RF (retention factor) values of pigments in chromatography are determined by several interrelated factors. Primarily, the polarity of the pigments plays a crucial role; pigments with a polarity similar to the solvent will travel further, resulting in higher RF values. Conversely, pigments that are less polar than the chromatography solvent will travel shorter distances. The type of solvent used is another significant factor, as different solvents can interact variably with pigments, affecting their travel distances on the chromatographic medium. Additionally, the affinity of pigments to the stationary phase (usually paper or silica gel) affects RF values; pigments with a higher affinity to the stationary phase will move slower and exhibit lower RF values. Factors such as the pH of the system and the temperature at which the chromatography is performed can also influence the RF values because they can alter the solubility and the state of ionization of the pigments. It's also important to note that the quality and type of paper or gel used in the chromatography can introduce variations in RF values due to differences in porosity and adsorptive properties.

Amino acids play vital roles in the human body, including serving as building blocks for proteins and sources of energy. They can be classified based on their metabolic fate into glucogenic, ketogenic, or both. Ketogenic amino acids are unique because they can be converted into acetyl-CoA or acetoacetate, which are precursors for ketone bodies production. Only two amino acids are exclusively ketogenic: leucine and lysine. Leucine, a branched-chain amino acid, is essential for protein synthesis and muscle repair. Lysine, another essential amino acid, plays a crucial role in collagen formation and calcium absorption. Both must be obtained through diet as the human body cannot synthesize them. Foods rich in these amino acids include meats, dairy products, and legumes.

Whether TPU (Thermoplastic Polyurethane) is better than PVC (Polyvinyl Chloride) largely depends on the application. TPU is known for its superior elasticity, excellent abrasion resistance, and ability to withstand higher temperatures and environmental stresses compared to PVC. This makes TPU a preferred material in industries requiring flexible, durable components such as automotive, medical devices, and footwear. However, TPU often comes at a higher cost due to its advanced properties and manufacturing processes. PVC, on the other hand, is less expensive and offers good flexibility, chemical resistance, and is easier to process, making it suitable for applications such as piping, electrical cable insulation, and clothing. In summary, both materials have their unique qualities and the choice between them should be based on specific requirements of the application like cost, performance, and environmental resistance.