Use of a feed device for introducing samples, in particular very small samples, into an device for treating samples, in particular very small samples, for separation in a gas chromatograph for elemental analysis with respect to carbon, nitrogen and / or sulphur, wherein the device for treating samples comprises - a first treatment device with an opening in which a sample which has been supplied to the first treatment device via the opening can be vaporised, at least in part, and which is set up to oxidise the at least partially vaporised sample in a first oxidation region for the first time, to reduce it in a reduction region for the first time, and to oxidise it in a second oxidation region for a second time, wherein the reduction region is arranged between the first and second oxidation regions (31a, 31c), and - a second treatment device which is connected to the first treatment device and which is set up to reduce, for a second time, the sample which has been vaporised, at least in part, in the first treatment device, wherein the feed device has an inlet opening, via which the feed device can be coupled to a feed apparatus for providing samples, in particular very small samples, and an outlet opening via which the feed device can be connected to the device, and is set up to guide, along a longitudinal axis through a heating region, a sample which has been introduced by means of the feed apparatus via the inlet opening, so that the sample is vaporised, at least in part, as it falls through the feed device and before exiting through the outlet opening, and wherein the feed device is selected, as a function of the sample quantity and / or at least one sample property, from a plurality of feed devices with different diameters and / or different lengths. - a first treatment device with an opening in which a sample which has been supplied to the first treatment device via the opening can be vaporised, at least in part, and which is set up to oxidise the at least partially vaporised sample in a first oxidation region for the first time, to reduce it in a reduction region for the first time, and to oxidise it in a second oxidation region for a second time, wherein the reduction region is arranged between the first and second oxidation regions (31a, 31c), and - a second treatment device which is connected to the first treatment device and which is set up to reduce, for a second time, the sample which has been vaporised, at least in part, in the first treatment device, wherein the feed device has an inlet opening, via which the feed device can be coupled to a feed apparatus for providing samples, in particular very small samples, and an outlet opening via which the feed device can be connected to the device, and is set up to guide, along a longitudinal axis through a heating region, a sample which has been introduced by means of the feed apparatus via the inlet opening, so that the sample is vaporised, at least in part, as it falls through the feed device and before exiting through the outlet opening, and wherein the feed device is selected, as a function of the sample quantity and / or at least one sample property, from a plurality of feed devices with different diameters and / or different lengths.