Capillary coupling techniques are suggested for the connection of a non-flow buffer-filled capillary to gel-filled capillaries as a low-background detection cell. The UV detection sensitivity of the resulting capillaries is improved at least fivefold, as demonstrated by using polyamino acids as test samples. The detection sensitivity can be further improved by using a low-background running buffer. Several ways are suggested to overcome the problems of resolution decrease and baseline drift which were observed after coupling.