Evaluation of different quantitative approaches for the determination of noneasily ionizable molecules by different atmospheric pressure interfaces used in liquid chromatography tandem mass spectrometry: Abamectin as case of study

Abstract

The liquid chromatography tandem mass spectroscopy residue determination of compounds without any acidic or basic centers such as abamectin has been investigated. Several approaches regarding the interface used and adduct formation have been compared. The low acidity of the hydroxyl groups only made deprotonation feasible using the atmospheric pressure chemical ionization (APCI) interface. To obtain sufficient sensitivity for residue analysis, the Ion Sabre APCI interface was necessary. However, the sensitivity attained was lower than for monitoring adducts in positive ion mode. Using electrospray ionization, different adducts with Na ϩ , NH 4 ϩ , and Li ϩ were tested and compared. The best results were obtained for the ammoniated adduct in electrospray ionization (ESI) because of its high sensitivity and the presence of several product ions with similar abundance. The highest sensitivity was reached using an in-source fragment as precursor ion, leading to a limit of detection (LOD) of 2 g/L with low relative standard deviation. The relatively high abundance of other transitions allowed abamectin confirmation at concentrations close to the LOD (6 g/L). Alkali ions were found to be a suitable alternative to determine and confirm abamectin at residue levels. The [M ϩ Na] ϩ also presented various product ions with similar abundance, which allowed confirmation at LOD levels. However, this LOD was found to be almost four times higher than with [M ϩ NH 4 ] ϩ because of the poor sensitivity of the transitions obtained. Although the use of Li ϩ facilitated the fragmentation of the adduct [M ϩ Li] ϩ , with similar sensitivity to [M ϩ NH 4 ] ϩ , this fragmentation preferentially generated only one product ion, which did not allow confirmation at concentration levels lower than 15 g/L. The use of APCI for monitoring adducts was also feasible, but with less sensitivity. The sensitivity increased with the Ion Sabre APCI, although it was still five times lower than with ESI. Other adduct formers such as Co 2ϩ and Ni 2ϩ also were tested with unsatisfactory results. (J Am Soc Mass Spectrom 2005, 16, 1619 -1630

Fast determination of toxic diethylene glycol in toothpaste by ultra-performance liquid chromatography–time of flight mass spectrometry

“…This poor fragmentation of sodium adducts has already been explained in the literature [20]. Although different ways to promote the formation of the protonated molecule or the ammonium or lithium adducts were attempted, like adding formic acid, ammonium acetate or lithium acetate [21] to the mobile phase or to the sample extract, no satisfactory results were obtained. Finally, the DEG sodium adduct was selected for determination in TOF mode.…”

Mass spectral behavior of the hydrolysis products of sesqui- and oxy-mustard type chemical warfare agents in atmospheric pressure chemical ionization

“…Although this approach may be sufficient for environmental samples, it is insufficient for complex biological matrices that often retain low-mass interferences even after multiple separation steps. To reduce the chemical noise and effectively discriminate between the analytes of interest and low-mass interferences, it is desirable to use°multi-stage°MS,°at°a°minimum°of°MS 2° [ 34].°Ideally, MS/MS allows measurement via MRM of a quantitative transition and at least one confirmation transition [34],°thus°improving°selectivity°as°well°as°sensitivity. Early experiments with ESI in our laboratory failed to produce abundant molecular ions suitable for quantification and confirmation by MRM.…”

“…Such adduct formation is generally observed more often in ESI than in APCI, with alkali metal ions exhibiting a strong affinity for oxygenated centers such as those in alcohol°groups° [34].°Adduct°formation°is°generally undesirable because it reduces sensitivity by splitting the analyte signal among multiple species and adducts°are°less°amenable°to°MS/MS° [27],°often°result-ing in product ion spectra consisting mostly of the adducted ion (i.e., Na ϩ or K ϩ ). Because insufficient fragmentation and poor reproducibility limit the use of°alkali°metal°adducts°for°quantitative°purposes° [34], we examined the more favorable ionization technique of APCI in an effort to quantitate these compounds in the low ng/mL range needed for biomonitoring purposes.…”

“…Such adduct formation is generally observed more often in ESI than in APCI, with alkali metal ions exhibiting a strong affinity for oxygenated centers such as those in alcohol°groups° [34].°Adduct°formation°is°generally undesirable because it reduces sensitivity by splitting the analyte signal among multiple species and adducts°are°less°amenable°to°MS/MS° [27],°often°result-ing in product ion spectra consisting mostly of the adducted ion (i.e., Na ϩ or K ϩ ). Because insufficient fragmentation and poor reproducibility limit the use of°alkali°metal°adducts°for°quantitative°purposes° [34], we examined the more favorable ionization technique of APCI in an effort to quantitate these compounds in the low ng/mL range needed for biomonitoring purposes. In the course of examining the ionization characteristics of BHETAs and BHETAEs in positive and negative APCI, the superoxide anion was observed in negative ion APCI MS. We have shown that this characteristic superoxide adduct ion, [M ϩ O 2 ] Ϫ , is abundant and amenable to MS/MS, and that product ion scans of [M ϩ O 2 ] Ϫ exhibit a sufficient number of high-mass, high-intensity precursor/product ion transitions for analysis by MRM.…”

Simultaneous Determination of Antimalarial Agents by LC-MS/MS and Its Application to Evaluation of Fixed-Dose Tablets

“…Adequate signal intensity was observed for all compounds when acetonitrile/water plus 0.1% acetic acid and 5 mmol L -1 ammonium formate was used. In the case of MFQ and IS, the generation of [ 24 sodium adducts are more stable than ammonium adducts, owing to the strong interaction with the oxygen atoms present in the molecule. Hence, the generation of ARS [M + Na] + adduct ion was evaluated.…”