Diaryl monoalkyl phosphites tend to be used with phenates and blends of phenates with carboxylates. In plasticized PVC compounds, both the metal ligand and the phosphite must be matched to the solubility parameter of the plasticizer. Long-chain alkyl phthalates, for example, should be accompanied by relatively long-chain metal carboxylates and dialkyl phosphites. More polar plasticizers call for the use of shorter-chain carboxylate or phennate ligands and diaryl monoalkyl phosphites. Tris nonylphenyl phosphite (TNPP) is poxy oducts currently the only FDA-sanctioned phosphite for use in plasticized PVC. Although triaryl phosphites are the least efficient in PVC (aryl groups cannot partici pate in the Arbuzov reaction), TNPP remains the only choice for food-contact applications.