The present invention provides a method and apparatus for rapid measurement of a fluid bulk analyte, requiring only microscale volumes. Several fluid bulk analytes can be measured simultaneously and, for biological samples, the cell content can also be measured simultaneously. The invention comprises reporter beads for chemical analysis of fluid bulk properties such as pH, oxygen saturation and ion content. Each reporter bead comprises a substrate bead having a plurality of at least one type of fluorescent reporter molecules immobilized thereon. The fluorescent properties of the reporter bead are sensitive to a corresponding analyte. Reporter beads are added to a fluid sample and the analyte concentration is determined by measuring fluorescence of individual beads, for example in a flow cytometer. Alternatively, reporter molecules which change absorbance as a function of analyte concentration can be employed.