Table 3.

The proposed configurations of the polar head group-related ions observed for the [M − H]⁻ ions of major phospholipid classes

Phospholipid	Head group	[M − H - R2(1) CO2H - R1(2)CH=CO]−	[M − H - R2CO2H - R1CO2H]−
GPEtn
* GPCho(M − 15)−
GPGro
GPIns
GPA	H
PS		Same as PA

^*The [M − 15]- ion from GPCho was formed from an adduct anion (such as Cl⁻) by loss of a methyl group (loss of methyl chloride).