The Agilent 5975B Gas Chromatograph Mass Spectrometer (GC/MS) is the latest version of the world's most popular GC/MS system. The instrument allows drug-testing laboratories to analyze saliva or hair rather than urine - at about half the cost of GCs using multiple mass filters - allowing users to easily and cost-effectively migrate to oral fluid and hair confirmatory testing. The key innovation of the instrument is the adaptation of the "Deans switch" technique for capillary GC. With the 5975B GC/MS, researchers no longer need to separate hundreds of peaks from long columns; instead, they can perform a preliminary separation with a first column and then direct the peak of interest to a second column for higher-resolution analysis. The 5975B GC/MS also features the first flow-controlling device that can be located inside the GC oven for good analytical performance that also withstands the constant temperature cycling of the oven without developing leaks.