Free radicals are highly reactive molecules or ions containing unpaired electrons. Free radicals are likely to take part in chemical reactions.

Gas chromatography is a process to separate gas molecules of different size due to their different adsorption at macroporous surfaces, e.g. at activated charcoal. The separation is managed by the use of starting gas or heating up.

Iodinated contrast agents (typically iodine-substituted benzene derivatives) are bound either in nonionic or ionic compounds. Ionic contrast agents consist of the negatively charged anion and the positively charged cation. Used components of the anion are for example diatrizoate, iodamide, iothalamate or metrizoate and of the cation the sodium or meglumine ion. The osmotic pressure depends on the number of particles in solution. Ionic contrast agents have a greater osmolarity; double that of nonionic contrast agents due to delivering more iodine atoms per molecule.
Ionic contrast agents were developed first and are still in use depending on the examination. Iodine based contrast media are water soluble and as harmless as possible to the body. However, ionic agents have more side effects compared to nonionic contrast agents due to their high osmolarity.

See also Ionic Dimer.

Ionization is the process of converting an atom or molecule with no electrical charge into an ion by adding or removing charged particles such as electrons or other ions, through high temperatures, electrical discharges, radiation etc.

See also Ion.

(K) The SI unit of temperature.
Definition: One Kelvin is 1/273.16 of the difference between the triple point of water (at exactly 273.16 K) and absolute zero.
The triple point of water is the temperature at which water can exist simultaneously in the gaseous, liquid, and solid states. Absolute zero is the temperature at which all molecular motion discontinues. 0 K is according to -273.15° Celsius and -459° Fahrenheit.