Standard Reference Material 2881 - National Institute of Standards ...
Standard Reference Material 2881 - National Institute of Standards ...
Standard Reference Material 2881 - National Institute of Standards ...
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The matrix was all-trans retinoic acid (RA). 25 mg RA in 0.5 mL unstabilized THF wasplaced in each <strong>of</strong> 22 bottles. Eleven bottles were labeled SA through SK designatingsamples A thru K. The other eleven bottles were marked BA through BK signifyingblank samples containing no polymer. The polystyrene and AgTFA solutions were madeat the beginning <strong>of</strong> the first day <strong>of</strong> each two-day experiment, while the matrix solutionswere made fresh daily. One-half mL <strong>of</strong> THF was added to SA and BA. The butyl amount<strong>of</strong> 60 μL was added to SA along with 60 μL <strong>of</strong> AgTFA. Just 60 μL <strong>of</strong> AgTFA was addedto BA. Sample A and sample G never contained the octyl-initiated polymer. All sampleswere deposited onto the MALDI sample target by electrospray (ES) to increase signalrepeatability and reduce “hot spots” following the work <strong>of</strong> Hanton, et al.1, 22Wefoundelectrospray sample preparation essential for experimental stability and reproducibility.The samples were electrosprayed using a voltage <strong>of</strong> 5 kV and a flow rate <strong>of</strong> 5 µL/min.The target was placed (4.0 ± 0.2) cm from the tip <strong>of</strong> the needle. Electrosprayed films onthe order <strong>of</strong> several micrometers thick were made to avoid depletion <strong>of</strong> the target duringthe taking <strong>of</strong> the spectra. The target was divided in half by placing double-sided stickytape down the center and placing Teflon film across one side. The right half <strong>of</strong> the targetwas electrosprayed with RA and AgTFA only (no polymer) to be used in the creation <strong>of</strong>background spectra. Reversing the film, the left half <strong>of</strong> the target was electrosprayed withpolystyrene mixture, RA, and AgTFA in a 6:50:6 ratio. Each mass spectrum was the sum<strong>of</strong> 500 laser shots. Five repeats each on both the “blank” (no polymer) and the sampleside <strong>of</strong> the target and was taken from randomized positions on the target.When finished the THF was added to BA and BB which sat on the counter whileSample A was run. Then according to the scheme 60 μL <strong>of</strong> butyl and 60 μL <strong>of</strong> AgTFAwas added to SB. The amount <strong>of</strong> octyl that already contained AgTFA was varied (e.g.,40 μL for a total <strong>of</strong> 100 μL <strong>of</strong> polystyrene). The total amount (100 in this case) <strong>of</strong>AgTFA was added to BB. We then proceeded as above and divided the target, spraying ½with polystyrene mix and half with just matrix and AgTFA. This process was continuallyrepeated running sample A thru F. The remaining jars containing RA only, along with thepolystyrene and AgTFA mixes were stored overnight in the refrigerator. This process wascontinued on day two running samples G thru K.24