Multiple isotope counting

Jakopic R, Richter S, Kuehn H, Aregbe Y (2008) Isotope ratio measurements of pg-size plutonium samples using TIMS in combination with the Multiple Ion Counting and filament carburization, INIS-FR-09-0127. In Atalante 2008 nuclear fuel cycle for a sustainable future, Montpellier, France, 19-23 May... 

Taylor, R.N., Wameke, T., Milton, J.A., Croudace, I.W., Warwick, P.E., and Nesbitt, R.W. (2003) Multiple ion counting determination of plutonium isotope ratios using multi-collector ICPMS, J. Anal. At. Spectrom., 18, 480-484. 

Snow, J.E. and Friedrich, J.M. (2005) Multiple in counting ICPMS double spike method for precise U isotopic analysis at ultra-trace levels. Int. J. Mass Spectrom., 242, 211-215. 

The first experiment to be recorded on isotope-labeled proteins is the [ N/HJ-HSQC experiment. Inspection of the [ N. HJ-correlalion map and simple counting of cross peaks reveals whether multiple conformers exist, whether some parts of the backbone signals are broadened, possibly because of slow conformational exchange, or whether parts of the sequence are not visible at all. As mentioned above, the spectrum will also show whether the protein is well folded or not. 

Equation 4.117 makes complete sense. One of the first things one learns in dealing with phase space integrals is to be careful and not over-count the phase space volume as has already been repeatedly pointed out. In quantum mechanics equivalent particles are indistinguishable. The factor n ni is exactly the number of indistinguishable permutations, while A accounts for multiple minima in the BO surface. It is proper that this factor be included in the symmetry number. Since the BO potential energy surface is independent of isotopic substitution it follows that A is also independent of isotope substitution and cannot affect the isotopic partition function ratio. From Equation 4.116 it follows... 

TIMS analysis was performed on a fully automated VG Sector 54 mass spectrometer with eight adjustable faraday cups and a Daly ion-counting photomultiplier system. Analysis was performed in static mode. Each sample was analyzed 50 times to ensure acceptable precision. The TIMS analysis was standardized by use of the NIST SRM981 common lead standard. Multiple analyses of the SRM981 standard were used to determine a fractionation correction of 0.12% per amu and an overall error 0.06% per amu. Errors between runs of the same sample were below 0.01% per amu. This level of precision is comparable to the archaeometry database for lead isotopes (8). 

Cell harvesters were developed to capture multiple samples of cells on membrane filters, wash away unincorporated isotopes, and prepare samples for liquid scintillation counting on special equipment developed to process and count multiple samples. Despite miniaturization and improvements in efficiency of this technique, the disadvantages of multiple liquid handling steps and increasing costs for disposal of radioactive waste materials severely limit its usefulness. Although specific applications require measuring DNA synthesis as a marker for cell proliferation, much better choices are available for detecting viable cell number for HTS. 

Modern TIMS instruments are equipped with multiple ion detectors (see Fig. 17.15). In the 1980s, Faraday cup arrays became commercially available, and these provided significant improvements in isotopic precision and sample utilization. In the 1990s, arrays of pulse counting ion detectors with very compact EM... 

Instrument specificity refers to counts in the " C detector, that are or ions scattered off residual gas in the instrument at low probabilities (10 — 10 ). This instrument background is insignificant compared to natural and processing backgrounds discussed below. The spectrometers themselves operate robustly in that multiple operators obtain the same raw isotope ratio for National Institute of Standards and Technology (NIST)—traceable standards to within a few percent over periods of years in routine operation. These external reference standards normalize even this imprecision from... 

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