A method and apparatus of converting a series of data words into modulated signals are provided. Interpath interference which arises due to non-zero cross and auto correlation of more than one spreading code is suppressed by estimating a transmitted signal stream, or a plurality of such signal streams in the case of a plurality of multipath components, respreading this estimated signal and subtracting non-orthogonal interference contributions from a received signal. The sol-gel titania-based coatings demonstrated strong pH stability and enhanced extraction capability over other commercially availble GC coatings.