The invention relates to a compound of the 1-aminoanthraquinone, anthanthrone, anthrapyrimidine, quinacridone, dioxazine, diketopyrrolopyrrole, flavanthrone, indanthrone, isoindolinone, isoviolanthrone, perinone, perylene, phthalocyanine, pyranthrone or thioindigo series, which compound has one or more sulfonate groups of formula (1) wherein R1 is methyl or ethyl, R2, R3 and R4 are each independently of the others C6-C24alkyl or C6-C24alkenyl, m is a number from 0.3 to 1.0 and n is a number from 0 to (1.0 m), the compound being suitable for use as a pigment dispersant and rheology improver. Also claimed are modified pigments having that compound on their surface, and also pigment compositions and dispersions comprising that compound.