We have obtained high and intermediate resolution optical spectra of the black-hole candidate Nova Sco 1994 in May/June 1998 , when the source was in complete ( X-ray ) quiescence . We measure the radial velocity curve of the secondary star and obtain a semi-amplitude of K _ { 2 } =215.5 \pm 2.4 km s ^ { -1 } , which is 6 per cent lower than the only previously determined value . This new value for K _ { 2 } thus reduces the binary mass function to f ( M ) = 2.73 \pm 0.09 M _ { \odot } . Using only the high resolution spectra we constrain the rotational broadening of the secondary star , v \sin~ { } i , to lie in the range 82.9–94.9 km s ^ { -1 } ( 95 per cent confidence ) and thus constrain the binary mass ratio to lie in the range 0.337–0.436 ( 95 per cent confidence ) . We can also combine our results with published limits for the binary inclination to constrain the mass of the compact object and secondary star to the ranges 5.5 – 7.9 and 1.7 – 3.3 M _ { \odot } respectively ( 95 per cent confidence ) . Finally , we report on the detection of the Lithium resonance line at 6707.8Å , with an equivalent width of 55 \pm 8 mÅ .