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

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