Sample Dilution The goal is to dilute the contaminants to the point where they no longer interfere with the analysis of the sample. Requires high enough analyte concentration in the sample to provide acceptable data after dilution.
On-Plate Washing Buffer and salt removal Dry sample and matrix Deposit L cold 0.1% TFA Leave for sec, then remove Detergent contamination use 5% isopropanol - cold Cell extract contamination Use 100% isopropanol- cold
Drop Dialysis To remove low molecular weight contaminants. Fill a 250 mL container with ultra pure water. Float the membrane on the water (shiny side up). Place L of sample solution on the membrane. Add 1 L of AcN to sample spot to increase surface area, Allow to sit for approximately 45 min. Remove with pipette, add matrix, spot.
Cation Exchange For removal of alkali metal ions. Prepare resin in NH 4 + form according to instructions. Place app. 0.1 mg of beads on a clear piece of parafilm. Add 5 L of sample and 5 L matrix to beads to make a slurry (the slurry should be app. 50% beads). Slowly mix up and down with a pipette times. Allow beads to settle for sec. Pipette supernatant onto sample plate. –Avoid getting beads onto plate. –Does not work for positively charged species.
Solid Phase Extraction - Zip Tip Zip tip - miniature column chromatography. Standard C18 zip tips have 0.6 L bed volume. Micro C18 zip tips have 0.2 L bed volume - better for automation. C4 zip tips for clean-up of protein samples. Other types available, e.g. metalchelating for phosphor peptides and cation exchange.
Procedure for Zip Tip Use Condition the tip according to instructions. Load the sample onto the tip by pipetting L of sample up and down several times and discard the liquid. Wash with 3 x 10 L 0.1% TFA to remove salts. Elute the sample using % AcN or matrix.