Described are devices for and methods of modulating a fluid sample. The devices (10, 40, 60, 80, 100, 130, 160, 220) include at least one sample-modulating component (20, 76, 78, 90, 110, 112, 116, 150, 152, 154, 162, 164, 182, 184, 186, 222, and 230) and, in some embodiments, two or more sample-modulating components. The sample-modulating components are each capable of performing a function selected from the following group: concentrating the sample to increase a concentration of a first constituent of the sample; diluting the sample to decrease a concentration of a second constituent in of the sample; desalinating the sample to decrease the total moles of salt in the sample volume or causing a temporary decrease in the osmolarity; adjusting pH of the sample to bring a pH of the sample into a predetermined range; absorbing one or more nonpolar substances to decrease a concentration of the nonpolar substances; and delivering one or more reagents to the sample to provide a desired concentration of the reagent in the sample.