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On-column internal standardisation as an alternative calibration strategy for speciation analysis


Speciation analysis by highly sensitive inductively coupled plasma mass spectrometry (ICP-MS) requires the separation of species by a preferentially on-line coupled separation module such as HPLC. Unfortunately, such separation procedure is often time consuming, prolonging the analysis time from a few seconds to minutes. Obtaining high accuracy from such analysis is hampered by matrix effects induced by the complex sample and the used mobile phase and signal drift during the analysis time. While signal drift in ICP-MS is often compensated by internal standardization, its use for hyphenated HPLC-ICP-MS is hampered by interaction of the internal standard with the separation column or mobile phase. Matrix effects can be corrected by the method of standard addition, however in the presence of drift, results may be biased.  When using ICP-MS as detection system under such conditions, the preferred method for quantification is isotope dilution (ID-MS). Unfortunately, in many cases IDMS calibration is either not applicable (e.g. for monoisotopic elements such as arsenic) or not feasible (e.g. limited by the cost and availability of isotopically enriched species).

The new study:
In order to minimise the impact of drift and matrix effects on the accuracy and precision of the speciation data, the researchers from LGC Ltd. (UK) propose a novel on-column species-specific internal standardisation approach as an alternative to species-specific-IDMS. The method is based on the use of an internal standard that is the same species as the analyte, thus resulting in an ideal response. The method is using a manifold allowing the precisely position the IS peak within the chromatogram for each particular speciation analysis.  

Figure: manifold for on-column internal standardization
  • An automatic six-port valve is placed just before the analytical column
  • While the sample is injected into the column, a loop is filled with a standard of the species of interest (A)
  • After certain time, the valve is switched to inject position and the standard is injected onto the column (B)
  • Standard and sample pass through the column simultaneously
The accuracy obtained by this approach was investigated by the determination of inorganic arsenic in rice samples. An expanded uncertainty (k = 2) of <10% was obtained for a mass fraction range of 60 to 300 mg/kg inorganic-As (i-As) in dry rice products. Moreover, the capability of the method to quantify more than one species under non-isocratic separation conditions was investigated through simultaneous determination of i-As and Methyl Arsonate (MA) in a standard mixture submitted to the same preparation procedure as the rice sample.

The authors concluded that the new method provides adequate accuracy as long as a good chromatographic selectivity is achieved that allows for the resolution between the analyte and the neighboring peaks.

The original publication

Panayot Petrov, Simon Cowen, Heidi Goenaga-Infante, On-column internal standardisation as an alternative calibration strategy for speciation analysis: feasibility demonstration through analysis of inorganic As in rice, Anal. Methods, 13/33(2021) 3641-3648. DOI: 10.1039/d1ay00699a

Related studies (newest first):

Antonín Kaňa, Zuzana Klimšová, Oto Mestek, Internal standardisation for arsenic and its species determination using inductively coupled plasma mass spectrometry, Talanta, 192 (2019) 86-92. DOI: 10.1016/j.talanta.2018.09.038

A.K. Hewavitharana , N.S.A. Kassim and P.N. Shaw, “Standard addition with internal standardisation as an alternative to using stable isotope labelled internal standards to correct for matrix effects—Comparison and validation using liquid chromatography- tandem mass spectrometric assay of vitamin D”, J. Chromatogr. A, 1553 (2018) 101-107. DOI: 10.1016/j.chroma.2018.04.026
J. Feldmann, A. Raab and E. M. Krupp, Importance of ICPMS for speciation analysis is changing: future trends for targeted and non-targeted element speciation analysis, Anal. Bioanal. Chem., 410 (2018) 661-667. DOI: 10.1007/s00216-017-0502-8

J. Rossmann, L.D. Renner, R. Oertel and A.E. Armouche, Post-column infusion of internal standard quantification for liquid chromatography-electrospray ionization-tandem mass spectrometry analysis – Pharmaceuticals in urine as example approach, J. Chromatogr. A, 1535 (2018) 80-87. DOI: 10.1016/j.chroma.2018.01.001

H.W. Liao, G.Y. Chen, M.S. Wu, W.C. Liao, I.L. Tsai and C.H. Kuo, Quantification of endogenous metabolites by the postcolumn infused-internal standard method combined with matrix normalization factor in liquid chromatography–electrospray ionization tandem mass spectrometry,  J. Chromatogr. A, 1375 (2015) 62-68. DOI: 10.1016/j.chroma.2014.11.073

K.M. Kubachka, N.V. Shockey, T.A. Hanley, S.D. Conklin and D.T. Heitkemper, Arsenic Speciation in Rice and Rice Products Using High Performance Liquid chromatography Inductively Coupled Plasma-Mass Spectrometric Determination, Elemental Analysis Manual, FDA: Version Draft 1.1, November 2012, https://www.fda.gov/media/95197/download

J.P. Jesus, C.A. Suárez, J.R. Ferreira and M.F. Giné, Sequential injection analysis implementing multiple standard additions for As speciation by liquid chromatography and atomic fluorescence spectrometry (SIA-HPLC-AFS), Talanta, 85 (2011) 1364-1368. DOI:  10.1016/j.talanta.2011.06.013

P. Kościelniak, M. Wieczorek, J. Kozak and M. Herman, Generalized Calibration Strategy in Analytical Chemistry,  Anal. Lett., 44 (2011) 411-430. DOI: 10.1080/00032719.2010.500782

H. Stahnke, T. Reemtsma and L. Alder, Compensation of Matrix Effects by Postcolumn Infusion of a Monitor Substance in Multiresidue Analysis with LC−MS/MS,  Anal. Chem., 81 (2009) 2185-2192. DOI: 10.1021/ac802362s

Stephen L.R. Ellison, Michael Thompson, Standard additions: myth and reality, Analyst, 133 (2008) 992–997. DOI: 10.1039/b717660k

Jinguo Kang, Larry A. Hick, William E. Price, Using calibration approaches to compensate for remaining matrix effects in quantitative liquid chromatography/electrospray ionization multistage mass spectrometric analysis of phytoestrogens in aqueous environmental samples, Rapid Commun. Mass Spectrom., 21/24 (2007) 4065-4072. DOI:  10.1002/rcm.3311

P. Araujo, F. Couillard, E. Leirnes, K. Ask, A. Bøkevoll and L. Frøyland, Experimental design considerations in quantification experiments by using the internal standard technique: Cholesterol determination by gas chromatography as a case study,  J. Chromatogr. A, 1121 (2006) 99-105. DOI: 10.1016/j.chroma.2006.03.119

E. Stokvis, H. Rosing and J. H. Beijnen, Stable isotopically labeled internal standards in quantitative bioanalysis using liquid chromatography/mass spectrometry: necessity or not?, Rapid Commun. Mass Spectrom., 19 (2005) 401-407. DOI: 10.1002/rcm.1790

K.G. Heumann, L. Rottmann, J. Vogl, Isotope-dilution ICP–MS for trace element determination and speciation: from a reference method to a routine method, Anal. Bioanal. Chem., 378/2 (2004) 318–329. DOI: 10.1007/s00216-003-2325-z

K.D. Altria and H. Fabre, Approaches to optimisation of precision in capillary electrophoresis,  Chromatographia, 40 (1995) 313-320. DOI:  10.1007/BF02290363

Y. Hayashi, R. Matsuda, Stochastic Utility of Internal Standard Method in Liquid Chromatography,  Anal. Sci., 11 (1995) 389-400. DOI: 10.2116/analsci.11.389

L. Rottmann, K.G. Heumann, Development of an on-line isotope dilution technique with HPLC/ICP-MS for the accurate determination of elemental species, Fresenius J. Anal. Chem., 350 (1994) 221-227. DOI: 10.1007/BF00322473

P. Haefelfinger, Limits of the internal standard technique in chromatography,  J. Chromatogr. A, 218 (1981) 73-81. DOI: 10.1016/S0021-9673(00)82048-8

Related EVISA Resources

Link Database: Analytical Methods for Arsenic Speciation Analysis
Brief summary: Standard methods for arsenic speciation analysis
Brief Summary: LC-ICP-MS: The most often used hyphenated system for speciation analysis

Related EVISA News (newest first):

November 17, 2020: Transformation of arsenic species during ultrasonic sample pretreatment

last time modified: September 15, 2021


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