soil loading the uk test soil and method for surgical instruments surgical instrument trays bowls dishes and receivers described in annex n of iso 15883 5 was used to assess cleaning efficacy against heavily soiled instruments 100 ml of fresh egg yolk was placed in a mixing bowl along with 10 ml of defribrinated horse blood serum australis and 2 0 g of porcine mucin sigma aldrich the ingredients were then mixed using an orbital blender until a homogeneous blend was achieved the test soil was then applied to various representative surgical instruments such as clamps forceps scissors speculums and retractors using a paint brush ensuring that the more complex and occluded parts of the instruments such as box hinges etc were liberally coated in soil the instruments were then allowed to dry for at least 1 hour before loading into the washer after cleaning the instruments were then inspected visually for the presence of soil and then swabbed and the swab tested with ninhydrin solution to determine the presence absence of protein after cleaning using the samsung washer using the u201c quick 50 u201d program the instruments were visibly clean swabbing the surface of the instruments particularly around the hinge joints etc with a cotton wool swab and then applying a drop of a 2 ninhydrin solution in ethanol followed by warming the swab to 60 u00b0 c in an oven demonstrated the absence of any protein residues three additional formulations were prepared two comparative formulations examples 7 and 8 were prepared using low foaming surfactants whereas examples 9 and 10 were prepared without surfactants but with triethanolamine phosphoric acid sodium gluconate and a blend.