We present B and R band spectroastrometry of a sample of 45 Herbig Ae/Be stars in order to study their binary properties .
All but one of the targets known to be binary systems with a separation of \sim 0.1 - 2.0 arcsec are detected by a distinctive spectroastrometric signature .
Some objects in the sample exhibit spectroastrometric features that do not appear attributable to a binary system .
We find that these may be due to light reflected from dusty halos or material entrained in winds .
We present 8 new binary detections and 4 detections of an unknown component in previously discovered binary systems .
The data confirm previous reports that Herbig Ae/Be stars have a high binary fraction , 74 \pm 6 per cent in the sample presented here .
We use a spectroastrometric deconvolution technique to separate the spatially unresolved binary spectra into the individual constituent spectra .
The separated spectra allow us to ascertain the spectral type of the individual binary components , which in turn allows the mass ratio of these systems to be determined .
In addition , we appraise the method used and the effects of contaminant sources of flux .
We find that the distribution of system mass ratios is inconsistent with random pairing from the Initial Mass Function , and that this appears robust despite a detection bias .
Instead , the mass ratio distribution is broadly consistent with the scenario of binary formation via disk fragmentation .