An MAS Topical Conference Colorado School of Mines

A new basaltic glass reference material for microanalytical techniques has been developed by doping a natural basaltic glass. This glass was produced for a round robin for the SEM/EDS, electron probe analysis (EPMA), laser ablation inductively coupled mass spectrometry (LA-ICP-MS), and secondary ion mass spectrometry (SIMS) communities. The glass lacks major chemical variation and is free of crystalline inclusions by observation of backscattered electron (BSE) images. In addition, EPMA show the major elements (Si, Al, Fe, Mg, Ca, Na, and K) to be homogeneous at the one percent precision level using a 20 m beam diameter. In addition, laser ablation inductively coupled mass spectrometry (LA-ICP-MS) results show most trace elements (<2000 ppm to 5 ppm) are within five percent relative standard deviation. Introduction: A new generation of microanalytical reference materials is needed to meet the demand for higher spatial resolution and higher sensitivity analyses performed with multiple techniques such as EPMA, LA-ICP-MS, and SIMS. A new basaltic glass RM has been developed by doping a natural basalt with 25 additional elements. Some elements were added at levels suitable for EPMA (> 1000 ppm) while others were added at levels suitable for SIMS (< 100 PPM). Several iterations were necessary to achieve a homogeneous glass that was free of crystalline inclusions. Initial characterization of the glass is complete and it is ready for distribution as a round robin material. Methods: EPMA data were collected at 15 keV and 20 nA (cup) current with a 20 m beam diameter. Using these conditions, volatile corrections for Na and K were unnecessary. The following silicate mineral standards and crystals were used; Tiburon albite (Na:TAP, Si:TAP), an in house orthoclase (K:PET), Miyake anorthite (Ca:PET, Al:TAP), Springwater forsterite (Mg:TAP), synthetic rutile (Ti:LiF), synthetic fayalite (Fe:LiF), synthetic spessartine (Mn:LiF), and synthetic nickel olivine (Ni:LiF) . A grid of data points, containing 30 to 100 points depending on area of glass exposed, was collected on 9 glass chips. The level of homogeneity as a percent of the concentration of each element was calculated with the Probe for EPMA software package [3] using the following equation from Goldstein et al. [4]: avg C n N n S t C W 2 / 1 1 1 1 ) 100 ( ) (         (1) where C is the actual concentration of the element in weight percent of the sample, is the Student t for a 1- confidence and n-1 degrees of freedom, n is the number of data points acquired, S    1 1 n t C is the standard deviation of the measured values (count intensity), and Navg is the average number of counts on the unknown. LA-ICP-MS analyses were conducted on 13 different glass chips. For two of the chips, analyses in rectangular grids of 100 and 120 spots were conducted. Random analyses were made across the remaining 11 grains. LA-ICP-MS analyses were conducted using a 193 nm excimer laser ablation system coupled to a quadrupole ICP-MS. A spot size of 85 μm was used for the LA testing. The energy density was 5 J/cm2, and the ablated material was transported to the ICP-MS in a stream of He (combined flow of 1.0 L/min). Ablation occurred in a 2-volume ablation chamber that is optimized for fast washout allowing microinclusions to be easily resolved based on chemical differences. Instrument response was calibrated using the USGS synthetic basalts GSE-1G and GSD-1G as well as the natural basalts NKT-1G and TB-1G. Concentrations were calculated using the equations of Longerich et al. [5]. Results and Conclusions: The WTB-2Ga glass appears to be free of mineral inclusions and is homogeneous for major elements (Si, Al, Fe, Mg, Ca, Na, and K) at the 1% precision level for electron microprobe analyses. Examination by LA-ICP-MS determined that intergrain and intragrain variations standard deviations were less than 5-10 % relative. As new directions in microanalytical techniques continue to develop, the need will increase for homogeneous reference materials with a wide range of matrices and elemental and isotopic concentrations. The development of reference materials such as this glass intended for several techniques (EPMA, SIMS, LA-ICP-MS, and others), coupled with round robin testing provides better certainty of results for microanalysis.