19. Describe the procedure followed to establish the accuracy and sensitivity of a new method proposed for measurement of a certain compound in a laboratory. State how the method is verified nationally and internationally. (12pts) 20. An ion-selective electrode method was compared with a standard iodometric method for determining the concentration of dissolved sulphide in groundwater using the following results from a Blocked test. Evaluate the data and determine whether the electrode method records statistically different values from the iodometric method. (12pts)