反向微柱的准备Preparation of Reversed-Phase Microcolumns
INTRODUCTION |
One versatile strategy for sample cleanup prior to MALDI-MS analysis uses microscale columns designed for direct sample elution onto the MALDI target plate. This protocol describes the fabrication of a reversed-phase microcolumn designed for this purpose. The microcolumns are prepared from GELoader tips. This protocol has been optimized for sample cleanup prior to MALDI-MS. However, with slight modifications, it works equally well with samples destined for ESI-MS. |
MATERIALS |
Reagents |
IMPORTANT: All reagents used in this protocol must be sequence grade.
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Equipment |
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METHOD |
Prepare a slurry of 100-200 µL of chromatography resin in 70% acetonitrile (use ~1.5 mg of resin/100 µL of acetonitrile). Steps 3-8 are illustrated in Figure 1. Load 20 µL of 70% acetonitrile in the top of the constricted GELoader tip, and add 0.5 µL of the resin slurry on top of the acetonitrile. Use a 1-mL syringe fitted to the GELoader tip with a disposable pipette tip to gently press the liquid down to create a small column at the end of the constricted microcolumn. Dry the column by letting all of the liquid escape from the bottom of the column before performing the next step. Apply 20 µL of 0.1% TFA to the top of the column. Equilibrate the column by gently pushing 10 µL of 0.1% TFA through it, using gentle air pressure generated by the syringe. The remaining 10 µL of 0.1% TFA should remain on top of the column bed. When the microcolumn is used as a cleanup step prior to nano-ESI-MS, 1% formic acid should be used instead of TFA, which is incompatible with ESI-MS. Apply the protein/peptide sample on top of the remaining 10 µL of 0.1% TFA. Press the liquid gently through the column by applying air pressure with the syringe. Do not allow the column to dry out; leave ~2 µL of solution on top of the column bed. Wash the column with 20 µL of 0.1% TFA, and allow the column to run dry. Elute the analytes, using 0.5 µL of matrix solution, directly onto the MALDI-MS target. The 0.5 µL of matrix solution should be spotted as several droplets (5-10) on the target. Alternatively, if the analytes are to be analyzed by ESI-MS, elute the peptides from the column using methanol/formic acid/H2O (50:1:49) either directly into the capillary needle or into a microcentrifuge tube. |
REFERENCES |
Gobom, J., Nordhoff, E., Ekman, R., and Roepstorff, P. 1997. Rapid micro-scale proteolysis of proteins for MALDI-MS peptide mapping using immobilized trypsin. Int. J. Mass Spectrom. Ion Proc. 169/170: 153-163. Kussmann, M., Lassing, U., Sturmer, C.A., Przybylski, M., and Roepstorff, P. 1997. Matrix-assisted laser desorption/ionization mass spectrometric peptide mapping of the neural cell adhesion protein neurolin purified by sodium dodecyl sulfate polyacrylamide gel electrophoresis or acidic precipitation. J. Mass Spectrom 32: 483-493. |
Anyone using the procedures in this protocol does so at their own risk. Cold Spring Harbor Laboratory makes no representations or warranties with respect to the material set forth in this protocol and has no liability in connection with the use of these materials. Materials used in this protocol may be considered hazardous and should be used with caution. For a full listing of cautions regarding these material, please consult: Proteins and Proteomics, A Laboratory Manual, by Richard J. Simpson, © 2003 by Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, p. 482-484. |