Mass Analysis of Water-Soluble Polymers by Mobility Measurement of Charge-Reduced Ions Generated by Electrosprays

Abstract

Aqueous solutions of poly(ethylene glycol) (PEG) in a 10 mM ammonium acetate buffer are electrosprayed, and the maximum charge state on the resulting gas-phase ions is reduced to unity using a radioactive source. The mobility distribution of these charged particles is then measured in air in a differential mobility analyzer of unusually high resolution. The relation Z(m) between the mobility Z of a polymer molecule and its mass m is determined by means of narrowly distributed PEG mass standards. The molecular weight range of available standards is extended by generating clusters containing from one up to six molecules of the primary PEG standard. The mass at the peak of the distribution of the lowest standard (PEG-4k) is determined by MALDI mass spectrometry and agrees with the manufacturer's value and previous MALDI literature data. The masses for the 50K and 120K standards are found to differ by 8.6 and 6.6%, respectively, from the manufacturer's value. Using known relationships, the particle diameter d of the ions is calculated from the measured mobility. Plots of d versus m(1/3) give straight lines over the full mass range studied (4000-700 000 Da, particle diameter from 3 to 12 nm), indicating that these PEG particles are indeed spherical and have a density rho independent of size. The slope of the d versus m(1/3) curve provides a density rho = 1.25 g/cm(3), close to the known bulk density, rho(PEG) = 1.21 g/cm(3).

Tandem mobility mass spectrometry study of electrosprayed tetraheptyl ammonium bromide clusters

“…This upper limit exceeds that inferred from the slope of Figure 5 by just 6.4%, confirming the notion that the clusters are fairly compact. Similar studies [24] with singly charged polyethylene glycol (PEG) clusters in the mass range from 4000 to 700,000 have reported a cluster density of 1.23 g/cc, in fair agreement with the known density of PEGs with masses above a few thousand ( PEG ϭ 1.21 g/cc [24]), apparently confirming the near spherical shape of these clusters. This study, however, did not measure ion mass directly, while a subsequent DMA-MS investigation has inferred the smaller value PEG ϭ 1.055 g/cc [25].…”

Electrospray–differential mobility analysis of bionanoparticles

“…Polyethylene glycols (PEGs) in the size range of 4k to 700 kDa were used to establish that molecular weight and mobility diameter could be correlated by a one-third power law [47] a correlation that had already been established for proteins three years prior [11]. Similar behavior has been reported for water insoluble polymers [48].…”

“…Using uncertainty analysis, it can be shown that a 15% variation in mobility diameter results in a 45% variation in density which partially explains this wide scatter of densities in the literature and strengthens the above hypothesis. The same rationale may also explain the scatter of densities found in PEGs [47,51]. Curiously, the lower density in all cases have been reported only with TSI Inc designed DMAs and this perhaps is because of inaccurate or imprecise DMA geometry designed and manufactured by them.…”

“…This limitation can however be overcome by using an electrometer instead of a CPC. Another group has also attempted determining the density of PEGs and there appears to be a significant variation amongst different groups (0.52 gm/cc to 1.3 gm/cc) [47,51]. The reason for this variation is discussed later.…”

Nano ES GEMMA and PDMA, new tools for the analysis of nanobioparticles—Protein complexes, lipoparticles, and viruses

“…The size range of 10 to 200 nm is therefore of great interest, and covered by the so-called nano-differential mobility analysis (nano DMA) [8]. Combined with a modified nano electrospray source (nES) for nanoaerosol generation, and bipolar charging process to deliver mostly singly charged ions [9,10], it has been demonstrated that the analysis of intact biospecific protein complexes [11,12], viruses [11], virus antibody [13], virus receptor [13], bacterio phages [14], and polymers [15,16] is possible, and delivers a lot of new knowledge.…”