UHPLC systems are plumbed with extremely narrow-bore tubing that is indiscernible to the naked eye. For this reason, tubing lengths are color coded based on internal diameter. Restek offers stainless-steel capillary tubing with colored bands: red = 0.005”; yellow = 0.007”; blue = 0.010”; and orange = 0.020”. Color coding varies by manufacturer; it is not universal. It’s also important to note that stainless-steel capillary tubing should be cut to length by the manufacturer, not by the customer. It is impossible to achieve a clean, square cut without professional machining cutters. Stainless-steel fittings with pre-swaged ferrules or EXP fittings with hybrid ferrules are used with stainless-steel tubing to achieve leak-tight seals for UHPLC at up to 20,000 psi.
The internal diameter of LC grade stainless-steel tubing is identified by the colored band on the precut lengths.
