Figure 1. Positive ion atmospheric pressure photoionization mass spectrum (APPI(+)-MS) of dihydroxy polyisobutylene (HO-PIB-OH) in CCl4 at toluene concentration of 0.067 v/v. The toluene concentration represents the volume fraction of the toluene with respect to the total (sample and carrier) feed. The concentration of the HO-PIB-OH in the sample feed was 0.5 mM. (Total flow rate: 225 mL/min).
Figure 2. APPI(+)-MS/MS spectrum of precursor ion of m/z 1486 of dihydroxy polyisobutylene (HO-PIB-OH). Collision energy = 50 eV (in the Lab frame). For other experimental details see Fig. 1 caption. a and b on the top of mass numbers represent the product ion series formed from precursor [HO-PIB-OH+H]+ ions by bond cleavage as indicated in Scheme 1.
Scheme 1. Formation of product ion series a and b from the [HO-PIB-OH+H]+ ions.
The measured and the calculated monoisotopic masses for the precursor ion (m/z 1486) are 1484.5769 and 1484.5778 (composition: C104H203O2), respectively. The good agreement between the measured and the calculated masses strongly supports the formation of [M+H]+ ions from HO-PIB-OH.
As seen in Fig. 2. and Scheme 1 two major product ion series (a and b) were formed by bond-cleavage as shown. The compositions of product ions were determined using their accurate m/z values. For example, the measured monoisotopic m/z value of the ion at m/z 115 is 115.1142 and the only composition calculated with m/z tolerance of 0.005 is C7H15O in good agreement with the composition of a-ion with m=0 (see Scheme 1). Similarly, the composition for the ion at m/z 171 was found to be C11H23O (measured/calculated m/z: 171.1779/171.1743, corresponding to an a-ion with m=1). The same procedure was applied for the b-ions to determine the composition unambiguously.
It is also evident from Fig. 2. that the intensities of a-ions are much higher than those of b-ions.
Interestingly, no formation of product ions associated with water or methanol losses were observed.