the present invention provides methods and systems for using a dental anesthetic cartridge or other medical solution container as a mixing vessel for combining an anesthetic or other medical solution with a buffering solution from a separate container . in an embodiment of the current invention , the problems associated with plunger displacement during ph buffering are overcome by configuring a dental anesthetic cartridge for use with a system that delivers a precise amount of buffering solution to the cartridge , using the anesthetic cartridge itself as the mixing chamber to combine the buffer solution and the anesthetic solution , while displacing the plunger no more than a precise amount calculated to allow the plunger to move a predetermined distance sufficient to accept the buffer solution without displacing the plunger past the end of the cartridge . a plug , cover or other element covers and protects the plunger end of the container which would otherwise be open to contamination . the plug or cover is configured so that it cannot be easily removed other than by injecting buffer into the container . as the buffer will not be injected until the anesthetic or other medical solution is ready for use , the possibility that the anesthetic will be used prematurely and / or that the cartridge will be contaminated prior to use is significantly reduced . a conventional anesthetic cartridge 10 is illustrated in fig1 and includes a glass tube 12 , a plunger 13 at one end of the glass tube 12 , a pierceable septum 14 at the other end of the glass tube , and a cap 15 covering the septum 14 . an interior volume 16 of the glass tube 12 is filled with an anesthetic solution , typically as described above . as can be seen in fig1 , if any significant volume of buffer were to be added to the volume of anesthetic which fills the interior 16 of the glass tube , the plunger 13 would be displaced outwardly , as shown in broken line in fig1 . while the displaced plunger 13 in fig1 is only partially displaced , it would be appreciated a slightly greater volume of buffer would completely dislodge the plunger from the tube , allowing the anesthetic and buffer to spill . even if the plunger 13 were only slightly displaced from the glass tube 12 , it is likely that the cartridge 10 would still not be useable since it would be difficult , if not impossible , to place the cartridge into most syringe assemblies intending to receive the cartridge , where the plunger 13 is expected to be flush within the glass tube 12 . as disclosed in commonly owned u . s . patent publ . no . 2011 / 0247722 , an improved arrangement of the anesthetic cartridge 10 has the plunger 13 initially displaced inwardly from the end of the cartridge , as shown in fig2 . if the dimensions of the glass tube 12 are identical to those of the conventional anesthetic cartridge in fig1 , then the volume of anesthetic within the cartridge will have been reduced somewhat , but there will be sufficient displacement room for the plunger 13 to move to the left . a membrane cover 20 protects the exposed plunger end of the cartridge from contamination , but the cover is easily removed even long before use . thus , the cartridge can become contaminated and the cartridge used prematurely prior to the addition of buffer as shown in fig3 , a buffer container 37 is used to transfer buffer to an interior 36 of an anesthetic cartridge 30 . for example , a transfer tube 38 may be inserted through the septum 34 of the anesthetic cartridge 30 at one end and inserted through the septum 36 of the buffer cartridge 37 at its other end . thus , a transfer path exists between the buffer solution and the anesthetic solution . buffer cartridge 37 may itself have a plunger ( not illustrated ) which allows transfer of the desired buffer volume to the interior 36 of the anesthetic cartridge 30 which will result in displacing ac plunger 33 to the position shown in fig4 . a transfer volume will be calculated in this method such that the target ph adjustment and the tonicity adjustment of the anesthetic solution will be achieved without displacing the cartridge 33 beyond the end of the glass tube 32 . of particular concern to the present invention , a plug 31 is placed in the open plunger end of the glass tube 32 . the plug has a proximal end 31 a which is configured and dimensioned to sit in , at or just outside of the open end of the glass tube . preferably , the proximal end will be sized or otherwise configured so that it cannot be pressed or pushed into the open end . a distal end 31 of the plunger 31 is dimensioned to fit inside of the open end of the cartridge and a stem 31 c or other portion or component between the proximal and distal ends will have a length selected so that the distal end will just touch the plunger 33 when the proximal end 31 a is located at the end of the glass tube 32 . thus , as soon as buffer is injected from the buffer container 37 , the plunger 33 will be displaced to the right as illustrated . when the desired volume of buffer has been transferred , the plug 31 will also be displaced to the right so that the proximal end 31 a is exposed and can be readily grasped and removed by the user . the cartridge 30 is then ready for insertion into a syringe for use . by storing a hypotonic anesthetic solution in a sealed cartridge that is intended to be buffered prior to use , it is possible to create an anesthetic that can be buffered to both an optimal ph using a known concentration of sodium bicarbonate solution and to an optimum ( or at least acceptable ) tonicity , typically where the buffered solution is isotonic after the buffering process has been completed . in this process , a hypotonic local anesthetic solution would be manufactured to a known and precise hypotonic osmolarity selected so that with the addition of a desired amount of a known concentration of sodium bicarbonate solution , for instance 0 . 18 ml of 8 . 4 % sodium bicarbonate , the resulting mixed solutions would be approximately isotonic ( 300 mosm / l ). the buffer can be transferred using the simple cartridge 37 as shown in fig3 and 4 or alternatively can be transferred using the systems described in the commonly assigned patents and publications which have been incorporated herein by reference . while the above is a description of a preferred embodiment of the invention , various alternatives , modifications , and equivalents may be used . therefore , the above description should not be taken as limiting the scope of the invention which is disclosed .
an anesthetic cartridge is adapted to receive a volume of buffer by displacing a plunger in one end of the anesthetic cartridge inwardly so that addition of the buffer volume will not displace the plunger excessively beyond the end of the cartridge body . the inwardly displaced end is protected by a plug or cover which prevents contamination and which is ejected when the buffer is added . the amount of buffer volume injected is selected to raise the ph of the anesthetic to a target value and to simultaneously achieve a target tonicity .