Formula mass uncertainty

Accurate Mass An experimentally determined mass of an ion that is used to determine an elemental formula. For ions containing combinations of the elements C, H, N, O, P, S, and the halogens, with mass less than 200 Da, a measurement with 5 ppm uncertainty is sufficient to uniquely determine the elemental composition. See also related entries on average mass dalton molar mass monoisotopic mass nominal mass unified atomic mass unit. 

Achieving high resolving power and high m/z measurement accuracy is one way of decreasing uncertainty when the determination of unknown analyte identity is the object of an experiment. But like many techniques, an increase in experimental or interpretive confidence does not come without some cost (e.g., instrument size, complexity, price, etc.). However, exact m/z measurements (and their associated elemental formula information) are but one type of information that can be derived from mass spectrometers. In the sections that follow, a variety of mass analyzers will be described in terms of their basic principles, functionality and applications. 

C. Extensions of helices having sensitivities of ca. 2 mg mm-- - were read to 0.01 mm with a precision of 0.02 g sorbate per 100 g sorbent. However, because of experimental uncertainties described later, the precision of uptakes is seldom better than 0.1 g/100 g, and sometimes worse. The helices were calibrated at five-degree temperature intervals between 5 and 50°C, and at 100-mg mass intervals up to U00 mg calibration formulae comprising functions of both independent variables were found by a polynominal least-squares fit of all the data. Pressures were measured with large-bore mercury manometers. 

The mole is associated with a specific chemical entity as defined by its chemical formula [15], Its structural formula, isotopic composition, isomeric form, crystal structure, or chirality may have to be given in order to completely specify the entity of interest. The achievable uncertainty of amount-of-substance measurement is limited by that of its apparent molar mass. This consideration affects not only measurements on entities with variable molar mass, but those on pure substances. It is related to the traditional and important concern about purity. 

When the accurate mass measurement is used for confirmation of the formula or for elemental composition analysis, all the candidates fitting the experimentally determined value and its reportable uncertainty must be considered. Setting fixed acceptable error limits for mass measurement is not correct. 

Prepare a spreadsheet similar to the one shown in Figure 3-7 for the gravimetric determination of nickel using dimethylglyoxime. See Section 37B-3 for details. Use the worksheet from Problem 3-9 to calculate the molar mass of Ni(DMG)2 if it is available. 3-4. Write an Excel formula using the FIND and MID functions to eliminate the square brackets and the uncertainty from the atomic mass of lithium in the lUPAC table and display the numeric characters of the atomic weight. 

Devise an Excel formula using the FIND and MID functions that will automatically display the uncertainties of the atomic masses in the lUPAC table. 3-7. Use the worksheet of Figure 3-15 to calculate the molar masses of the following compounds. 

The molecular formula of C3F( was definitely established from its mass spectrum, but there is some uncertainty about its structure. The... 

In some cases it may be useful to make a rough estimation of the measurement uncertainty of a method at the target concentration, for example, at the MRL of a veterinary drug, to help to determine whether the method will be tit for purpose before undertaking a full validation and measurement uncertainty estimation exercise. This can be done by applying the Horwitz formula to obtain an estimate applicable to inter-laboratory reproducibility data, or a suitably adjusted version for intra-laboratory data. " The Horwitz formula, as initially applied to interlaboratory (between-laboratory) reproducibility data R) in percentage, and with the concentration C expressed as a mass fraction, is ... 

The magnitudes of the spinning radius rc and of the rest mass mo are related by the Compton formula rc.moc = h/2, which expresses the uncertainty principle for position rc and momentum moc. Rest mass and spin motion thus appear as essentially related quantum properties, a kind of zero-point vibration energy for a charged entity with respect to some inertial frame. 

Then find the uncertainty in the sum of atomic masses by the formula for addition ... 

As has been outlined in Chap. 2 uncertainties or errors of measured data constitute an important part of any kind of experimental work and hence always should be considered [2.18], However, for sake of brevity we here provide the reader only with the formulae allowing one to calculate uncertainties or mean square deviations (MSD) (cj ge) of th Gibbs excess mass (m g) of an adsorbate which has been measured gravimetrically by using a two beam balance. This mass can be calculated from eq. (3.14) combined with eqs. (3.10) and (3.13). By using Gauss law ofpropagation of uncertainties we have... 

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