D3 m1a

Acetonitrile of chromatographic grade was purchased from Merck KGaA (Darmstadt, Germany). A solution of formic acid (HCOOH) was purchased from Fluka (Muskegon, USA). Ammonium formate and malic acid were obtained from Sigma-Aldrich (St Louis, MO, United States). Adenosine, N⁶-methylAdenosine, N¹-methylAdenosine, 2′-O-methylguanosine (G_m), N¹-methylguanosine, N²-methylguanosine (m²G), 2′-O-methylcytidine, uridine, 3-methyluridine (m³U), 5-methyluridine (m⁵U), and 2′-O-methyluridine and isotopically labeled standards, including [¹³C₅] A, [D₃] m⁶A, [D₃] m¹A, [D₃] C_m, [¹³CD₃] m⁵C, [¹³C₅N₂] U, [D₃] U_m, [¹³C₅] m⁵U, and [D₆] m^2,2G, were purchased from Toronto Research Chemicals (Toronto, Canada). In order to purify water, a Milli-Q water purification device was used (Millipore, Milford, MA, United States).

Chromatographic grade acetonitrile was bought from Merck KGaA (Darmstadt, Germany). Formic acid was obtained from Fluka (Muskegon, MI, USA) and water was obtained from a Milli-Q water purification apparatus (Millipore, Milford, MA, USA). Malic acid, ammonium formate and m⁵C were bought from Sigma-Aldrich (St Louis, MO, USA). Nine other methylated nucleosides, [D₃]m⁶A, [D₃]m¹A, [D₃]m⁶A_m, [D₃]U_m, [¹³C₅]m⁵U, [¹³C¹⁵N₂]G and [¹³C₅]C, were purchased from Toronto Research Chemicals (Toronto, Canada); [¹³C₅]A_m and [¹³C₅]m⁵C were synthesized previously [3 (link),4 (link)].