The invention relates to a wavelength dispersive apparatus (210) for analyzing a fluid using x-rays, comprising: means for exposing the fluid to focused x-rays to cause at least one component of the fluid to x-ray fluoresce, including: a first focusing optic for focusing the x-rays on the fluid, and at least one x-ray exposure chamber, having an exposure aperture less than about 10 mm in diameter; means for analyzing x-ray fluorescence to determine at least one characteristic of the fluid, including: at least one x-ray detector having an active area operating at a temperature greater than about 0 degrees centigrade and substantially uncooled; and a second focusing optic to collect x-ray fluorescence from the fluid, and focus said x-ray fluorescence on the detector; wherein at least one of the first or second focusing optics is a monochromating optic providing wavelength dispersion for the focused x-rays and/or the x-ray fluorescence from the sample.