These sterile, polystyrene loops and needles are calibrated using a standard urea solution. A Thermo Scientific Nunc™ calibration certificate can be obtained upon request. With no need to flame, these loops and needles save you time. The risk of contamination is eliminated since these instruments are disposable. The surface of each loop and needle receives a special hydrophilic treatment to enhance the adhesion of droplets and prevent accidental discharge. Loops are color coded for easy identification.