We present the results of observations of the \lambda 3130.4 Å interstellar absorption line of ^ { 9 } Be \sc ii in the direction of \zeta Per .
The data were obtained at the Canada-France-Hawaii 3.6m Telescope using the Coudé f/4 Gecko spectrograph at a resolving power \lambda / \Delta \lambda \simeq 1.1 \times 10 ^ { 5 } , and a signal-to-noise ratio { S / N } \simeq 2000 .
The ^ { 9 } Be \sc ii line is not detected , and we obtain an upper limit on the equivalent width W _ { 3130.4 } \leq 30 \mu Å .
This upper limit is 7 times below the lowest upper limit ever reported hitherto .
The derived interstellar abundance is ( ^ { 9 } Be/H ) \leq 7 \times 10 ^ { -13 } , not corrected for the depletion of ^ { 9 } Be onto interstellar grains ; it corresponds to an upper limit \delta _ { Be } \leq - 1.5 dex on the depletion factor of ^ { 9 } Be .
As such , it argues in favour of models of formation of dust grains in stellar atmospheres .