Direct cellular assays using off-line capillary electrophoresis with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) offers the ability to assay complex samples such as biological tissues directly. However, one must utilize different MS approaches and perform multiple chemical and enzymatic tests on a sample to more completely characterize complex tissue samples. An off-line capillary electrophoresis-MALDI-MS technique was developed that allows nanoliter volume samples to be separated and multiple assays performed on each sample spot after the separation. The method was used too assay a single atrial gland from the sea slug Aplysia californica. Post-source decay and in-source decay analyses were used to confirm the identity of several peptides. An on-target enzymatic digestion with carboxypeptidase Y was performed to gain additional amino acid sequence information from a peptide not part of the egg laying hormone gene family. Single cells also were analyzed, illustrating the capability to assay mass-limited samples.