Negative ion mode atmospheric pressure ionization methods in lignin mass spectrometry: A comparative study

Abstract

Photoionization using acetone as a dopant is distinguished by a significantly higher intensity of signals and the lowest sensitivity to contaminants present in the lignin preparation. This ionization method can be considered as preferred for studying the dioxane lignin preparations of woody plants. Copyright © 2016 John Wiley & Sons, Ltd.

Atmospheric pressure ionization mass spectrometry as a tool for structural characterization of lignin

“…The problem of a limited m/z range has been overcome only recently by Kosyakov et al, who demonstrated the analysis of lignin isolated from spruce with the mass range up to m/z 1700 with a M n of 640 Da (Figure 2). 23 While this is the broadest mass range reported at this time, the MS results do not fully agree with the aqueous SEC data which showed an M n of 1.4 kDa and an M W of 8.2 kDa 23 . Nevertheless, due to the aforementioned limitation of SEC, particularly with the use of polystyrene sulfonate standards, it is difficult to determine which technique is more accurate.…”

“…Both APCI and APPI predominantly result in the formation of singly charged species and thus the mass range may be limited by the range of the mass analyzer. Nevertheless, recent studies noted that the MW range of lignin species was perhaps overestimated and a more efficient ionization using APPI and APCI was demonstrated than with ESI 23 …”

“…The negative mode APPI method was reported to promote a more efficient ionization than both ESI and APCI (Figure 2), especially when targeting lignin oligomers. It also allowed a more comparable abundance distribution for low and high m/z ions to be obtained 22,23 . It is of note that in contrast to previous work conducted in aqueous methanol with the addition of acetic or formic acid (Table 1), these studies recognized the role of solvents 22,23 .…”

“…As mentioned above, both APCI and APPI target primarily smaller molecules (<1000 Da) and thus are typically employed for the analysis of lignin degradation products and non‐polar species, although only a few studies have reported the characterization of intact lignin utilizing these techniques (Table 1). These studies were carried out predominantly in the negative ion mode promoting the deprotonation of phenolic units, 19–21,23 although a successful application in the positive ion APPI mode was reported for effective tandem mass spectrometric (MS/MS) identification of oligomeric species 22 …”

“…It also allowed a more comparable abundance distribution for low and high m/z ions to be obtained 22,23 . It is of note that in contrast to previous work conducted in aqueous methanol with the addition of acetic or formic acid (Table 1), these studies recognized the role of solvents 22,23 . Kosyakov et al demonstrated an effective use of an unconventional solvent system, i.e., 0.1% ammonia in a water/acetone (1:9) mixture, to improve the deprotonation of analytes in APPI and APCI.…”