Trace Metals Analysis
Trace Metals in Seawater or Brackish Waters
Determining metals concentrations in seawater is challenging due to the high total dissolved solids present which interfere with many analyses yielding false positive, false negative or biased results. These interferences can be minimized through sample dilution but then reporting limits are elevated accordingly. The major ions present in seawater (calcium, potassium, magnesium and sodium) can be determined following varied dilutions to get the analyte concentration within the linear dynamic range of the instrument. Though ICP/MS is an extremely sensitive technique, the linear dynamic range extends to high ppm concentrations.
A number of analytical methods are utilized at Alpha Analtyical to analyze seawater for trace metals which minimize or eliminate analytical interferences while yielding low reporting limits.
Chelation Extaction Technique
Chelation extraction and pre-concentration procedures could be necessary when analyzing seawater to alleviate two analytical problems: 1) very high concentrations of sodium present spectroscopic intereferences limiting the accuracy of the analysis or requiring sample dilution and elevated detection limits; and 2) the required trace metals detection lmits are extremely low. The chelation extraction procedure achieves quantitative removal of the metal analyte from the seawater matrix into a clean acid matrix without ionic interference, while concentrating the analyte up to 100-fold.
If chelate extraction is requested, a separatory funnel solvent extraction is performed utilizing two chelating agents to extract cadmium, cobalt, copper, iron, lead, nickel, silver, vanadium and zinc. Using this procedure, analytes are completely removed from the seawater matrix prior to analysis thus eliminating any interferences. Sample aliquots from 10mL to 200mL are prepared yielding pre-concentration factors of 1 to 20 prior to analysis by ICP/MS. The sensitivity of ICP/MS coupled with the pre-concentration factors associated with the extraction produces low detection limits for these analytes without analytical interference.
Hydride Generation Atomic Fluorescence
Hydride generation atomic fluorescence (HGAF) is used for the analysis of arsenic and selenium in seawater or other challenging matrices. Hydride generation is a technique where volatile derivatives of arsenic and selenium are generated with a strong reductant and then purged from the seawater matrix. These derivatives are then passed through a hydrogen flame and reduced to elemental form for analysis. Atomic fluorescence is an extremely sensitive analytical method which can yield low detection limit, interference-free sample results.