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Failure of purification of nitrated phenylvaleric acid reaction mixtures by conventional recrystallization and column chromatographic methods using silica gel, led to a trial of counter-current chromatography. Poor solubility of the nitration products precluded the use for aqueous systems and let to the examination of systems using ethylene glycol or formamide as the stationary phase, with chloroform and other solvents as mobile phases. Prospective solvent pairs were first screened by a micropartitioning method and then by counter-current chromatography in an analytical micro counter-current chromatograph. Partition coefficients derived from these methods facilitated optimization of the solvent system and scale-up to a preparative counter-current chromatography range. Using the system chloroform-ethylene glycol, crude product was readily purified and then identified as 5-(2,4-dinitrophenyl)valeric acid. Purification using a 292-ml column provided high resolution and required 6 h. Purification with lower resolution on a 56-ml column required 2 h.