Introduction − 87 87 1 7 84 86 87 88 87 8 9 2 10 11 21 Description of instrument setups 1 Fig. 1  ESA  Laser ablation systems 22 23 24 11 12 1 25 26 Table 1 Instrument setups and materials analysed in eleven publications on Sr isotope analyses by LA-MC-ICPMS Reference Laser type Pit sizes (μm) Materials (Sr concentration) Instrument Sensitivity/blank levels 11 −1 Spot 20–40 and 150–300 Carbonate (2,000 ppm) VG P54 LA 2,000 ppm, sample material gives >3 V total Sr Feldspar (2,000 ppm) No blank reported 12 Nd:YAG, 266 nm, 5–20 Hz, 1.2 mJ, carrier gas not specified Spot 100–300, raster Plagioclase (1,200–2,100 ppm) IsoProbe No blank reported 13 Nd:YAG, 266 nm, 10 Hz, 0.66 mJ, carrier gas not specified Spot 70, raster Carbonate, fresh water otolith (ca. 500 ppm) VG P54 No blank reported 14 Nd:YAG, 266 nm and 213 nm, 20 Hz, 4 mJ, carrier gas Ar Spot 10–200 Plagioclase, apatite sphene, clinopyroxene otolith VG Axiom −1 88 85 88 15 −2 Spot 150–330 Apatite (>3,000 ppm) IsoProbe Not reported Carbonate (>3,000 ppm) 16 15 Spot 330 Clinopyroxene (100–400 ppm), plagioclase, carbonate IsoProbe Not reported 17 −2 Spot 80, raster 160 × 500 Carbonate (1,000 ppm) ThermoFinnigan Neptune 88 Plagioclase (900 ppm) Clinopyroxene (50 ppm) Basaltic groundmass (400 ppm) 18 −2 Spot 10–350, raster Carbonate otolith Nu Plasma Not reported 19 Nd:YAG, 213 nm Raster 60–500, 80 deep Carbonate, fresh water otolith (ca. 300–800 ppm) ThermoFinnigan Neptune Not reported 20 Excimer, 193 nm, 5 Hz, 50 mJ, carrier gas He Raster, 80 wide Carbonate, otoliths ThermoFinnigan Neptune Not reported 21 Nd:YAG, 213 nm, 20 Hz Spot 120, raster Melt inclusions ThermoFinnigan Neptune −1 88  Blank not reported −1 1 27 1 28 28 87 87 −1 2 Fig. 2 −1 12 −1 88 88  −1 18 88 2 MC-ICPMS instruments 1 87 87 Materials ablated 1 21 87 86 29 15 21 87 86 Factors influencing the data quality of Sr isotope analysis by LA-MC-ICPMS The following factors influence the quality of data which can be obtained by LA-MC-ICPMS: (1) counting statistics, (2) blank levels, (3) instrumental mass discrimination and laser-induced elemental and isotopic fractionation and (4) molecular interferences. Counting statistics 2 12 88 Background (blank levels) 88 85 14 17 1 87 84 14 13 21 Instrumental mass discrimination and laser-induced elemental and isotopic fractionation 30 24 31 32 86 88 30 13 86 88 87 87 21 Similarly, most authors make the Kr corrections on the Sr masses by assuming that the laser-induced isotope fractionation and instrument discrimination are the same for Sr and Kr. For a good Kr correction, the mass bias has to be established in an independent way. We will use the term mass bias to describe both the laser-induced isotope fractionation and the instrument mass discrimination. Molecular interferences 2 Table 2 Sr isotope masses and possible interferences in the mass region 82–89 Source of interference Mass 82 83 84 85 86 87 88 89 Sr   84  86 87 88  Kr 82 83 84  86    Rb    85  87   REE Y        89 2+   168 2+ 170 2+ 172 2+ 174 2+ 176 2+  2+  166 2+ 168 2+ 170 2+     2+       176 2+  2+      174 2+ 176 2+  Fe/Zn/Ga oxides 54     54 16 2 54 16 17 54 16 18        54 17 2  56       56 16 2  66  66 17       67  67 16       68   68 16 68 17 68 18    70     70 16 70 17 70 18  69     69 17 69 18   71      71 16 71 17  Ca dimers  40 43 40 44 42 43 40 46  40 48      42 44  42 46      43 2 43 44 44 2  Ca argides  43 40 48 36        46 38  48 38      44 40  46 40  48 40  Ca-P      40 31 16   17 Rubidium 87 33 1 85 87 87 85 87 33 2 88 86 21 85 87 20 21 17 21 12 Krypton 84 86 1 18 14 17 21 18 21 83 2 82 83 11 12 14 20 83 82 84 86 84 86 11 86 88 87 86 86 83 34 82 83 82 83 14 83 21 82 83 83 82 82,83 84 84 84 88 34 86 88 84 86 87 86 84 86 21 Calcium dimers and argides 35 14 15 44 40 17 87 86 21 87 86 18 87 86 18 84 86 42 40 42 40 84 86 21 82 83 REE 2 17 17 14 17 168 2+ 170 2+ 84 85 2 87 86 17 85 87 87 86 84 86 84 84 86 168 2+ 2 87 86 86 88 84 86 17 167 2+ 168 2+ 171 2+ 173 2+ 17 171 2+ 171 173 17 176 2+ Zn, Ga and Fe 16 54 32 2 56 32 2 16 17 71 16 + 68 16 + 17 Calcium phosphates 40 31 16 87 2 36 37 Proposed solutions to correct for isobaric interferences 2 87 3 21 84 Fig. 3 Order of interference corrections in the eleven publications concerning Sr isotope analysis by LA-MC-ICPMS. **Not mentioned in publication, but inferred from published isotope ratios. See text for discussion  11 83 85 86 88 3 17 18 17 18 21 Precision and accuracy of Sr isotopes by laser ablation 38 10 4 4 Fig. 4 87 86 LA 87 86 TIMS 87 86 TIMS 6 87 86 a 84 86 c 6 87 86 b 84 86 d  1 11 11 21  grey shaded area 38  87 86 4 18 87 86 4 87 86 17 11 14 12 12 14 17 87 86 16 4 Sr isotopes by laser ablation analysis of other geological materials also looks promising (e.g. groundmass), whereas apatite and sphene require such large corrections that accurate results will be difficult to obtain. 84 86 18 4 38 84 86 84 86 Future directions 25 26 24 21 39 The interferences of the REE are probably only important for materials that contain significant amounts of REE. Experimenting with optimal plasma conditions, which reduce the creation of doubly charged REE, is important. The situation with Ca argides and dimer is unclear. More experimental work is needed, especially by ablating Ca-rich materials, which do not contain Sr. Conclusions 87 87 86 84 86 Doubly charged REE interferences are only a problem in materials where significant REE contents are present, such as clinopyroxene. However, successful correction is possible by collecting data at half masses. 87 86 84 86 84 86