# High-Resolution Graphite Furnace Atomic Absorption Spectrometry Determination of Bismuth in Lithium Niobate Optical Crystals

## TL;DR

This paper presents a method using high-resolution atomic absorption spectrometry to measure bismuth in lithium niobate crystals.

## Contribution

The study introduces optimized solid and solution sampling methods for accurate bismuth determination in high-purity crystals.

## Key findings

- Optimal pyrolysis and atomization temperatures for bismuth were 1000 and 1800 °C for solid samples.
- Solution sampling achieved lower optimal temperatures of 500 and 1300 °C.
- The LOD for solid and solution analysis was 0.4 and 0.3 μg/g, respectively.

## Abstract

High-resolution continuum source graphite furnace atomic
absorption
spectrometry (HR-CS-GFAAS) methods with solid and solution sampling
were developed for the determination of the Bi dopant in high-purity
lithium niobate (LiNbO3) crystals. Samples were cut from
the cylindrical crystal bulks, cleaned, and pulverized. A HF–HNO3 mixture was applied for microwave digestion of LiNbO3 (≈0.07 g per sample). Atomization transients, pyrolysis,
and atomization curves were studied with various media and chemical
modifiers, e.g., triammonium citrate (TAC), Pd–Mg­(NO3)2. For solid samples, the optimal pyrolysis and atomization
temperatures of Bi were found at 1000 and 1800 °C, respectively,
whereas, for solution samples, much lower values of 500 and 1300 °C
were obtained. TAC slightly, but Pd–Mg considerably increased
the optimal pyrolysis and atomization temperatures, i.e., up to 1300
and 2100 °C, respectively. The dissolved LiNbO3 matrix
acted as an internal modifier, exhibiting optimal pyrolysis and atomization
temperatures for Bi. For solid sample analysis, 0.05–0.4 mg
(average: 0.1 mg) of LiNbO3 powder was dosed into graphite
boats, while conventional standard addition and three-point estimation
were used for calibration. The limit of detection (LOD) was 0.4 and
0.3 μg/g for solid and solution analysis, respectively, using
Bi I 227.6580 nm and Bi I 223.0608 nm lines, respectively. Utilizing
the latter for solid sampling, an LOD of 0.03 μg/g can be attained.
The analytical results for all methods were in good agreement (mean
bias: <12%). The precision of the solid and solution sample methods
was at 6–16% (average: 12%) and 1–13% (average: 4.4%),
respectively. The Bi content of the crystals ranged from 56 to 311
μg/g. The characteristic mass for solid and solution sampling
was 220 and 17 pg, respectively. The accuracy of the method was checked
against the GBW07407 (laterite soil) certified reference material.