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

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where p is any instrument parameter. Notice as before we have taken the term0( Q k )( M )1+ to be very near 1 and second order in all corrections to the derivative. All0 wBA− M0other terms are independent of ( Q k 0).In Table 2 we show theindividual derivatives obtained for each machine parameter and theireffect on the uncertainty of the MALDI calibration parameter as found in Table 1. Inspection ofTable 1 tells us that the statistical uncertainty dominates all Type B uncertainty.We need to point out that the optimization method along with the calibration model allowsus to estimate the Type B uncertainty which have been optimized by the method described in thatpaper. Generally this is much simpler that what had to be done previously.11.2 Sample preparation contribution to Type A and Type B uncertaintyThis section considers the estimated error involved in sample preparation, particularly thegravimetric aspects. Specifically, this involves the masses of each of the polymers in thesolutions, the volumes of solution used to make up the concentration ratio, and finally therepeatability of the MALDI made from two different solutions of the apparently sameconcentration ratio.11.2.1 Mass and Volume effectsInitial solutions were made from polymer samples weighing from 5 mg to 6 mg precise to0.1 mg and added to 4 mL of THF. The weighing was found stable to 0.1 mg thus we estimatean uncertainty of [√2 · (0.1/5.0)] ≈ 3 %. Once the stock solutions were prepared volumes werecombined to create various polymer mixtures. Although pipettes were initially used to measureout solutions, these were found to poorly reproduce volumes in the μL range for THF. Instead,Hamilton glass syringes of 100 μL total volume were used and found to reproduce the volumeswell. The reproducibility of the 100 μL syringe was determined to be about 3 %. Repeatabilityof a 5 mL glass syringe for a 4 mL volume used to make up the initial solutions of polymers wasdetermined to be about 4 %. To avoid contamination and calibration problems separate syringeswere used for each polymer throughout the experiments.33
Two other methods were used to check the reproducibility of the data. First, linearity ofconcentration versus signal intensity was found for all data sets. Second, all data sets had a few( at least two) sets of data points in which the concentration ratios of the two polymers wererepeated. In all these the noise within one repeat of five data sets (to be described later) waslarger than the repeatability between the solutions made up the same—indicating therepeatability of our making of the solutions was excellent. This showed that the samplepreparation method used within one set of experiments was good.11.2.2 Type B uncertainty related to sample preparation and ablationThe repeatability of the electrospray part of the sample preparation andrepeatability of the ablation was difficult to determine. Once a target was sprayed, it asplaced in the instrument and 500 laser shots for the sample side of the target were takenfollowed by 500 laser shots of the blank side of the target. This was repeated five times.Mass peaks were then integrated and separated into their appropriated groups by endgroup mass. Next the ratios from these integrated peak sums taken to give the integratedratios between the two polymers in the sample. These integrated ratios are displayed oneach graph in Figures 4, 6 and 8. Uncertainty in the results can be traced to therepeatability of the MALDI measurement. Even when going to great lengths in samplepreparation and by using a large number of laser shots per spectrum, the MALDI processitself proved to be highly variable. Thus we take the type B uncertainty of this process tobe covered by the Type A (random) uncertainty.34
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 and 8: BHT), was used as the solvent. The
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: 11. Discussion of Type B Uncertaint
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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