Type 28 cells are identical to Type 18 Micro cells, except these cells are supplied with a PTFE stopper to fit in a ground cone to reduce evaporation of volatile samples (The Type 28B comes with stoppers). The external height is 48mm plus the stopper. Micro cells are available with either clear walls which will transmit energy or opaque black walls for improved sensitivity. Alignment of Micro cells in instrument cell holders is critical.
Smaller sample volumes can be achieved by using cell Type 28/9 or 28B9 with a 9mm instead of a 3mm thick base.