https://digital.library.unt.edu/ark:/67531/metadc780990/m2/1/high_res_d/861115.pdf

Laser ablation in analytical chemistry - A review

In situ analysis of trace elements in quartz by using laser ablation inductively coupled plasma mass spectrometry

Modern chemical sediments display a distinctive rare earth element + yttrium (REE + Y) pattern involving depleted LREE, positive La/La*SN, Eu/Eu*SN, and YSN anomalies (SN = shale normalised) that is related to precipitation from circumneutral to high pH waters with solution complexation of the REEs dominated by carbonate ions. This is often interpreted as reflecting precipitation from surface waters (usually marine). The oldest broadly accepted chemical sediments are c. 3,700 Ma amphibolite facies banded iron-formation (BIF) units in the Isua supracrustal belt, Greenland. Isua BIFs, including the BIF international reference material IF-G are generally considered to be seawater precipitates, and display these REE + Y patterns (Bolhar et al. in Earth Planet Sci Lett 222:43–60, 2004). Greenland Eoarchaean BIF metamorphosed up to granulite facies from several localities in the vicinity of Akilia (island), display REE + Y patterns identical to Isua BIF, consistent with an origin by chemical sedimentation from seawater and a paucity of clastic input. Furthermore, the much-debated magnetite-bearing siliceous unit of “earliest life” rocks (sample G91/26) from Akilia has the same REE + Y pattern. This suggests that sample G91/26 is also a chemical sediment, contrary to previous assertions (Bolhar et al. in Earth Planet Sci Lett 222:43–60, 2004), and including suggestions that the Akilia unit containing G91/26 consists entirely of silica-penetrated, metasomatised, mafic rock (Fedo and Whitehouse 2002a). Integration of our trace element data with those of Bolhar et al. (Earth Planet Sci Lett 222:43–60, 2004) demonstrates that Eoarchaean siliceous rocks in Greenland, with ages from 3.6 to 3.85 Ga, have diverse trace element signatures. There are now geographically-dispersed, widespread examples with Isua BIF-like REE + Y signatures, that are interpreted as chemically unaltered, albeit metamorphosed, chemical sediments. Other samples retain remnants of LREE depletion but are beginning to lose the distinct La, Eu and Y positive anomalies and are interpreted as metasomatised chemical sediments. Finally there are some siliceous samples with completely different trace element patterns that are interpreted as rocks of non-sedimentary origin, and include metasomatised mafic rocks. The positive La/La*SN, Eu/Eu*SN and YSN anomalies found in Isua BIFs and other Eoarchaean Greenland samples, such as G91/26 from Akilia, suggests that the processes of carbonate ion complexation controlling the REE − Y patterns were already established in the hydrosphere at the start of the sedimentary record 3,600–3,850 Ma ago. This is in accord with the presence of Eoarchaean siderite-bearing marbles of sedimentary origin, and suggests that CO2 may have been a significant greenhouse gas at that time.

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Seawater-like trace element signatures (REE + Y) of Eoarchaean chemical sedimentary rocks from southern West Greenland, and their corruption during high-grade metamorphism

On-line isotope dilution in laser ablation inductively coupled plasma mass spectrometry using a microflow nebulizer inserted in the laser ablation chamber

Major and trace element compositions of fifteen silicate rock reference materials have been determined by a combined XRF and laser ablation ICP-MS (LA-ICP-MS) technique on glasses prepared by fusing the sample with a lithium borate flux (sample:flux = 1:3). Advantages of this technique include the ability to measure major and trace element abundances on a single sample using a quick and simple preparation that attacks resistant phases such as zircon without the need for acid dissolution. The method is suitable for a wide variety of bulk compositions including mafic, intermediate and silicic rocks.



Abundance-normalized mass response patterns (the ratio of signal intensity to element concentration) of the LA-ICP-MS analyses vary systematically with major element composition, demonstrating the presence of a matrix effect that cannot be compensated by normalisation to a single internal standard element. Increasing the sampling distance between the ICP-MS cone and the torch reduces the magnitude of this effect, suggesting that a mechanism related to residence time of ablated particles in the plasma may be at least partially responsible for the observed variations in mass response patterns. When using a matrix-matched calibration, agreement of the LA-ICP-MS results with published reference values or those obtained by solution ICP-MS is 10% relative. Analytical precision based on replicate analyses is typically 5% RSD. Procedural detection limits that include contributions from gas background and flux are 0.01-0.1 μg g-1 for the heavy mass trace elements (Rb-U). Major element analyses by XRF show excellent agreement with results obtained using a conventional heavy element absorbing flux. High quality major and trace element data for silicate rocks can be achieved by a combined XRF and LA-ICP-MS analysis of Li2B4O7/LiBO2 fused glasses provided an appropriate matrix-matched calibration is adopted.



Les compositions en elements majeurs et en trace de quinze materiaux silicates de reference ont ete analyses en combinant XRF et ICP-MS couplea un laser (LA-ICP-MS) sur des verres prepares par fusion des echantillons avec un fondant au borate de lithium (rapport echantillon/fondant = 1:3). Les avantages de cette technique portent, entre autres, sur la possibilite de mesurer elements majeurs et en trace sur un meme echantillon, en utilisant une preparation simple et rapide qui attaque les phases resistantes telles que les zircons, sans necessiter une mise en solution par des acides. La methode est tres adaptee a une grande variete de compositions globales, couvrant les roches basiques, intermediaires et acides.



La courbe de reponse en masse, apres normalisation (le rapport entre l'intensite du signal et la concentration de l'element) de l'ICP-MS couplea un laser varie systematiquement avec la composition en elements majeurs de l'echantillon, montrant bien qu'il existe un effet de matrice, lequel ne peut pas etre compense par une normalisation a un seul standard interne. Une augmentation de la distance entre le cone de l'ICP-MS et la torche reduit l'amplitude de cet effet, suggerant en cela qu'un mecanisme lie au temps de residence des particules ablatees dans le plasma doit etre responsable, au moins partiellement, des variations observees. Quand on utilise une calibration avec des standards de meme matrice, l'accord entre valeurs mesurees par LA-ICP-MS et valeurs de references (ou valeurs obtenues par analyse ICP-MS en solution) est de 10% en relatif. La precision analytique basee sur des analyses dupliquees est typiquement 5% RSD. Les limites de detection typiques de cette procedure, qui recouvrent la contribution du bruit de fond et celle du fondant sont de 0.01 a 0.1 μg g-1 pour les elements de masse entre Rb et U. Les analyses des elements majeurs par XRF montrent un excellent accord avec les resultats obtenus en utilisant un fondant conventionnel.



En conclusion, des donnees de tres bonne qualite, pour les elements majeurs et en trace peuvent donc etre obtenues sur les roches silicatees en combinant l'analyse par XRF et LA-ICP-MS sur des verres avec les fondants Li2B4O7/LiBO2, si une calibration avec des standards de meme matrice est adoptee.

Major and Trace Element Analysis of Silicate Rocks by XRF and Laser Ablation ICP-MS Using Lithium Borate Fused Glasses: Matrix effects, Instrument Response and Results for International Reference Materials

Results of the use of a double-focusing, magnetic sector inductively coupled plasma mass spectrometer (ICP-MS) with ultraviolet (UV) laser ablation (LA) are presented for the bulk analysis of rare earth elements (REEs) in rocks fused with Li2B4O7. The sample preparation procedure used a sample to flux weight ratio of 1 : 7, and was identical with a procedure routinely used for X-ray fluorescence (XRF) analyses of major and minor elements in geological materials. Calibration was based on a total of 18 international standard reference materials (SRMs), and Ba was used as an internal standard element for all REEs. The calibration curves were constructed using a weighted regression model. The use of internal standard, without exception, improved the correlation coefficients significantly. The 3σ detection limits were established by a blank sample of SiO2 spiked with Ba, and were in the range from 0.003 μg g–1 (159Tb) to 0.051 μg g–1 (140Ce). The use of a large set of SRMs for calibration gave a good basis for the evaluation of analytical quality, and extensive data for calculated analytical uncertainty are presented. Instrumental precision and the repeatability of the method were studied separately, and no significant difference in these two sets of parameters were found, indicating that the spread of results predominantly was connected to the instrumental measurements. Repeated ablations on the surface of a disk did not influence subsequent measurements with XRF, showing that the fused disks can be stored for future use in XRF and/or LA-ICP-MS analysis.

Application of a double-focusing magnetic sector inductively coupled plasma mass spectrometer with laser ablation for the bulk analysis of rare earth elements in rocks fused with Li2B4O7

B. Flem

Papers

Application of a double-focusing magnetic sector inductively coupled plasma mass spectrometer with laser ablation for the bulk analysis of rare earth elements in rocks fused with Li2B4O7