Precise mass

ASTM E617, Standard Specijication fiorEaboratoy Weights and Precision Mass Standards, American Society for Testing and Materials, Philadelphia, Pa., 1991, p. 2. 

Precision mass and volumetric methods use very precise measurements of pressure and/or level in the tank to detect leaks. The tank must be closed so that no Hquid enters or leaves the tank. The threshold of detection and fuimel required to perform a rehable test become greater as tank size increases. 

Qualitatively, the spark source mass spectrum is relatively simple and easy to interpret. Most instrumentation has been designed to operate with a mass resolution Al/dM of about 1500. For example, at mass M= 60 a difference of 0.04 amu can be resolved. This is sufficient for the separation of most hydrocarbons from metals of the same nominal mass and for precise mass determinations to identify most species. Each exposure, as described earlier and shown in Figure 2, covers the mass range from Be to U, with the elemental isotopic patterns clearly resolved for positive identification. 

Different isotopes differ in their atomic masses. The intensities of the signals from different isotopic ions allow isotopic abundances to be determined with high accuracy. Mass spectrometry reveals that the isotopic abundances in elemental samples from different sources have slightly different values. Isotopic ratios vary because isotopes with different masses have slightly different properties for example, they move at slightly different speeds. These differences have tiny effects at the level of parts per ten thousand (0.0001). The effects are too small to appear as variations In the elemental molar masses. Nevertheless, high-precision mass spectrometry can measure relative abundances of isotopes to around 1 part in 100,000. 

Li WX, Lundberg J, Dickin AP, Ford DC, Schwarcz HP, McNutt R, Williams D (1989) High precision mass-spectrometric uranium-series dating of cave deposits and implications for paleoclimate studies. Nature 339 534-536... 

Figure 2.4. Peptide fingerprinting by MALDI-TOF mass Spectrometry. Proteins are extracted and separated on by 2D gel electrophoresis. A spot of interest is excised from the gel, digested with trypsin, and ionized by MALDI. The precise mass of proteolytic fragments is determined by time-of- flight mass spectrometry. The identity of the protein is determined by comparing the peptide masses with a list of peptide masses generated by a simulated digestion of all of the open reading frames of the organism.

Ko ma In the mouse, if one performs a two-third hepatectomy, the remaining liver mass proliferates and then stops at the weight corresponding to the liver initially. The liver is very complex. It consists of multiple lobes with specific shapes, but if part of these lobes is taken away, the fiver does not regrow its initial shape, but it certainly recovers its initial mass. There is precise mass control. 

The absence of a sharp line at approximately 14 ppm indicated that ring opening to a n-butyl substituent did not occur. Precise mass measurements further showed that each concentrate has the same molecular weight (186) which confirmed that ring opening did not occur as implied by the work of Curran et al. [7] in which experimention was done with Tetralin. 

It is widely recognized that dendrimers are the first synthetic structure controlled polymers that rival the control and monodispersity observed for proteins. Their precise masses and behavior as analytes on electrophoretic gels demonstrate the contention that dendrimers (i.e. specifically poly(amidoamines)) may be viewed as artificial proteins . 

The second method relies on the partial interpretation of the spectra. A short amino acid stretch of one to three amino acids is read out. This sequence, together with its precise mass location in the peptide of a given mass, is used to identify the whole peptide in the database (Mann, 1996). Since the algorithms depend only on individual peptides, expressed sequence tag databases can be searched successfully. 

CAI s that were once molten (type B and compact type A) apparently crystallized under conditions where both partial pressures and total pressures were low because they exhibit marked fractionation of Mg isotopes relative to chondritic isotope ratios. But much remains to be learned from the distribution of this fractionation. Models and laboratory experiments indicate that Mg, O, and Si should fractionate to different degrees in a CAI (Davis et al. 1990 Richter et al. 2002) commensurate with the different equilibrium vapor pressures of Mg, SiO and other O-bearing species. Only now, with the advent of more precise mass spectrometry and sampling techniques, is it possible to search for these differences. Also, models prediet that there should be variations in isotope ratios with growth direction and Mg/Al content in minerals like melilite. Identification of such trends would verify the validity of the theory. Conversely, if no correlations between position, mineral composition, and Mg, Si, and O isotopic composition are found in once molten CAIs, it implies that the objects acquired their isotopic signals prior to final crystallization. Evidence of this nature could be used to determine which objects were melted more than once. 

For this experiment Bainbridge used the high-precision mass spectrograph he had developed by combining a Wien filter with a 180° magnetic analyzer.13... 

The precise mass corresponding to the molecular formula C15H120 calculated with the more abundant isotopic masses present is as follows ... 

Perfluoroalkyl-l,3,5-triazines are very stable to oxidation and heat. They have potential as lubricating fluids for use in aerospace work (B-74MI22003). Their polymeric products are stable elastomers with excellent rubber-like properties for use as electrical wire insulation and seals for hydraulic, lubricating and fuel systems of aircraft (B-80MI22001). Perfluoro-2,4,6-tri-n-heptyl-l,3,5-triazine is a valuable reference standard for precise mass... 

Support Protocol Density measurement The required time depends strongly on the equipment being used. Modern analytical equipment can correctly measure density within minutes. If the density measurement is conducted using the specific gravity bottle method, then an initial calibration is required that can take up to several hours (due to the fact that the volume of the bottle has to be determined as a function of temperature). After the initial calibration curve has been obtained, tests can be conducted within 15 to 20 min since only a precise mass determination is necessary. 

Figure 14.1. Temperature-resolved intensities of precise masses in a high-resolution Py-FIMS measurement of wheat straw. The thermograms of palmitic acid (m/z 256.240) and a thermal fragment (m/z 256.108) of the lignin dimer C16Hi404 (m/z 270.089) are shown with a mass window of +30mmu.

The Py-MS technique has been used extensively to characterize synthetic polymers, biopolymers, and fossil fuels (5-8,10, 11). In this work the technique has been modified by using a mass spectrometer which provides precise mass measurements directly upon pyrolysis. The advantage of this approach is two... 

The Py-MS experiments have provided detailed information on the labile organic structures found in the maceral concentrates. The utility of being able to obtain precise mass measurements is demonstrated in Table II where a small selection of peaks from the pyrolysis of the Brazil Block seam sporinite is listed. Note that at nominal m/z = 108 and 122 there are actually three distinct peaks corresponding to a quinone, an alkyl-phenol and a hydrocarbon. Normally with nominal mass pyrolysis data these peaks would only be assigned to alkyl phenols. All three peaks... 

This study has demonstrated that the Py-MS technique using precise mass measurements can be useful for characterizing macerals. Furthermore, the information derived from the... 

Annual Book of ASTM Standards, ANSI/ASTM E617-97 Standard Specification for Laboratory Weights and Precision Mass Standards, Book of Standards Vol. 14.04, ASTM, 2003. 

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