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Mass measurement

Another specialized application of EM image contrast is mass measurement. Using the elastic dark-field image in the STEM or the inelastic image in the EETEM, a direct measurement of the scattering mass can be performed. Eor reviews on this teclmique see [60.61]. [Pg.1645]

For simple FI, the substance to be mass measured is volatilized by heating it close to the emitter so that its vapor can condense onto the surface of the electrode. In this form, an FI source can be used with gas chromatography, the GC effluent being passed over the emitter. However, for nonvolatile and/or thermally labile substances, a different approach must be used. [Pg.26]

Another type of ion is formed almost uniquely by the electrospray inlet/ion source which makes this technique so valuable for examining substances such as proteins that have large relative molecular mass. Measurement of m/z ratios usually gives a direct measure of mass for most mass spectrometry because z = 1 and so m/z = m/1 = m. Values of z greater than one are unusual. However, for electrospray, values of z greater than one (often much greater), are quite coimnonplace. For example, instead of the [M + H]+ ions common in simple Cl, ions in electrospray can be [M + n-H]- where n can be anything from 1 to about 30. [Pg.57]

Electrospray alone is a reasonably sensitive technique for use with many classes of compounds. Spectacular, unprecedented results have been obtained with accurate mass measurement of high-... [Pg.59]

A typical TIC chromatogram from an analysis of peptides resulting from enzymatic digest of myoglobin. The peaks represent individual peptides eluting from an LC column and being mass measured by a spectrometer coupled to it through a dynamic-FAB inlet/ion source. [Pg.84]

The transfer efficiencies for ultrasonic nebulizers (USN) are about 20% at a sample uptake of about 1 ml/min. Almost 100% transfer efficiency can be attained at lower sample uptakes of about 5-20 pl/min. With ultrasonic nebulizers, carrier gas flows to the plasma flame can be lower than for pneumatic nebulizers because they transfer sample at a much higher rate. Furthermore, reduction in the carrier-gas flow means that the sample remains in the mass measurement system for a longer period of time which provides much better detection limits. [Pg.148]

In general terms, the main function of the magnetic/electric-sector section of the hybrid is to be able to resolve m/z values differing by only a few parts per million. Such accuracy allows highly accurate measurement of m/z values and therefore affords excellent elemental compositions of ions if these are molecular ions, the resulting compositions are in fact molecular formulae, which is the usual MS mode. Apart from accurate mass measurement, full mass spectra can also be obtained. The high-resolution separation of ions also allows ions having only small mass differences to be carefully selected for MS/MS studies. [Pg.157]

High-Resolution, Accurate Mass Measurement Elemental Compositions... [Pg.269]

In a mass spectrum, removal of an electron from a molecule (M) gives a molecular ion (Equation 38.1). The mass of an electron is very small compared with the mass of even the lightest element, and for all practical purposes, the mass of M +is the same as that of M. Therefore, mass measurement of a molecular ion gives the original relative molecular mass of the molecule. [Pg.270]

Finally, accurate mass measurement can be used to help unravel fragmentation mechanisms. A very simple example is given in Figure 38.2. If it is supposed that accurate mass measurements were made on the two ions at 203.94381 and 77.03915, then their difference in mass (126.90466) corresponds exactly to the atomic mass of iodine, showing that this atom must have been eliminated in the fragmentation reaction. [Pg.271]

Therefore, for accurate mass measurement, a standard mass peak (M,) is selected, and the accelerating voltage (V) is changed until the sample ion peak (M ) exactly coincides with the position of Mj. This technique is called peak matching, and the ratio between the original and new voltages (VA ) multiplied by mass (Mj) gives the unknown mass, M . [Pg.274]

Other techniques for mass measurement are available, but they are not as popular as those outlined above. These other methods include mass measurements on a standard substance to calibrate the instrument. The standard is then withdrawn, and the unknown is let into the instrument to obtain a new spectrum that is compared with that of the standard. It is assumed that there are no instrumental variations during this changeover. Generally, this technique is less reliable than when the standard and unknown are in the instrument together. Fourier-transform techniques are used with ion cyclotron mass spectrometers and give excellent mass accuracy at lower mass but not at higher. [Pg.274]

Accurate mass measurement requires high resolving power. The difference in degrees of difficulty between measuring an m/z of 28 and one of 28.000 is likely to be large. Table 39.3 shows the broad mass ranges achievable with various analyzers. [Pg.281]

This last m/z value is easy to measure accurately, and, if its relationship to the true mass is known (n = 10), then the true mass can be measured very accurately. The multicharged ions have typical m/z values of <3000 Da, which means that conventional quadrupole or magnetic-sector analyzers can be used for mass measurement. Actually, the spectrum consists of a series of multicharged protonated molecular ions [M + nWY for each component present in the sample. Each ion in the series differs by plus and minus one charge from adjacent ions ([M + uH] + n -an integer series for example, 1, 2, 3,. .., etc.). Mathematical transformation of the spectrum produces a true molecular mass profile of the sample (Figure 40.5). [Pg.291]

Once the peaks have been collected and stored, the computer can be asked to work on the data to produce a mass spectrum and print it out, or it can be asked to carry out other operations such as library searching, producing a mass chromatogram, and making an accurate mass measurement on each peak. Many other examples of the use of computers to process mass data are presented in other chapters of this book. [Pg.320]

The upper part of the figure illustrates why the small difference in mass between an ion and its neutral molecule is ignored for the purposes of mass spectrometry. In mass measurement, has been assigned arbitrarily to have a mass of 12.00000, All other atomic masses are referred to this standard. In the lower part of the figure, there is a small selection of elements with their naturally occurring isotopes and their natural abundances. At one extreme, xenon has nine naturally occurring isotopes, whereas, at the other, some elements such as fluorine have only one. [Pg.338]

A positive ion formed on such a tip held at a high positive potential is repelled and flies olf the tip almost immediately after formation and into the mass spectrometer, where its m/z value is measured. Similarly, negative ions can be mass measured. [Pg.386]

In field ionization (or field desorption), application of a large electric potential to a surface of high curvature allows a very intense electric field to be generated. Such positive or negative fields lead to electrons being stripped from or added to molecules lying on the surface. The positive or negative molecular ions so produced are mass measured by the mass spectrometer. [Pg.387]

When multicharged ions are formed, the simple rule of thumb used widely in mass spectrometry that m/z = m because, usually, z = 1 no longer applies for z > 1 then m/z < m, and the apparent mass of an ion is much smaller than its true mass. Accurate mass measurement is much easier at low mass than at high, and the small m/z values, corresponding to high mass with multiple charges, yield accurate values for the high mass. [Pg.390]

Through the application of DC and RF voltages to an assembly of four parallel rods, ions can be filtered along their central axis and mass measured to give a mass spectrum. In the all-RF mode, the assembly is used as a guide for ions of all m/z values. [Pg.406]

A simple mass spectrometer of low resolution (many quadrupoles, magnetic sectors, time-of-flight) cannot easily be used for accurate mass measurement and, usually, a double-focusing magnetic/electric-sector or Fourier-transform ion cyclotron resonance instrument is needed. [Pg.416]

Accurate mass measurement on a molecular ion of any substance gives directly the molecular formula for fragment ions, similar measurement gives their elemental compositions. [Pg.416]

Process industries frequently need to weigh and control the flow rate of bulk material for optimum performance of such devices as grinders or pulverizers, or for controlling additives, eg, to water suppHes. A scale can be installed in a belt conveyor, or a short belt feeder can be mounted on a platform scale. Either can be equipped with controls to maintain the feed rate within limits by controlling the operation of the device feeding the material to the conveyor. Direct mass measurement with a nuclear scale can also be used to measure and control such a continuous stream of material. [Pg.333]


See other pages where Mass measurement is mentioned: [Pg.1645]    [Pg.232]    [Pg.60]    [Pg.158]    [Pg.160]    [Pg.186]    [Pg.219]    [Pg.269]    [Pg.270]    [Pg.271]    [Pg.271]    [Pg.272]    [Pg.272]    [Pg.281]    [Pg.292]    [Pg.323]    [Pg.333]    [Pg.547]    [Pg.548]   
See also in sourсe #XX -- [ Pg.367 ]

See also in sourсe #XX -- [ Pg.57 ]

See also in sourсe #XX -- [ Pg.52 ]

See also in sourсe #XX -- [ Pg.27 , Pg.28 ]




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Accelerator mass spectrometry measurements

Accurate Mass Measurements in FAB

Accurate Mass Measurements in FAB Mode

Accurate mass measurement Drug screening

Accurate mass measurement Metabolism

Accurate mass measurement Natural products

Accurate mass measurement Proteomics

Accurate mass measurements

Analyte, solution mass spectra measured

Analyzer mass spectra measured

CELL MASS MEASUREMENT

Carbon isotope mass-transfer measurement

Charge/mass measurements

Direct mass measurement

Exact Mass Measurements (High Resolution)

Exact mass measurement

Flow measurement momentum mass

Flow measurements inferential mass flowmeter

Flow measurements mass flowmeters

High-Resolution, Accurate Mass Measurement Elemental Compositions

High-accuracy mass measurement (

Hypersensitive Measurement of Proteins by Capillary Isoelectric Focusing and Liquid Chromatography-Mass Spectrometry

Ionization methods, mass measurements

Isotope Ratio Measurements by Gas Source Mass Spectrometry

Isotope ratio measurements, mass

Liquid chromatography mass spectrometry measurements

Liquid chromatography tandem mass measurement

Loading sample strontium solution on a filament for measurement in the thermal ionization mass spectrometer (TIMS)

Mass Deposit Measurements

Mass Transfer Measurements The Electrochemical Probe

Mass accuracy measurement

Mass calibration measurements

Mass distribution, particulate measurement

Mass flow measurement

Mass flow measurement absorption, mechanism

Mass flow measurement coefficients

Mass flow measurement distillation

Mass flow measurement drops

Mass flow measurement flowmeter, direct

Mass flow measurement indirect

Mass flow measurement overall

Mass flow measurement packed column

Mass flow measurement spectrometer

Mass flow measurement steps

Mass flow measurement transfer

Mass loss measurements

Mass measurement error, protein

Mass measurement, atomic

Mass measurement, high-resolution, accurate

Mass spectrometer-target collection technique, measurement

Mass spectrometric measurements

Mass spectrometry exchange measurements

Mass spectrometry measuring concentration rang

Mass spectrometry particle measurements using

Mass spectroscopy Quantitative measurements

Mass transfer coefficient measurement

Mass transfer coefficients nonreactive measurement

Mass transfer coefficients reactive measurement

Mass transfer measurements probe

Mass-resolved ion yield measurements

Mass-transfer measurements

Mass-transfer measurements basic theory

Mass-transfer measurements effective diffusivities

Mass-transfer measurements limiting-current technique

Mass-transfer rate measurement

Measured accurate mass

Measurement of Cell Mass

Measurement of Mass Transfer Coefficients

Measurement of mass

Measurement of mass isotopomer distributions

Measurement of mass, volume, and pressure

Measurement of the apparent partial volume per mass

Measurement techniques mass spectrometry applications

Measurement units molecular mass limit

Measurement, multicomponent mass

Measurements atomic mass units

Measurements of Length, Volume, and Mass

Measuring Mass

Measuring Mass

Measuring Mass and Volume

Measuring Radioactivity and the Mass of Radionuclides

Measuring the Masses of Large Molecules or Making Elephants Fly

Metabolite accurate mass measurement

Metabolite identification mass measurements

Methods for measurement of number-average molar mass

Molar mass distribution measure

Molar mass measure

Molar mass measurements

Molecular mass measurement

Molecular mass measurement of proteins

Number average molar mass measurement

Particle Concentration and Mass Flux Measurements by PDA

Peptide mass mapping measurement

Post-translational modifications molecular mass measurement

Precision mass measurement

Proteins mass measurement

Quadrupole accurate mass measurement

Quantitative Measurements by Mass Spectrometry

Scanning transmission electron microscopy mass measurement

Solid-liquid mass transfer measurement

Spectrometry Measuring the Mass of Atoms and Molecules

Stable isotope measurement mass spectrometry

Summary mass transfer measurements

Tandem accurate mass measurement

The Value of Accurate Mass Measurement

The measurement of mass flow

Thermogravimetric analysis mass measurement

Through-Plane Mass Transport Measurements

Weight and Mass Measurement

Weight average molar mass measurement

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