Isotope interferences

A peak is the sum of the contributing species weighted by the isotope abundance of each species on this isotope (interference equation)... 

We continued our efforts for a more efficient operation. All isotope interference corrections, except for the aluminum correction on magnesium, were computerized. This saved more manpower in data reduction. By using routine scheduling of both long- and short-term irradiations and counting, we eventually achieved an optimum situation on both manpower and counting equipment availability. This optimum situation permitted analysis of 20-24 samples/wk with a total manpower of 3 to 3.5 hrs/sample expended. 

To confirm the absence of appreciable isotopic interference by oxygen exchange between the H2O and either the H2O2 or the O2, before, during, or after the oxidation reactions, the reaction was carried out in the presence of three different water supplies of various 61BO. The results in Figure 1 show that the 5lsO of the CO2 product was unaffected by the 180 of the water solvent. 

The amount of analyte x in a sample is calculated from the isotopic intensities I and I and the amount of labeled component y, determined in a standard mixture with a known concentration of analyte. The factors ft and f2, which represent the signal ratio III (qtlq in the pure labeled product and the inverse ratio I 11 (pJPi) of pure analyte, were determined originally by measuring the isotopic interferences in the labeled product and analyte. Later, a correction of Eq. (8) was proposed (Siekmann, 1982) in which a proportional factor f0 was introduced ... 

It is important to check for the presence of isotopic interferences, for example, by comparing spiked and unspiked standards or samples. There are various ways to overcome problems caused by coincident ion interferences ... 

IDMS will only give accurate results if the measured isotopic abundance ratio is accurate. Hence it is essential to check both isotopes for isobaric or other isotopic interferences. Other effects due to the sample matrix or the instrument, should be evaluated. 

The detection of Kr, produced by cosmic rays, is of great importance for dating samples from the Earth s crust, groundwater, and polar ice cores. Measurement of Kr in groundwater is a unique analytical problem as its concentration is ca. 1400 atoms per liter. The problem is further complicated by isotopic interference of stable krypton isotopes ( Kr/ Kr is about I0 ). Prior to final analysis by RIS-TOF [8] several consecutive steps of field sampling and isotope concentration were necessary. All steps required extreme care to avoid sample contamination. Water samples of 50- 100 L were necessary to detect Kr above the background. This value is more than 100 times less than for the routine technique of Ar dating. 

Interferences mostly result from coeluting peaks or from background noise. The mass spectrum obtained is a mixture of two mass spectra and false interpretation is possible. Isotope interference is another possibility [2]. This phenomenon may occur with any isotope C is used here as an example. Carbon has two natural isotopes C and C with a ratio of 98.9 to 1.1 (the exact figures are rounded for simplicity). In residue analyzes, three important parameters should be taken into account ... 

In summary, if n A + 2 elements are present, the (A + 1) peak [and possibly other (A + 2n + 1) peaks] will contain isotopic contributions from the (A — 1) peak [and possibly other (A — 2n — 1) peaks]. In calculating the number of carbon atoms by using [(A + 1)]/[A], one should correct for such isotopic interferences. Alternatively, use [(A + 2n -I- 1)]/[A - - 2n)] corresponding to the peaks of highest mass, since the (A — 1) peak cannot make an isotopic contribution to these. 

Although cold plasmas have benefits in removing interfering ions such as ArO+, they are not necessary for other applications where interferences are not a problem. Thus, in laboratories where a range of isotopes needs to be examined, the plasma has to be changed between hot and cold conditions, whereas it is much simpler if the plasma can be run under a single set of conditions. For this reason, some workers use warm plasmas, which operate between the hot and cold conditions. 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

Thermal ionization has three distinct advantages the ability to produce mass spectra free from background interference, the ability to regulate the flow of ions by altering the filament temperature, and the possibility of changing the filament material to obtain a work function matching ionization energies. This flexibility makes thermal ionization a useful technique for the precise measurement of isotope ratios in a variety of substrates. 

For several reasons — including the complete breakdown of sample into its substituent elements in the plasma and the use of an unreactive monatomic plasma gas (argon) — background interferences in the resulting mass spectra are of little importance. Since there are no or very few background overlaps with sample ions, very precise measurements of sample ion abundances can be made, which facilitate the determination of precise isotope ratios. 

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

Detection limits in ICPMS depend on several factors. Dilution of the sample has a lai e effect. The amount of sample that may be in solution is governed by suppression effects and tolerable levels of dissolved solids. The response curve of the mass spectrometer has a large effect. A typical response curve for an ICPMS instrument shows much greater sensitivity for elements in the middle of the mass range (around 120 amu). Isotopic distribution is an important factor. Elements with more abundant isotopes at useful masses for analysis show lower detection limits. Other factors that affect detection limits include interference (i.e., ambiguity in identification that arises because an elemental isotope has the same mass as a compound molecules that may be present in the system) and ionization potentials. Elements that are not efficiently ionized, such as arsenic, suffer from poorer detection limits. 

Nuclear reaction analysis (NRA) is used to determine the concentration and depth distribution of light elements in the near sur ce (the first few lm) of solids. Because this method relies on nuclear reactions, it is insensitive to solid state matrix effects. Hence, it is easily made quantitative without reference to standard samples. NRA is isotope specific, making it ideal for isotopic tracer experiments. This characteristic also makes NRA less vulnerable than some other methods to interference effects that may overwhelm signals from low abundance elements. In addition, measurements are rapid and nondestructive. 

Since NRA focuses on inducing specific nuclear reactions, it permits selective observation of certain isotopes. This makes it ideal for tracer experiments using stable isotopes. Generally, there are no overlap or interference effects because reactions have very different Qvalues, and thus different resultant particle energies. This permits the observation of species present at relatively low concentrations. A good example is oxygen and O can be resolved unambiguously, as they are... 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

Other reasons for investigating plutonium photochemistry in the mid-seventies included the widely known uranyl photochemistry and the similarities of the actinyl species, the exciting possibilities of isotope separation or enrichment, the potential for chemical separation or interference in separation processes for nuclear fuel reprocessing, the possible photoredox effects on plutonium in the environment, and the desire to expand the fundamental knowledge of plutonium chemistry. 

Mossbauer resonance of Zn to study the influence of the gravitational field on electromagnetic radiation. A Ga ZnO source (4.2 K) was used at a distance of 1 m from an enriched ZnO absorber (4.2 K). A red shift of the photons by about 5% of the width of the resonance line was observed. The corresponding shift with Fe as Mossbauer isotope would be only 0.01%. The result is in accordance with Einstein s equivalence principle. Further gravitational red shift experiments using the 93.3 keV Mossbauer resonance of Zn were performed later employing a superconducting quantum interference device-based displacement sensor to detect the tiny Doppler motion of the source [66, 67]. 

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