Determination of trace elements in marine suspended particulate material using inductively coupled plasma mass spectrometry

The importance of trace metals to primary productivity in the ocean, and the ability of plankton to decrease inorganic carbon concentrations in the ocean's surface thereby facilitating diffusion of CO2 into the ocean, is extremely important to investigate. Studies of trace metals in the ocean are complicated by generally low concentrations (typically picomolar to nanomolar), a high potential for contamination, and interactions between dissolved species and suspended particulate matter (SPM), which influence the distribution and concentration of trace elements. Research using inductively coupled plasma mass spectrometry combined with trace metal 'clean' techniques has introduced opportunities to advance our knowledge of the trace metal content of SPM. This research was focused on determining Al, P, S, Cr, Mn, Fe, Co, Ni, Cu, and Zn in planktonic material and SPM using ICP-MS. This was done by sampling the Equatorial Pacific. Water samples from this region were filtered and digested in order to be introduced into a Thermo Finnigan Element ICP-MS for determination of trace metals. The use of external standard curves versus standard addition curves for quantification was also examined. A cocktail of internal standards, In, Sc, Y, and Ge, were used to help correct for instrumental instability. It was found that instrumental LODs were below the concentrations of Equatorial Pacific samples. However, filter blanks constituted a non-negligible fraction of the SPM analytical signal for several elements, introducing uncertainty in quantification. External standard curves were found to be more precise and more applicable for studies using low volume samples. Determining the proper internal standard was difficult since there were a large number of elements and one internal standard will not have similar physical and chemical properties to all the elements investigated, but it was found that In or Sc worked the best for correcting for instrumental instability when examining a large suite of elements. Samples from the Equatorial Pacific were found to have similar metal to P (M:P) ratios compared to previous studies. The M:P ratios were 5.86, 0.89, and 1.12 mmol/mol for Fe/P, Mn/P and Ni/P respectively. The mean Fe (+/-SD) concentrations by station were 43.0+/-42.6, 59.8+/-29.4, 41.2+/-20.9, 46.2+/-16.3, and 59.0+/-23.4 pM for stations 4, 7, 10, 22, and 29. Cobalt mean concentrations were 7.2+/-2.1, 3.0+/-1.3, 2.6+/-1.8, 4.1+/-0.05, 2.5+/-2.6, and 3.4+/-2.7 pM for stations 2, 4, 7, 10, 22, and 29. The mean concentrations by station for Ni were 9.3+/-3.5, 7.0+/-3.3, 8.1+/-5.9, 3.7+/-3.8, 23.5+/-12.1, and 15.8+/-7.6 pM for stations 2, 4, 7, 10, 22, and 29.