High Precision Neodymium Data

We’ve recently been running a series of high precision Neodymium (Nd) standard data on a series of machines on our factory floor. This is data is typical for every Isotopx Phoenix instrument.

Replicate measurements of 600ng of the JNd_i Nd standard were made. An improved sample loading technique has been utilised where 2 microlitres of 0.1M phosphoric acid was added to the evaporation filament prior to loading the Nd. Samples were loaded at 1 amp filament current and the filament current increased to about 2 amps until it just glowed in air. The Nd was loaded onto a triple rhenium filament. Analyses took place with a source vacuum of <2e-8mbar without liquid nitrogen in the cold trap and an analyser vacuum of <2e-9 mbar, which yielded an abundance sensitivity at 237 wrt 238U of less than 2ppm. At 1 amu with respect to Nd, the uncorrected contribution of a high mass peak on an adjacent low mass peak would be about 0.5ppm, e.g. an increase in the 143Nd of 1ppm.

The centre ionizing filament was maintained at 4.7 amps throughout the analysis and the evaporation filament current adjusted to maintain a 142Nd ion beam of 5 volts using 1e11 ohm resistor. Data was taken in the multidynamic mode in a 3 jump sequence. Integration time at each mass position was 10 seconds with a 1 second delay between ion integrations to allow the resistor and amplifier to attain baseline between mass jumps. Baseline was measured for 30 seconds at +/-0.5amu at the start of each block of data. Each block comprised 20 cycles. Ion beam focussing and peak centering was conducted at the start of each block. The ion beam remained at 5volts 142Nd for a period of over 8 hours. Samples were not run to exhaustion but the analysis of 500 ratios did not result in extremely fractionated samples.

600ng Nd Multidynamic data

600ng Nd JNd-i StandardMultidynamic data

These Neodymium data show that the reproducibility of all the ratios is consistent with no obvious second order mass fractionation effects. Precisions of 1ppm 1rse can be attained on 5 volt ion beams, which is considerably lower than that reported in the literature (10v+). The multidynamic measurement routine is immune to cup poisoning effects which are a problem with static analyses. Thus the long term reproducibility (years) for these measurements will remain consistent. Increasing the peak flat by making the collector slit wider may improve the reproducibility further by minimizing errors due to the peak flatness.

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Category: Geology, Applications
Published: Sunday, February 14th, 2016 at 2:51 pm

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