Figure 2.

The sensitivity of the nanoflow LC-LTQ-Orbitrap MS system. (a) Correlation between the signal intensity of [CACCA-OH]²⁻ ion and the amount applied to the LC-MS system. The graph is enlarged in the boxed inset to display below 1 fmol. The system exhibited essentially the same sensitivity for the oligonucleotides UUUCGUdCdA-OH, CUCAGUdTdT-OH, or AAUUCGAdTdT-OH (data not shown). (b and c) Mass chromatogram and spectrum of the synthetic oligonucleotides (100 amol). Chromatography was performed at a flow rate of 100 nl/min as described in the Methods section. (b) Extracted ion monitoring of four oligonucleotide ions extracted from a single LC-MS chromatogram. The mass of each oligonucleotide and mass window used were: CACCA-OH; 754.63 ± 0.5 Da, UUUCGUdCdA-OH; 1206.16 ± 0.5 Da, CUCAGUdTdT-OH; 1220.18 ± 0.5 Da and AAUUCGAdTdT-OH; 1396.71 ± 0.5 Da. (c) the MS spectrum of [CACCA-OH]²⁻ ion.