Speciation has been defined as ‘the distribution of an element amongst defined chemical species in a system’. Chemical species include isotopic composition, electronic or oxidation states and molecular structures. Speciation analysis is the analytical process of identifying and/or measuring the amounts of one or more individual chemical species in a sample.
Why is speciation important? Speciation analysis has become important for food, environmental, and pharmaceutical industries, where simply measuring the total amount of an element is insufficient. Identifying the different species and concentrations of those species provides a more informed understanding of the environmental or health related impact associated with a particular sample. The clinical or environmental approach would be very different depending on the concentration of the toxic species. For example, an exposure to toxic inorganic arsenic (arsenite and arsenate) is a much bigger concern than an exposure to the mildly toxic organic arsenic species. In contrast, organic mercury species are more toxic than inorganic mercury species, so an exposure to methylmercury or ethylmercury poses a more severe health risk.
How is speciation analysis performed? IC-ICP-MS provides a complete inorganic elemental analysis solution for speciation analysis.
-Metal-free ion chromatography (IC) separates the individual ionic species without contributing trace metal contamination -Ion Chromatography-Inductively Coupled Plasma Mass Spectrometry (IC-ICP-MS) performs trace elemental detection and quantification
Metal-free IC (with high resolution ion exchange columns and simple online connectivity) together with high sensitivity ICP-MS and integrated software are a powerful combination for fast and efficient metal speciation.
Chromium
Location: Group 6, Period 4 Atomic Weight: 51.9961 Coordination Number: 6 Chemical Form in Solution: Cr(H2O)63+
Storage & Handling: Keep tightly sealed when not in use. Store and use at 20 ± 4°C. Do not pipet from container. Do not return portions removed for pipetting to container.
Chemical Compatibility: Stable in HCl, HNO3, H2SO4, HF, H3PO4. Avoid basic media. Stable with most metals and inorganic anions in acidic media.
Stability: 2-100 ppb levels stable for months in 1% HNO3 / LDPE container. 1-10,000 ppm solutions chemically stable for years in 1-5% HNO3 / LDPE container.
Cr Containing Samples (Preparation & Solution): Metal (soluble in HCl); Oxides / Ores (chrome ore/oxides are very difficult to dissolve. The following procedures A - D are commonly used:
A. Fusion with KHSO4 and extraction with hot KCl. The residue fused with Na2CO3 and KClO3, 3:1 B. Fusion with NaKSO4 and NaF, 2:1 C. Fusion with magnesia or lime and sodium or potassium carbonates, 4:1 D. Fusion with Na2O2 or NaOH and KNO3 or NaOH and Na2O2.
Nickel, iron, copper, or silver crucibles should be used for D. Platinum may be used for A, B, and C; Organic Matrices (ash at 450°C followed by one of the fusion methods above or Sulphuric / hydrogen peroxide acid digestions may be applicable to non oxide containing samples).
Atomic Spectroscopic Information: (red text indicates severe at ~ concs.)
Technique / Line
Estimated D.L.*
Order
Type
Interferences
ICP-OES 205.552 nm
0.006/.0008 µg/mL
1
ion
Os
ICP-OES 284.325 nm
0.008/.0007 µg/mL
1
ion
ICP-OES 276.654 nm
0.01/.001 µg/mL
1
ion
Cu, Ta, V
ICP-MS 52 amu
40 ppt
n/a
M-
36S16O, 36Ar16O**
*ICP-OES D.L.'s are given as radial / axial view **The 50Cr, 53Cr, 54Cr lines suffer from many more potential interferences from Sulphur, chlorine, and argon compounds of oxygen, nitrogen, and carbon.
