} = - 2.521X_{Cu}^2 + 0.948 (0 \leqslant X_{Ge} \leqslant 0.2) \hfill \\ \log \gamma _{Cu} = - 0.048X_{Ge}^2 - 0.466 (0 \leqslant X_{Cu} \leqslant 0.2) \hfill \\ \end{gathered} $$ for the Ge-Cu system at 1525°C and by $$\begin{gathered} \log \gamma _{Ge} = - 2.327X_{Au}^2 + 0.465 (0 \leqslant X_{Ge} \leqslant 0.35) \hfill \\ \log \gamma _{Au} = - 0.510X_{Ge}^2 - 0.489 (0 \leqslant X_{Au} \leqslant 0.30) \hfill \\ \end{gathered} $$ for the Ge-Au system at 1400°C. An experimental technique is presented for determining the contribution of dissociative ionization of polymer species to the measured monomeric ion current ratio . The effect of dissociative ionization of the germanium polymer species present in the Knudsen ceil effusate was determined to be negligible.

Time resolved measurements in high pressure mass spectrometry: An analysis of assumptions

The assumptions underlying the use of time resolved measurements for the determination of ion–molecule reaction rate constants in high pressure chemical ionization sources have been examined and problems introduced by diffusion and drift are presented; these require conversion from ion currents to ion concentrations in the presence of applied fields when ion current ratios of different ions are used. Moreover, the existence of an irresolvable difference in the significance of arrival times of product and reactant ions is demonstrated, but it is shown how this error can be minimized. A method for the measurement of total disappearance rate constants for association reactions is demonstrated and applied to the reaction CO+2+2CO2→ (CO2)+2+CO2; the third order rate constant for this process is 1.5±0.1×10−28 cm6 sec−1 at 409° K.

Calibration methods for the ion probe determination of fluorine in mineralized tissue

An ion micro-analyzer (Cameca IMS 300 with a TD 1000 computer unit) has been calibrated for quantitative point determination of fluorine in apatites, including tooth and bone material. Samples with macroscopically measured F concentrations were used as external standards. The samples were bombarded with O− primary ions. Secondary positive ion currents were registered as mass spectra containing mass numbers 19, 20, 31, 44, 59, 60 and 61. The latter mass numbers were used in isotopic correction to subtract oxide and hydroxide contributions from the fluoride 59 peak. For each bombarded spot, the ratios19F+/40Ca2+, respectively59CaF+/44Ca+, were plotted in a log-log graph against40Ca2+/44Ca+, the abscissa providing a measure of ionization efficiency. The plots yielded two sets of parallel straight lines, with ordinate values proportional to the respective F/Ca concentration ratios, in agreement with earlier theory. Each set of lines constitutes a calibration graph, where the fluorine concentration at an investigated spot is obtained when substituting the measured ion current ratios. With biological apatites, account must also be taken of effects due to, among other things, adsorbed humidity, other contaminations, and non-stoichiometry. When all precautions are taken, the accuracy of the determined F contents in the point analysis of an area some 100 μm in diameter can be expected to be better than 6% at 1500 ppm F, and better than 25% at 100 ppm F. The calibration is effective down to about 20 ppm F. Applications have been carried out on samples of human tooth enamel.

Abstract: Chemisorption states of CO on W(110)

When CO chemisorbed at low temperature on W(110) is heated, a variety of binding states are exhibited. This investigation follows the changes in a chemisorbed layer from 20 K to the desorption temperature on a polished single crystal face 1.5×0.25 cm in ultrahigh vacuum better than 10−12 Torr (1.33×10−10 Pa). A closely positioned field-emission tip measures the thermal desorption for each temperature increment by a method due to Bell and Gomer. Alternatively, flash desorption spectra for specific molecular masses can be obtained with a mass spectrometer. Binding states of CO on the surface are characterized by the ions observed in electron impact desorption (EID) as well as the change produced in the surface work function as measured with a vibrating condenser arrangement. Decay of ion signals for large electron currents yields the total EID cross section useful for identification too. A uniform layer of virgin CO forms on adsorption at 20 K from an effusion beam. The work function increases by 0.6 eV. EID yields predominantly CO+. Heating to 300–400 K desorbs 60% of this layer with disappearance of CO+ and simultaneous appearance of O+ in EID. The work function meanwhile reverts to approximately the clean metal value. With further heating, O+ diminishes without thermal desorption, suggesting the formation of an intermediate β-precursor state from virgin CO with subsequent conversion to β-CO, β-CO then desorbs between 900 and 1200 K with complete isotope mixing. More evidence for binding-state mutation between 400 and 900 K was sought by readsorbing CO at 20 K on β- or β-precursor-CO heated to a specified temperature. The readsorbed CO, isotope labeled, was found to be accomodated in two states thermally desorbable in a continuous spectrum up to 400 K. Both yield CO+ on EID but are distinguishable from each other and virgin CO by the thermal desorption temperature, work function change, and EID cross section. The weaker binding state, previously unknown, was named γ CO to distinguish it from the more strongly bound α-CO. While the nature of the readsorption states did not depend on the temperature to which the β- or β-precursor- CO had been heated before readsorption, the amount of readsorption possible increased with that temperature. This fact suggests an increasing extent of some kind of conversion, possibly from β-presursor to β. In addition, the presence of α- and γ-CO was found to suppress O+ ions from the β precursor in EID. A small amount of conversion of α-CO into β precursor was detected with isotope labelling. Isotope effects in the EID total cross sections for virgin and β-precursor states are small. The total cross section for virgin 12C16O is 10% larger than for 12C18O. The ionic cross sections show more pronounced differences as shown by the ratio of ion currents from a mixture of equal amounts of each isotope labelled species. C16O+/C18O+ ?1.6 for virgin CO. 16O+/18O+?1.3 for β precursor. The CO+-yielding virgin state can be converted to an O+-yielding state by the impact of low energy electrons (∠200 eV). Work function, however, suffers little or no change in this conversion, quite unlike the thermal conversion to β precursor. Readsorption on a layer thus produced by electron impact yields essentially virgin CO rather than α- and γ-CO as shown by subsequent thermal desorption. The electron-induced O+-yielding state is thus different from the O+-yielding β or β precursor. If this O+-yielding state is subjected to prolonged electron impact, the O+ ion signal is reduced to a very small value, with a concurrent decrease in the work function. On heating, the O+ ion signal increases to a maximum at about 200 K and then decreases with rising temperature to zero at the β-CO desorption temperature.

クヌーセンセル-マスフィルタによるCd-Zn系の活量測定

A Knudsen cell-quadrupole mass filter combination system was constructed for the purpose of studying the physical chemistry of metallurgical solutions.This analyzer was employed because of several advantages inherent in its measuring principles.The applicability of the apparatus for the determination of activities was examined by conducting the measurement of activities in the liquid Cd-Zn system. The system was chosen because of experimental easiness, i.e., low fusing temperature of the alloy and similar vapor pressures of the components. Furthermore, the comparison with the literature data can be made. Ion intensities of the principal isotopes of the components (48114Cd and 3064Zn) which are thought to be proportional to the equilibrium partial pressures over the alloy were recorded over the temperature range 450∼700 K and the whole region of the binary system. By using the ion-current ratio method, the thermodynamic property at 667 K was calculated. The activity coefficients can be represented over the whole composition region by the following equations: logγCd(1)=(1.35⁄2)XZn2 and logγZn(1)=(1.35⁄2)XCd2 at 667 K. These results were converted to those at 800 K on the assumption of regular-solution behavior, and it was found that they are in good agreement with the values proposed by Hultgren et al.

Thermodynamics of AgCl + Ag 2S and AgBr + Ag 2S melts by mass spectrometry

The activities of AgX (where X = Cl or Br) in molten mixtures of AgX and Ag 2S were determined by mass spectrometry using the monomer to trimer ion-current ratio technique. Both systems exhibited positive deviations from ideality. Both melts were found to be regular over the entire composition range. The characteristic parameter w for the two mixtures was found to vary linearly with temperature. For AgCl plus Ag 2S in the liquid range, the excess Gibbs energy can be represented, between 850 and 1050 K, by the following equation: G E = X 1X 2{(5660 ± 130) - (3.02 ± 0.02)(T/K)} cal th mol−1 Similarly for AgBr plus Ag 2S, between 850 and 975 K, G E = X 1X 2 {(3590 ± 90) - (0.45 ± 0.02)(T/K)} cal th mol−1

Alloy thermodynamics by mass spectrometry: A critical review

Mass spectrometric techniques of sufficient accuracy to permit reliable measurement of alloy activity as a function of temperature have been developed. These offer the advantages that derive from sensitivity, speed of measurement and ability to work easily with complex vapors. Two methods require that the two components be volatile; ratios of ion currents are measured. The ratio/model method (Hoch et al.) invokes the regular solution model. The ratio/ Gibbs - Duhem (Lyubimov et al.; Belton and Fruehan; Neckel et al.) method invokes the Gibbs - Duhem equation. Internal standard (I.S.) methods incorporated concurrent measurement of a reference materials. The I.S./ isotope or “triple cell” method (Hoch et al.) requires isotopically enriched materials, while the I.S./dual or multiple cell methods (Stafford, Whitmore et al.; De Maria et al.) use mechanical motion under vacuum to select the sample studied. Details and difficulties of the methods, listed above in order of increasing information output, are presented, compared and critically evaluated. A complete listing of the applications to date is presented.

Effect of temperature and electron energy on the mass spectrum of silver chloride

The ion-current ratios ( I Ag 3 Cl 2 + I Ag 3 Cl 3 + ) were measured over the temperature range 900–1080 K using several electron energies. The variation of these ratios with temperature was found to be independent of the excitation energy of Ag 3Cl 3 +. The effect of thermal energies was calculated to be even smaller than the effect of the change in excitation energies. Hence, thermal energies cannot be responsible for the variation of ( I Ag 3 Cl 2 + I Ag 3 Cl 3 + ) with temperature. The existence of Ag 3Cl 2 + as a parent ion is postulated. Similar results were obtained for the silver bromide system and the existence of Ag 3Br 2 + as a parent ion is postulated.

Secondary Ion Microanalysis of Fluorine in Apatites of Biological Interest

Abstract A Cameca IMS 300 ion analyzer has been used to measure fluorine concentrations in tooth material. Samples of human and shark teeth were studied. Negative oxygen primary ions produce secondary mass spectra in which positive as well as negative fluorine ion peaks are well re­ presented. With constant measuring conditions, the reproducibility of the F/Ca ion ratios is satisfactory. Fluorine concentrations in the 10 ppm region are easily recorded. By means of samples previously measured by macroscopic F-determining methods, a calibration can be effected to obtain, from the ion current ratios, at least semiquantitative values of F-concentrations. In a sample of human enamel, the F-concentration was found to vary from about 3000 ppm at the surface to about 100 ppm in the interior. In shark enamel the composition at the surface cor­ responded to nearly saturated fluorapatite, 3.6% F, but the fluorine concentration decreased distinctly at increasing depth.

Micro-sample analysis by spark source mass spectrometry

The abundances of the neodymium isotopes in a 1 microgram sample of neodymium oxide have been determined using the AEI MS702R spark source mass spectrometer in order to evaluate the precision of analysis for small samples. Gold was used as the support material for the sample. Three different modes of analysis have been evaluated, namely (1) simultaneous detection of all masses on the photographic plate, (2) magnetic scanning, with electrical detection of the individual and total ion currents and recording of the individual/total ion current ratio, and (3) electrical switching between masses, with electrical detection as in (2). It is shown that satisfactory results are obtained for all three modes of analysis. The time required for acquiring the data and subsequent evaluation is discussed for each mode. The neodymium isotope abundances are calculated and compared with published values for natural neodymium.

Simultaneous ion-beam collection for precise measurement of nuclidic ion-current ratios in spark-source mass spectrometry

Simultaneous ion-beam collection techniques make significant improvement possible in the precision of measurements when electrical ion-detection is used with the spark ion-source. The advantage of reference of specific ion-current signals only to those from desired regions of the mass spectrum is that reproducible measurements may be made on heterogeneous samples such as oxide-graphite pellets. For example, isotopic ratio measurements from separate samplings of an oxide (pelleted with graphite) are reproducible to better than +/-0.5%. The technique is also advantageous when sparking dissimilar electrodes, such as a gold probe and a metal bar.

クヌーゼンセル-質量分析法による溶鉄中のイオウの活量係数の測定

The Knudsen cell mass spectrometer combination was used to determine the activity coefficient of sulfur dissolved in liquid iron. The ion current ratios of dimeric vapor specy of sulfur and monomeric vapor specy of iron were measured as a function of temperature and composition, and the activity coefficients and the interaction parameters were calculated using a modified form of the Gibbs-Duhem equation. The results were represented by the following equation:e(s) s=-225/T+0.0704

Thermodynamic properties of the liquid Ge-Cu and Ge-Au systems by mass spectrometry

The activities and partial molar heats of mixing have been determined for the liquid Ge-Cu system at 1525°C and the liquid Ge-Au system at 1400°C. The experimental technique consisted of analyzing Knudsen cell effusates with a TOF mass spectrometer. The ion current ratios for the monomeric vapor species were measured as a function of temperature and composition and the thermodynamic properties calculated using a modified form of the Gibbs-Duhem equations. Both systems exhibited negative deviations from ideal behavior. The results for the Raoultian activity coefficients can be partially represented by $$\begin{gathered} \log \gamma _{Ge} = - 2.521X_{Cu}^2 + 0.948 (0 \leqslant X_{Ge} \leqslant 0.2) \hfill \\ \log \gamma _{Cu} = - 0.048X_{Ge}^2 - 0.466 (0 \leqslant X_{Cu} \leqslant 0.2) \hfill \\ \end{gathered} $$ for the Ge-Cu system at 1525°C and by $$\begin{gathered} \log \gamma _{Ge} = - 2.327X_{Au}^2 + 0.465 (0 \leqslant X_{Ge} \leqslant 0.35) \hfill \\ \log \gamma _{Au} = - 0.510X_{Ge}^2 - 0.489 (0 \leqslant X_{Au} \leqslant 0.30) \hfill \\ \end{gathered} $$ for the Ge-Au system at 1400°C. An experimental technique is presented for determining the contribution of dissociative ionization of polymer species to the measured monomeric ion current ratio . The effect of dissociative ionization of the germanium polymer species present in the Knudsen ceil effusate was determined to be negligible.

Determination of thermodynamic interaction parameters in solid V-Ti-Cr alloys using the mass spectrometer

The Knudsen effusion method was combined with a mass spectrometer sensing technique in order to determine thermodynamic interaction parameters of solid solution bcc alloys of V-Ti-Cr. A regular solution model was used to relate the vaporization data to ion current ratios obtained from the mass spectrometer. The temperature range of the vaporization experiments was 1400° to 1700°C, with alloy compositions ranging from 10 to 66 at. pct of each of the three components in the ternary system. Modified interaction parameters were calculated by assuming only binary interactions (which is a good approximation at low third component concentrations). The results are: ΩTiV = 1.8 ± 0.2 kcal/g-atom; 0 <NCr < 0.2 ({iT}AV = 1800 K) ΩTiCr = 1.9 ± 0.4 kcal/g-atom; 0.1 <NV < 0.4 ({iT}AV = 1750 K) ΩVCr = 3.1 ± 0.7 kcal/g-atom; 0.1 <NTi < 0.4 ({iT}AV = 1850 K) A temperature dependent form was an appropriate refinement of the results for the Ti-Cr system from 1500 to 1840 K. That expression is $$\Omega {\text{ = 28 (1 - }}\frac{T}{{1840 K}}{\text{ kcal/g - atom}}$$ Overall, experimental results show important, but not complete, agreement with estimates from phase diagrams and theoretically calculated values.

The determination of activities by mass-spectrometry—some additional methods

Further consideration is given to the determination of the thermodynamic properties of metallurgical solutions by mass-spectrometric analysis of the equilibrium vapor effusing from a Knudsen cell. Equations are presented which permit the application of the integration of ion-current ratios to complex species, thus avoiding problems caused by fragmentation ionization. The method is applied to a limited study of the Bi-Te system at 750°C. Ternary systems are considered and the method for the determination of the properties from measurements of a pair of ion-currents is demonstrated. Equations are also derived for the treatment of a ternary system which is saturated with respect to an involatile component. Finally, a method is presented for correcting the monomer-dimer ratio technique of Berkowitz and Chupka for fragmentation ionization effects.