The interfacial chemistry of solvent cast films of block copolymers of poly(ethylene oxide) (PEG) and poly(lactic and glycolic acid) (PLGA) have been investigated over a wide range of compositions. X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS) were utilized to provide both elemental and structural data. In all cases it is found that the PLGA component preferentially resides at the copolymer surface, and this is demonstrated by the use of the variable electron takeoff angle XPS. SSIMS confirms the low concentrations of PEO at the copolymer surface. Radical cation intensities within the SSIMS spectra have been correlated to PLGA block compositions. It is demonstrated that these ion intensities may be used to estimate the PLGA surface chain sequence composition and its short-range order.