Gradient elution molecular weight effect

Fig. 14 a, b. Effect of gradient steepness on the very fast separation of polystyrene standards in a molded monolithic poly(styrene-co-divinylbenzene) column (Reprinted with permission from [121]. Copyright 1996 Elsevier). Conditions column, 50 mm x8 mm i.d., mobile phase, linear gradient from 100% methanol to 100% tetrahydrofuran within a 1 min b 12 s, flow rate, 20 ml/min, peaks represent polystyrene standards with molecular weights of 9200,34,000 and 980,000 (order of elution), 3 mg/ml of each standard in tetrahydrofuran, injection volume 20 pi, UV detection, 254 nm... 

Further purification of the crude acid was effected by chromatography on Amberlite XAD-2 polystyrene resin with a linear gradient produced by adding 0.1 N methanolic ammonia, to 0.01 N aqueous ammonia. A series of low molecular weight acids was eluted first, followed by a fraction (30-60% elution) that possessed the major part of the antibacterial (biological) activity. 

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