Repeating Units Observed in LC-MS Background

Ion Mass Accurate Mass (Da) Mode Compound
+14n14.0157+[CH2], Alkane chains
+15n15.9949+O, Oxidation
+18n18.0106+/-Water clusters
+28n28.0313+[C2H4], natural alkene chains
+32n32.0262+Methanol clusters
+41n41.0266+Acetonitrile clusters
+42n42.0470+[C3H6], propyl repeating chains
+44n44.0262+Polyethylene glycol related (-CH2CH2O-)n, PEG
+50n49.9968+[CF2], perfluoro compounds
+53n53.0032+Ammonium chloride adducts (NH4Cl)
+56n56.0626+[C4H8], Butyl repeating units
+58n58.0419+Polypropylene glycol related (CH2CH2CH2O)n
+58n57.9586+NaCl adducts (distinguishable from PPG by Cl Isotope pattern)
+63n63.032+Ammonium formate adducts (HCOONH4)
+68n67.9874+/-Sodium formate adducts (HCOO-Na)
+72n72.0395+Replacement of –OH by –OSi(CH3)3
+74n74.0188+/-Polysiloxanes (Si(CH3)2O)
+74n73.9326+KCl adducts (distinguishable by Cl isotope pattern)
+77n77.0477+Ammonium acetate salts (CH3COONH4)
+78n78.0139+DMSO adducts ((CH3)2SO)
+82n82.0031+/-Sodium acetate adducts (CH3COONa)
+114n113.9929-TFA (trifluoroacetic acid) adducts (CF3COOH)
+122n121.9383-Sodium perchlorate adducts (NaClO4)
+136n135.9748+/-Sodium TFA (trifluoroacetic acid) adducts (CF3COONa)
+162n162.0528+Polysaccharides (C6H10O5)
+226n226.1681+[C12H22N2O2] cyclic oligomers from polyamide
+288n288.1371-SDS (sodium dodecylsulfate) adducts (CH3(CH2)11OSO3Na)