Abstract:

Trace element analyses of marine sediments provide important information on past oceanographic and climatic changes. Five samples consisting of grey to black marls with layers of carbonate nodules (so called “Terre Noires” from a 102 m long profile from Oze, Southern France) were prepared in three different ways to find the most appropriate preparation technique for major, minor and trace elements by LA-ICP-MS analysis:

1. Powder pills were dry pressed after milling 30 g of a sample down to fine powder (around 1 μm in size).

2. Cubes of marl were cut out of the hand specimens and analyzed directly after polishing.

3. Fused glasses were prepared by mixing a 5:1 ratio of flux (Li2B4O7) to finely ground samples.

The LA ICP-MS analysis was performed using a pulsed 193 nm ArF Excimer laser (with a homogenized beam profile) in combination with an ELAN 6100 DRC ICP-MS. Samples were measured for the following elements: Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Sn, Cs, Ba, La, Ce, W, Tl, Pb, Bi, U. Analytical precision based on replicate analyses depends strongly on the preparation method. Typical RSDs (relative standard deviations) from analyses of the mentioned elements in powder pills range between 5 % (Mn, Sr) and 50 % (Zn). For the cubes generally higher RSDs were found than in the powder pills, between 5 % (Sc) and 90 % (Cu). Generally, RSDs from fused glass pills were lower than 6 %. Heterogeneous element distribution in the cubes leads to non-representative sampling by the laser and these data can therefore not be considered for interpretation of the results. From the statistics it can be seen that the analyses of powder pills are better but the RSDs are still unacceptably high. Statistically the best analytical results are obtained from the homogeneous glass pills. Therefore lithium borate fused glasses is the preferred method of preparation for sediment analysis.