Application of High-Precision X-ray Fluorescence Elemental Analyzer for the Determination of Trace Sulfur and Chlorine in Heat Transfer Oils

This application note presents a solution for the analysis of trace sulfur and chlorine elements in various heat transfer oils using the E-lite 500 monochromatic X-ray

Application Overview

Commonly used heat transfer oils include biphenyl‑diphenyl ether, alkylbenzene, and hydrogenated terphenyl. As per the national standard GB 23971‑2009, the sulfur content is specified at no more than 0.2% (g/g), and chlorine content at no more than 20 mg/kg. Current industry practices for sulfur determination employ energy dispersive X‑ray fluorescence (EDXRF) and ultraviolet fluorescence methods, while chlorine is typically measured by microcoulometry. The microcoulometry approach is operationally demanding, requiring electrode treatment, electrolyte preparation, and experienced operators.

This application employs monochromatic X‑ray fluorescence for the simultaneous analysis of sulfur and chlorine in heat transfer oils. The method offers straightforward operation, does not require gases, gas generators, or external water cooling, and delivers reliable accuracy with good repeatability.

Reference Standards: GB/T 11140, ASTM D7536, ASTM D7039, ASTM D7220, SH/T 0977, ASTM D4294.

Technical Principles

The High-Precision X-ray Fluorescence Elemental Analyzer (HPXRF) utilizes Monochromatic Focusing Doubly Curved Crystal (DCC) optics, which monochromatize polychromatic X-rays from the source and effectively focus them onto the sample. This greatly enhances the instrument's signal-to-noise ratio. Upon monochromatization, elements in the sample emit characteristic X-ray fluorescence signals. These signals are collected and processed by a high-resolution Silicon Drift Detector (SDD), and the software's Fundamental Parameter (FP) algorithm calculates the elemental content in the sample.

Sample Testing

This solution utilizes a specially designed, easy-to-clean, low-background, and reusable stainless steel sample cup, along with supporting tooling. It features simple operation, low cost, and excellent test repeatability.

Side-Loading Design

The E-lite series features an innovative side sample introduction system that directs accidental sample spills into a drip tray, preventing leaked oil from contaminating valuable components.

Performance Data

Standard Curves

Utilizing the patented monochromatic Fundamental Parameter (FP) software and after standard sample calibration, the linear correlation coefficient for sulfur (S) in the range of 5–600 mg/kg is 0.9991, and for chlorine (Cl) in the range of 1–60 mg/kg is 0.9996, demonstrating excellent correlation.

Repeatability

An actual biphenyl-diphenyl ether heat transfer oil sample was tested 11 consecutive times. The relative standard deviations (RSD) for sulfur and chlorine over the 11 tests were 0.74% and 1.19%, respectively. The repeatability is far superior to the precision requirements of GB 11140 and SH/T 0977.

Installation Requirements

Technical Specifications

Features and Advantages