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Speciation matters even if the interest is in total element concentration


Total element concentration is a kind of "sum parameter", summing up all the different element species that are present as:
  • dissolved, colloidal or particular species,
  • uncharged, negatively charged or positively charged species,
  • free, sorbed, complexed or bound species,
  • inorganic, metallorganic or organic compounds.

The prerequisite for total element concentration analysis is that all different species do participate on the generation of the element signal with the same sensitivity. Unfortunately that working hypothesis is more often invalid than analysts believe. Bias may occur in all steps of the analytical procedure:

Sampling: Has to assure that all different species have the same chance to end up in the sample. It is very difficult to create sampling conditions that fulfil this prerequisite. Analyte species can be lost due to sorption to sampling devices, volatilization from the sample or fractionation effects. Main losses occur for colloidal, particular or organic species that get lost by sorption on sampling funnels, container walls or filtration devices. Other losses may occur for dissolved gaseous or volatile species (e.g. Hg(0), methylated species).

Optimum sample storage conditions are different for different element species. While total element concentration analysis is not interested in preserving the speciation, storage conditions should be chosen that are optimum for the different element species present. Most often the original sample cannot be preserved for the different species but has to be pre-treated (digestion, preservation) in order to transform the different species into one stable form that can be stored.

Sample preparation:
Sample preparation has to assure that different element species are transformed to a single one that can easily be detected (mineralization). If some species resist such pre-treatment, they may get lost in the final determination step (hidden species).

In case that the sample has not been efficiently pre-treated in order to transform the different species into a single one (direct analysis) the sample presentation, sample introduction and the final measurement step must assure that all different species contribute to the final signal with the same sensitivity. Bias occurs because of differences in charges, hydrophilicity, volatility and other characteristics of the different species. The sensitivity of different species might also be influenced by interference effects specific to a special species (cationic, anionic).

The degree of bias is increasing with the chemistry/physics involved for sample presentation and signal generation. In atomic spectrometry colder sources (graphite furnace, flames) are more prone to such effects than hotter plasma sources. Direct sample injection is less problematic than sample nebulisation, simple nebulisation is less problematic than nebulisation/desolvation and chemical vapour generation is even more problematic than nebulisation. Anyhow, even liquid sample introduction by simple nebulisation creates different transport efficiency for different species. Unfortunately, pneumatic nebulisers are "poor pumps and inferior subsamplers". The transport efficiency for different element species is influenced by the interaction with the sample introduction system (sampling capillary, pump tube, valves, transfer lines, nebuliser, spraychamber) mainly because of differences in sorption behaviour (to the different materials in contact with the sample) or different volatility. Especially volatile species have much higher transport efficiency than non-volatile species but also can be lost quite easily on membrane desolvation units. The degree of such effects depends also on the type of nebuliser with pneumatic nebulisers less critical in comparison to ultrasonic nebulisers and thermospray nebulisers.

Effects of the valency state of elemental species on their sensitivity have been observed for  Cr(III)/Cr(VI), Fe(II)/Fe(III),  V(IV)/V(V),  Te(IV)/Te(VI), Ru(III)/Ru(V) in flame AAS,  for Se(IV)/Se(VI) in graphite furnace AAS, and for As(III)/As(V), Bi(III)/Bi(V), Se(IV)/Se(VI), Sb(III)/Sb(V), Sn(II)/Sn(IV), Te(IV)/Te(VI) in hydride generation AAS. Sensitivity differences of elemental species of different valency states have also been observed in ICP spectrometry for As(III)/As(V), Os(IV)/Os(VIII),  Te(IV)/Te(VII). Sensitivity differences have also been observed for inorganic/organic species with respect to Hg for GFAAS and ETV-ICP-MS, Se for GFAAS and ICP-MS, Iodine in ICP-MS and Si in ICP-OES. The analyte speciation also has a significant influence on direct sample introduction methods such as laser ablation or spark ablation.

To summarize, it is very complex to assure that different species contribute to an element signal with the same sensitivity, making direct analysis (dilute and shoot) for total element determinations very problematic. Validation by a recovery test of a spiked standard is not sufficient to prove trueness of obtained results !

Michael Sperling

Related Publications

 Ignacio López-García, Clare O'Grady, Malcolm Cresser, Pneumatic Nebulizers - Poor Pumps and Inferior Sub-samplers, J. Anal. At. Spectrom., 2/2 (1987) 221-225. DOI: 10.1039/JA9870200221

Maciej Stafinski, Marcin Wieczorek, Pawel Koscielniak, Influence of the species effect on trueness of analytical results estimated by the recovery test when determining selenium by HG-AFS, Talanta, 117 (2013) 64–69. doi: 10.1016/j.talanta.2013.08.046

Effect of the valency state of different species on their detection by flame AAS

Masaaki Yanagisawa, Masami Suzuki, Tsugio Takeuchi, Cationic interferences in the atomic absorption spectrophotometry of chromium, Anal. Chim. Acta, 52 (1970) 386-389. doi:10.1016/S0003-2670(01)80974-0

 Jeffrey A. Hurlbut, C.D. Chriswell, Suppression of Interferences by Sodium Sulfate in Trace Chromium Analyses by Atomic Absorption Spectrometry, Anal. Chem., 43/3 (1971) 465-466. DOI: 10.1021/ac60298a026

 H.C. Green, The effect of valency state on the determination of chromium in perchloric acid media by atomic absorption spectrophotometry, Analyst (London), 100 (1975) 640-642. DOI: 10.1039/AN9750000640

 Malcolm S. Cresser, R. Hargitt, The significance of the CrO4˛- <=> HCrO4- equilibrium in the determination of chromium(VI) by flame spectrometry, Talanta, 23 (1976) 153-154. doi:10.1016/0039-9140(76)80040-9   

 John Aggett, Glennys A. O'Brian, Formation of Chromium Atoms in Air-Acetylene Flames. Part 1. Atom Formation from Pure Chromium Compounds, Analyst (London), 106 (1981) 497-505. DOI: 10.1039/AN9810600497

 R. Kaszermann, K. Theurer, Effect of Valence State on the Determination of Arsenic by Flame Atomic Absorption, At. Absorpt. Newsletter, 15/6 (1976) 129-133.

 K. Clive Thompson, K. Wagstaff, Some Observations on the Determination of Iron by Atomic-absorption Spectrophotometry Using Air-Acetylene Flames, Analyst (London), 105 (1980) 641-650. DOI: 10.1039/an9800500641

 J. Kragten, Improved Determination of Vanadium by Flame AAS by Preventing Polynuclear Hydroxide Complex Formation, At. Spectrosc., 2/4 (1981) 135-136.

 V.N. Pichkov, O.V. Rudnitskaya, The effect of ruthenium forms in solution on its atomic absorption determination, Zh. Anal. Khim., 43 (1988) 677-679.

 J. B. Willis, B. T. Sturman, Observations on the effect of oxidation state on the sensitivity of flame AAS determinations of tellurium, J. Anal. At. Spectrom., 14/5 (1999) 895-896. DOI: 10.1039/a900416e

Effect of the valency state of different species on their detection by graphite furnace AAS

 Bernhard Welz, Gerhard Schlemmer, Uwe Völlkopf, Influence of the valency state on the determination of selenium in graphite furnace atomic absorption spectrometry, Spectrochim. Acta, Part B, 39/2-3 (1984) 501-510.  DOI: 10.1016/0584-8547(84)80057-9

 Viliam Krivan, M. Kückenwaitz, Preatomization behaviour of Se(-II), Se(IV), and Se(VI) in the graphite furnace without and with matrix modifier, Fresenius J. Anal. Chem., 342/9 (1992) 692-697. doi: 10.1007/BF00321857

 F. Sahin, M. Volkan, O.Y. Ataman, Effect of nitric acid for equal stabilization and sensitivity of different selenium species in electrothermal atomic absorption spectrometry, Anal. Chim. Acta, 547/1 (2005) 126-131. doi:10.1016/j.aca.2005.05.046

Irina B. Karadjova, Panayot K. Petrov, Ivan Serafimovski, Trajce Stafilov,
Dimiter L. Tsalev, Arsenic in marine tissues - The challenging problems to electrothermal and hydride generation atomic absorption spectrometry, Spectrochim. Acta, Part B, 62/3 (2007)  258-268. doi:10.1016/j.sab.2006.10.008

Effect of the valency state of different species on their detection by hydride generation AAS

Bernhard Welz, Marianne Melcher, Influence of Valence State on the Determination of Antimony in Steel using the Hydride AA Technique, At. Spectrosc., 1/5 (1980) 145-147.

 Hans-Werner Sinemus, Marianne Melcher, Bernhard Welz, Influence of Valence State on the Determination of Antimony, Arsenic, Bismuth, Selenium and Tellurium in Lake Water Using the Hydride AA Technique, At. Spectrosc., 2/3 (1981) 81-86.

 Bernhard Welz, Marianne Melcher, Mechanisms of Transition Metal Interferences in Hydride Generation Atomic-absorption Spectrometry Part 2. Influence of the Valency State of Arsenic on the Degree of Signal Depression Caused by Copper, Iron and Nickel,  Analyst (London), 109/5 (1984) 573-575. DOI: 10.1039/an9840900573

Juan Ramon Castillo-Suarez, M.C. Martinez, J.M. Mir, Interference on Antimony Determination by Hydride Generation - Atomic Absorption Spectrometry. Influences of the Valence State of Antimony on these Interferences, At. Spectrosc., 9/5 (1988) 179-180.

 Juan Ramon Castillo-Suarez, J.M. Mir, Study of the conditions for generating volatile covalent hydrides (VCH) of tin from solutions of tin(II) and tin(IV) and atomization in a silica tube, Microchem. J., 39 (1989) 119-125. doi:10.1016/0026-265X(89)90017-9 

 Ragnar Bye, Considerations on the Different Oxidation States of Antimony, Arsenic and Selenium in the Determination of the Elements by Hydride Generation - Atomic Spectrometry, Talanta, 37/10 (1990) 1029-1030. doi:10.1016/0039-9140(90)80146-7   

 Z. Slejkovec, J.T. van Elteren, U.D. Woroniecka, Underestimation of the total arsenic concentration by hydride generation techniques as a consequence of the incomplete mineralization of arsenobetaine in acid digestion procedures, Anal. Chim. Acta, 443/2 (2001) 277-282. doi:10.1016/S0003-2670(01)01223-5 

 Irina B. Karadjova, Panayot K. Petrov, Ivan Serafimovski, Trajce Stafilov,
Dimiter L. Tsalev, Arsenic in marine tissues - The challenging problems to electrothermal and hydride generation atomic absorption spectrometry, Spectrochim. Acta, Part B, 62/3 (2007)  258-268. doi:10.1016/j.sab.2006.10.008

Petra Taurková, Milan Svoboda, Stanislav Musil and Tomáš Matoušek, Loss of di- and trimethylarsine on Nafion membrane dryers following hydride generation, J. Anal. At. Spectrom., 26/1 (2011) 220-223. DOI: 10.1039/C0JA00136H

Effect of the valency state of different species on their detection by ICP spectrometry

K.D. Summerhays, P.J. Lamothe, T.L. Fries, Volatile Species in Inductively Coupled Plasma Atomic Emission Spectroscopy: Implications for Enhanced Sensitivity, Appl. Spectrosc., 37/1 (1983) 25-28. DOI: 10.1366/0003702834634136

 J.M. Bazan, Enhancement of Osmium Detection in Inductively Coupled Plasma Atomic Emission Spectrometry, Anal. Chem., 59/7 (1987) 1066-1069. DOI: 10.1021/ac00134a031

 Angel López-Molinero, J.R. Castillo-Suarez, J.M. Mermet, Observations on the determination of osmium by inductively-coupled plasma atomic emission spectroscopy,
Talanta, 37/9 (1990) 895-899. doi:10.1016/0039-9140(90)80249-F

 T.D. Martin, C.A. Brockhoff, J.T. Creed, Trace metal valence state consideration in utilizing an ultrasonic nebulizer for metal determination by inductively coupled plasma atomic emission spectrometry (ICP-AES), ICP Inf. Newsl., 19 (1994) 730.

 John T. Creed, Theodore D. Martin, Carol A. Brockhoff, Ultrasonic Nebulization and Arsenic Valence State Considerations Prior to Determination via Inductively Coupled Plasma Mass Spectrometry, J. Anal. At. Spectrom., 10/6 (1995) 443-447. DOI: 10.1039/JA9951000443

 Jin-fu Yang, John A. Koropchak, Valence Discrimination Effects with Thermospray Sample Introduction: Characterization and Prevention, Appl. Spectrosc., 51/10 (1997) 1573-1578. DOI:10.1366/0003702971939127

 R.C. Richter, S.R. Koirtyohann, S.S. Jurisson, Determination of technetium-99 in Aqueous Solutions by Inductively Coupled Plasma Mass Spectrometry: Effects of Chemical Form and Memory, J. Anal. At. Spectrom., 12/5 (1997) 557-562. DOI: 10.1039/a606483c

 Assad S. Al-Ammar, Rajesh K. Gupta, Ramon M. Barnes, Correction for volatility differences between organic sample analytes and standards in organic solutions analyzed by inductively coupled plasma-atomic emission and mass spectrometry, J. Anal. At. Spectrom., 14/5 (1999) 793-799. DOI: 10.1039/a808391f

 Lee L. Yu, Therese A. Butler, Gregory C. Turk, Effect of Valence State on ICP-OES Value Assignment of SRM 3103a Arsenic Spectrometric Solution, Anal. Chem., 78/5 (2006) 1651-1656. doi: 10.1021/ac051732i

Tomohiro Narukawa, Takayoshi Kuroiwa, Koichi Chiba, Mechanism of sensitivity difference between trivalent inorganic As species [As(III)] and pentavalent species [As(V)] with inductively coupled plasma spectrometry, Talanta, 73/1 (2007) 157-165. doi: 10.1016/j.talanta.2007.03.021

Tomohiro Narukawa, Koichi Chiba, Takayoshi Kuroiwa, Kazumi Inagaki, Differences in sensitivity between As(III) and As(V) measured by inductively coupled plasma spectrometry and the factors affecting the incoherent molecular formation (IMF) effect in the plasma, J. Anal. At. Spectrom., 25/11 (2010) 1682-1687. DOI: 10.1039/C0JA00011F

Marco Grotti, Francisco Ardini, Amanda Terol, Emanuele Magi, Jose Luis Todolí, Influence of chemical species on the determination of arsenic using inductively coupled plasma mass
spectrometry at a low liquid flow rate
, J. Anal. At. Spectrom., 28 (2013) 1718-1724. DOI: 10.1039/c3ja50159k

Koichi Chiba, Tomohiro Narukawa, The Effect of Plasma Reactions on Arsenic Measurement by ICP Spectrometry, Anal. Sci., 30/1 (2014) 175-181. doi: 10.2116/analsci.30.175

Effect of inorganic/organic species on element sensitivity

 David E. Nixon, Garry V. Mussmann, Steven J. Eckdahl, Thomas P. Moyer, Total Arsenic in Urine: Palladium-Persulfate vs Nickel as a Matrix Modifier for Graphite Furnace Atomic Absorption Spectrophotometry, Clin. Chem. (Winston-Salem, N.C.), 37/9 (1991) 1575-1579. PDF available at: http://www.clinchem.org/cgi/reprint/37/9/1575

 Francisco Laborda, Jorge Vińuales, José M. Mir, Juan R. Castillo, Effect of Nickel and Palladium as Chemical Modifiers and Influences of Urine Matrix on Different Chemical Species of Selenium in Electrothermal Atomic Absorption Spectrometry, J. Anal. At. Spectrom., 8/5 (1993) 737-743. DOI: 10.1039/JA9930800737

 Michelle Deaker, William Maher, Determination of Selenium in Seleno Compounds and Marine Biological Tissues Using Electrothermal Atomization Atomic Absorption Spectrometry, J. Anal. At. Spectrom., 10/6 (1995) 423-431. DOI: 10.1039/JA9951000423

 Vera I. Slaveykova, Faramarz Rastgar, Maurice J.F. Leroy, Behaviour of Various Arsenic Species in Electrothermal Atomic Absorption Spectrometry, J. Anal. At. Spectrom., 11/10 (1996) 997-1002. DOI: 10.1039/JA9961100997

 Alain Leblanc, Urine Selenium Determination by Electrothermal Atomic Absorption Spectrometry : Influence of Urinary Phosphates on the Trimethylselenonium Ion Signal, J. Anal. At. Spectrom., 11 (1996) 1093-1098. DOI: 10.1039/JA9961101093

 Jin-fu Yang, John A. Koropchak, Valence Discrimination Effects with Thermospray Sample Introduction: Characterization and Prevention, Appl. Spectrosc., 51/10 (1997) 1573-1578. DOI:10.1366/0003702971939127

 Bente Gammelgaard, Erik H. Larsen, Sensitivities of selenite, selenate, selenomethionine and trimethyl-selenonium ion in aqueous solution and in blood plasma - ETAAS compared with ICP-MS, Talanta, 47/2 (1998) 503-507. doi:10.1016/S0039-9140(98)00056-3   

 De-qiang Zhang, Zhe-ming Ni, Han-wen Sun, Stabilization of organic and inorganic mercury in the graphite furnace with ammonium hexachloropalladate/ammonium hexachlororhodate as a mixed chemical modifier, Spectrochim. Acta, Part B, 53/6-8 (1998) 1049-1055. doi:10.1016/S0584-8547(98)00100-1

 James P. Snell, Erik Björn, Wolfgang Frech, Investigation of errors introduced by the species distribution of mercury in organic solutions on total mercury determination by electrothermal vaporisation-inductively coupled plasma mass spectrometry, J. Anal. At. Spectrom., 15/4 (2000) 397-402. DOI: 10.1039/a909801a

 B. Langlois, Determination of iodine at ppt level in a nitric acid medium by ICP sector field mass spectrometry : influence of chemical forms, Ph.D. Thesis, University Lyon I, France, 2001, pp. 300.

 Ma. Eva Moreno, Concepción Pérez-Conde, Carmen Cámara, The effect of the presence of volatile organoselenium compounds on the determination of inorganic selenium by hydride generation, Anal. Bioanal. Chem., 375/5 (2003) 666-672. doi: 10.1007/s00216-003-1774-8

 A.M. Featherstone, A.T. Townsend, G.A. Jacobson, G.M. Peterson, Comparison of methods for the determination of total selenium in plasma by magnetic sector inductively coupled plasma mass spectrometry, Anal. Chim. Acta, 512/2 (2004) 319-327. doi:10.1016/j.aca.2004.02.058

 Dijana Juresa, Doris Kuehnelt, Kevin A. Francesconi, Consequences of Vapor Enhancement on Selenium Speciation Analysis by HPLC/ICPMS, Anal. Chem., 78/24 (2006) 8569-8574. DOI: 10.1021/ac061496r

 Dijana Juresa, Jerome Darrouzes, Norbert Kienzl, Maite Bueno, Florence Pannier, Martine Potin-Gautier, Kevin A. Francesconi, Doris Kuehnelt, An HPLC/ICPMS study of the stability of selenosugars in human urine: implications for quantification, sample handling, and storage, J. Anal. At. Spectrom., 21/7 (2006) 684-690. DOI: 10.1039/b602976k

 T. Narukawa, T. Kuroiwa, T. Yarita, K. Chiba, Analytical sensitivity of arsenobetaine on atomic spectrometric analysis and the purity of synthetic arsenobetaine, Appl. Organomet. Chem., 20/9 (2006) 565-572. doi: 10.1002/aoc.1091

 Irina B. Karadjova, Panayot K. Petrov, Ivan Serafimovski, Trajce Stafilov, Dimiter L. Tsalev, Arsenic in marine tissues - The challenging problems to electrothermal and hydride generation atomic absorption spectrometry, Spectrochim. Acta, Part B, 62/3 (2007)  258-268. doi:10.1016/j.sab.2006.10.008

Raquel Sánchez, José-Luis Todolí, Charles-Philippe Lienemann,  Jean-Michel Mermet, Effect of the silicon chemical form on the emission intensity in inductively coupled plasma atomic emission spectrometry for xylene matrices, J. Anal. At. Spectrom., 24/4 (2009) 391-401. doi: 10.1039/b806594m

Raquel Sánchez, José Luis Todolí, Charles-Philippe Lienemann, Jean-Michel
Mermet, Minimization of the effect of silicon chemical form in xylene on ICP-AES
performance, J. Anal. At. Spectrom., 24/10 (2009) 1382-1388.  DOI: 10.1039/b906568g

Javier Montiel, Guillermo Grindlay, Luis Gras, Margaretha T.C. de Loos-Vollebregt, Juan Mora, The influence of the sample introduction system on signals of different tin compounds in inductively coupled plasma-based techniques, Spectrochim. Acta Part B, 81 (2013) 36-42. doi: 10.1016/j.sab.2012.12.008

Influence of analyte species on element sensitivity in direct solid sampling

 M. Motelica-Heino, Olivier F.X. Donard, J.M. Mermet, Laser ablation of synthetic geological powders using ICP-AES detection: effects of the matrix, chemical form of the analyte and laser wavelength, J. Anal. At. Spectrom., 14/4 (1999) 675-682. DOI: 10.1039/a808088g

 Volker Thomsen, Spectroscopy Tutorial: Fractals in Spectrochemistry, The Spark OES Pulse-Height Distribution for Inclusions in Metals, Spectroscopy (Eugene, Oreg.) , 16/12 (2001) 20-22

Influence of analyte species (or phases) on isotope ratio determinations by mass spectrometry

L.R. Riciputi, J.P. Greenwood, Analysis of sulfur and carbon isotope ratios in mixed matrices by secondary ion mass spectrometry: Implications for mass bias correction, Int. J. Mass Spectrom., 178/1-2 (1998) 65-71. doi:10.1016/S1387-3806(98)14086-1   

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EVISA News, March 31, 2009: ICP-OES sensitivity for silicon depends on silicon-species

last time modified: April 21, 2014


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