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

The matrix was all-trans retinoic acid (RA). 25 mg RA in 0.5 mL unstabilized THF wasplaced in each of 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 of the first day of each two-day experiment, while the matrix solutionswere made fresh daily. One-half mL of THF was added to SA and BA. The butyl amountof 60 μL was added to SA along with 60 μL of AgTFA. Just 60 μL of 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 of Hanton, et al.1, 22Wefoundelectrospray sample preparation essential for experimental stability and reproducibility.The samples were electrosprayed using a voltage of 5 kV and a flow rate of 5 µL/min.The target was placed (4.0 ± 0.2) cm from the tip of the needle. Electrosprayed films onthe order of several micrometers thick were made to avoid depletion of the target duringthe taking of 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 of the targetwas electrosprayed with RA and AgTFA only (no polymer) to be used in the creation ofbackground spectra. Reversing the film, the left half of the target was electrosprayed withpolystyrene mixture, RA, and AgTFA in a 6:50:6 ratio. Each mass spectrum was the sumof 500 laser shots. Five repeats each on both the “blank” (no polymer) and the sampleside of 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 of butyl and 60 μL of AgTFAwas added to SB. The amount of octyl that already contained AgTFA was varied (e.g.,40 μL for a total of 100 μL of polystyrene). The total amount (100 in this case) ofAgTFA 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