Methods of testing HIV viral load are described. The methods comprise detecting HIV viral RNA in a sample of leukocyte-depleted blood. Such methods can be carried out on low-volume samples obtained without the need for venipuncture or a centrifuge. The methods are particularly suited for HIV viral load testing in resource-limited settings. Methods for monitoring HIV infection are also described, as well as kits for carrying out the methods.

The present disclosure is directed to methods and systems for detecting a substance in a sample gas. The methods and systems include separating the substance of interest in the sample gas, and introducing the separated sample gas into a detector. The systems and methods further include performing an analysis of the substance of interest.

A system and method for performing staggered separations are described. The system includes a plurality of solvent pumps; a plurality of proportioning valves each being in fluid communication with one of the solvent pumps, each proportioning valve having an inlet to receive a solvent from the respective one of the solvent pumps and having a plurality of outlets, wherein the proportioning valves are configured to control a flow of the solvent from each of the outlets; and a plurality of separation devices each in fluid communication with one of the outlets. Each of the separation devices receives a solvent mixture having a composition defined by the flows of the solvents from each of the respective outlets.