Glossary of Terms - X

X Chromosome
A sex chromosome that usually occurs paired in each female cell and single in each male cell in species in which the male typically has two unlike cell chromosomes.

Xenobiotics
Industrial chemicals that have a chemical structure not found in natural compounds that may resist degradation by microorganisms.

XPS(X-Ray Photoelectron Spectroscopy) or ESCA (Electron Spectroscopy for Chemical Analysis)
A surface-sensitive technique capable of detecting all elements with an atomic number greater than that of helium. ESCA provides data on the outermost several atomic layers of a material, and has a sensitivity in the order of 0.5 atomic percent. A primary advantage of ESCA is that it can both determine and quantify the chemical state of the elements detected (i.e. metallic state or oxide state).