Abstract: A system and method to extend a dynamic range of fluorescence measurements. The system includes a neutral density filter stack apparatus including a plurality of neutral density filters. The neutral density filter stack modulates the intensity of light from a source. This modulation improves the ability to detect emissions from a wider-range of fluorophore concentrations, specifically addressing inner-filter effects at higher concentrations that would normally require sample dilution. It can be used in a system in which absorbance and fluorescence measurements are carried out, wherein the intensity of the light source is modulated with the apparatus for the fluorescence measurements. In this hybrid system, the stack modulates the intensity of the excitation light source for fluorescence measurements to be made at very low concentrations of analyte. The hybrid system also includes optics for absorbance measurements to be made at concentrations of analyte that are higher than those detected by fluorescence.

Abstract: A plug for an osmometry sample cup or vial is provided that seals the sample cup or vial to prevent significant evaporation of a sample solution in the cup or vial prior to obtaining an osmolality measurement.