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A new concentric nebulizer for ICP sample introduction at nL-sample flow rates

(25.01.2006)


Nebulizer design
 
Figure A: The nanoNebulizer with its small spraychamber coupled to the ICP torch
 
The direct coupling of nanoHPLC to ICPMS avoids complication by a second pump needed for a make-up flow, resulting in analyte dispersion and loss of chromatographic resolution and detection limits.
 
Figure B: Design of the nanoNebulizer fitted via miniSpraychamber to ICP torch
 
The nanoflow nebulizer nDS-200 is using a hollow fused-silica capillary needle (3) as nebulizer capillary. The small needle tip (i.d. 10 µm, o.d. 20 µm) is centered in a 254-µm i.d. sapphire orifice (4) allowing a stable and continuous nebulization of nanoliter flow rates of less than 500 nl/min. Nebulization characteristics can be optimized by adjusting the position of the needle tip in the nebulizer orifice.
 
The outlet capillary (1, 20-µm i.d, 280-µm o.d.) of the nanoHPLC column is fitted into the nebulizer via a zero-dead-volume connection to the nebulizer needle in order to avoid excessive band broadening of the narrow chromatographic peaks. This zero-dead-volume connection is realized by a port (i.d. 1.6 mm) for the capillary collumn surrounded by a piece of plastic tubing (orange in Figure B) having a small through-hole (2, i.d. 300 µm) into which the HPLC capillary fits allowing a precise abutting of the capillaries.
 
The small inner diameter of the nebulizer tip results in a velocity of the liquid flow (~ 4.2 cm/s at 200 nL/min) that is similar to that in a commercially available nebulizer operated at 5 µL/min.
 
 
Nebulizer characteristics
 
body material: FEP
nebulizer gas flow: 0.9 -1.2 l/min (1.05-1.15 l/min optimum)
sample flow: 50 - 2000 nl/min (250-450 nl/min optimum)
precision:  < 5% RSD for flows > 250 nl/min
mode of operation: pumped sample flow (non self-aspirating)
 
The efficient nebulization results in complete evaporation of droplets already within the tiny spraychamber. Therefore the sample flow rate has no influence on the oxide formation and doubly charged ions within the ICP, both beeing kept at very low values.
 
Sensitivity is linearly increasing with sample flow rate over the working range and precision is better than 5% RSD for sample flow rates bigger than 200 nl/min.
 
Since the plasma solvent load is orders of magnitude lower than with micro- or conventional nebulizers, selection of the mobile phase is not restricted by plasma stability problems.
 
The characteristics of the nanoNebulizer can be summarized:
  • No metal parts in contact with sample flow
  • Minimized dead-volume for reduced dispersion not restricting the obtainable resolution by nanoHPLC
  • High sensitivity through quantitative nebulization
  • Free selection of mobile phase due to reduced solvent load
  • High stability due to robust construction
  • High detection power due to improved S/N ratio by very narrow peaks
  • Direct coupling of nanoHPLC with ICP-MS
  • Direct comparison with nanoESI-MS possible (similar flow conditions)
 

 Related Studies:
 
 Pierre Giusti, Dirk Schaumlöffel, Jorge Ruiz Encinar, Joanna Szpunar, Interfacing reversed-phase nanoHPLC with ICP-MS and on-line isotope dilution analysis for the accurate quantification of selenium-containing peptides in protein tryptic digests, J. Anal. At. Spectrom., 20/10 (2005) 1101-1107. DOI: 10.1039/b506620d
 
 Pierre Giusti, Dirk Schaumlöffel, Hugues Preud'homme, Joanna Szpunar,
Ryszard Lobinski, Selenoprotein mapping in a selenium-yeast protein digest by parallel nanoHPLC-ICP-MS and nanoHPLC-electrospray-MS/MS after on-line preconcentration, J. Anal. At. Spectrom., 21/1 (2006) 26. DOI: 10.1039/b511288e

 Pierre Giusti, Ryszard Lobinski, Joanna Szpunar, Dirk Schaumlöffel, Development of a Nebulizer for a Sheatless Interfacing of NanoHPLC and ICPMS, Anal. Chem., 78 (2006) in print. DOI: 10.1021/ac051656j

last time modified: March 18, 2010



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