Sample preparation effects in matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry of partially depolymerised carboxymethyl cellulose

Abstract

Sample preparation effects in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) of partially depolymerised carboxymethyl cellulose (CMC) have been investigated. The depolymerisation was either enzymatic or acidic. Fractions of enzymatically depolymerised CMC were collected from size-exclusion chromatography (SEC) and further investigated by MALDI-TOFMS. 2,5-Dihydroxybenzoic acid was used as matrix, dissolved in H(2)O due to the poor solubility of CMC in suitable organic solvents. The samples were dried by two methods, in ambient atmosphere and at reduced pressure. Under reduced pressure the sample spot homogeneity increased. This drying method, however, produced additional adduct peaks in the mass spectra originating from ion exchange on the CMC oligomers. Analysis of CMC could be performed in both negative and positive ion modes. Mass discrimination and variation in ionisation efficiency were demonstrated by comparing mass spectra with SEC data. Measurements of the degree of substitution (DS) were performed on three CMCs with different DS values, which were depolymerised in trifluoroacetic acid. The three CMCs were easily distinguished from one another, but the obtained DS values deviated from the values supplied by the manufacturer.

Sample preparation effects in matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry of partially depolymerised methyl cellulose

“…Analyte signal was obtained over the whole sample spot indicating a homogeneous distribution of the analyte in the crystals. As for carboxymethyl cellulose (CMC),17 the signal lasted much longer at each laser spot for the DHB/H 2 O preparation, sometimes more than 100 laser shots, whereas for organic solvent preparations the signal typically lasted around 5–15 shots. The mass resolution did not vary significantly between the matrices and solvents with the exception of H 2 O for which the resolution was significantly lower.…”

“…Both the acidic and enzymatic depolymerisations were performed according to the methods described in Ref. 17 with some modifications. For the acidic depolymerisation the time was 1 h, and, after dilution in H 2 O, the TFA was evaporated under a stream of N 2 and heating to 50°C.…”

“…MALDI‐TOFMS experiments were performed using a PerSeptive Voyager‐DE STR (Applied Biosystems, Framingham, MA, USA) instrument, see Ref. 17 for details and acquisition method. Mass spectra were acquired in positive ion mode.…”

Liquid chromatography combined with mass spectrometry for the investigation of endoglucanase selectivity on carboxymethyl cellulose

“…Although no quantitative conclusions on the relative abundance can be made from the peak intensities, it is clear that the non-substituted species dominate, especially since monosubstituted monomers can be expected to have a higher response factor in MS than the non-substituted. 21 Figure 10 displays the CID-spectra from the three peaks (labeled as shown in Fig. 9) and a CID-spectrum of 1 0 [R]-monomers.…”

Investigation of endoglucanase selectivity on carboxymethyl cellulose by mass spectrometric techniques

“…Na and 1 2 [B] ? 2Na) compared to the nonand mono-substituted peaks is probably partly due to a high relative abundance and partly due to that the ionization yield increases with the number of substituents (Momcilovic et al 2003a). Therefore, no conclusions on the quantities of the different monomers can be drawn from the mass spectrum.…”