Certified reference materials (CRMs) are the backbone for qualitative and quantitative determination of pesticides in technical materials, formulations, and food matrices. However, their stringent expiry date, limited shelf life, and diminishing purity with time, limits their use beyond expiry. Stability study of 89 CRMs of multiclass pesticides, stored at − 25 °C, has been conducted to assess the purity of CRMs beyond their expiry date. It was evident that > 96 % of the CRMs remained optimally stable with respect to their observed purity even after their expiry date as per certificate of analysis. Percentage deviations in purity of expired and valid CRMs posited well below 7 % and are within ± 10 % acceptable range as recommended by the SANTE. During 2013–2017, performance of the valid and expired CRMs was evaluated through 44 z -scores obtained in 14 international and national proficiency testing programmes. All the z -scores received for 15 expired and 29 valid CRMs were found satisfactory. Inter-laboratory comparison of 6 randomly selected expired and valid CRMs was tested at three different ISO/IEC 17025 accredited laboratories and their % difference between purities ranged from − 2.35 % to + 0.95 %. It was inferred that by maintaining proper storage conditions and continuous monitoring of purity, the expired CRMs can give comparable results as valid CRMs.

中文翻译：

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在过期前后长期储存期间监测多类农药 CRM 的纯度和稳定性

有证标准物质 (CRM) 是技术材料、配方和食品基质中农药定性和定量测定的支柱。然而，它们严格的有效期、有限的保质期以及随着时间的推移纯度降低，限制了它们的使用。已对 89 种多类农药的 CRM 进行稳定性研究，这些农药在 - 25 °C 下储存，以评估超过有效期的 CRM 的纯度。很明显，> 96% 的 CRM 就其观察到的纯度而言仍保持最佳稳定状态，即使在根据分析证书的有效期后也是如此。过期和有效 CRM 纯度的百分比偏差远低于 7%，并且在 SANTE 建议的 ±10% 可接受范围内。2013-2017 年期间，通过在 14 个国际和国家能力测试计划中获得的 44 个 z 分数评估有效和过期 CRM 的性能。所有收到的 15 个过期 CRM 和 29 个有效 CRM 的 z 分数都令人满意。在三个不同的 ISO/IEC 17025 认可实验室测试了 6 种随机选择的过期和有效 CRM 的实验室间比较，它们的纯度差异百分比范围从 - 2.35 % 到 + 0.95 %。据推断，通过保持适当的储存条件和持续监测纯度，过期的 CRM 可以提供与有效 CRM 相当的结果。在三个不同的 ISO/IEC 17025 认可实验室测试了 6 种随机选择的过期和有效 CRM 的实验室间比较，它们的纯度差异百分比范围从 - 2.35 % 到 + 0.95 %。据推断，通过保持适当的储存条件和持续监测纯度，过期的 CRM 可以提供与有效 CRM 相当的结果。在三个不同的 ISO/IEC 17025 认可实验室测试了 6 种随机选择的过期和有效 CRM 的实验室间比较，它们的纯度差异百分比范围从 - 2.35 % 到 + 0.95 %。据推断，通过保持适当的储存条件和持续监测纯度，过期的 CRM 可以提供与有效 CRM 相当的结果。