Mass Trace

The application of trifluoroacetic acid (TFA) for ion pairing purposes in LC separation led to a retention shift of all constituents contained in the formulation. The AS and AES that eluted first, but were delayed compared with RP-Ci8 gradient elution, could be observed with a tremendous improvement in peak shape (RT = 9.0—12.5 min) in the total ion mass trace after ESI(+) ionisation (Fig. 2.5.11(c)). AE and amine oxides were not observed during the recording time of 30 min. 

Therefore, a C13-AE, a cationic (quaternary ammonium) surfactant (quat), an amphoteric Ci2-alkylamido betaine, and the non-ionic fatty acid diethanol amide (FADA) as presented with their FIA-MS spectra in Fig. 2.5.12(a)-(d) were analysed as pure blends and as mixtures always obtained from two blends in FIA-MS multiple ion detection mode (MID). Mixtures as well as pure blends contained identical concentrations of surfactant homologues. For AE quantitation the mass traces of all A m/z 44 equally spaced homologues (m/z 306-966) of the C13-AE were recorded. The cationic (quaternary ammonium) surfactant, the amphoteric Ci2-alkylamido betaine, and the non-ionic FADA were quantified recording the mass traces at m/z 214 and 228, or 184, 212, 240, 268, 285, 296, 313, 324 and 341, or 232,260, 288, 316 and 344, respectively. 

To recognise ion suppression reactions, the AE blend was mixed together either (Fig. 2.5.13(a) and (b)) with the cationic quaternary ammonium surfactant, (c, d) the alkylamido betaine compound, or (e, f) the non-ionic FADA, respectively. Then the homologues of the pure blends and the constituents of the mixtures were quantified as presented in Fig. 2.5.13. Ionisation of their methanolic solutions was performed by APCI(+) in FIA-MS mode. The concentrations of the surfactants in the mixtures were identical with the surfactant concentrations of the blends in the methanolic solutions. Repeated injections of the pure AE blend (A 0-4.0 min), the selected compounds in the form of pure blends (B 4.0—8.8 min) and their mixtures (C 8.8— 14.0 min) were ionised and compounds were recorded in MID mode. For recognition and documentation of interferences, the results obtained were plotted as selected mass traces of AE blend (A b, d, f) and as selected mass traces of surfactant blends (B a, c, e). The comparison of signal heights (B vs. C and A vs. C) provides the information if a suppression or promotion has taken place and the areas under the signals allow semi-quantitative estimations of these effects. In this way the ionisation efficiencies for the pure blends and for the mixture of blends that had been determined by selected ion mass trace analysis as reproduced in Fig. 2.5.13, could be compared and estimated quite easily. 

Fig. 2.6.2. APCI-LC-MS(+) TIC chromatogram (6) and selected mass traces of (2) and (3) of octylphenolethoxylates (OPEOs) together with (4) and (5) their alicyclic homologues, the octylcyclohexanolpolyglycolether (1) UV trace 220 nm presenting...

For confirmation of low concentrations of NPEO homologues in complex samples from the Elbe river, APCI—LC—MS—MS(+) was applied to record the substance-characteristic ion mass trace of m/z 291. The SPE isolates contained complex mixtures of different surfactants. The presence of NPEOs in these complex samples was confirmed by generating the precursor ion mass spectrum of m/z 291 applying MS— MS in the FIA-APCI(+) mode. This spectrum, showed in Fig. 2.6.5, presents the characteristic series of ions of NPEOs at m/z 458, 502,...,678, all equally spaced with A m/z 44 u. Besides the NPEOs, small amounts of impurities could be observed because of the very low concentrations of NPEOs in the water sample [25]. In the foam sample, the identity of NPEOs could be easily confirmed by APCI-FIA-MS-MS(+) because of their high concentrations in this matrix. The LC-... 

Fig. 2.8.8. APCI-MS and HPLC-APCI-MS of a PEMS and PEG. (a) APCI-FIA-MS(+) overview spectrum of a commercial blend of PEMS showing the precursor PEGs (starting at m/z 300,... A m/z 44 u) from chemical synthesis (b) Averaged APCI-LC-MS(+) mass spectrum of PEMS (RT 10.0-13.5 min) from the chromatogram shown in (c) (c) APCI-LC-MS(+) chromatogram of a commercial blend of PEMS acquired in total ion current (TIC) mode (d)-(g) selected mass traces of [M + NH4P ions of PEMS (m/z 516, 560, 604 and 648) and PEG homologues (m/z 520, 564, 608 and 652) (h) APCI-LC-MS(+) chromatogram of PEG in TIC mode [41].

Surface water samples often contain surfactants and their metabolites. After Cis-SPE combined with selective elution [7,9,10] the metabolites, PEG and PPG, were observed in the ether fraction (PPG) or in the combined methanol-water and methanol (PEG) fractions, respectively. They could be ionised in the form of their [M + NH4]+ ions applying ESI-FIA-MS(-I-) in combination with ammonium acetate for ionisation support. ESI-LC-MS(-I-) resulted in an excellent separation of both metabolites, as presented in the total ion current (TIC) trace in Fig. 2.9.6(7) together with selected mass traces of PEG (m/z 300, 344 and 388) and PPG (m/z 442, 500, 558) (Am/z 44 and 58) in Fig. 2.9.6(l)-(6) [36],... 

Fig. 2.9.6. (Inset) ESI-FIA-MS(+) overview spectrum of (a) PEG homologues and (b) PPG homologues contained in wastewater effluent SPE extract (7) ESI-LC-MS(+) RIC and selected mass traces of (l)-(3) PEG and (4)-(6) PPG homologues from mixture of (a) and (b) CiS-SPE with selective elution, compounds ionised as [M + NH4]+...

Fig. 2.9.7. (a) ESI-FIA-MS(+) and (b) APCI-FIA-MS(+) overview spectra of synthetically produced mixture of di-carboxylated PEG homologues (f) APCI-LC-MS(+) and (j) APCI-LC-MS(-) RICs of mixture as in (a,b) (c-e) selected mass traces of di-carboxylated PEG homologues under positive and (g-i) negative ionisation. Gradient elution separated by RP-Ci8 column [24]. 

The RIC of LC separation performed in a very time consuming manner using RP-C1H was not very convincing, whereas mass trace analysis showed a separation [16]. As an example of the results obtained... 

Under RP-Cis column separation conditions, no differentiation between conventional AE and fluorinated AE in retardation behaviour could be observed. The application of a perfluorinated RP-C8 column to a mixture of standards of non-ionic fluorinated surfactants and the extracts of wastewater sludges spiked with these compounds using realistic concentrations, however, resulted in good separation of AE and fluorinated AE (cf. mass traces and TIC in Fig. 2.9.46(a), (b) or (e) and Fig. 2.9.46(c), (d) or (e), respectively) or matrix and fluorinated AE surfactants (Fig. 2.9.46(f), (g) or (h), respectively) [52]. 

Fig. 2.9.46. (e) APCI-LC-MS(+) RIC of a mixture of standards containing a conventional AE blend (C12 and C14 homologues) and a fluorinated non-ionic surfactant blend (C F2 +i-(CH2-CH2-0)m-H n = 6 and 8) (a)-(d) selected mass traces of conventional C12 and C14 AE compounds or CB and Cg fluorinated AE compounds (h) APCI-LC-MS(-I-) RIC of wastewater sludge extract containing non-ionic fluorinated surfactants (f) and (g) selected mass traces of C6 and C8 fluorinated AE compounds extracted from sewage sludge. Gradient elution separated on perfluorinated RP-Cg column [52]. 

The RP-Cis LC separation of this mixture of aliphatic linear alkane sulfonates (CnH2n+i—SO3) and SAS from an industrial blend in combination with APCI—LC—MS(—) detection is presented as total ion mass trace (Fig. 2.11.2(f)) together with selected mass traces (m/z 277, 291, 305 and 319 for (re +x = 11-14)) in Fig. 2.11.2(b)-(e), respectively. The resolved mass traces proved the presence of large number of isomers of every SAS homologue in this blend. This complexity is generated because of the linear isomer precursor and the mixture of branched alkyl precursor compounds applied to chemical synthesis [22], In parallel to elution behaviour observed in GC the branched isomers of alkylsulfates in LC separation were expected to elute first. 

For comparison of the different ionisation methods and detection modes, the results obtained as FIA overview spectra are presented in Figs. 2.11.7 and 2.11.8. Reconstructed ion chromatograms (RIC) of APCI and ESI combined with selected mass traces of all LC separations and, in parallel, the selected standardised mass traces of the C42 and C14 homologues containing three ethoxy chain links recorded in the negative mode are presented in Fig. 2.11.9. These results again demonstrate the quite large variation in the ionisation efficiency of... 

Fig. 2.11.13. APCI-LC-MS(+/-) RICs and selected mass traces of an AEC blend as in Fig. 2.11.12 gradient elution separated by RP-Clg column [61].

The FIA-MS(—) overview spectrum is presented in Fig. 2.11.16. It shows the di-NPEC homologue ions all equally spaced by Am/z 44. The ion starting at m/z 535 contains three ethoxylate units while the homologue at m/z 1019 represents a molecule with 14 EO units. In the APCI-LC-MS(+/—) mode, RICs and the selected mass traces at m/z 760 or 799 represent the di-NPEC homologue with nine EO units in the form of [M — CH2 — C02 + NH4]+ or [M — H] ions as shown in Fig. 2.11.17. Under positive ionisation conditions, the detection of the NPEO homologues ionised as [M + NH4]+ ions are favoured in the reconstructed ion mass trace (b) [22,61]. 

Fig. 2.11.19. APCI-LC-MS(+) (2) and APCI-LC-MS(—) (4) reconstructed ion current chromatograms (RIC) and (1) (m/z 420), (3) (m/z 401) selected mass traces of nonylphenol diethoxy sulfonate blend Triton X-200 (NP(EO)2-SC>3) gradient elution separated by EP-...

Fig. 2.11.21. (a) APCI-FIA-MS(—) and (d) APCI-LC-MS(—) reconstructed ion current chromatogram (RIC) and (b) and (c) selected mass traces of NPEO-SO4 (C9H19-C6H4-O-(CF -CHg-Olx-SOsH) column separation performed by RP-Clg gradient elution [15]. 

The APCI-RP-C 1 s - h - i I S ( / ) separation of this mixture consisted of the anionic nonylphenol derivatives besides synthetic by-products to the total ion current traces and selected mass traces as presented in Fig. 2.11.23. By-products from synthesis could be confirmed as... 

A mixture of these fluorinated surfactants was separated according to the method applied by Popenoe et al. [52]. For ionisation and detection, ESI-MS in the negative mode was applied. The result of LC separation is presented in the RIC in Fig. 2.11.26(a). Some of the separated compounds in the TIC and mass traces could be identified as perfluoro alkylsulfonates and perfluoro alkylcarboxylates such as... 

From the separation of a mixture of both compounds applying RP-Cis and ESI-MS(—), it was recognisable from mass trace analysis that the Ci2 derivative eluted first as shown in Fig. 2.11.36(c) and (d) [64]. The signals in the reconstructed ion current trace (e) contained the same ions at mtz 745 or 639 and at m/z 372 or 319 as also observed under ESI-FIA-MS(—) conditions. 

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