Automated fragment formula annotation for electron ionisation, high resolution mass spectrometry: application to atmospheric measurements of halocarbons

Table 5 Behaviour of the likelihood estimator: ten first knapsack fragments for CFC-11 and \(\text {CCl}_{{4}}\), set out in order according to their likelihood value calculated at the first iteration of Step 5. Some fragments may be deleted at subsequent iterations

Fragment	Exact mass	% Assigned signal of the fragment	% Assigned signal of all (sub)fragments	Likelihood	Ranking	Maximal fragment?
CFC-11 (\(\text {CFCl}_{{3}}\))
\(\text {CFCl}_{{3}}^{+}\)	135.90496	0.0	98.4	88.6	1	True
\(\text {CFCl}_{{2}}^{+}\)	100.93611	81.9	96.3	84.3	2	False
CFCl\(^{+}\)	65.96726	5.6	11.9	11.9	3	False
*CHFCl\(^{+}\)	66.97508	0.0	12.0	9.3	4	True
\(\text {CCl}_{{3}}^{+}\)	116.90656	2.1	10.0	8.0	5	False
* \(\text {CHCl}_{{3}}^{+}\)	117.91438	0.0	10.2	7.9	6	True
\(\text {CCl}_{{2}}^{+}\)	81.93771	2.6	8.0	6.0	7	False
* \(\text {CHCl}_{{2}}^{+}\)	82.94553	0.0	8.1	5.8	8	False
CCl\(^{+}\)	46.96885	3.1	5.4	5.4	9	False
\(\text {C}_{{3}}\text {Cl}_{{2}}^{+}\)	105.93771	0.0	8.0	3.2	10	False
\(\text {CCl}_{{4}}\)
\(\text {CCl}_{{3}}^{+}\)	116.90656	71.2	92.4	73.9	1	False
* \(\text {CHCl}_{{3}}^{+}\)	117.91438	0.4	93.9	73.0	2	True
* \(\text {CHCl}_{{2}}^{+}\)	82.94553	0.5	22.3	16.0	3	False
\(\text {CCl}_{{2}}^{+}\)	81.93771	11.6	21.2	15.9	4	False
*\(\text {COCl}_{{2}}^{+}\)	97.93262	0.3	21.8	12.1	5	True
CCl\(^{+}\)	46.96885	5.5	9.5	9.5	6	False
* HCl\(^{+}\)	35.97668	0.7	4.7	4.7	7	False
Cl\(^{+}\)	34.96885	4.0	4.0	4.0	8	False
* \(\text {CF}_{{2}}\)Cl\(^{+}\)	84.96566	0.2	9.7	3.6	9	True
* \(\text {OCl}_{{2}}^{+}\)	85.93262	0.3	4.3	2.2	10	False

\(1^{\mathrm{st}}\) column: chemical formula of the fragment, containing only abundant isotopes. * indicates that the fragment is not part of the molecular ion. \(2^{\mathrm{nd}}\) col.: calculated exact mass of ionised fragment. \(3^{\mathrm{rd}}\) col.: percent signal of the fragment and its isotopocules relative to the total measured signal. \(4^{\mathrm{th}}\) col.: percent signal of the fragment, all its sub-fragments and all associated isotopocules relative to the total measured signal, computed from Eq. (5). \(5^{\mathrm{th}}\) col.: likelihood value computed from Eq. (6). \(6^{\mathrm{th}}\) col.: ranking according to decreasing likelihood value. For CFC-11, \(\text {CFCl}_{{3}}\) ranked first is the molecular ion

ISSN: 1758-2946