There are strictly two types of relative recoveries. One is the recovery test method and the other is the spiked sample recovery test method. The former is the addition of drugs in the blank matrix, the standard curve is also the same, this determination is used more, but there is a suspicion that the standard curve duplicate determination. The second is to add drugs in the known concentration of the sample, to and standard curve than the standard curve, the standard curve is also in the matrix with drugs.