# New Trends in Separation Techniques of Lithium Isotopes: A Review of Chemical Separation Methods
## 1 Introduction
### Challenges in Development of Separation Methods for Lithium Isotopes Using Electrochemical
#### 2.4.2 Analysis Methods for Lithium Isotopes Using MC-ICP-MS Methods  
Many studies are using inductively coupled plasma multicollector mass spectrometry (MC-ICP-MS) [50; 51; 52; 53] to determine lithium isotope ratios from artificial and environmental samples (see Figure 5). Comparing with ICP-Q-MS, the MC-ICP-MS methods appear to be more appropriate for low quantities of environmental samples. Nevertheless, historically, MC-ICP-MS methods had some drawbacks: a relatively high sensitivity to matrix interferences, mass bias due to matrix, the occurrence of lithium fractionation inside the instrument, and the requirement of a relatively high level of lithium into the sample (2 to 40 ng) [17; 47]. Figure 5: Schematic setup of an MC-ICP-MS with a magnetic sector analyser in Nier-Johnson geometry, used in lithium isotope analysis. Adapted from Ref. [54]. Adapted with permission from Ref. [55]. Copyright 2024 Elsevier. [PERSON] et al. were first to report reliable and precise measurements of Li isotopes with MC-ICP-MS [47]. This study determined the lithium isotope ratios from seawater and a basalt standard (JB-2) [47]. Upon digestion, as in the case of ICP-Q-MS, this study used cation exchange resin (AG50W-x8 type) to separate the lithium followed by MC-ICP-MS analysis, while the precision of the measurements was calculated to \(\pm\)1.1% vs. L-SVEC [47]. [PERSON] et al. performed an accurate determination in environmental materials with MC-ICP-MS but with a much higher precision of \(\pm\)0.12% vs. L-SVEC (\(n\) = 46), while requiring just about 1.2 ng Li per sample [56]. [PERSON] et al. used an optimised procedure with high chemical yields due to one-step column chromatographic separation involving lower procedure blanks (\(<\)5 pg) to record the lithium isotope ratios of two seawater references as ranged 30.88 \(\pm\) 0.12% to 30.73 \(\pm\) 0.15 vs. L-SVEC at a low mass resolution of 500 (valley definition of 5% peak height) [56]. [PERSON] et al. [57] determined the isotope ratio of lithium in reference materials (andesite (AGV-2), basalt (BHVO-2) and IRMM-016 reference standard) using MC-ICP-MS. Prior to the MC-ICP-MS analysis, lithium was enriched in stages on three different columns (the first two eluted with HCl of different concentration and the 3 rd with 30% ethanol) using synthetic cation-exchange resin [57]. The first stage removed the major cations from the matrix, the second stage removed the major elements except sodium, and the third stage removed the sodium ions from the matrices [57]. The precision of lithium isotope ratio determination with MC-ICP-MS was calculated \(\pm\)0.72-1.04% (2\(\sigma\)), but overall, this study showed the complexity of sample preparation required for lithium isotope measurements in some materials [57]. In the last years, MC-ICP-MS, in combination with laser ablation (LA) (thus LA-MC-ICP-MS) became a popular technique for lithium isotope determination directly from solid phases, thus preserving spatial resolution, as this technique is capable of sampling a volume of \(>\)1 \(\upmu\)m in depth and approximately 10-100 \(\upmu\)m in diameter [58]. The main advantage of LA-MC-ICP-MS for lithium isotopes over classical MC-ICP-MS appears to be minimal sample preparation, but there are also other advantages such as good spatial resolution, low sample size, high sample throughput, and a low likelihood of contamination [58]. The main disadvantage of LA-MC-ICP-MS is the occurring isotopic fractionation during laser ablation [59; 60; 61], an effect that can be limited in the case of using femtosecond (fs) laser ablation (in contrast with nanosecond LA) by reducing the ablation crater in the sample to nm-sized diameter [62]. Some studies used fs-LA-MC-ICP-MS for _in situ_ measurements of lithium isotope ratios. [PERSON] et al.