Determination of trace elements in aqueous solutions using the EMMA miniprobe XRF analyzer
✍ Scribed by Andriy K. Cheburkin; William Shotyk
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 109 KB
- Volume
- 28
- Category
- Article
- ISSN
- 0049-8246
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✦ Synopsis
The energy-dispersive miniprobe multielement analyzer (EMMA) is an XRF instrument to measure trace elements (As, Cr, Cu, Fe, Ga, Ge, Hf, Mn, Ni, Pb, Rb, Se, Sr, Th, Y, U, Zn) in small samples (down to ca 10 µm). Originally designed and constructed for analyzing individual mineral grains from rocks, EMMA can also be used for analyzing small volumes of aqueous solutions such as natural waters and acid digests. Liquid samples (100-150 µl) are evaporated on to a thin (4 µm) Teflon film in increments of 10 µl by heating with a lamp. This process leaves a circular residue which is then excited using a monochromatic x-ray beam (0.1 × 2.5 mm). Because monochromatic x-radiation is used for excitation (17.44 keV, Mo Ka), a low background is achieved and detection limits are excellent, ranging from 20 pg Sr to 700 pg Pb (ca 0.02-0.7 ng ml -1 ) for 100 µl of dilute natural water. Using an internal Y standard to quantify elemental concentrations, analyses of NIST SRM 1643C Trace Elements in Water were in good agreement with the certified values. With respect to acid digests of modern plant material, compared with solid samples the digests are characterized by a significantly lower background and improved detection limits. For example, Pb in a solid sample of NIST SRM 1515 Apple Leaves (0.47 µg g -1 ) was below the limit of detection using EMMA (0.6 µg g -1 ). However, Pb could easily be quantified in the acid digest of the same material, and was in excellent agreement (0.46 µg g -1 ) with the certified value. Similarly, acid digestion allowed the quantitation of Se in peat samples from continental bogs and As, Se and Pb in peat samples from maritime bogs. The main advantages of this method are the small volumes of solution required, the multielement capability [from Z = 19 (K) to Z = 92 (U)], sensitivity and low cost of analysis per sample. Unlike total reflection XRF (TXRF) methods, the detection limits which can be achieved using the EMMA technique are less dependent on the concentration of the matrix, making it useful for solutions ranging in ionic strength from rainwater to acid digests of biological and geological solid samples.