Standard Reference Material 2881 - National Institute of Standards ...

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and 999.0 indicate some similarity between chromatograms, but the result should be interpretedwith care. All values below 900.0 are interpreted as an indication of different chromatograms 7 .For each polymer the chromatograms were run in groups of eight solutions on different days.Match factors against the average chromatogram of all the runs were obtained for the region ofthe analyte main peak. All chromatograms from the analyte main peak in this study had matchfactors against the mean chromatogram of greater than 999.0. An ANOVA (Analysis ofVariance) calculated using the NIST interactive software for statistical and numerical dataanalysis called PC-OMNITAB (see NISTIR 4957) made on the match factors obtained from thechromatograms indicated that the match factors of chromatograms from vials of SRM 2881 werenot different using a significance level of 0.05.From the above considerations, we conclude that the vials of SRM 2881 are indistinguishablefrom one another.4. Discussion of the Certification Method Developed for SRM 2881Synthetic polymers are never obtained as a single molecular mass but rather as a distributionof molecular masses. The molecular mass distribution (MMD) and the mass moments (MM)derived from it are used in areas of polymer science as diverse as fundamental physicalstudies, polymer processing, and consumer product design. For example, the observed MMDis often compared to predictions from kinetic or mechanistic models of the polymerizationreaction itself 8, 9 . Similarly, the tensile strength, melt flow rate, and many other physicalproperties are dependent on MMD. Determination of the MMD is used for quality control inpolymer synthesis and as specification in international commerce. MALDI-TOF massspectrometry to obtain the MMD of synthetic polymers has been integrated into variousinternational standards such as ASTM D7034-05 entitled "Standard Test Method forMolecular Mass Averages and Molecular Mass Distribution of Atactic Polystyrene by MatrixAssisted Laser Desorption/Ionization (MALDI) Time of Flight (TOF) Mass Spectrometry(MS)”. Similar standards are available from Deutsches Institut für Normung (DIN 55674)and the International Organization for Standardization (ISO WD 10927). SRM 2881 is7
anticipated to be a useful material for laboratories to check their proficiency in applying thesestandard methods.Various averages, or molecular moments, can be defined as useful summaries of the MMD.Measuring and computing these summary statistics has comprised a major part of traditionalpolymer analysis. The three most common measures of the MMD are the number averagerelative molecular mass, M n , the mass average relative molecular mass, M w and the z-averagerelative molecular mass, M z .Mn= ∑ mjnj/ ∑ nj[4.1]jj2Mw= ∑mjnj/j∑jm njj[4.2]PD = M w/ M n[4.3]Mz= ∑mj3jnj∑j2j/ m n[4.4]jwhere m j is the mass of a discrete oligomer, n j is the number of molecules at the given massm j. The experimental moments from MALDI-TOF MS are defined as M n , M w , and M z , whilethe “true” values are given as M 0 n, M 0 w, and M 0 z. PD defines the polydispersity index whichis a measure of the breadth of the polymer distribution. When PD is equal to one (i.e., instatistical terms the variance of MMD is zero), all of the polymer molecules in a sample are ofthe same molecular mass and the polymer is referred to as monodisperse. Natural polymers,such as proteins, are typically monodisperse. This is seldom the case for synthetic polymers,which have a non-point-mass MMD, whose width depends in a complex fashion on thepolymerization chemistry, specifically its mechanism, kinetics, and reaction conditions. Ingeneral, no two polymerization reactions yield precisely the sample MMD no matter howcarefully conditions are controlled. This means that the product each polymerization reactionmust be measured to obtain a reliable MMD.8
Page 1 and 2: NISTIR 7512A Report on the Certific
Page 3 and 4: ABSTRACTThe certification of an abs
Page 5 and 6: 1. IntroductionThe certification of
Page 7: BHT), was used as the solvent. The
Page 11 and 12: sample using a separate method, or
Page 13 and 14: 6.0. Signal Axis Calibration Proced
Page 15 and 16: 6.2 Mathematical Model for Gravimet
Page 17 and 18: Here Q is a function of all the exp
Page 19 and 20: Let us consider this final equation
Page 21 and 22: GGexpTAexpTBGG0TA0TB=⎧⎨1+⎩0(
Page 23 and 24: were also used in this experiment:
Page 25 and 26: The matrix was all-trans retinoic a
Page 27 and 28: educes the data set to groups of th
Page 29 and 30: atios of the two sets of data is ag
Page 31 and 32: An analysis of variance (ANOVA) 5 w
Page 33 and 34: 11. Discussion of Type B Uncertaint
Page 35 and 36: Two other methods were used to chec
Page 37 and 38: certified by this method with the u
Page 39 and 40: References1. S. D. Hanton, I. Z. Hy
Page 41 and 42: Figures1. MALDI-TOF mass spectra of
Page 43 and 44: Figure 242
Page 45 and 46: Figures 5 (inset) and 6 (main)44
Page 47 and 48: Figure 946
Page 49 and 50: Tables1. Q/k 0 with its estimated u
Page 51 and 52: Table 2Instrument Parameter Optimal
Page 53 and 54: 103 10840.42 0.0063 8.93 % 14.72 %
Page 55 and 56: 99 10423.86 0.0139 0.0008 93.9 %100
Page 57 and 58: INSTRUCTIONS FOR USEStorage: The SR
Page 59:
REFERENCES[1] See ASTM D5296 05 “
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