# A simple hydrofluoric acid-free pressurized-cavity microwave-assisted acid digestion method for determination of impurity elements in recycled carbon fibers with ICP-MS

## TL;DR

This paper introduces a safer, simpler method to determine impurity elements in recycled carbon fibers without using hydrofluoric acid.

## Contribution

A novel HF-free microwave-assisted acid digestion method for analyzing impurity elements in recycled carbon fibers.

## Key findings

- The proposed method achieved dissolution of impurity elements at 280°C under pressurized conditions.
- The method showed lower contamination and detection limits for ten out of thirteen elements compared to HF-added methods.
- The method's safety and simplicity are enhanced by avoiding hazardous HF and its elimination treatment.

## Abstract

A simple method was proposed for the determination of 13 impurity elements (Na, Mg, Al, K, Ca, Ti, Cr, Fe, Co, Ni, Cu, Zn, and Pb) in recycled carbon fibers (rCFs) using pressurized-cavity microwave-assisted acid digestion without hydrofluoric acid (HF) combined with inductively coupled plasma mass spectrometry. Elevating the digestion temperature to 280 °C under pressurized conditions facilitated the dissolution of the target elements in rCF, even when present in refractory forms. Because certified reference materials of rCF samples for determining impurity elements were unavailable, the validity of the proposed method was confirmed by comparing its analytical results with those obtained using a HF-added digestion method, which completely decomposes silica, followed by the dissolution of the bound target elements. The proposed method was further validated by analyzing carbon- and metal-based certified reference materials and metal oxides as analogous to the refractory components of rCF. However, the limited decomposition of refractory rutile-type titania suggests an upper limit of 890 mg/kg for titanium determination using the proposed HF-free method. The limits of detection ranged from 0.0014 mg/kg for cobalt to 0.72 mg/kg for potassium. Ten of the 13 elements showed lower limits than those of the HF-added method because of less contamination. Operationally, the HF-free method is safer and simpler because it avoids the use of hazardous HF and does not require HF-elimination treatment.

The online version contains supplementary material available at 10.1007/s44211-026-00886-1.