Geometric dilution

Step 3 Determine the capsule size by using the rule of six. Capsule size 3 can hold 3 grains or 195 mg. Weigh 200 mg of the tablet mixture (which is obtained as 2000 mg of total powder/10 capsules) and try to fill in capsule size 3. If the capsule is not filled or it is too full, go for the next capsule size, i.e., 2 which holds approximately 4 grains or 260 mg of powder. Verify the appropriateness by filling one or two capsules of size 2. If appropriate, select this size. For 10 capsules, the total powder should be 2600 mg. Therefore add 600 mg of lactose in the tablet mixture of 2000 mg by geometric dilution. Transfer the 2600 mg of powder on a clean paper or an ointment tile, compress as a cake, and fill all the capsules by a sliding motion. 

Step 3 By the rule of six capsule size 4 can hold a total powder quantity of about 130 mg. Considering this amount, the total amount of powder for twelve capsules of size 4 is 1560 mg. The amount of lactose that should be added for twelve capsules is 1080 mg (calculated as 1560 mg - 480 mg = 1080 mg). Therefore, weigh 1080 mg of lactose and add to the drug mixture by geometric dilution. As a confirmation of the size, fill one or two capsules of size 4 with 130 mg of the mixture and determine the appropriateness. If the capsule size is correct, punch out the remaining capsules after forming a cake on a powder paper or an ointment tile. 

If a preliminary dilution step is deemed necessary before the geometric dilution series, as recommended in the case of heavily polluted wastewater, the preliminary dilution step, for example, should be 1 64 or 1 128. If it is necessary to obtain LC0 values for determining the pT-value, then the geometric dilution series with the factor of 1 2 must be followed through from the first dilution step. This is required in the fish test according to DEV L31 (1989) (Section 5.3). The same is required for other quantal tests like the Daphnia test, where 9 of 10 animals must survive. 

Table 2. Geometric dilution series, pT-values andpT-indices for wastewater effluents. The pT-values of receiving surface waters and of final effluents from wastewater treatment plants determined thus far are marked by the sign +.

The pT-values of geometric dilution series are always integers, and the resulting pT-value of 11.6, as in this example, is ultimately reported as a pT-value of 12. Hence, by convention, calculated pT-values, determined from the relationship between concentration and effect, are always rounded-up to integers. 

The pT-values obtained without calculation from the standard pT-method are also listed in Table 3. As explained previously (Section 5.4), pT-values of each geometric dilution series are rounded up to whole numbers from IC 19 values. 

Figure 1. Multiple bioassay examination of porewater and elutriate of sediment core sample AS 3" collected from the River Saar. The pT-scale is based on a geometric dilution series with the factor 2 (Krebs, 1999).

The sensory evaluation differentiates between the stimulation threshold (a just detectable level where a perceptible but not yet definable deviation of the sample from the standard is observed) and the recognition threshold, a level where the odor is identifiable or creates odor problems (a no longer tolerable quality deterioration caused by a definite off odor and/or taste). The difference between a perceptible and identifiable level is usually only one to two steps of a geometric dilution series. Therefore, only undifferentiated odor and taste thresholds are given in Table 13-6, because of the very different sensitivities of individual testers. The perceptible (stimulation) levels of a less sensitive tester can overlap with the identifiable (recognition) level of another more sensitive tester. 

Geometrically dilution (Triturating) Mixing using the ratio 1 1 repeatedly... 

For small batches it is a good choice to break up the agglomerates in a plastic or stainless steel mortar with a plastic pestle. The agglomerated active substance may be triturated with some other solid substance or with no more than an equal volume of molten base. After trituratirai with a solid, the mixture is incorporated in the molten base, at first in an equal volume, thereafter the remaining base is added part by part (geometric dilution, see Sect. 29.4.4). 

Subsequently the triturate has to be mixed with the remainder of the base by geometrical dilution, see Sect. 29.7.2. 

Isosorbide dinitrate is used in the treatment of anal fissures. The substance is explosive. For safety reasons it is used as a 40 % dry mixture with a powder base. According to Ph. Eur. it may contain mannitol or lactose monohydrate. Commercially available mixtures usually contain lactose monohydrate and isosorbide dinitrate in a crystalline or amorphous form. They are mixed with the cutaneous base via geometrical dilution (see Sect. 29.4.1). 

Stir if necessary the active substance intensely with a small amount of base as a premix, comparable to the first step in geometric dilution using mortar and pestle (see Sect. 29.3.3). 

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