Figure 1: Specificity of method. A) MRM of blank plasma, B) MRM of spiked plasma, C) MRM of samples from patients after NVP+AZT+LPV+RTV treatment, a,b,c,d,e,f,g and h represent the spectrum of IS, NVP, 3TC, d4T, AZT, EFV, LPV and RTV respectively.