A General, Positive Ion Mode ESI-MS Approach for the Analysis of Singly Charged Inorganic and Organic Anions Using a Dicationic Reagent

Abstract

Anion analysis continues to be of great importance to many scientific and technical fields. We propose here a general and sensitive method of detecting singly charged anions by ESI-MS and LC-ESI-MS as positive ions. This method utilizes a dicationic reagent to form a complex with the anion that retains an overall positive charge for analysis by MS. Nitrate, thiocyanate, perchlorate, perfluorooctanoic acid (PFOA), halogenated acetic acids, and various other inorganic and organic anions and are investigated. The use of tandem mass spectrometry to enhance the detection limits of some of the anions is demonstrated. Chaotropic anions provided the lowest detection limits, with PFOA detected at the hundreds of femtograms level. Indeed, this single approach provides the lowest reported detection limits for a variety of anions, especially PFOA, nitrate, monochloroacetic acid, dichloroacetic acid, and bromochloroacetic acid, among others. The integrated areas and signal-to-noise ratios for five ions during a chromatographic run in both the positive and negative ion modes are compared. The ability of this method to detect differences in related ions is shown for four arsenic species. Finally, a tap water sample is analyzed for the anions in this study using the dicationic reagent method.

The evaluation and comparison of trigonal and linear tricationic ion-pairing reagents for the detection of anions in positive mode ESI-MS

“…Phenyl phosphate had lower LODs than hydrogen phosphite. This result is in general agreement with earlier work that used dicationic reagents and singly charged anions, which found that more oxidized species had better LODs [42].…”

Electrospray Ionization Mass Spectrometry for the Quantification of Inorganic Cations and Anions

“…As for F -, the LOD value shows that Al 3+ affords better detection performance than In 3+ in accordance with the stability of the Al-and In-F complexes in aqueous solution: log K1 = 6.13 for Al-F, and 3.70 for In-F. 40 The LOD value for Cl -was higher than those for Br -and I -, and this was considered to be mainly due to Clcontamination. The LOD values for Cl -(0.32 ng in 30 mm 3 ), Br -(9.1 pg) and I -(6.1 pg) listed in Table 5, were, however, much lower than conventional methods, such as IC, ISE, and solution spectrophotometry, 41,42 being comparable to those of ESI tandem mass spectrometry (ESI-MS/MS), [31][32][33] and capillary electrophoresis (CE).…”

“…Based on Ternary Complex Formation 7,14 3·1 Determination of ternary complex of halides, metal and APC So far, several techniques have been reported for the determination of halide anions by ESI-MS. [30][31][32][33] A direct determination of halide anions with an LOD of about 1 ppb has been reported, but a strong interference was observed due to the matrix effect. 30 The determination of inorganic anions as well as halides as ion-pairs with organic dications was studied by Armstrong, Dasgupta, and coworkers.…”

“…30 The determination of inorganic anions as well as halides as ion-pairs with organic dications was studied by Armstrong, Dasgupta, and coworkers. [31][32][33] Picogram LODs were obtained for I -in positive ion mode with ESI-MS. [31][32][33] Br -and Cl -were also detected with LODs of 60 pg and 1.8 μg, respectively. 31 In our research, methods for the determination of halides (F -, Cl -, Br -, I -) using ternary complex formation with metal-APC complexes have been developed.…”

“…The ion-pair of CN -with the dication was determined by ESI-MS in positive ion mode in the same way as with the other inorganic anions. 31 Minakata et al have reported the determination of CN -and I -by ESI-MS/MS where Au(CN) 2-and AuI 2-were measured after ion-pair extraction into 4-methyl-2-pentanone, respectively. 44 In the present study, the formation of the ternary complex of the analyte was used to determine CN -.…”