APPLICATIONS
Metal speciation by ICP-MS
What is metal speciation?
The distribution of the different metallic forms is called “metallic speciation”. Metal speciation refers to the different chemical forms of the metal either as a free ion or complexed with a ligand or biomolecule (also called metalloids). These species of the same metal can be found in solid, liquid or gas phase. As a result, the chemical species of the element determines its mobility and toxicity in the environment.
Metal speciation by ICP-MS is based on chromatographic separation, such as gas chromatography (GC) or high performance liquid chromatography (HPLC), coupled to an elemental ionization source (ICP-MS). For this purpose, a chromatographic column coupled to ICP-MS is required to separate the different species of the same metal in order to quantify the metal species of interest.
ISC-SCIENCE has been implementing speciation methodologies for more than 15 years for four metals in particular: mercury (Hg), arsenic (As), tin (Sn) and chromium (Cr). For more information, please fill out our form.
Mercury speciation (Hg)
General information on Hg species
Hg can exist in three oxidation states: gaseous mercury (Hg(0)), mercurous mercury (Hg(I)), which exists as a dimer (Hg2+2), and divalent inorganic mercury (Hg(II)). In fact, only oxidizing compounds with potentials between -0.8 V and -0.85 V are able to oxidize Hg(0) to Hg2+2. Since no oxidizing compounds are found in the environment, oxidation of Hg(0) forms Hg(II).
Hg(II) can form organometallic Hg compounds by covalent bonds with carbon atoms. The most common species of organo-metallic Hg compounds in the hydrosphere are monomethylmercury (CH3-Hg+, MeHg) and dimethylmercury (CH3-Hg-CH3, DMeHg). MeHg is soluble in water, whereas DMeHg is a volatile compound with chemical properties similar to Hg(0). Although both organometallic compounds are stable to atmospheric oxidation and hydrolysis, they may degrade due to exposure to light or heat. Other organometallic Hg compounds found are ethyl mercury (EtHg) and phenyl mercury (Ph-Hg).
Analysis of Hg species
The simultaneous determination of Hg(II), MeHg and EtHg is usually based on gas chromatography (GC) or liquid chromatography (LC) coupled on-line to ICP-MS. Normally, the analysis of Hg(II), MeHg and EtHg is done by GC-ICP-MS as it provides lower detection limits. However, a derivatization step is required in which the Hg compounds are usually propylated or ethylated and subsequently transferred in organic solvent prior to injection into the GC port. This sample preparation may result in degradation of Hg compounds or losses due to incomplete recoveries during the derivatization step.
Although quantification of Hg compounds can be carried out by various methodological calibrations such as external calibration, standard additions or by internal standards, only the use of isotopically enriched Hg standards allows correcting for compound losses of Hg species during sample preparation.
Applications
ISC-SCIENCE has implemented Hg speciation applications in different analytical laboratories. The main fields of application in which our team is specialized are:
ENVIRONMENTAL ANALYSIS
- Inland and wastewater analysis.
- Soil, sediment and sludge analysis.
- Analysis of atmospheric particles.
AGRI-FOOD ANALYSIS
- Drinking water analysis.
- Food analysis.
- Animal feed analysis.
ANALYSIS IN THE PHARMACEUTICAL INDUSTRY
- Determination of metals according to USP and ICH standards.
Chromium (Cr) speciation
General information on Cr
The two main forms of Cr are Cr(III) and Cr(VI). Trivalent Cr can be considered an essential nutrient for human health, as it is involved in the metabolism of glucose, insulin and proteins. However, Cr(VI) is classified as a Group A human carcinogen, causing serious health problems in the respiratory tract, liver, kidneys, gastrointestinal and immune systems. Therefore, several directives have been adopted at European and international level to carry out Cr speciation studies.
Analysis of Cr
The analysis of chromium species is performed by anion exchange liquid chromatography, where the two Cr species are separated, coupled to ICP-MS. The main problem is the interconversion of Cr species during sample preparation, which is highly dependent on the type of matrix and the type of extraction solution in sample preparation.
For example, the determination of Cr(VI) in toy samples according to COMMISSION directive (EU) 2018/725 is necessary since children are exposed to potential oral cancer. In this matrix it is often complicated to measure Cr species since quantitative extraction of the contaminant must be ensured and Cr(III)-Cr(VI) redox interconversion reactions during extraction and subsequent chemical analysis must be avoided. For this reason, isotope dilution mass spectrometry (IDMS) is the most efficient analytical strategy to accurately quantify Cr(VI).
The determination of Cr (VI) in soil samples can be complex. The analytical procedure, standardized by USEPA as method 6800 requires the addition of known amounts of isotopically enriched Cr(III) and Cr(VI) to the samples prior to extraction.
Applications
ISC-SCIENCE has implemented Cr speciation applications in different analytical laboratories. The main fields of application in which our team is specialized are:
Analysis of consumer goods
- Analysis of toys.
- Textile analysis.
Environmental analysis.
- Water analysis.
- Soil analysis.
Speciation of arsenic (As)
General information on As species
The toxicity of As species depends on their oxidation state and whether or not they are organometallically complexed. Unlike other chemical elements, the As species with the highest toxicity are inorganic (As(III) and As(V)). These As species cause serious diseases such as dermatitis, skin cancer and other cancers.
Analysis of As species
The presence of As naturally in soils makes plant species that are easily transported in it, as is the case of rice. Because rice is the most consumed food worldwide, the maximum levels of inorganic As in this food are currently legislated at the European level and are found in COMMISSION REGULATION (EU) 2015/1006 of 25 June 2015. To carry out its determination, the technique par excellence for such analysis is based on a separation of the different species by liquid chromatography (anion exchange) coupled to ICP-MS where ISC-SCIENCE staff is an expert.
Applications
ISC-SCIENCE has implemented As speciation applications in different analytical laboratories. The main fields of application in which our team is specialized are:
agri-food ANALYSIS
- Food analysis (rice).
Environmental analysis
- Water analysis.
- Soil analysis.
Tin (Sn) speciation
General information on Sn species
Tributyltin (TBT) and its degradation products dibutyltin and monobutyltin (DBT and MBT) have been described as the most toxic substance ever deliberately introduced as a biocide into the marine environment. Its use as a fungicide, bactericide, insecticide and wood preservative is now known to be harmful to a wide range of aquatic organisms, including microalgae, mollusks and crustaceans, fish and some invertebrates. When TBT began to be widely used in antifouling paints, scientists began to find increasingly high concentrations of TBT in areas where there were large crowds of ships, boats and vessels, such as in marinas and commercial harbors. As a result, several countries have introduced controls to limit the use of TBT in antifouling paints on small ships.
Analysis of Sn species
ICP-MS has been to date the most widely used detector in GC when using the ID technique in speciation studies. However, the cost of such GC-ICP-MS methodology can be very high for control laboratories. Alternatively, there is the possibility to measure isotope ratios of heteroelements present in organic molecules accurately using simpler, cheaper and more accessible instrumentation than GC-ICP-MS such as GC-MS equipment with electron impact ionization source. The advantages provided by isotope dilution analysis are not only reflected in the quality of the analytical results obtained, but also in the drastic reduction of analysis time (both in sample preparation and analytical measurement).
Applications
ISC-SCIENCE has implemented Sn speciation applications in different analysis laboratories. The main fields of application in which our team is specialized are:
Environmental analysis
- Drinking water analysis
- Surface water analysis.
- Marine water analysis.
- Sludge and sediment analysis.
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