End point evaluation

The collection of problems at the formulation stage, which identifies the compound or activity of concern, the persons or species to be protected, and the effect and end-point evaluation. 

A neuropsychological evaluation of 148 of the Boston cohort children at age 10 years confirmed the continued presence of the association noted at 5 years of age (Bellinger et al. 1992). The primary end points evaluated were the WISC-R and the Kaufman Test of Educational Achievement (K-TEA). 

Properly defined BE end points (evaluated by Clinical Team)... 

The subcommittee found the Dulaney et al. (1985) studies to be even weaker than the Bucci et al. (1992) study for deriving the RfD for GA. Only one dose was used in the 85-day study and the only toxicity end points evaluated were growth rate and AChE activity in the brain. Similarly, even though the 25-day study included two doses, the only effect considered was mortality, an inappropriate end point for deriving RfDs. The subcommittee found no oral studies that involved repeated exposure to GA and no other suitable toxicity studies for deriving the RfD for GA. Thus, the subcommittee agrees with ORNL that the study by Bucci et al. (1992) is the most appropriate of the available studies for derivation of the RfD for GA. 

Presentation of each study by the research team that conducted the study was followed by an expert panel evaluation that examined each study, taking into consideration the exposure data, experimental design and statistical analysis, potential confounders and variables, and neurobehavioral end points evaluated. 

Under the conditions of this study and based on the toxicoiogicai end-points evaluated, the NOEL was the highest dose tested—nameiy, 1100 mg/kg, equivaient to 92 and 97 mg/kg bw per day in the non-recovery group male and female rats, respectively, and 94 and 97 mg/kg bw per day in the recovery group male and female rats, respectively (Everds, 2005 Funk, 2005 Merkel, 2005). 

Sketching an Acid—Base Titration Curve To evaluate the relationship between an equivalence point and an end point, we only need to construct a reasonable approximation to the titration curve. In this section we demonstrate a simple method for sketching any acid-base titration curve. Our goal is to sketch the titration curve quickly, using as few calculations as possible. 

Oil Absorption. The Gardner mb-out (ASTM D281) method is used for this evaluation. A 5-g sample of mica is placed on a smooth glass plate, and linseed oil is added by drops. The mica is constantiy mixed while the oil is being added. The end point is reached when the mica becomes saturated with oil. The amount of oil per 45.4 kg of mica is calculated as follows ... 

In acid-base titrations the end point is generally detected by a pH-sensitive indicator. In the EDTA titration a metal ion-sensitive indicator (abbreviated, to metal indicator or metal-ion indicator) is often employed to detect changes of pM. Such indicators (which contain types of chelate groupings and generally possess resonance systems typical of dyestuffs) form complexes with specific metal ions, which differ in colour from the free indicator and produce a sudden colour change at the equivalence point. The end point of the titration can also be evaluated by other methods including potentiometric, amperometric, and spectrophotometric techniques. 

Procedure. Place 45 mL of the supporting electrolyte in the cell and fill the isolated cathode compartment with the same solution to a level well above that in the cell. Pipette 5.00, 10.00, or 15.00 mL of the 0.01 M antimony solution into the cell and titrate coulometrically with a current of 40 milliamps. Stir the solution continuously by means of the magnetic stirrer and take e.m.f. readings of the Pt-S.C.E. electrode combination at suitable time intervals the readings may be somewhat erratic initially, but become steady and reproducible after about 3 minutes. Evaluate the end point of the titration from the graph of e.m.f. vs counter reading this shows a marked change of e.m.f. at the end point. If it proves difficult to locate the end point precisely, recourse may be made to the first- and second-differential plots. 

Plot the titration curve (potential in millivolts vs S.C.E. against volume of standard EDTA solution) and evaluate the end point. In general, results accurate to better than 0.1 per cent are obtained. Brief notes on determinations with various metal ion solutions follow. 

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