Method and apparatus for interfacing ion and molecular selecting devices with an ion counter

An apparatus comprising:

• (i) a molecule selecting device;
• (ii) an individual ion counter device which comprises a tagged ions separator and a tagged ions counter selected from an optical particle counter and a condensation particle counter;
• (iii) an interface device integral with the molecule selecting device and being located at a downstream outlet thereof, the interface device comprising (a) an ionisation chamber containing an ionising device for ionising molecules received from the molecule selecting device;
• (b) a tagging particle generator;
• and (c) a tagging chamber, wherein the tagging chamber has:
• a sample ion inlet for receiving ions from the ionisation chamber;
• a tagging particle inlet, and
• an extraction outlet;
• the individual ion counting device being one which does not have its own operational tagging chamber and tagging particle generator;
• the sample ion inlet being arranged to receive a cloud of ions from the ionisation chamber;
• the tagging particle inlet being in fluid communication with a gas conduit supplying uncharged neutral tagging particles from the tagging particle generator;
• and the extraction outlet being in fluid communication with the tagged ions separator of the individual ion counter device;
• the tagging chamber being formed from an electrically conductive material or a material treated to render it electrically conductive;
• wherein the apparatus is set up so that selected molecules leaving the molecule selecting device enter the ionisation chamber where they are ionised and then enter the tagging chamber through the sample ion inlet whereupon they are exposed to an excess, relative to the number of ions, of uncharged neutral tagging particles so that the ions collide with the tagging particles to form a mixture of tagged ions, said tagged ions being tagging particles with an electric charge, and uncharged neutral tagging particles;
• the mixture of tagged ions and uncharged neutral tagging particles being drawn through the extraction outlet into the tagged ions separator of the individual ion counting device where the tagged ions are separated from the uncharged neutral tagging particles and are then counted by the tagged ions counter;
• and wherein the apparatus is set up so that the tagging chamber has an outlet flow rate (Qout) which is greater than a flow rate (Otag) of neutral tagging particles into the tagging chamber through the tagging particle inlet, thereby to prevent tagging particles from entering the ionisation chamber through by reverse flow through the sample ion inlet.

An interface device for connecting an ion selecting device to an individual ion counter device, the individual ion counter device being one which has a tagged ions separator for separating tagged ions and uncharged neutral tagging particles prior to counting of the tagged ions but does not have its own operational tagging chamber and tagging particle generator;

• the interface device comprising a tagging particle generator and a tagging chamber, the tagging chamber having:
• a sample ion inlet;
• a tagging particle inlet;
• and
• a extraction outlet;
• the sample ion inlet being arranged to receive a cloud of ions of a selected mobility from the ion selecting device;
• the tagging particle inlet being in fluid communication with a gas conduit supplying uncharged neutral tagging particles from the tagging particle generator;
• and the extraction outlet being connectable to the individual ion counter device;
• wherein the interface device apparatus is operable so that the cloud of ions of selected mobility entering the tagging chamber through the sample ion inlet is exposed to an excess, relative to the number of ions, of uncharged neutral tagging particles so that the ions collide with the tagging particles to form a mixture of tagged ions, said tagged ions being tagging particles with an electric charge, and uncharged neutral tagging particles;
• the mixture of tagged ions and uncharged neutral tagging particles being drawn through the extraction outlet into the tagged ions separator of the individual ion counting device where the tagged ions are counted;
• and wherein the interface device is operable so that the tagging chamber has an outlet flow rate (Qout) which is greater than a flow rate (Otag) of neutral tagging particles into the tagging chamber through the tagging particle inlet, thereby to prevent tagging particles from entering the ion selecting chamber through by reverse flow through the sample ion inlet.