Improved liquid chromatography systems having components made of titanium, stainless steel, or organic polymeric material are useful in the separation of polynucleotide fragments, particularly large fragments of double-stranded polynucleotides, by Matched Ion Polynucleotide Chromatography. The diplexer has an input terminal to receive an input signal. In the first print mode, a sheet is conveyed at a defined speed in the monochromatic print processing and is conveyed at a speed lower than the defined speed in the color print processing. The interaction of these elements provides vertical restraint for the rail brace.