hi im currently running a sample for amino acid quantification. i ran some standards last week and got great results. i thought i could start running calibration curves but when i tried to run the standards to see if the machine was ok this week only solvent peaks are seen. Nothing on the machine has been changed as i am the only one using it. ive checked all my solvents and solutions and everything is great. when i run concentrated samples the results are fine. but the concentrations used last week are not seen at all. has anyone had this problem before. I have a feeling it is the detector. how do i check this?