Colorimetric ultramicro method for the determination of free fatty acids

Previously described colorimetric ultramicro methods for the determination of serum and tissue fatty acids have been improved in sensitivity and selectivity by extracting cobalt rather than copper soaps by means of a solvent lighter than water instead of chloroform. The complex of Co++ with α-nitroso-Β-naphthol is measured at 500 mμ.