小中大可能是你的溶剂（甲醇和乙腈或者其他溶剂）带来的，下面是一些容易污染质谱的化合物，279就在其中：
m/z Ion Compound
42 (M+H)+ acetonitrile
59 (M+NH4)+ acetonitrile
64 (M+Na)+ acetonitrile
65 (2M+H)+ methanol
79 (M+H)+ DMSO
83 (2M+H)+ acetonitrile
85 (M+H)+ d6-DMSO
101 (M+Na)+ DMSO
102 (M+H)+ triethylamine (TEA)
104/106 (M+Cu)+ acetonitrile
105 (2M+Na)+ acetonitrile
120 (M+Na+CH3CN)+ DMSO
122 (M+H)+ Tris
123 (M+H)+ dimethylaminopyridine (DMAP)
130 (M+H)+ diisopropylethylamine (DIPEA)
144 (M+H)+ tripropylamine (TPA)
145/147 (2M+Cu)+ acetonitrile
146 (3M+Na)+ acetonitrile
150 (M+H)+ phenyldiethylamine
153 (M+H)+ 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
157 (2M+H)+ DMSO
159 (M+Na)+ sodium trifluoroacetate
169 (2M+H)+ d6-DMSO
179 (2M+Na)+ DMSO
186 (M+H)+ tributylamine
214 (M+H)+ unidentified contaminant, maybe related to methanol
225 (M+H)+ dicyclohexyl urea (DCU)
239/241 [(M.HCl)2-Cl]+ triethylamine
242 M+ tetrabutylammonium (C4H9)4N+
243 M+ trityl cation
257 (3M+H)+ DMSO
273 M+ monomethoxytrityl cation (MMT)
279 (M+H)+ dibutylphthalate (plasticiser)
301 (M+Na)+ dibutylphthalate (plasticiser)
317 (M+K)+ dibutylphthalate (plasticiser)
338 (M+H)+ erucamide
360 (M+Na)+ erucamide
391 (M+H)+ diisooctyl phthalate (plasticiser)
413 (M+Na)+ diisooctyl phthalate (plasticiser)
425 (M+Na)+ unidentified contaminant (plasticiser)
429 (M+K)+ diisooctyl phthalate (plasticiser)
449 (2M+H)+ dicyclohexyl urea (DCU)
454 (M+Na+CH3CN)+ diisooctyl phthalate (plasticiser)
798 (2M+NH4)+ diisooctyl phthalate (plasticiser)
803 (2M+Na)+ diisooctyl phthalate (plasticiser)
