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Trace Metals Analysis

Alpha Analytical utilizes inductively coupled plasma mass spectrometry (ICP/MS) with collision/reaction cell technology for trace metals analysis that may result in false positives/biased results in standard ICP/MS, because analyte ions for certain masses have isobaric interferences.

Trace Metals in Seawater or Brackish Waters

Determining metals concentrations in seawater is challenging, due to the high total dissolved solids present that interfere with many analyses yielding false positive, false negative or biased results. Although these interferences can be minimized through sample dilution, 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 Analytical to analyze seawater for trace metals which minimize or eliminate analytical interferences while yielding low reporting limits. 

Chelation Extraction Technique

Chelation extraction and pre-concentration procedures could be necessary when analyzing seawater to alleviate two analytical problems: 1) extremely high concentrations of sodium cause spectroscopic interferences that limit the accuracy of the analysis (or requires sample dilution and elevated detection limits); and 2) the required trace metals detection limits are extremely low. The chelation extraction procedure achieves quantitative transfer 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 produced 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 that can yield low-detection limit, interference-free sample results.

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