A method was developed for the determination of trace anions in battery-grade lithium carbonate. In this method, lithium carbonate was dissolved in ultrapure water with ultrasound assistance, and its matrix was removed using an on-line matrix-removal method. In the matrix-removal process, the sample was first passed through an ADRS600(4 mm) suppressor (suppressor current, 150 mA; external water flow rate, 2 mL/min). Hydrogen and lithium ions were then completely exchanged via the ion-exchange membrane in the suppressor, converting the lithium carbonate into carbonic acid. The carbonic acid entered the waste-liquid channel in the form of carbon dioxide through a CRD 200(4 mm) carbonate removal device to remove the lithium carbonate matrix. Finally, the target anions were automatically enriched on an IonPac UTAC-LP2 concentration column (35 mm×3 mm) and automatically transferred to a chromatographic system using valve-switching technology. The chromatographic system featured an IonPac AG18 column (50 mm×2 mm) as the protection column and an IonPac AS18 column (250 mm×2 mm) as the analytical column. The column temperature was 30 ℃, gradient elution was performed using KOH solution as the eluent, and the pump flow rate was 0.30 mL/min. An ADRS600(2 mm) suppressor, suppressor current of 25 mA, injection volume of 250 μL, and conductance detector were also used. The results showed good linear relationships (r≥ 0.999) for F-, Cl-, [Formula: see text] in their respective concentration ranges. The limits of detection (LODs) and quantification (LOQs) were 0.05-0.88 and 0.15-2.92 μg/L, respectively. Lithium carbonate samples were tested six consecutive times, and the relative standard deviations (RSDs) of the peak areas of each ion were less than 0.73%. The same lithium carbonate samples were injected after 0, 2, 4, 8, 12, 18, and 24 h, and the RSD of the peak areas of each ion was less than 0.96%. The average recoveries ranged from 93.3% to 99.3%, and the RSDs (n=6) of samples spiked at three levels were in the range of 0.97%-3.45%. The proposed method has a low method limit of quantification of only 0.5 mg/kg for each ion analyzed and is capable of the simultaneous analysis of multiple ions. Thus, it is suitable for the detection of trace anions in battery-grade lithium carbonate.
建立了一种测定电池级碳酸锂中痕量阴离子的方法。用超纯水超声辅助溶解碳酸锂,采用在线基体去除法去除碳酸锂基体,基体去除过程中,样品首先流入到ADRS600(4 mm)抑制器(抑制电流150 mA,抑制器再生液外接水流速2 mL/min)中,在抑制器内通过离子交换膜作用,碳酸锂中的锂离子与氢离子置换,碳酸锂变成碳酸;然后经过CRD 200(4 mm),碳酸以二氧化碳的形式排出离子色谱系统,从而达到去除碳酸锂基体的目的;最后待分析阴离子被自动富集在IonPac UTAC-LP2浓缩柱(35 mm×3 mm)上,通过阀切换技术将阴离子自动转移到色谱分析系统中。在色谱分析系统中,以IonPac AG18(50 mm×2 mm)为保护柱,IonPac AS18(250 mm×2 mm)为分析柱,柱温箱为30 ℃, KOH溶液为淋洗液进行梯度洗脱,泵流速0.30 mL/min,抑制器为ADRS600(2 mm),抑制电流25 mA,进样体积为250 μL,检测器为电导检测器。结果显示:F-、Cl-、NO2-、Br-、NO3-及SO42-离子在各自的线性范围内具有良好的线性关系(r≥0.999);各离子的检出限和定量限分别为0.05~0.88 μg/L和0.15~2.92 μg/L;碳酸锂样品连续6针进样各离子峰面积的相对标准偏差(RSD)均≤0.73%;同一碳酸锂样品处理完后分别放置0、2、4、8、12、18、24 h后进样,各离子峰面积的RSD均≤0.96%;在3个添加水平下,各离子加标回收率为93.3%~99.3%, RSD(n=6)为0.97%~3.45%;本方法具有方法定量限低(各离子定量限均为0.5 mg/kg)及多种离子同时分析的优势,适用于电池级碳酸锂中痕量阴离子的检测。
Keywords: anions; double-inhibition; ion chromatography (IC); lithium carbonate; on-line matrix-removal.