Isotopes detection limit

Isoihamnetin la 323 Isothiazolone, microbiocidal la 45 Isothiocyanates la 75 lb 312 Isothiocyanate anions lb 307 Isotopes, detection limits la 41 Itaconic acid, reduction la 61 lodazide reaction lb 301,303... 

Thus, the noble gases are trace elements par excellence. As an example, a not unreasonable value of Xe concentration in a rock is some 10 11 cm3 STP/g (about 3 x 108 atoms/g), or 0.00006ppb. It is nevertheless quite feasible to perform an adequate analysis on a 1-g sample of such a rock, in the sense of a sample to blank ratio in excess of 102, 5-10% uncertainty in absolute abundance, and 1% or less uncertainty in relative abundances of the major isotopes. Detection limits are much lower than this, and for the scarcer isotopes the blank and thus the quantity necessary for analysis are two to three orders of magnitude lower. It is worth noting that the reason why such an experiment is possible is the same reason why noble gases are so scarce in the first place their preference for a gas phase and the ease with which they can be separated from more reactive species. 

NMR isotope measured. For example, for the detection of phosphorus by NMR in a sample containing 3 wt.% phosphorus, approximately 10 mg of sample are required. By contrast, the corresponding detection limit for Si in a similar situation is 22 dmes higher, due to the much lower natural abundance (4.7%) of the Si isotope. 

The SIMS analytical ion signal of a specific element or isotope also can be enhanced by selective ionization of particular atoms, and the detection limit for that element thereby improved. This mode of SNMS is important to specific applications, but it lacks the generality inherent in nonselective SNMS methods. The focus of this article will be on the methods for obtaining complete, accurate, and matrix-independent compositions of chemically complex thin-film structures and materials. 

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. 

Today dynamic SIMS is a standard technique for measurement of trace elements in semiconductors, high performance materials, coatings, and minerals. The main advantages of the method are excellent sensitivity (detection limit below 1 pmol mol ) for all elements, the isotopic sensitivity, the inherent possibility of measuring depth profiles, and the capability of fast direct imaging and 3D species distribution. 

Isonicotinic acid hydrazide reagent 318 Isoprenaiine 395,396 Isoprenoid compounds 44 Isopulegol 59 Isoquercitrin 279, 280, 323 Isoquinoline alkaloids 46, 66, 262 Isorhamnetin 323 Isothiazolones, microbiocidal 45 Isothiocyanates 75 Isotopes, j8-radiation-emitting 41 -, detection limits 41 Itaconic acid 61... 

In the past three years, MC-ICPMS has emerged as an alternative to TIMS for precise measurement of the U-series isotopes with comparable or better precision. U-Th isotopes can now be routinely measured at the sub-permil level. Previously, this had only been demonstrated using charge-collection TIMS applied to thorium isotope measurement. Data collection efficiency, sample size requirements, and detection limits can also be greatly improved over TIMS. For the U- U- Th system applied to carbonate samples, this has extended the dating range beyond 600,000 years, and °Th-age uncertainties of 2000 years are now attainable on 300,000 year-old samples (e g., Stirling et al. 2001). 

IEC continues to have numerous applications to the detection and quantification of various inorganic ions.1 1 This is particularly true in water analysis.5-14 Inorganic ions in a variety of other sample types, such as food and beverages,1518 rocks,19-23 biological fluids, (blood, urine, etc.),24-31 pharmaceutical substances,32 33 concentrated acids,34 alcohols,35 and cleanroom air36 have also been analyzed by IEC. IEC has also been employed in isotopic separation of ions,37 including the production of radioisotopes for therapeutic purposes.3839 Typical IEC sample matrices are complex, and may contain substances that interfere with measurement of the ion(s) of interest. The low detection limits required for many IEC separations demand simple extraction procedures and small volumes to avoid over-dilution. Careful choice and manipulation of the eluent(s) may be needed to achieve the desired specificity, especially when multiple ions are to be determined in a single sample. 

Mass spectrometry is the only universal multielement method which allows the determination of all elements and their isotopes in both solids and liquids. Detection limits for virtually all elements are low. Mass spectrometry can be more easily applied than other spectroscopic techniques as an absolute method, because the analyte atoms produce the analytical signal themselves, and their amount is not deduced from emitted or absorbed radiation the spectra are simple compared to the line-rich spectra often found in optical emission spectrometry. The resolving power of conventional mass spectrometers is sufficient to separate all isotope signals, although expensive instruments and skill are required to eliminate interferences from molecules and polyatomic cluster ions. 

SSMS can be classified among the milliprobe techniques (Figure 8.3), i.e. it is a unique link between microprobe techniques and macroanalytical methods that are characterised by poor lateral and in-depth resolutions (as in OES), or that have no lateral resolution whatsoever (as in NAA). Also, the achievable precision and accuracy are poor, because of the irreproducible behaviour of the r.f. spark. Whereas analysis of metals, semiconductors and minerals is relatively simple and the procedures have become standardised, the analysis of nonconducting materials is more complex and generally requires addition of a conducting powder (e.g. graphite) to the sample [359]. Detection limits are affected by the dilution, and trace contamination from the added components is possible. These problems can be overcome by the use of lasers [360]. Coupled with isotope dilution, a precision of 5% can be attained for SSMS. 

Table 8.62 shows the main characteristics of ICP-MS, which is widely used in routine analytical applications. The ICP ion source has several unique advantages the samples are introduced at atmospheric pressure the degree of ionisation is relatively uniform for all elements and singly charged ions are the principal ion product. Theoretically, 54 elements can be ionised in an ICP with an efficiency of 90 % or more. Even some elements that do not show ionic emission lines should be ionised with reasonable efficiency (namely, As, 52 % and P, 33%) [381]. This is one of the advantages of ICP-MS over ICP-AES. Other features of ICP-MS that make it more attractive than ICP-AES are much lower detection limits ability to provide isotopic ratio information and to offer isotope dilution capabilities for quantitative analysis and clean and simple spectra. The... 

Flegal and Stukas [406] described the special sampling and processing techniques necessary for the prevention of lead contamination of seawater samples, prior to stable lead isotopic ratio measurements by thermal ionisation mass spectrometry. Techniques are also required to compensate for the absence of an internal standard and the presence of refractory organic compounds. The precision of the analyses is 0.1 -0.4% and a detection limit of 0.02 ng/kg allows the tracing of lead inputs and biogeochemical cycles. 

Wu and Boyle [837] have developed a method using magnesium hydroxide coprecipitation and isotopic dilution mass spectrometry to determine lead, copper, and cadmium in 1 ml seawater samples, with detection limits of 1,40, and 5 pM, respectively. 

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