Standard operating procedures , versus

Procedure Concomitantly determine the absorbance of each Standard Preparation and of the Sample Preparation at 422.7 nm, with a suitable atomic absorption spectrophotometer, following the operating parameters as recommended by the manufacturer of the instrument. Plot the absorbance of the Standard Preparations versus concentration of calcium, in micrograms per milliliter, and from the curve so obtained determine the concentration, C, in micrograms per milliliter, of calcium in the Sample Preparation. Calculate the quantity, in milligrams, of calcium in the sample taken by the formula... 

Each technique has common problems that make quantitation difficult. These include (1) the nature of the surface (smooth versus pitted, flat versus irregular), (2) definition of area to be sampled, (3) amount of pressure applied to surface, and (4) the time of application. Further, one cannot be certain of complete recovery of microbes from a cotton swab. By standardizing the sampling procedure, one can improve success and make general observations that is, the operation maybe rated as good, fair, or poor. ... 

---