A method for transferring ions, the method comprising: creating a pressure differential between a first chamber and a second chamber such that the second chamber has a pressure less than a pressure of the first chamber, wherein: the first chamber and the second chamber are separated by a wall; and an ion transfer device (188, 404, 504, 604) extends through the wall and comprises an ion inlet section (414, 514, 614) and a main capillary section (418, 518, 618); the ion inlet section (414, 514, 614) comprises an inlet leading to a lumen (422, 522, 622); the main capillary section (418, 518, 618) comprises a bore (430, 530, 630) communicating with the lumen and leading to an outlet; and the lumen has a lumen inside diameter and the bore has a bore inside diameter greater than the lumen inside diameter; producing ions in the first chamber; drawing the ions into the inlet; transporting the ions from the inlet through the lumen and into the bore, and through the bore to the outlet; and emitting the ions from the outlet into the second chamber, wherein ion inlet section and the main capillary section are configured such that the lumen inside diameter has an average value that is less than an average value of the bore inside diameter, a difference between the average value of the lumen inside diameter and the average value of the bore inside diameter is large enough to cause the gas flow to become fully supersonic downstream from the transition from the lumen to the capillary bore, and the gas flow is not supersonic upon exiting the main capillary section, and wherein the main capillary section (418, 518, 618) comprises a plurality of capillary tube segments serially positioned adjacent to each other, the inside diameters of the bores of the capillary tube segments successively increasing from one capillary tube segment to another in a direction toward the bore outlet, or wherein the bore inside diameter of the main capillary section gradually increases from a bore inlet of the bore up to the bore outlet. creating a pressure differential between a first chamber and a second chamber such that the second chamber has a pressure less than a pressure of the first chamber, wherein: the first chamber and the second chamber are separated by a wall; and an ion transfer device (188, 404, 504, 604) extends through the wall and comprises an ion inlet section (414, 514, 614) and a main capillary section (418, 518, 618); the ion inlet section (414, 514, 614) comprises an inlet leading to a lumen (422, 522, 622); the main capillary section (418, 518, 618) comprises a bore (430, 530, 630) communicating with the lumen and leading to an outlet; and the lumen has a lumen inside diameter and the bore has a bore inside diameter greater than the lumen inside diameter; the first chamber and the second chamber are separated by a wall; and an ion transfer device (188, 404, 504, 604) extends through the wall and comprises an ion inlet section (414, 514, 614) and a main capillary section (418, 518, 618); the ion inlet section (414, 514, 614) comprises an inlet leading to a lumen (422, 522, 622); the main capillary section (418, 518, 618) comprises a bore (430, 530, 630) communicating with the lumen and leading to an outlet; and the lumen has a lumen inside diameter and the bore has a bore inside diameter greater than the lumen inside diameter; producing ions in the first chamber; drawing the ions into the inlet; transporting the ions from the inlet through the lumen and into the bore, and through the bore to the outlet; and emitting the ions from the outlet into the second chamber, wherein ion inlet section and the main capillary section are configured such that the lumen inside diameter has an average value that is less than an average value of the bore inside diameter, a difference between the average value of the lumen inside diameter and the average value of the bore inside diameter is large enough to cause the gas flow to become fully supersonic downstream from the transition from the lumen to the capillary bore, and the gas flow is not supersonic upon exiting the main capillary section, and wherein the main capillary section (418, 518, 618) comprises a plurality of capillary tube segments serially positioned adjacent to each other, the inside diameters of the bores of the capillary tube segments successively increasing from one capillary tube segment to another in a direction toward the bore outlet, or wherein the bore inside diameter of the main capillary section gradually increases from a bore inlet of the bore up to the bore outlet. wherein ion inlet section and the main capillary section are configured such that the lumen inside diameter has an average value that is less than an average value of the bore inside diameter, a difference between the average value of the lumen inside diameter and the average value of the bore inside diameter is large enough to cause the gas flow to become fully supersonic downstream from the transition from the lumen to the capillary bore, and the gas flow is not supersonic upon exiting the main capillary section, and wherein the main capillary section (418, 518, 618) comprises a plurality of capillary tube segments serially positioned adjacent to each other, the inside diameters of the bores of the capillary tube segments successively increasing from one capillary tube segment to another in a direction toward the bore outlet, or wherein the bore inside diameter of the main capillary section gradually increases from a bore inlet of the bore up to the bore outlet.