From the article above:
"To use the commercial product, a laboratory reconstitutes the vial of freeze-dried LAL with endotoxin-free water. An equal amount of reconstituted LAL, usually 0.1 ml, is then added to the sample solution in a small, glass, endotoxin-free test tube. The mixture is then incubated at 37C for one hour. At the end of this time, the mixture is examined for gel formation by gently inverting the tube. If sufficient endotoxin was present in the sample, a firm gel, one that can withstand inversion of the tube, is formed. Knowing the sensitivity of the LAL then allows the investigator to determine the quantity of endotoxin in the sample. If the sample is found to contain an amount that exceeds the limit set by the FDA, the sample failsand the lot of pharmaceutical product must be rejected."