Patent ID: 7843560

Claim:
A turbidity calibration standard comprising: (a) a number of from 1 to 5 sequentially-interfaced layers, wherein each layer independently comprises a light-permeable polymer or light-permeable interpolymer; (b) a measured light transmission modulating amount of at least one light transmission modulator, which is distributed in any one or more of the layers; and (c) a light-permeable container, which contains the layers and the at least one light transmission modulator; wherein the turbidity calibration standard is prepared by a process comprising the following steps: (a) independently providing at least one polymerizable monomer; (b) optionally, independently providing a light transmission modulator; (c) if a light transmission modulator is provided in step (b), distributing the light transmission modulator in the at least one polymerizable monomer to give a mixture of the light transmission modulator distributed in the at least one polymerizable monomer; (d) adding the at least one polymerizable monomer of step (a) and, if provided, the light transmission modulator of step (b) or adding the mixture of step (c) to a light-permeable container; (e) polymerizing the at least one polymerizable monomer in the light-permeable container to yield a first layer comprising a first light-permeable polymer or a first light-permeable interpolymer, and, optionally, a light transmission modulator distributed in the first light-permeable polymer or the first light-permeable interpolymer; and (f) repeating steps (a) to (e) from 0 to 4 more times, each time independently selecting at least one polymerizable monomer and, optionally, a light transmission modulator to further yield second to fifth layers, respectively; wherein at least one of the first to fifth light-permeable layers contains a light transmission modulator distributed therein.