Standard precision weight

The National Bureau of Standards at Washington recognises the following classes of precision weights ... 

The variations in isotopic composition of many elements in samples of different origin limit the precision to which a relative atomic mass can be given. The standard atomic weights revised biennially by the IUPAC Commission on Atomic Weights and Isotopic Abundances are meant to be applicable for normal materials. This means that to a high level of confidence the relative atomic mass of an element in any normal sample will be within the uncertainty limits of the tabulated value. By normal it is meant here that the material is a reasonably possible source of the element or its compounds in commerce for industry and science and that it has not been subject to significant modification of isotopic composition within a geologically brief period [43]. This, of course, excludes materials studied themselves for very anomalous isotopic composition. 

Units of sulfur in milligrams per litre of sample are preferred as this is independent of the density of the carrier liquid. The following equation is used to calculate the volume of solvent requir to dissolve a precise weight of sulfur compound, of known composition and purity to prepare a liquid standard ... 

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

Determinarion of MW and MWD by SEC using commercial narrow molecular weight distribution polystyrene as calibration standards is an ASTM-D5296 standard method for polystyrene (11). However, no data on precision are included in the 1997 edition of the ASTM method. In the ASTM-D3536 method for gel-permeation chromatography from seven replicates, the M of a polystyrene is 263,000 30,000 (11.4%) for a single determination within the 95% confidence level (12). A relative standard deviation of 3.9% was reported for a cooperative determination of of polystyrene by SEC (7). In another cooperative study, a 11.3% relative standard deviation in M, of polystyrene by GPC was reported (13). 

The simplest sound level meter consists of a microphone, an amplifier and a meter of some type. Sound level meters are graded according to British and international standards, and the most common type used for accurate measurement purposes it known as the Precision Grade or Type 1 meter. In practice, a basic sound level meter will incorporate weighting networks with either in-built octave filters or provision for connecting an external filter set (Figure 42.6). 

Class S For use as working reference standards or as high-precision analytical weights. 

Curve-fitting need not be abandoned in this case, but some modifications are necessary so that precisely measured points influence to a greater degree the form of the curve, more so than a similar number of less precisely measured ones. Thus, a weighting scheme is introduced. There are different ways of doing this the most accepted model makes use of the experimental standard deviation,namely ... 

VOLUME.dat Section 1.1.2 A set of five precision weighings of a water-filled 100 ml flask the weights in grams were converted to milliliters using the standard density-vs.-temperature tables. Use with MSD to test the effect of truncation errors on the calculation of the standard deviation. (See Table 1.1.)... 

Under some conditions, it is difficult to incorporate an internal standard into a method. If the chromatogram is very complex, an internal standard may interfere with quantitation of a peak of interest. The development of highly precise sample transfer techniques, including modem autoinjectors, reduces the dependence of the experimentalist on the use of an internal standard to correct for effects of dilution and transfer losses. In many cases, external standardization can be used effectively. The weight percent purity is determined by comparing the area of each peak in a chromatogram with those generated by separately injected pure standards of known concentration. 

It is a well-known fact that the precision in trace analysis decreases with diminishing concentration in a similar way as it does with decreasing sample weight (Sect. 2.1). The dependency of the repeatability and reproducibility standard deviation on the concentration of analytes has been investigated systematically at first by Horwitz et al. [1980] on the basis of thousands of pieces of interlaboratory data (mostly from food analysis). The result of the study has been represented in form of the well-known Horwitz trumpet which is represented in Fig. 7.3. 

However, IHC as a practical method continues to evolve with increasing demands for standardization, and for true quantification of protein analytes by weight, in the context of their cellular microenvironment. Further studies combining proteomics by mass spectrometry and IHC are likely to lead to the refinement of both methods in the analysis of FFPE tissues. The end result may be the creation of a broader field that defines and quantifies protein expression at a cellular level, incorporating the advantages of the wide spectrum of proteins demonstrable by mass spectrometry and the precise localization offered by IHC. 

Using zinc oxide as the internal standard, the relative amounts of two polymorphic forms of fenretinide were quantified [55], Mixtures containing 25, 50, and 75% w/w form I were prepared by mixing authentic standards of form I and form II fenretinide. After the addition of the internal standard, the maximum intensities (peak heights) of the 4.6 A line (peak at 19.1° 20) of fenretinide form I (/19. i) and the 2.8 Aline (peak at 31.8° 20) of zinc oxide (/318) were determined. A plot of the intensity ratio (/19.//31.8) as a function of the weight percent form I was linear. The method was reported to be precise and accurate to within 6%. 

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