High-performance liquid chromatography/mass spectrometry (HPLC/MS) analysis of anionic species such as sulphonic acid dyes and intermediates requires volatile ion-pairing mobile phase additives. Six di- and trialkylammonium acetates were compared with tetraalkylammonium salts and ammonium acetate in the concentration range 0-20 mmol l(-1) as mobile phase additives for HPLC/MS of polysulphonated compounds. The effects of the structure and concentration of the ion-pairing reagents on the electrospray response of mono-, di- and tetrasulphonic aromatic acids and acid dyes were studied in detail. Further, five different mass analysers and instrument geometries were compared. A higher signal decrease is observed with linear geometry instruments in comparison to orthogonal or even Z-spray geometry mass spectrometers. The concentration of mobile phase additives has a significant influence on the abundance ratios of multiply charged ions in the mass spectra of polysulphonated compounds. The competing ions of sulphonic acids may also cause significant signal suppression.

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A library of negative ion electrospray ionization mass spectra and tandem mass spectra (MS/MS) of sulfonated dyes has been developed for fast identification purposes. The uniform protocol has been elaborated and applied to the measurements of more than 50 anionic dyes. Three collision energies are selected in our protocol which ensures that at least one of them provides a suitable ratio of product ions to the precursor ion. The robustness is investigated with altered values of tuning parameters (e.g. the pressure of the nebulizing gas, the temperature and the flow rate of drying gas, and the mobile phase composition). The results of the inter-laboratory comparison of product ion mass spectra recorded on seven different tandem mass spectrometers (three ion traps, two triple quadrupoles and two hybrid quadrupole time of flight instruments) are presented for four representative anionic dyes--azo dye Acid Red 118, anthraquinone dye Acid Violet 43, triphenylmethane dye Acid Blue 1 and Al(III) metal-complex azo dye. The fragmentation patterns are almost identical for all tandem mass analyzers, only the ratios of product ions differ somewhat which confirms the possibility of spectra transfer among different mass analyzers with the goal of library formation.

Occurrence of radical molecular ions in atmospheric pressure chemical ionization mass spectra of heterocyclic compoundsIt is well-known that the use of atmospheric pressure ionization (API) techniques, such as electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI), is associated with the formation of even-electron ions, 1 for example, protonated molecules [M C H] C , adducts with alkali metal ions [M C Na] C and [M C K] C , adducts with ammonium ions [M C NH 4 ] C in the positive-ion mode and deprotonated molecules [M H] and some adducts with small inorganic anions in the negative-ion mode. The relative abundances of fragment ions are generally low to negligible and mostly they have also even number of electrons, otherwise even-electron rule would be contradicted. Odd-electron ions do not typically occur in ESI/APCI mass spectra, but some exceptions are known, 2 for example, radical molecular ions M ž formed by an electron capture 3 or charge exchange mechanisms 4,5 in the negative-ion APCI mode, and radical molecular ions M C ž formed by the charge exchange mechanism in case of nonpolar polyaromatic hydrocarbons. 6,7 In the present communication, we would like to highlight few well-pronounced examples on the formation of radical molecular ions both in the positive-ion and negative-ion APCI modes using an ion trap Esquire 3000 (Bruker Daltonics, Bremen, Germany) or a single quadrupole Platform (Micromass, Manchester, UK) under the following experimental conditions: the mass range m/z 50-1000, the target mass m/z 250 and the compound stability 20% for alkyl series from C2 to C4, the target mass m/z 350 and the compound stability 100% for alkyl series from C5 to C10, pressure of the nebulizing gas 15 psi, the drying gas flow rate 4 l/min, temperature of the ion source 350°C and temperature of drying gas 300°C. The samples were dissolved in acetonitrile and delivered into the system by an infusion pump at the flow rate of 5 µl/min. In some experiments, different solvents (methanol, benzene, or water) were used to compare results with the measurements in acetonitrile.Unlike the conventional electron ionization, the formation of odd-electron molecular ions is quite unusual in API mass spectra. The preference of radical ion formation depends on the structure, the ionization mode, and the experimental conditions, for example solvents used for the analysis. In ESI, the occurrence of molecular radical ions is very rare and it is usually attributed to the electrochemical processes on the electrospray needle or different oxidation states of metal ions. On the other hand, the presence of radical molecular ions in the latest API technique, atmospheric pressure photoionization (APPI), is relatively common due to the different ionization mechanism. 5 The presence of molecular radical ions is not typical for APCI, but some examples have been reported for polyaromatic hydrocarbons without other functionalities in the positive-ion mode 6,7 or for compounds with the high electron affinity and low gas-phase...

The title dyes, a group of new homo‐bireactive disazo reactive dyes having molecular masses of 1000–1400 Da, were developed because of their potential use as low salt, easy wash‐off colorants for cotton. Following dye synthesis from diaminobiphenyls with and without substituents in the 2,2′‐positions, negative‐ion electrospray ionisation mass spectrometry (ESI‐MS) was used to characterise the dyes. The MS obtained were characterised by signals arising from [M − xH]x− ions plus fragment ions produced by cleavage at C–N bonds adjacent to the azo linkage. In addition, better results were produced when J‐acid was the coupler employed rather than H‐acid. The characteristic fragmentation behaviour of the studied dyes is discussed and illustrated on selected example.