Ultra-Low P, S, Cl Analysis in Liquids with a Benchtop WDXRF Spectrometer

Introduction

Phosphorous, sulphur and chlorine are commonly analysed elements in liquids such as petroleum products and organic solvents. For example, phosphorous is added to lubricating oils to prevent wear of gears under high pressure. Sulphur content in automotive fuel oils is regulated by the US environmental protection agency (EPA) and directives such as EURO VI to minimise air pollution due to automotive vehicles. Chlorine, contained for example in crude oil, is an unwanted element known for corroding oil processing installations and liquid transmission pipelines.

To better meet demands of such applications, the benchtop wavelength dispersive X-ray fluorescent (WDXRF) spectrometer Supermini200’s analysing crystal set has been newly reconfigured to optimise performance for trace level analysis of P, S and Cl.

XRF analysis allows rapid and precise elemental characterisation of such samples with minimum sample preparation. Laborious sample treatment such as acid digestion or serial dilution are not required. Liquid samples are simply poured into a plastic cup covered with film for measurement and results can be obtained in minutes.

Instrument

The Supermini200 is a benchtop sequential WDXRF spectrometer designed specifically to deliver excellent performance while eliminating typical installation requirements such as cooling water, special power supply and large floor space.

Equipped with a unique air cooled 200-watt X-ray tube, two detectors and three analysing crystals, the Supermini200 is capable of measuring elements from oxygen to uranium. Analysis of P, S and Cl is optimised with the analysing crystal RX9 newly available on the Supermini200. Standardless semi-quantitative analysis is also available allowing quick and simple characterisation of non-routine samples.

Calibration and measurement

P, S, and Cl calibrations were setup on a Supermini200 with analysing crystal RX9. Calibration range, accuracy and lower limit of detection (LLD) are shown in Table 1 with measurement condition shown in Table 2.

Test samples with P, S, Cl at 0.5, 1 and 5 mg/kg were prepared by mixing and diluting 3 single element standards obtained from ASI Standards. Short term reproducibility test was performed by consecutively running 20 aliquots. Long term reproducibility test was performed by running 2 aliquots per day (morning and afternoon) over 10 days. Instrument was shut down for one week between short and long terms tests.

Sample preparation

About 4 grams of sample was poured into a liquid cell (Chemplex® 2140). Prolene® film (Chemplex® 416) with 4 μm thickness was used as sample film.

Conclusion

Short- and long-term analysis results for P, S, Cl test samples at 0.5, 1 and 5 mg/kg can be found in this application note. The data shows Supermini200’s capability to perform high precision analysis with high accuracy over both short- and long-term durations.

Instrument meets precision required by test methods such as ASTM D2622-16, ISO 20884:2011 and JPI-5S-73-2014. Measurement result can be obtained in minutes with quick and easy sample preparation allowing processing of large quantities of samples. Minimal installation prerequisites, not requiring expensive consumables and dangerous acids contributes to safe and low cost of ownership.