Standards for Laboratory Weights

STANDARDS FOR LABORATORY WEIGHTS Thomas J. Bruno and Paris D. N. Svoronos... 

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. 

From ASTM Designation E 617 Standard Specification for Laboratory Weights And Precision Mass Standards, reprinted with permission. 

Percentage compaction usually is used to measure soil density in a fill situation. Generally, the maximum Proctor specific weight (dry, Ib/ft ), determined by a standard laboratory test, is set up as the standard for the soil. Normally, 90-100% compaction is specified. 

Gel permeation chromatograms were generated from a Waters Associates, Inc. GPC equipped with a refractive index detector. The following operating conditions were employed mobile phase, THF flow rate 1 ml/min., columns ICP, 10, 500, 100 A . Sample concentrations were prepared at 0.2% (w/w) a 100 microliter aliquot was used for molecular weight analysis. Standard polystyrene samples (Polymer Laboratories, Inc.) were used to create a calibration curve. 

The absolute amount of product resulting from solid-phase synthesis can often be readily determined by 1H NMR with an internal standard or, less efficiently, by purification of the product followed by weighing and full characterization. Volatile samples can be cleaved with a calibrated mixture of hexamethyldisiloxane/TFA/CDCl3, from which 1H NMR spectra can be recorded directly [16]. In our laboratory, we use DMSO-dg as solvent and DMSO-internal standard for yield determination by 1H NMR. The weight of crude products obtained from solid-phase synthesis is generally unsuitable for estimating the true yield, because these products are often contaminated with significant amounts of salts, which lead to overestimation of the yield. 

The traceability associated with chemical standards will depend on the purity of the substance used as the RM and on the weights and volumes measured during the preparation and dilution of the standards. Sometimes this traceability is provided by the supplier. However, it is also common practice for laboratories to prepare their own standards, form general purpose chemicals. Where this is done, it is the laboratory s responsibility to establish their traceability as described above. 

Wherever possible, testing should be carried out in accordance with an approved standard. These include the standards issued by the International Standards Organization (ISO), the American Society for Testing and Materials (ASTM), and the Deutsches Institut fur Normung (DIN). There are many other standards of international repute, such as the NF, JIS, and BS standards. Most countries have their own standards. These are adjusted to suit local requirements but are based on the main international standards. Evaluations carried out to these standards in a laboratory compliant with the ISO 9001 quality standard carry more weight than those tested under other conditions. Other standards, such as aviation and maritime specifications, are also recognized in their fields. In all cases, the most recent issue of the standard or specification must be used. 

Tolerances The analytical weights meet the tolerances of the American National Standard ANSI/ASTM E617, Laboratory Weights and Precision Mass Standards. This standard is incorporated by reference and should be consulted for full descriptions and information on the tolerances and construction of weights.3 Where quantities of 25 mg or less are to be accurately weighed, any applicable corrections for weights should be used. 

Class 2 weights are used as working standards for calibration, built-in weights for analytical balances, and laboratory weights for routine analytical work. 

The original soybean oil (SBO), the processed soybean oil under similar conditions without catalyst (SBO control), and polymers of soybean oil (PSBO) were dissolved in THF. Molecular weights and molecular weight distribution were measured by GPC with a differential refractive index detector using THF as an eluent. The flow rate was 1.00 mL/min at 40 C. The injection volume was 100 pL. Linear polystyrene standards (Polymer Laboratories (PL), Mn = 580-lOOK, Mw/Mn = 1) were used for calibration of molecular weights of all polymers of PSBO. 2 PL gel 3 pm mixed E columns (300 mm x 7.5 mm) in series were used to resolve the samples. 

The application of dual detection [UV and refractive index (RI)] to the SEC analysis of polystyrene-poly(methyl methacrylate) (PS-PMMA) has already been studied in this laboratory (2). Both MWD and CCD were determined using a methodology outlined by Runyon et al. (3). This approach relies on SEC column calibration with narrow polydis-persity standards for each of the homopolymers as well as a measure of the detector response factors for each homopolymer to produce a copolymer MWD. In the case of PS and PMMA this is feasible, but in other block copolymer systems the availability of suitable molecular weight standards may be more limited. In addition, this procedure does rely on true SEC and is not valid for block copolymers for which the universal calibration does not hold true for both blocks in a given solvent system. 

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