A hand-held gaseous injector apparatus, comprising: a syringe body (520; 1120) with an outlet; a plunger (160; 860) slidably disposed in the syringe body and with the syringe body, defining a mixing chamber within the syringe body; a metering device, configured to control a volume of at least the mixing chamber when a first fluid is introduced into the mixing chamber, and a filling mechanism configured to direct the first fluid into the mixing chamber of the syringe body so as to move the plunger and expand the mixing chamber, wherein the metering device comprises a metering dial (120; 820) configured to attach to the syringe body, wherein the metering dial comprises a metering body (122; 822) and a metering cap (124; 824), wherein the metering body (122, 822) comprises a generally cylindrical member (130; 830) and a flange (132; 832) at a top portion of the metering body, wherein the generally cylindrical member is configured to be received within the syringe body when the metering dial is attached to the syringe body, and configured to receive the plunger (160, 860), and wherein the metering body comprises a plurality of slots (138, 838) located on an inner surface of the metering body and stops corresponding with each of the slots, the stops extending inwardly from the slots and extending different distances toward a bottom end of the cylindrical member, depending upon the concentration to which the stop corresponds, wherein the stops interact with components contained in the plunger (160, 860), said components comprising a latch (228, 928), and wherein the plunger is configured to be oriented in different angular positions to select a concentration, wherein the latch (228, 928) is brought into alignment with one of the stops of the metering body, wherein each of the stops comprises a surface configured to contact the latch (228, 928) to limit movement of the plunger (160, 860) to one of a plurality of different positions, each different position corresponding to a different expansion volume of the mixing chamber. a syringe body (520; 1120) with an outlet; a plunger (160; 860) slidably disposed in the syringe body and with the syringe body, defining a mixing chamber within the syringe body; a metering device, configured to control a volume of at least the mixing chamber when a first fluid is introduced into the mixing chamber, and a filling mechanism configured to direct the first fluid into the mixing chamber of the syringe body so as to move the plunger and expand the mixing chamber, wherein the metering device comprises a metering dial (120; 820) configured to attach to the syringe body, wherein the metering dial comprises a metering body (122; 822) and a metering cap (124; 824), wherein the metering body (122, 822) comprises a generally cylindrical member (130; 830) and a flange (132; 832) at a top portion of the metering body, wherein the generally cylindrical member is configured to be received within the syringe body when the metering dial is attached to the syringe body, and configured to receive the plunger (160, 860), and wherein the metering body comprises a plurality of slots (138, 838) located on an inner surface of the metering body and stops corresponding with each of the slots, the stops extending inwardly from the slots and extending different distances toward a bottom end of the cylindrical member, depending upon the concentration to which the stop corresponds, wherein the stops interact with components contained in the plunger (160, 860), said components comprising a latch (228, 928), and wherein the plunger is configured to be oriented in different angular positions to select a concentration, wherein the latch (228, 928) is brought into alignment with one of the stops of the metering body, wherein each of the stops comprises a surface configured to contact the latch (228, 928) to limit movement of the plunger (160, 860) to one of a plurality of different positions, each different position corresponding to a different expansion volume of the mixing chamber.