A detector comprising: an analytical apparatus for detecting a substance of interest, and a detector inlet, the detector inlet comprising: a flow conduit for carrying a flow of fluid provided by a flow provider, the flow conduit comprising a sampling volume; and a flow director arranged to vary a spatial distribution of particulates transverse to the direction of flow of the fluid relative to the shape of said distribution upstream of the flow director to provide a depleted region of the cross section of the flow conduit through which relatively few particulates flow, while the majority of the particulates are carried through other parts of the cross section of the flow conduit, the depleted region defining the sampling volume; a sampling inlet adapted to collect samples of the fluid from the sampling volume as the fluid flows past the sampling inlet, and to provide the samples to the analytical apparatus, wherein the flow of fluid carries particulates; the detector is characterized in that the sampling inlet comprises at least one of a pinhole inlet, a membrane inlet, and a capillary inlet and the flow director is provided by a bend in direction of the flow conduit. an analytical apparatus for detecting a substance of interest, and a detector inlet, the detector inlet comprising: a flow conduit for carrying a flow of fluid provided by a flow provider, the flow conduit comprising a sampling volume; and a flow director arranged to vary a spatial distribution of particulates transverse to the direction of flow of the fluid relative to the shape of said distribution upstream of the flow director to provide a depleted region of the cross section of the flow conduit through which relatively few particulates flow, while the majority of the particulates are carried through other parts of the cross section of the flow conduit, the depleted region defining the sampling volume; a sampling inlet adapted to collect samples of the fluid from the sampling volume as the fluid flows past the sampling inlet, and to provide the samples to the analytical apparatus, wherein the flow of fluid carries particulates; the detector is characterized in that the sampling inlet comprises at least one of a pinhole inlet, a membrane inlet, and a capillary inlet and the flow director is provided by a bend in direction of the flow conduit. a flow conduit for carrying a flow of fluid provided by a flow provider, the flow conduit comprising a sampling volume; and a flow director arranged to vary a spatial distribution of particulates transverse to the direction of flow of the fluid relative to the shape of said distribution upstream of the flow director to provide a depleted region of the cross section of the flow conduit through which relatively few particulates flow, while the majority of the particulates are carried through other parts of the cross section of the flow conduit, the depleted region defining the sampling volume; a sampling inlet adapted to collect samples of the fluid from the sampling volume as the fluid flows past the sampling inlet, and to provide the samples to the analytical apparatus, wherein the flow of fluid carries particulates; the detector is characterized in that the sampling inlet comprises at least one of a pinhole inlet, a membrane inlet, and a capillary inlet and the flow director is provided by a bend in direction of the flow conduit.