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1.
Results are presented from the seventy two laboratories participating in GeoPT5, round five of the international proficiency testing programme for analytical geochemistry laboratories. The sample for round five, AMH-1 (Mount Hood andesite), was distributed during March 1999 and participating laboratories were asked to analyse the sample using their routine techniques and submit results to the steering by 15th June 1999. In this report, contributed data are listed together with the derived z-scores from which participating laboratories can assess their analytical performance. Z-scores in the range -2 to 2 are considered satisfactory. Z-score values that lie outside this range may indicate unsuspected analytical bias. The distinctive feature of the present round is that AMH-1 is a candidate reference material prepared by the USGS and it is intended that the present proficiency testing data will contribute to the reference material characterisation programme.  相似文献   

2.
Results are presented from the seventy five laboratories participating in GeoPT4, round four of the international proficiency testing programme for analytical geochemistry laboratories. Laboratories were required to analyse the sample OU-2 (Belford dolerite) using routine methods of analysis. The sample was distributed during September 1998 with a deadline for the submission of results of 15th January 1999. In this report, contributed data are analysed and z-scores calculated. Z-score values provide participating laboratories with information concerning the quality of their results and indicate data that may be subject to unsuspected analytical bias. Laboratories are invited to examine these data and take the appropriate action.  相似文献   

3.
Results from seventy two laboratories participating in GeoPT3, round three of the international proficiency testing programme for analytical geochemistry laboratories, are presented. The report includes analytical results contributed by participating laboratories, together with the z-scores derived from these results using appropriate fitness for purpose criteria. These data are available for use as part of the laboratories' quality control procedures to assess the reliability of analysed results.  相似文献   

4.
Results from sixty laboratories participating in GeoPT2, the international proficiency testing programme for analytical geochemistry laboratories, are reported. Compared with 71.3% in the last round, 74.6% of the reported data complied with the laboratories' selected fitness for purpose criteria.  相似文献   

5.
The original certification protocol, published by the International Association of Geoanalysts in 2003, specified that the competence of laboratories selected as competent to contribute certification measurements should be evaluated from their performance in the GeoPT proficiency testing programme. Round 39 of the IAG GeoPT proficiency testing programme provided an opportunity to examine four methods of evaluating laboratory competence based largely on the use of proficiency testing z‐scores as performance indicators. This opportunity arose because two test materials were co‐analysed by participating laboratories in this round: a syenite, SyMP‐1, supplied by the USGS, and an established CRM, the nepheline syenite, CGL 006. The performance of laboratories was assessed in four ways; in each case, consensus values and their uncertainties as derived from selective data sets of competent laboratories were compared with results derived from the routine GeoPT data assessment, involving all submitted measurements. An overall comparison of results showed no significant statistical differences in either consensus values or uncertainties between these data sets. This conclusion was unexpected and calls into question the widely held assumption that ‘better’ consensus data would be obtained from a subset of laboratories judged to be competent on the basis of proficiency testing performance indicators.  相似文献   

6.
In this study, we used the modified Horwitz expression (Hc= 0.01c0.8495, which gives the precision as a function of concentration) to evaluate and control the accuracy of results of silicate rock analysis obtained by X-ray fluorescence spectrometry. This expression is currently used by the organisers of the GeoPT international proficiency tests, to assign the precision limits of each analyte and subsequently to evaluate the data provided by laboratories whose main application is geochemistry. Results for major and trace elements, determined in glass disk and pressed pellets, respectively, were evaluated. Nine international silicate rock reference materials were analysed and results were compared to the recommended values plus and minus the limits given by the above expression. Those limits are easily attained for most major elements, but not for trace elements. Sample preparation and sub-sampling contributions to precision were evaluated by analysis of an in-house reference sample. In our results, precision does not follow the Horwitz expression relationship with concentration. It is known that the final accuracy in XRF analysis depends strongly on instrumental settings and on the uncertainties associated with the certified or recommended values of the reference materials used to calibrate the spectrometer, but our results indicate that the precision expression can be useful, especially to inspect and correct calibration curves and to check routine instrumental accuracy.  相似文献   

7.
ISO Guide 35:2017 provides, for the first time, an alternative way of characterising certified reference materials using proficiency testing. In this paper, the properties of assigned values derived from the well‐established GeoPT proficiency testing scheme are examined. This scheme, designed for laboratories that undertake the routine analysis of silicate rocks and related materials, routinely has over 100 participants contributing results. Following a detailed assessment of the metrological properties of GeoPT assigned values in relation to Guide 35 recommendations, it is demonstrated that these values may be regarded as certified values, provided a number of criteria are met. These criteria include the following: a demonstration of sufficient homogeneity of the candidate CRM; circulation, when judged to be appropriate, of an established matrix‐matched CRM for co‐analysis in that round; the robust statistical analysis of data sets using GeoPT established criteria; a decision whether assigning a value is justified (including a requirement of a minimum of fifteen valid results); and an expert group to manage the certification and the maintenance of appropriate records. In summary, the GeoPT proficiency testing scheme, subject to the arrangements summarised above, is considered to be competent for the certification of geological reference materials.  相似文献   

8.
Although over recent years, sensitivity and precision of modern analytical techniques have continuously improved, traditional analytical specification for the particle size of samples has remained at 74 μm (-200 mesh). For this reason, the uncertainty caused by inhomogeneity in test portions of the sample itself has become a more and more significant contribution to the total analytical uncertainty. Therefore, to reduce this total uncertainty, the first step is to improve the homogeneity by reducing the particle size of a sample. For this purpose, we have investigated a method for the preparation of ultra-fine reference materials. Using the modern ultra-fine crushing technique (jet mill), six marine sediment samples MSAn and MSCS-1 to 5 were prepared and the particle distributions of these samples were measured using a laser particle-analyser. The average particle size of these samples was 4–5 (im and the largest particle size was less than 30 (im. MSAn will be used as the sample for a future GeoPT(tm) proficiency testing round and MSCS-1 to 5 will be prepared as reference materials. All geochemical laboratories are welcome to participate in this co-operative research programme. The processing and use of ultra-fine samples (< 30 μm) will have a significant influence on the future development of geoanalytical techniques as a consequence of the potential reduction in the mass of test portion and the development of new geoanalytical systems.  相似文献   

9.
A new proficiency testing sample, OPY‐1 (ultramafic rock), the basis of the twentieth international proficiency test of analytical geochemistry laboratories (GeoPT 20), was recently prepared by the International Association of Geoanalysts (IAG). This paper reports analytical data for Os, Ir, Ru, Rh, Pt and Pd with different digestion techniques, including an improved Carius tube, Carius tube combined with HF dissolution and alkaline fusion. About 4–15% of the PGEs are in the silicate phase, which cannot be leached by aqua regia even when digested at 300 °C with the Carius tube technique. Both the Carius tube technique combined with HF dissolution and alkaline fusion can obtain reliable data. The results demonstrated that OPY‐1 is sufficiently homogeneous at a 2 g test portion level to be suitable as a reference material for method validation. The procedure for sealing the Carius tube was simplified and the recommended digestion procedures are provided.  相似文献   

10.
A fusion procedure commonly used for major element analysis of silicate rocks (1:5 sample to flux ratio, using 0.7 g of sample) was used to determine a small group of trace elements (Cu, Zn, Rb, Sr, Y, Zr, Nb) by X-ray fluorescence. Compton scatter peak ratioing was successfully used for matrix corrections, despite the thickness of the glass discs being only 1.7 mm. Precision and detection limits were compared with pressed pellet values. For most elements, routine analytical precision is better with powder pellets and detection limits are worse in glass discs, by an average factor of 2, considering all elements analyzed. Accuracy was evaluated with international reference materials and for most of the determinations, good or excellent agreement with recommended values was obtained. The main advantages of using glass discs for the trace element determination are the possibility of analyzing small amounts of sample and the suppression of any mineralogical effects in the glass discs, which can also be used to determine major elements.  相似文献   

11.
A method of preparation of homogeneous glass beads by direct fusion of bulk rock powders on an iridium-strip heater, and the quantitative analysis of these glasses using an electron microprobe fitted with an Si(Li) detector, are described. Major element concentrations obtained for international geochemical reference standards are of high precision, and agree well with recommended values obtained by other methods.  相似文献   

12.
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13.
Re‐issuing the same test material, its true identity unknown to participants, in two rounds of the GeoPT proficiency testing programme 18 years apart has demonstrated remarkable similarity, and therefore stability, of consensus values independently estimated for over fifty measurands in each round. A comparison of the two data sets, GeoPT5 (AMH‐1) from 1999 and GeoPT41 (ORA‐1) from 2017, shows that corresponding consensus values, rigorously derived by current procedures for complete compatibility, are for the most part statistically indistinguishable when account is taken of their associated uncertainties. Inferences that may be drawn from this exceptional agreement include: (a) the consensus estimation procedure was robust and gave consistent results; (b) overall, the balance of the contributed data was unaffected by significant changes in: (i) the populations of laboratories participating, (ii) the proportions of laboratories producing results by different techniques, (iii) the manner in which systems were calibrated, or (iv) the aspirations of laboratories to attain higher quality results over time; and (c) unsurprisingly perhaps, that the test material itself had remained stable and unchanged during that time. Additionally, a statistical comparison of the original values for AMH‐1 with consensus values derived by current procedures demonstrates that they are also effectively indistinguishable.  相似文献   

14.
探索了利用高温炉合成玄武岩玻璃制作原位微区主微量元素含量分析的标准物质的实验条件.选取玄武岩标准物质GBW07105(GSR-3)进行高温熔融、淬火实验研究,获得玄武岩玻璃,为合成其他地质样品微区分析标准参考物质的研制提供了参考方法.用激光剥蚀-四极杆等离子体质谱(LA-Q-ICPMS)对样品微区46个主元素和微量元素...  相似文献   

15.
The results of the first international proficiency test (GeoPT1) of geochemical laboratories are presented. A total of 49 laboratories contributed analytical data on G94, a sample of Threlkeld microgranite which had been collected at the International Conference, Geoanalysis 94. Assigned values were derived by robust statistical analysis of contributed data for 12 major elements and 39 trace elements, of which 3 (As, Pb and The) were provisional values. Z-scores were calculated, as required by the protocol using either 'pure geochemistry'or 'applied geochemistry'fitness for purpose criteria selected by contributing laboratories. An overview of the z-score results indicates that 28.7% of contributed data fell outside the -2相似文献   

16.
《Geochimica et cosmochimica acta》1999,63(11-12):1805-1813
A comparison of two independent techniques was used to assess the homogeneity of CO2 and H2O concentrations in a number of natural basaltic glasses. Variations in carbon concentration and isotopic ratio were determined by comparison of stepped heating data obtained in two different laboratories. Dissolved volatile concentrations were also obtained by stepped heating and Fourier Transform Infrared (FTIR) spectroscopy. Replicate stepped heating analyses of a mid-ocean ridge basaltic glass show that the concentration and 13C/12C of bulk magmatic and dissolved CO2 vary by less than ±10% and ±0.5‰, respectively. A similar degree of correlation is observed for replicate stepped heating analyses of Mariana Trough glasses conducted in two different laboratories. Dissolved CO2 concentrations determined by stepped heating also correlate well with concentrations measured by FTIR spectroscopy. The correspondence of results obtained in these experiments provide an upper limit to the degree of natural variation in concentrations and isotopic ratios of these volatiles in basaltic glasses and suggest that intrinsic, magmatic carbon has a relatively homogeneous distribution in these glasses. Water concentrations determined through extraction by heating and FTIR also show excellent agreement.  相似文献   

17.
Incompatible trace element abundances have been determined in mantle-derived clinopyroxenes by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in a comparative study with established microanalytical and bulk techniques. Individual clinopyroxene grains were sampled for the laser ablation study from sieved mineral separate fractions, from which similar mineral grains had been previously extracted for microprobe (SIMS) and bulk (INAA and ID-TIMS) analysis. Mineral grains were ablated with variable degrees of surface spatial resolution (50-200 μm) in order to maximise ICP-MS analyte count rates and to improve detection limits. A comparison of results from the different techniques reveals that for the most homogeneous samples LA-ICP-MS can achieve excellent levels of agreement with other techniques (10%) and good precision for most of the studied elements (1-5% RSD). Variations in calculated concentrations by LA-ICP-MS confirm inter- and intra-mineral heterogeneity determined by SIMS, reflecting changes in sample composition and texture. The long-term reproducibility of the technique is shown by the consistency of results for one sample analysed on thirteen occasions over a period of nine months.  相似文献   

18.
This work considers petrogenesis of the largest Holocene basaltic fissure eruptions of Iceland, which are also the largest in the world: Laki (1783-84 AD, 15 km3), Eldgjá (934 AD, 18 km3), Veidivötn (900, 1480 AD, multiple eruptions, >2 km3), Núpahraun (ca. 4000 BP, >1 km3) and Thjórsárhraun (ca 8000 BP, >20 km3). We present oxygen isotope laser fluorination analyses of 55 individual and bulk olivine crystals, coexisting individual and bulk plagioclase phenocrysts, and their host basaltic glasses with average precision of better than 0.1‰ (1SD). We also report O isotope analyses of cores and rims of 61 olivine crystals by SIMS with average precision on single spots of 0.24‰ (1SD) in 13 samples coupled with electron microprobe data for major and trace elements in these olivines. Within each individual sample, we have found that basaltic glass is relatively homogeneous with respect to oxygen isotopes, plagioclase phenocrysts exhibit crystal to crystal variability, while individual olivines span from the values in equilibrium with the low-δ18O matrix glass to those being three permil higher in δ18O than the equilibrium. Olivine cores with maximum value of 5.2‰ are found in many of these basalts and suggest that the initial magma was equilibrated with normal-δ18O mantle. No olivines or their intracrystalline domains are found with bulk or spot value higher than those found in MORB olivines. The δ18O variability of 0.3-3‰ exists for olivine grains from different lavas, and variable core-to-rim oxygen isotopic zoning is present in selected olivine grains. Many olivines in the same sample are not zoned, while a few grains are zoned with respect to oxygen isotopes and exhibit small core-to-core variations in Fe-Mg, Ni, Mn, Ca. Grains that are zoned in both Mg# and δ18O exhibit positive correlation of these two parameters. Electron microprobe analysis shows that most olivines equilibrated with the transporting melt, and thin Fe-richer rim is present around many grains, regardless of the degree of olivine-melt oxygen isotope disequilibrium.The preservation of isotopic and compositional zoning in selected grains, and subtle to severe Δ18O (melt-olivine) and Δ18O (plagioclase-olivine) disequilibria suggests rather short crystal residence times of years to centuries. Synglacially-altered upper crustal, tufaceous hyaloclastites of Pleistocene age serve as a viable source for low-δ18O values in Holocene basalts through assimilation, mechanical and thermal erosion, and devolatilization of stoped blocks. Cumulates formed in response to cooling during assimilation, and xenocrysts derived from hyaloclastites, contribute to the diverse δ18O crystalline cargo. The magma plumbing systems under each fissure are likely to include a network of interconnected dikes and sills with high magma flow rates that contribute to the efficacy of magmatic erosion of large quantities (10-60% mass) of hyaloclastites required by isotopic mass balance.Olivine diversity and the pervasive lack of phenocryst-melt oxygen isotopic equilibrium suggest that a common approach of analyzing bulk olivine for oxygen isotopes, as a proxy for the basaltic melt or to infer mantle δ18O value, needs to proceed with caution. The best approach is to analyze olivine crystals individually and demonstrate their equilibrium with matrix.  相似文献   

19.
This protocol has been developed by the International Association of Geoanalysts to demonstrate procedures for the certification of geological and environmental reference materials to comply to the fullest extent possible with recommendations of the International Organisation for Standardisation (ISO Guide 35). A practical approach is described on the assumption that certifications will be normally be based on collaborative analysis programmes in which participating laboratories are preselected on the basis of performance in a proficiency testing programme or on the basis of other criteria of merit.  相似文献   

20.
Quantitative microanalysis of entire silicate and sulfide melt inclusions by Excimer Laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICPMS) has been applied to extrusive and shallow intrusive rocks from the andesitic Farallón Negro Volcanic Complex (northwestern Argentina). Silicate melts are trapped in pyroxene, amphibole, plagioclase and quartz, and sulfide melts are trapped in amphibole. Details of the analytical approach and the quantification procedure are given and the results are evaluated to test the accuracy of the technique and the validity of the interpretation of analytical signals. Similar compositions of silicate melt inclusions trapped in truly co-precipitating minerals show that the quantification approach of melt inclusion compositions from LA-ICPMS signals through an internal standard is valid. This correspondence also shows that melt inclusions investigated in this study are not significantly influenced by the boundary layer around a growing crystal or by post-entrapment modifications. Post-entrapment diffusive re-equilibration only affected the Fe and Mg content of melt inclusions in mafic phases. Thus, melt inclusions are representative samples of the melt from which the host mineral crystallized, with regard to most major and trace elements. Sulfide melt inclusions (present as pyrrhotite with exsolution of Au and Cu in phases separated during cooling) were analyzed for their bulk Fe, Cu and Au content, and the abundance of these elements was quantified using a silicate glass as external standard. The validity of this calibration was tested by comparing electron microprobe analyses of Fe, Cu, Ni and Co in homogeneous sulfide minerals with LA-ICPMS results. Identical results within calculated uncertainty (one standard deviation of five to nine analyses, mostly between 1 and 5 wt% RSD) demonstrate that for these elements, measured element ratios are independent of the matrix using our analytical setup.Editorial responsibility: T.L. Grove  相似文献   

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