B.P. Datta

Thermal ionisation mass spectrometry of Li2BO+2 ions: determination of the isotopic abundance ratio of lithium

Abstract Thermal ionisation mass spectrometric investigations of Li2BO+2 ions have been carried out. The central idea is to study the feasibility of making an accurate isotopic analysis of lithium employing an experimentally measured intensity ratio(s) of Li2BO+2 ions of different specific charges (m/z). This paper presents the results along with a discussion on the merits and demerits of the method. The studies show that the intensity ratios of Li2BO+2 ions are definitely changing with time owing to a certain amount of fractionation of lithium isotopes, the extent of which could, however, be controlled, leading to the determination of the 6Li/7Li abundance ratio with a reasonable accuracy without applying any correction factor. Factors affecting the accuracy of this molecular ion beam method of isotopic analysis are discussed. It is shown that the accuracy is governed by error propagation rather than by the achievable precision and accuracy of mass spectrometric measurements. This particular point is illustrated with examples of varying isotopic abundance patterns of lithium and boron. As a logical consequence, it is pointed out that a mere selection of the most abundant Li2BO2 molecules as monitors for mass spectrometric measurements may not always ensure accurate isotopic analysis of a constituent element.

R.f. spark source mass spectrometric studies of molecular ions

Abstract The small molecular ions such as the carbides (MC +,2+ n ), oxides (MO +,2+ n ) and some other matrix-sensitive ions in the beam produced from an r.f.-spark ion source have been studied for a number of elements (M) of varying electronic configurations. The MC + n ions of a given element, M, generally follow either of the following two yield distribution patterns, namely, (i) a monotonic decrease in the MC + n ion yield as n increases and (ii) a zigzag abundance distribution with the peaks appearing at even n values. The oxide ions, MO + n , due to any given element (M) show only the decreasing trend in yields with n and the higher oxides ( n ⩾ 3) are generally rare. The other molecules, some of which are metal or matrix-sensitive and which may be of concern for elemental analysis, include metal hydride (MH), hydroxide (MOH), halide (MX), cyanide (MCN), polymeric species such as M n , M m C n , M m O n , M m O n H p , M m X n , etc. The studies show that, unless the nature of the molecular mass spectrum for a given matrix is predetermined, the elemental analysis may turn out to be erroneous. Factors governing the abundance of molecules in the recorded ion beam and the probable processes of their formation are discussed.

ISOTOPIC ANALYSIS OF A 6LI ENRICHED LITHIUM SAMPLE EMPLOYING THE LI2BO2+ ION BEAM METHOD: VERIFICATION OF THE THEORETICAL ACCURACY

Abstract It was predicted recently by us (Int. J. Mass Spectrom. Ion Processes, 116 (1992) 87) that accurate measurements of the Li2BO2+ ion yield ratio(s) do not always imply accurate determination of the elemental isotopic abundance ratio(s). Further insight into this aspect is provided here by demonstrating that the results of the isotopic analysis of a 6Li enriched lithium sample using different pairs of isotopic Li2BO2+ ions as monitors show considerable variations, irrespective of the actual experimental errors. A theoretical explanation of the observations is presented. The present investigation provides the guidelines for selecting the proper monitor Li2BO2+ ion-pair(s) and discusses the other analytical requirements for making possible accurate isotopic analysis of lithium of any given isotopic composition. Experimental observations showing the effect of isotopic fractionation on the formation of the Li2BO2+ ions are also elaborated and discussed.

An experimental evaluation of procedures used for quantitative analysis in RF-spark source mass spectrometry

Abstract The determination of trace constituents in materials of high purity using spark source mass spectrometry normally employs the sensitivity calibration technique. In this technique, either the matrix element is used as reference or certain selected elements known as internal standards are used as reference. The photoplate evaluation procedure adapted for quantitative analysis is a matter of choice from the various procedures available in the literature. Investigations were carried out on the adaptability of these methods and different photoplate evaluation procedures. This paper describes the precision and accuracy achievable, as well as the relative advantages and disadvantages of these methods when the matrix or an element closely resembling the element being determined is used as reference element.

Relative sensitivity factors for the determination of rare earth elements in uranium oxide by Spark Source Mass Spectrometry

ZusammenfassungDie relativen Empfindlichkeitsfaktoren für die Elemente Ce, Nd, Sm, Eu, Gd, Dy, Er und Lu in U3O8 wurden mit der Funken-Massenspektrometrie mit elektrischem Nachweis (peak switching) bestimmt. Früher sind diese Faktoren in Uranylnitrat bestimmt worden und es wurde erwartet, daß trotz unterschiedlicher absoluter Werte der Trend derselbe wäre. Es zeigte sich jedoch, daß auch der Trend verschieden ist. Die Werte der vorliegenden Untersuchung stimmen mit theoretischen Berechnungen aus den Zersetzungsenergien der Seltenerdoxide überein und bestätigen die Ergebnisse anderer Autoren für die Y2O3-Matrix.SummaryRelative Sensitivity Factors (RSFs) for the rare earth elements Ce, Nd, Sm, Eu, Gd, Dy, Er and Lu in U3O8 have been determined by Spark Source Mass Spectrometry (SSMS) using the electrical detection system in peak switching mode. Earlier RSFs for these elements were determined in uranyl nitrate and it was expected that though the absolute value of the RSFs may be different, the trend would be the same. However, the present work shows that apart from the magnitude, the trend in RSF values is also different. The data from the present work are in agreement with the theoretical calculations based on the decomposition energies of the rare earth oxides and support the work carried out by others in the case of Y2O3 matrix.

Determination of zirconium in U−Zr−Al and Pu−Zr−Al alloys by isotope dilution thermal ionization mass spectrometry

An isotope dilution thermal ionization mass-spectrometric (ID-TIMS) method is described for the determination of Zr in U−Zr−Al and Pu−Zr−Al alloy samples. Problems encountered in the chemical exchange between the zirconium isotopes in the spike and sample, particularly Pu−Zr−Al samples, are discussed and a method has been standardized to eliminate it. Separation of Zr from U, Pu and Al was achieved by employing ion exchange procedures. A precision of better than 1% is possible in the determination of Zr with the method reported here.

Correlation of spark source mass spectrometric sensitivity calibration factors with the element-sensitive physicochemical properties

Abstract The sensitivity calibration factor commonly expressed as relative sensitivity coefficient (RSC) is used in quantitative spark source mass spectrometry. The RSC was studied from the viewpoint of element-sensitive physicochemical properties and a linear correlation was attempted. Statistical analysis of the experimental data was carried out to justify the linear correlation. This permits quantitative spark source mass spectrometric analysis of trace constituents whose relative sensitivity coefficients have not been experimentally determined. The variation of RSC with respect to specific element-sensitive properties was shown to be the same for certain oxide/graphite-type matrices.

Error-systematics of determining elemental isotopic abundance ratios by the molecular ion beam method: a case study for the simultaneous isotopic analysis of lithium and boron as Li2BO2+

The simultaneous isotopic analysis of lithium and boron by the Li2BO2+ ion beam method involves measurements of two different molecular abundance ratios (say, Rj+/-delta(j) and Rk+/-delta(k)), and subsequently extensive calculations to arrive at the analyte isotopic ratios (say, L and Y). It is not presently known how the measurement errors (delta(j) and delta(k)) are transformed into the errors of analysis (deltaL and deltaY). This work addresses this question from fundamental considerations. In the literature, the calculations are sometimes simplified using Ri formulae based on Li2B16O2+ ions and then applying correction factors for the actual Li2BO2+ ions, but this procedure is not generally applicable. We show how equations based on true Li2BO2+ ions (with full isotopic variations of all the constituent elements) can be solved, and illustrate the procedure with several examples. These studies show that accuracy of analysis depends not only on the accuracies of measurements, delta(j) and delta(k), but also on the particular isotopic Li2BO2+ ion-pairs (j and k) used as the monitor pairs. Moreover, this dependence is shown to be different for the different isotopic ratios (L and Y) to be determined simultaneously. Therefore, proper selection of monitor molecular pairs is a requirement for avoiding larger (propagated) errors in the analysis. Similar arguments would, in fact, apply to any arbitrarily chosen case of determining two or an even greater number of isotopic abundance ratios (Eis) by the molecular ion beam method, irrespective of whether the different analyte ratios, Eis, relate to a single multi-isotopic element, or different elements.

Charge distribution of elements in the ion beam produced from an RF-spark ion source

Abstract The ion yield distribution of elements with respect to charge in the beam produced from an rf-spark ion source has been studied for eight matrices. The thermochemical behaviour of the elements as well as the features of the matrix plasma are found to be the key factors. It is shown that the consideration of charge distribution helps to improve the precision of the spark source mass spectrometric analysis. It is argued that, in the course of the development of the matrix plasma, the vaporised particles in the sparking zone undergo element-sensitive multiple ionization. It is further concluded that, during the process of expansion of the plasma into the vacuum, the ions of different elements suffer different rates of recombination. Thus, the ionization energy available per particle controls the charge distribution of the elements in the plasma while the abundances of ions according to charge in the beam are regulated by the average energy available per particle and different recombination rates.

Yield distribution of M+n ions due to a given multi-isotopic element (M) and given n in the beam produced from an r.f.-spark ion source

Abstract The yields of different probable homo- and heteronuclear M+n ions due to a given multi-isotopic element M and a given value of n in the ion beam produced from an r.f.-spark ion source have been measured for eleven elements using different matrices. For each of the elements carbon, chlorine, potassium, strontium, antimony, tellurium and barium, the abundance distribution of M+n ions for given M and n in the recorded ion beam follow the statistical abundance distribution governed by , where xi is the fractional isotopic abundance of the ith isotope of the element (M). However, among the elements studied a divergence from the statistical prediction is observed for a few other elements such as nickel, zinc and especially molybdenum. That the matrix plays an important role is implied in the studies of Ag+2 ions using the matrices of silver alone and a mixture matrix of silver and graphite. The yield distribution of Ag+2 ions among its two homonuclear (107Ag+2 and 109Ag+2) and heteronuclear (107Ag109Ag)+ component ions in the beam from silver metal matrix obeys the statistical model, , while this is not true for silver graphite matrix.