A chart for concentrational calculations in quality control.

S EVERAL DIFFERENT TYPES of commercially available control specimens (Chemonitor,* Enzatrol,* and Versatol, A, A Alt., E, and E-Nt) are employed by many laboratories for quality control purposes. These control specimens may be submitted each day for each determination performed in the laboratory. Unless the concentrations of these control specimens are made to vary in some unpredictable fashion, unconscious bias on the part of the technician can detract somewhat from the value of any quality control system. The desired “blind” samples can most easily be obtained by varying the dilution of the control specimen. Those preparations which are in the dry form and are reconstituted with distilled water are the easiest to use for this purpose in that any volume from about 60 to 140% of the recommended volume may be effectively used. By thus varying the volume of water added, concentrations much higher or lower than the stated value are obtained. Of course, only one value is stated by the manufacturer for each constituent, namely, that obtained when the recommended reconstitution volume is used. For example, in the case of Versatol and Chemonitor, this value is given for dilution by the addition of 5.0 ml. of water, and in the case of Versatol E and E-N and of Enzatrol, the value is given for 3.0 ml. of water. The concentration is not simply inversely proportional to the volume added when other than the recommended volume is used. In order to calculate the concentration of a given constituent when other than the