A detector cell assembly for use in a spectrophotometer comprises a thermally insulating body having a bore with open ends therethrough and transparent windows closing the ends of the bore. An inlet passage and an outlet passage open into the bore adjacent to opoosite ends thereof for flowing fluid therethrough. The body has size defined by an outer surface spaced laterally from the bore by a distance of at least about two times the bore diameter. Preferably the thermally insulating body is polymeric and has an outwardly facing annular surface respectively encircling each end of the bore approximately normal thereto and in contact with a corresponding surface on the respective window. A spring urges each respective transparent window against the respective annular surface to effect a fluid seal between the body and each window.
