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

More documents

Recommendations

Info

2.2 Initial Homogeneity and End-Group Composition TestingBefore certification, the within-lot homogeneity and approximate MMD of the candidatepolymer were verified by size exclusion chromatography (SEC) to be what was requested byNIST and claimed by the manufacturer. Its end-group composition and number-averagemolecular mass were obtained by nuclear magnetic resonance (NMR). NMR found the expectedn-octyl and proton end groups, an M n in agreement with the value found by SEC, and indicationsof a trace (< 1 % by mass) of an aromatic solvent, likely a residual of the synthesis. Since thecertification of SRM 2881depends on comparisons between gravimetric and mass spectrometriccompositions of polymer mixtures, all polystyrenes used were vacuum dried at 60 °C for 72 h toremove excess solvent.From the above results we concluded the polymer was of the correct molecular structureand of the necessary purity to serve as a candidate for certification.2.3 Bottling and SamplingA total of 69 individual samples of SRM 2881 were prepared in screw-cap glass vials eachcontaining about 0.25 g of polymer. The vials were divided into five subsets. One vial wasrandomly selected from each subset for bottle-to-bottle homogeneity testing of the packagedmaterial. The first and last bottles were also taken for study. Furthermore, one bottle (containingabout 2.5 g) was retained for use in future experiments. This bottle was also sampled forhomogeneity as a matter of course.3. Bottle-to-Bottle Homogeneity TestingBottle-to-bottle homogeneity testing was accomplished using size-exclusionchromatography (SEC). An Alliance 2000 GPC Liquid Chromatograph (Waters Corp., Milford,MA) with a differential refractive index detector and two Styragel 300 mm x 7.5 mm ID 10 μmHT6-E columns, and one Styragel 300 mm x 7.5 mm ID 10 μm HT-2 column (Waters Corp.,Milford, MA) was used in this study. The chromatography was run at a 1.0 mL/min solvent flowrate. The injector and column compartment of the chromatograph were controlled at 40 °C for allmeasurements. Tetrahydrofuran (Mallinckrodt Specialty Chemicals, Paris, KY) with addedantioxidant, 2,6-di-tert-butyl-4-methyl phenol (commonly known as butylated hydroxytoluene or5
BHT), was used as the solvent. The addition of 5 μL of toluene per mL of THF created an SECpump marker.Two polymer solutions in tetrahydrofuran were made from each polymer sample vial. Thepolystyrene samples were dissolved in the solvent at a concentration of approximately1.5 mg/mL. The order of preparing the solutions and the order of running the chromatogramswas randomized 6 . SEC was performed using two injections from each solution.After baseline subtraction, the SEC chromatograms were normalized to unit peak height andcompared by simple overlaying to decide initially if there were visible differences outside thenoise. The chromatograms from different solutions all superimpose on each other. Thispreliminary comparison showed that polymer samples taken from all the vials producedqualitatively identical chromatograms. In the next section, statistical analysis on thechromatography confirms quantitatively these initial visual observations.3.1 Statistical Method to Compare Chromatograms: the Match FactorIn previous SRM homogeneity testing employing SEC a numerical match factor was used tocompare one chromatogram with all the others. In this study, the match factor for chromatogrami is defined as the correlation coefficient between chromatogram i and the average chromatogramof the entire testing series. The match factor defined by Huber 7 asMatchFactor = 103⎧⎨Σxy−⎩2( Σx⋅ Σy) ⎫ ⎡⎧( Σx⋅Σx) ⎫⎧( Σy⋅Σy) ⎫⎤⎥⎦p⎬⎭⎢⎨Σx⎣⎩2−p⎬⎨Σy⎭⎩2−p⎬⎭[3.1]is simply the cross-correlation of two chromatograms. The value of x is the measured signal inthe i th chromatogram and y is the measured signal from the average of all chromatograms at thesame elution time; p is the number of data points in the chromatogram. The sums are taken overall data points in a region near the polymer peak of the chromatogram. At the extremes, a matchfactor of zero indicates no match while 1000.0 indicates an identical chromatogram. Generally,values above 999.0 indicate that the chromatograms are almost identical. Values between 900.06
Page 1 and 2: NISTIR 7512A Report on the Certific
Page 3 and 4: ABSTRACTThe certification of an abs
Page 5: 1. IntroductionThe certification of
Page 9 and 10: anticipated to be a useful material
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 “
show all

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

Create successful ePaper yourself

Delete template?

Save as template?