Nano-electrospray ionization mass spectrometry: addressing analytical problems beyond routine

For the analysis of native glycans using tandem mass spectrometry (MS), it is desirable to choose conditions whereby abundances of cross-ring cleavages indicative of branch positions are maximized. Recently, negative ion tandem mass spectrometry has been shown to produce significantly higher abundances of such ions in glycans compared to the positive ion mode. Much of this prior work has concerned fragmentation patterns in asialo glycans. The present work compares the abundances of critical cross-ring cleavage ions using negative mode tandem mass spectrometry for milk oligosaccharides and N-linked glycans. For comparison, product ion formation was studied for deprotonated and nitrated ions formed from asialo glycans and deprotonated ions from sialylated glycans. Breakdown profiles demonstrate clearly that more energy was required to fragment sialylated compounds to the same extent as either their asialo or nitrate adducted counterparts. The extraction of a proton from a ring hydroxyl group during the ionization process may be viewed, qualitatively, as imparting significantly more energy to the ion than would that from a molecule bearing an acidic group, so that acidic glycans are more stable in the gas phase, as the negative charge resides on the carboxyl group. These results have strong practical implications because a major portion of glycans released from mammalian proteins will be sialylated. T he most information-rich tandem mass spectra of oligosaccharides are those in which a combination of abundant glycosidic bond and cross-ring cleavages is observed. Cross-ring cleavages at branching residues and those where linkages are known to vary in the given oligosaccharide or glycoconjugate class provide particularly valuable information. Although abundant A-type and X-type cross-ring cleavages are observed using high-energy collisionalinduced dissociation (CID) [1,2], most modern mass analyzers operate in the low-energy regime. Thus, positive ion CID MS using triple quadrupole, ion trap, quadrupole orthogonal time-of-flight, and FT-ICR analyzers results in low-energy fragmentation in which Band Y-type ions and only those cross-ring cleavage ions that result from particularly facile processes are abundant [3]. Recently, high-energy CID fragmentation, including X-type cross-ring cleavage ions, has been observed for a variety of nonacidic oligosaccharides using matrix-assisted laser desorption/ionization (MALDI) tandem time-of-flight analyzers [4,5]. However, since fragile oligosaccharides, particularly polysialylated [6], and polysulfated molecules [7,8] have been observed to undergo prompt fragmentation in the vacuum MALDI source and metastable decomposition in the analyzer, they are more amenable to electrospray ionization. Negatively charged neutral oligosaccharides undergo fragmentation at very low collision energies [9 -11], and such ions are also more amenable to electrospray ionization than MALDI. Now, there remains no commercial instrument option for producing high-energy CID for fragile molecules. Introdu...

Section: Discussionmentioning

confidence: 99%

The influence of sialylation on glycan negative ion dissociation and energetics

Seymour

Costello

Zaia

2006

“…The actual flow rate is usually a few nL/min to a few tens of nL/min, controlled by the diameter of the tip, the voltage applied, and the backpressure which is sometimes applied to the tube content. Karas et al [3][4][5] have nicely shown that, in comparison with electrospray, nano-ESI reduces interference effects from salts and other species and provides better sensitivity toward a variety of analytes, including peptides and oligosaccharides, in samples contaminated by high levels of salts. They attributed this to the reduced droplet size compared with electrospray at higher flow rates.…”

mentioning

confidence: 99%

Efficiency of nano-electrospray ionization

El-Faramawy

Siu²,

Thomson³

2005

141

130

The efficiency of nano-electrospray ionization, defined as the flux of ions reaching the detector of a triple-quadrupole mass spectrometer divided by the flux of analyte ions leaving the needle, has been measured in a series of controlled experiments with dodecyltrimethyl ammonium (DDTMA) bromide, myoglobin, Glu-[1]-fibrinopeptide, and gramicidin S. By varying the flow rate from each needle, the optimum efficiency was determined. In general, the efficiency increased as the flow rate decreased. For DDTMA, efficiencies of up to 12% were measured, although efficiencies of ϳ1% were more common. Ion current measurements indicated efficient transfer of ions from the needle through to the detector. Significant needle-to-needle variations in efficiency were encountered and attributed to variations in ion-generation efficiency. ano-electrospray ionization (nano-ESI) is generally recognized as the most efficient method of introducing a liquid sample for direct analysis by mass spectrometry. Broadly speaking, nano-ESI is a form of electrospray, with the same fundamental ionization process of droplet formation followed by multiple uneven Rayleigh divisions, and finally desorption of pre-formed ions from the droplet [1, 2]. The technique is distinguished from more conventional forms of electrospray by the fashion in which it is carried out. One to two microliters of sample is deposited into a glass or quartz tube that has a tip diameter in the order of 1 m, and is sprayed from the tip by applying a voltage to the solution. The actual flow rate is usually a few nL/min to a few tens of nL/min, controlled by the diameter of the tip, the voltage applied, and the backpressure which is sometimes applied to the tube content. have nicely shown that, in comparison with electrospray, nano-ESI reduces interference effects from salts and other species and provides better sensitivity toward a variety of analytes, including peptides and oligosaccharides, in samples contaminated by high levels of salts. They attributed this to the reduced droplet size compared with electrospray at higher flow rates. Nano-ESI is typically used for peptide and protein analysis because of the ability to analyze a small volume of sample, and to make the sample last for many minutes so that various experiments can be performed. Noncovalent complexes are usually analyzed by nano-ESI, partly because of the small sample volumes which are typically available, but also because it is widely assumed to work better than electrospray for large complexes in aqueous solvents at low or neutral pH, although we are not aware of any systematic experiment that has demonstrated this fact.The defining characteristic of low flow is assumed to be responsible for the beneficial effect of high ionization and sampling efficiency, presumably because the droplets are very small and therefore can become well desolvated, given the experimental conditions employed. The overall efficiency can be determined by comparing the ion flux at the detector measured in ion counts per second at the...

“…SORI-CID of m/z 1367.017 first produced a fragment at m/z 1085.048, the B 5 ion formed from the loss of [G4SNa] (282 u) at the terminal reducing end ( Figure 5 and Table 3). The ion at m/z 941.077, which is assigned to [(A Ϫ G4SNa Ϫ A2SNa Ϫ G4SNa) ϩ Na Ϫ H 2 intermediates eventually underwent fragmentation enabling the complete sequencing of the alternating units of 4-linked 3,6-anhdrogalactopyranosyl and 3-linked galactopyranosyl 4-sulfate residues in neocarradecaose-4 1,3,5,7,9 -pentasulfate. SORI-CID MS/MS gave glycosidic bond cleavage with retention of the sulfate substituents.…”

Section: Neocarratetraose (Dp ϭ 2)mentioning

confidence: 99%

“…One of the techniques being explored for the analysis of carbohydrates is nanoelectrospray ionization mass spectrometry (nanoESI-MS) [2,3]. This technique offers high sensitivity with a detection limit down to 10 Ϫ8 M [4].…”

mentioning

confidence: 99%

“…In addition, it is a soft ionization technique that is ideal for polysaccharides with labile substituents. Since nano-ESI requires only a small amount of sample, a number of experiments such as high-resolution and collision-induced dissociation (CID or MS/MS) determinations can be performed with 1 picomole [2]. Nano-ESI can be coupled to different mass analyzers such as quadrupole time-of-flight (qTOF,) ion trap, triple quad, and Fourier transform ion cyclotron resonance-mass spectrometry (FTICR-MS) [5][6][7][8][9].…”

mentioning

confidence: 99%

See 1 more Smart Citation

Structural analysis of κ-carrageenan sulfated oligosaccharides by positive mode Nano-ESI-FTICR-MS and MS/MS by SORI-CID

Aguilan

Dayrit

Zhang

et al. 2006

Structural analysis of sulfated oligosaccharides from -carrageenan of up to ten residues (MW Ͼ2 kDa) was successfully carried out by positive mode nano-ESI-FTICR-MS together with MS/MS using sustained off-resonance irradiation-collision induced dissociation (SORI-CID). Glycosidic bond cleavage reactions via the B-and Y-types of fragmentation were observed and enabled complete sequencing of the oligosaccharide samples. The positions of the labile sulfate substituents were observable using SORI-CID, enabling the determination of the sequence of the sulfated residues. (J Am Soc Mass Spectrom 2006, 17, 96 -103)