Preliminary measurement of gas concentrations of perfluropropane using an analytical weighing balance

We describe the use of an analytical weighing balance of measurement accuracy 0.00001 g for determination of concentrations of perfluropropane (C3F8) gas used in ophthalmic surgical vitrectomy procedures. A range of test eyes corresponding to an eye volume of 6.1 ml were constructed using 27 gauge needle exit ducts and separately 20 gauge (straight) and 23 gauge (angled) entrance ports. This method allowed determination of concentration levels in the sample preparation syringe and also levels in test eyes. It was determined that a key factor influencing gas concentrations accuracy related to the method of gas fill and the value of dead space of the gas preparation/delivery system and with a significant contribution arising from the use of the particle filter. The weighing balance technique was identified as an appropriate technique for estimation of gas concentrations.