Agilent provides a series of blind Quality Control Standards used to check whether or not your analytical system is in control. These Quality Control Samples are designed to mimic real-world samples for specific EPA methods, and are run as blind samples. The analytical data generated using the method is then compared to the true values supplied with the Agilent standard. Agreement between the data generated for the Quality Control Standard is used as a blind sample and the true values of the standard indicates that your analytical system is in control.