Sasi S. Kannamkumarath

Capillary electrophoresis-inductively coupled plasma-mass spectrometry: an attractive complementary technique for elemental speciation analysis.

Some basic and practical aspects of interfacing capillary electrophoresis to inductively coupled plasma-mass spectrometry (CE-ICP-MS) are reviewed in this article with emphasis on the use of this hyphenated technique for elemental speciation analysis. The principles behind the techniques of both CE and ICP-MS are introduced. The interfacing of CE to ICP-MS is discussed including several devices and nebulizers reported in literature. A brief account of their advantages and limitations is given. The various CE-ICP-MS applications for elemental speciation analysis are also reviewed. Some issues concerning the future of CE-ICP-MS for the elemental speciation analyses are discussed.

Determination of As(III), As(V), monomethylarsonic acid, dimethylarsinic acid and arsenobetaine by HPLC-ICP-MS: analysis of reference materials, fish tissues and urine

In this study, a rapid and sensitive high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) determination of primary As species in fish tissues and urine is reported. The separation was achieved on an Altima C18 column with a mobile phase containing citric acid and hexanesulfonic acid (pH 4.5). As(V), monomethylarsonic acid (MMA), As(III), dimethylarsinic acid (DMA) and arsenobetaine (AsB) were separated in less than 4 min with retention times of 83, 99, 130, 166 and 208 s, respectively. This separation of five species in less than 4 min should be attractive to those interested in As speciation. The quantification limits were 44, 56, 94, 64, 66 ng l(-1) and the relative standard deviations (R.S.D.) for day-to-day injections of As at 2 mug l(-1) were 2.0, 3.1, 2.4, 3.8 and 4.0%. The procedure was tested using two reference materials (DORM-2 dogfish muscle tissue, NIST SRM 2670 Freeze-dried Urine, normal level) and then applied to real-world samples. The results obtained demonstrate the suitability of the procedure for screening and quantification at physiological levels of primary As species in biological samples.

Identification and characterization of selenium species in enriched green onion (Allium fistulosum) by HPLC-ICP-MS and ESI-ITMS

In this study speciation of selenium in selenium-enriched green onions (Allium fistulosum) was done with reversed-phase ion-pairing high performance liquid chromatography (RP-IP-HPLC) and size-exclusion chromatography (SEC) coupled on-line to ICP-MS for selenium specific detection. The plant extract obtained using sodium hydroxide (0.1 mol l−1) analyzed by SEC (CAPS 10 mmol l−1, pH 10.0) with ICP-MS detection showed the incorporation of selenium in both high (∼12 kDa) and low molecular weight (0.36–2 kDa) fractions. Presumably protein bound selenoamino acids were released using enzymes (Proteinase K and Protease XIV) and selenoamino acids found in cytosol in their free form were extracted using 0.1 M HCl. The extracts were analyzed for speciation studies by RP-IP-HPLC [0.1% (v/v) heptafluorobutyric acid, 5% (v/v) methanol, pH 2.5]. Matching the chromatographic retention times with commercially available standards provided evidence for the presence of Se-cystine, methylselenocysteine, Se-methionine, and inorganic selenium. Electrospray ionization ion trap mass spectrometry (ESI-ITMS) confirmed the presence of γ-glutamyl-Se-methylselenocysteine in green onions as has been reported in other onion types.

Iodine speciation studies in commercially available seaweed by coupling different chromatographic techniques with UV and ICP-MS detection

Speciation of iodine in commercially available commonly consumed seaweed samples was performed using a multidimensional chromatographic approach coupled with inductively coupled plasma mass spectrometry (ICP-MS) for element specific detection. Analysis of alkaline extract (0.1 mol l−1 NaOH) by size-exclusion chromatography coupled to ICP-MS (0.03 mol l−1 Tris-HCl, pH 8.0) indicated the association of iodine with both high as well as low molecular weight fractions in Wakame, while in case of Kombu, only low molecular weight iodine species were found. Likely association of iodine with protein as well as polyphenolic species was indicated in the case of Wakame. Anion-exchange chromatography coupled to ICP-MS (0.005 mol l−1 NaOH) confirmed that the most predominant inorganic iodine species present in both type of seaweeds is iodide. Protein bound iodinated species were hydrolyzed by enzymatic digestion using Proteinase K. Analysis of the hydrolysate using reversed-phase HPLC-ICP-MS (0.01 mol l−1 Tris-HCl pH 7.3 ∶ 0.01 mol l−1 Tris-HCl pH 7.3 and 50% MeOH) revealed the presence of monoiodotyrosine and di-iodotyrosine in Wakame, which was later identified by matching the chromatographic retention time with the retention time of commercially available standards.

Studying the distribution pattern of selenium in nut proteins with information obtained from SEC-UV-ICP-MS and CE-ICP-MS

In this work, size exclusion chromatography (SEC) with UV and inductively coupled plasma mass spectrometry (ICP-MS) detection was used to study the association of selenium to proteins present in Brazil nuts (Bertholletia excelsa) under five different extraction conditions. As expected, better solubilization of proteins was observed using 0.05molL(-1) sodium hydroxide and 1% sodium dodecylsulfate (SDS) in Tris/HCl buffer (0.05molL(-1), pH 8) as compared to 0.05molL(-1) HCl, 0.05molL(-1) Tris/HCl or hot water (60 degrees C). Due to non-destructive character of Tris-SDS treatment, this was applied for studying molecular weight (MW) distribution patterns of selenium-containing nut proteins. Three different SEC columns were used for obtaining complete MW distribution of selenium: Superdex 75, Superdex Peptide, and Superdex 200 were tested with 50mmolL(-1) Tris buffer (pH 8), 150mmolL(-1) ammonium bicarbonate buffer (pH 7.8), phosphate (pH 7.5), and CAPS (pH 10.0) mobile phases. Using Superdex 200 column, the elution of at least three MW fractions was observed with UV detection (200-10kDa) and ICP-MS chromatogram showed the co-elution of selenium with the two earlier fractions. The apparent MWs of these selenium-containing fractions were respectively about 107 and 50kDa, as evaluated from the column calibration. For further characterization of individual selenium species, the defatted nuts were hydrolyzed with proteinase K and analyzed by capillary electrophoresis (CE) with ICP-MS detection. The suitability of CE for the separation of selenite, selenate, selenocystine and selenomethionine in the presence of the nut sample matrix is demonstrated. Complete separation of the above mentioned selenium species was obtained within a migration time of 7min. In the analysis of nut extracts with CE-ICP-MS, selenium was found to be present mainly as selenomethionine.

Determination of levothyroxine and its degradation products in pharmaceutical tablets by HPLC-UV-ICP-MS

A new analytical methodology using high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) was applied to study the presence of possible degradation products in levothyroxine tablets. The analytical methodology takes advantage of the element-specific and highly-sensitive I detection provided by ICP-MS and is applied to the speciation of: 3,3′,5,5′-tetraiodothyronine (T4); 3,3′,5-triiodothyronine (T3); 3,5-diiodothyronine (T2); 3,3′,5,5′-tetraiodothyroacetic acid (TTAA4); 3,3′,5-triiodothyroacetic acid (TTAA3); and 3,5-diiodothyroacetic acid (TTAA2). Chromatographic conditions were optimized by using UV absorption at 225 nm and ICP-MS detection of 127I. Complete chromatographic resolution of the levothyroxine degradation products within 25 min was obtained using 22% (v/v) acetonitrile at pH 2.3, adjusted with 0.08% (v/v) trifluoroacetic acid. The introduction of the mobile phase containing acetonitrile was performed by post column on-line dilution (1∶3.3) of the chromatographic eluent with a 2% (v/v) nitric acid solution using a PTFE tee. The separations with either detector were good with little detector effect on the resolution. The peak broadening caused by on-line dilution was insignificant. The detection limits obtained with UV detection ranged from 28.9 to 34.5 µg l−1, whereas those obtained with the plasma detector were about 175–375 times better (lower). Finally, the analytical methodology was applied to the determination of possible iodine species originated by degradation of T4 in synthetic and commercial levothyroxine sodium tablets.

Determination of 2,4,6-triiodophenol and its metabolites in human urine by anion-exchange chromatography with ICP-MS detection

An analytical method using high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) was developed for the separation and determination of iodophenol compounds in human urine samples. The advantages of using highly-sensitive 127I detection provided by ICP-MS for the speciation of 2,4,6-triiodophenol, 4-iodophenol and 2-iodophenol are shown in this work. 2,4,6-triiodophenol is also referred to as Bobel-24, an anti-inflammatory. Chromatographic conditions were optimized using UV absorption at 254 nm and ICP-MS detection of 127I and a comparative study between these two detection systems was developed. The separation of iodophenol species was studied by two different chromatographic modes: reversed-phase and anion-exchange chromatography. Complete chromatographic resolution of the iodophenol species was obtained in 100% aqueous phase solution using gradient elution of NaOH (50 mmol l−1) and NaOH (50 mmol l−1) with hexadecyltrimethylammonium bromide (CTAB). Total resolution was obtained in a minimal retention time of 7 min. Since the separation of the iodophenol species was performed in an aqueous mobile phase, high sensitivity was obtained with the ICP-MS instrument. The detection limits obtained were between 0.08–0.22 µg l−1 as iodophenol compounds. On the other hand, the detection limits obtained with UV detection were 300–325 times higher with ICP-MS. Finally, the analytical methodology was applied for the determination of iodophenols in human urine.

Environmentally friendly sample treatment for speciation analysis by hyphenated techniques

Trace element speciation has become an important issue in different fields of science. Research interests have moved from total element composition of the sample toward characterization of species that are responsible for biochemical and geochemical behavior of the elements. In this report, two important environmental aspects of trace element speciation by hyphenated techniques are discussed. First, the analytical results that are useful in assessing pollution and evaluating possible toxicological risks followed by designing the remediation strategies are considered. On the other hand, performing the analytical procedures involves a certain environmental impact. Within this context, current hyphenated techniques are reliable analytical tools and also present relatively low environmental hazards. However, the successful application of these techniques for the analysis of complex samples relies on the use of suitable pretreatment procedures that should be considered as the main source of wastes in the analysis. Several modern sample preparation techniques offer improved efficiency and selectivity over classical extractions: short extraction times, reduced solvent utilization and possible miniaturization and automation. In this article, the advantages and limitations of solid phase extraction, solid phase microextraction and supercritical fluid extraction are discussed and their applications in trace element speciation briefly reviewed.