Determination of sodium lactate
AN-T-227
2021-11
zh
Comparison of USP–NF 2021, Issue 2 and a modified method for absolute sodium lactate content via titration
USP-NF 2021 第 2 期与通过滴定法测定乳酸钠绝对含量的改进方法的比较 乳酸钠是乳酸的一种盐形式，用于许多受管制的行业，因此需要准确测定乳酸的含量，这已在多个规范中有所涉及。美国药典》（USP）中的一种专著可实现较高的精确度和清晰的滴定曲线，但其使用的滴定剂和溶剂成本较高。 相比之下，瑞士万通推出的改进方法需要 1:1 的水和丙酮混合物，并使用盐酸水溶液作为滴定剂，因此与 USP 方法（USP-NF 2021，第 2 期）相比，每次滴定的成本估计可降低 40%。此外，每次分析所需的时间仅为 USP 方法的 12%（不包括空白测定）。 本应用说明介绍了测定乳酸盐含量的两种方法，并展示了在 OMNIS 系统上获得的结果。
Sodium lactate is a salt form of lactic acid used in foodstuffs, cosmetics, paper, clothes, biopolymers, and in medicine. As it is used in many regulated industries, an accurate determination of the lactate content is required and is already covered in several norms. One exemplary monograph by the US Pharmacopoeia (USP) results in high accuracies and well-defined titration curves but uses titrants and solvents that are more costly than necessary. This USP method requires a blank determination, glacial acetic acid and acetic anhydride as solvents, and a solution of perchloric acid in acetic acid as titrant.
In comparison, the presented modified method from Metrohm requires a 1:1 mixture of water and acetone and uses aqueous hydrochloric acid as titrant, resulting in an estimated cost reduction of 40% per titration compared to the USP method (USP–NF 2021, Issue 2). Furthermore, the time needed for each analysis is reduced to just 12% of the USP method (excluding blank determination).
This Application Note presents both methods to determine lactate content and shows the results obtained on an OMNIS system.
Solid sodium lactate (300 mg) is dissolved in 100 mL of deionized water.
USP: Sample equivalent to 300 mg lactate is weighed accurately and dissolved in a 5:1 mixture of acetic anhydride and glacial acetic acid. The sample is allowed to stand for 20 minutes. Blank samples are also prepared.
Metrohm: Dilute a sample equivalent to 300 mg in a 1:1 mixture of acetone and water.
USP: Titrate the blank and sample with 0.1 N perchloric acid until after the first equivalence point.
Metrohm: Titrate the sample directly with 0.1 mol/L HCl solution until after the first equivalence point (EP).
| Method | Recovery | RSD (%) |
|---|---|---|
| USP | 97.77 | 0.53 |
| Metrohm | 96.56 | 0.93 |
Both methods for the determination of lactate show comparable results. The USP method is slower and more expensive but the obtained EP has a higher potential jump and ERC. However, the method gives a second EP after this region that is unrelated to sodium lactate. The Metrohm modified method is faster and cost-efficient but shows slightly lower recoveries and the EP is less pronounced. In contrast to the USP method, the Metrohm method does not show a second EP and is therefore less ambiguous as well.
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