The therapeutic dose of lithium (Li) compounds, which are widely used for the treatment of psychiatric and hematologic disorders, is close to its toxic level; therefore, drug monitoring protocols are mandatory. Herein, we propose a fast, simple, and low-cost analytical procedure for the traceable determination of Li concentration in human serum, based on the monitoring of the Li isotope dilution through the partially resolved isotope shift in its electronic transition around 670.80 nm using a commercially available high-resolution continuum source graphite furnace atomic absorption spectrometer. With this technique, serum samples only require acidic digestion before analysis. The procedure requires three measurements—an enriched ⁶Li spike, a mixture of a certified standard solution and spike, and a mixture of the sample and spike with a nominal ⁷Li/⁶Li ratio of 0.82. Lanthanum has been used as an internal spectral standard for wavelength correction. The spectra are described as the linear superposition of the contributions of the respective isotopes, each consisting of a spin-orbit doublet, which can be expressed as Gaussian components with constant spectral position and width and different relative intensity, reflecting the isotope ratio in the sample. Both the spectral constants and the correlation between isotope ratio and relative band intensity have been experimentally obtained using commercially available materials enriched with Li isotopes. The Li characteristic mass (m_c) obtained corresponds to 0.6 pg. The procedure has been validated using five human serum certified reference materials. The results are metrologically comparable and compatible to the certified values. The measurement uncertainties are comparable to those obtained by the more complex and expensive technique, isotope dilution mass spectrometry.

Graphical abstract

中文翻译：

---

同位素稀释原子吸收光谱法测定人血清中的锂

广泛用于治疗精神和血液疾病的锂（Li）化合物的治疗剂量接近其毒性水平；因此，药物监测协议是强制性的。在此，我们提出了一种快速、简单且低成本的分析程序，用于可追溯地测定人血清中的锂浓度，该程序基于通过在 670.80 nm 附近的电子跃迁中的部分分辨同位素位移监测锂同位素稀释度，使用市售高分辨率连续源石墨炉原子吸收光谱仪。使用这种技术，血清样品只需要在分析前进行酸性消化。该程序需要进行 3 次测量 — 丰富的⁶Li 加标，经认证的标准溶液和加标的混合物，以及标称⁷ Li/ ⁶ Li 比率为 0.82 的样品和加标的混合物。镧已被用作波长校正的内部光谱标准。光谱被描述为各个同位素贡献的线性叠加，每个同位素由一个自旋轨道双峰组成，可以表示为具有恒定光谱位置和宽度以及不同相对强度的高斯分量，反映了样品中的同位素比率. 光谱常数和同位素比与相对带强度之间的相关性均已使用富含锂同位素的市售材料通过实验获得。Li 特征质量 ( m _c) 获得对应于 0.6 pg。该程序已使用五种人血清认证的参考材料进行了验证。结果在计量上与认证值具有可比性并兼容。测量不确定度与通过更复杂和昂贵的技术同位素稀释质谱法获得的不确定度相当。

图形概要