Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood

Peng Zhao; Xiaojun Wu; Yunfeng Zhang

doi:doi:10.11648/j.sr.20261405.13

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Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood

Peng Zhao, Xiaojun Wu, Yunfeng Zhang^*

Published in Science Research (Volume 14, Issue 5)

Received: 11 July 2026 Accepted: 27 August 2026 Published: 4 September 2026

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Abstract

This study investigated the effects of storage temperature and freeze-thaw cycles on the stability of flunitrazepam, clonazepam, and their 7-amino metabolites in whole blood, and clarified the patterns of concentration changes of the four target analytes in the whole-blood matrix over storage time, thereby providing scientific data support for interpreting discrepant results between initial and re-testing in actual cases arising from different storage conditions. In the experiments, blank whole blood was used as the matrix and spiked with reference standards to prepare samples at two concentration levels (10 ng/mL and 100 ng/mL). The samples were stored under refrigeration at 4°C and frozen at –20°C. At various time points, aliquots were taken to determine the relative peak?area ratios of each target analyte to the internal standard diazepam-D₅. In parallel, the changes in relative content of the four drugs after 1 to 5 freeze?thaw cycles under short-term storage conditions were also evaluated. The results demonstrated that storage temperature significantly influenced drug stability; higher temperatures accelerated the degradation rate and led to more decreases in the concentrations of the target analytes in whole blood. Notably, at the early stage of storage, flunitrazepam and clonazepam showed a slight increase in concentration, which could be attributed to protein?binding effects. However, under short?term storage at –20°C with 1–5 repeated freeze-thaw cycles, the concentrations of the four target analytes did not exhibit any significant decline and remained relatively stable overall. Based on these findings, it is recommended that biological specimens collected after an incident should undergo qualitative and quantitative testing as soon as possible, and that low?temperature conditions be maintained throughout transportation and storage to minimize drug degradation. For samples requiring long-term preservation, the potential impact of storage duration on drug concentrations should be fully considered when interpreting the final results, and conclusions should be drawn cautiously to avoid misinterpretation.

Published in	Science Research (Volume 14, Issue 5)
DOI	10.11648/j.sr.20261405.13
Page(s)	280-285
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2026. Published by Science Publishing Group

Keywords

Forensic Science, Stability, Benzodiazepines, Clonazepam, Interpretation of Results

1．引言

苯二氮卓类药物（Benzodiazepines, BZDs）是一种使用广泛的处方药，因其具有安眠、镇静和抗焦虑的作用，常被用于癫痫、抑郁和失眠的治疗，在我国被列为第二类管制精神药品

[1]

。由于监管不规范、使用不当等原因，近年来BZDs的滥用现象十分严重，常导致误服、自杀等引发的中毒事件，还常常被不法分子用于麻醉抢劫、迷奸等案件

[2-4]

。在法庭科学领域，此类中毒案件需提取被害人血液、尿液或毛发等等生物样本进行药物分析。从提取检材样本到毒物分析一般会冷冻保存一定时间，有时根据办案需要初检后仍要进一步储藏以便二次分析

[5]

。在保存期间由于储藏温度、反复冻融、微生物等诸多因素的影响，生物检材中的BZDs可能被破坏或降解，导致两次结果产生差异，为保证检验结果的科学可靠性，亟需对BZDs及其代谢产物的稳定性加以研究。

目前，关于生物检材中滥用药物的稳定性研究报道相对较多，研究范围主要集中于卡西酮

[6]

、可卡因

[7]

、吗啡

[8]

、MDA

[9]

、甲基苯丙胺

[10, 11]

等毒品方面的研究，然而，针对BZDs在生物样本中稳定性的有关研究则相对匮乏，系统性的数据积累尚显不足。国外研究表明，血浆中地西泮的浓度在-20°C保存60天几乎无变化

[12]

，在室温和4°C冷藏条件下保存时，血中BZDs更易发生降解

[13]

，提示温度对该类药物稳定性具有重要调控作用。除温度外，微生物活动

[14]

、光照

[15]

和基质差异均会导致BZDs发生一定程度的降解。在此研究基础上，本文以全血中氟硝西泮、氯硝西泮及其主要7-氨基代谢物为研究对象，考察储藏温度和冻融循环次数两种因素对BZDs稳定性的影响，旨在为BZDs法医毒物检验结果的科学解释提供实验数据支撑与参考依据。

2．材料与方法

2.1．仪器、试剂与材料

LC-30A型超高效液相色谱仪（日本Shimadzu公司）、QTRAP 5500 三重四极杆串联质谱仪（美国AB Sciex公司）配有电喷雾离子源（ESI）、CM-1000振荡器（日本EYELA公司）、Biofuge Primo R 高速离心机（美国Thermo公司）、移液器。

乙腈、甲酸（均为色谱纯，购自美国Fisher Scientific公司），氯硝西泮、7-氨基氯硝西泮、氟硝西泮、7-氨基氟硝西泮和地西泮-D5浓度均为 100 μg/mL（购自天津阿尔塔科技有限公司），配制成10 μg/mL标准物质工作溶液，-20°C环境下保存。

研究使用的空白血液由医院提供。

2.2．生物样品前处理方法

2.2.1．样品制备

温度对药物稳定性影响：取新鲜空白血液，添加4种BZDs混合标准标准物质工作溶液，使血中药物浓度为10 ng/mL和100 ng/mL，涡旋振荡30 min使其均匀，分装至2mLEP管中，分别置于4和-20°C冰箱内储存，4°C保存样品在制备后的第0、1、2、4、6、12周进行提取检验，-20°C保存样品在制备后的第0、1、2、4、6、12、48周进行提取检验，每个时间平行3个样品。

冻融循环次数对BZDs稳定性影响：取新鲜空白血液，添加4种BZDs混合标准标准物质工作溶液，使血中药物浓度为100 ng/mL，涡旋振荡30 min使其均匀，分装至2mLEP管中，置于-20°C冰箱内储存，室温条件下融解2h后，继续放置冰箱内冷冻，依次冻融1~5次，每天进行融化-冷冻操作1次，每个冻融次数平行3个样品。

2.2.2．样品前处理

取待测血液0.50 mL，加入15 mL塑料离心管中，添加10 μg/mL内标工作溶液10 μL后混匀，加入1.5 mL乙腈，涡旋振荡10 min，离心（8000 r/m，10 min），取上层清液经0.22 μm微孔滤膜过滤，供LC-MS/MS检验。

2.3．LC-MS/MS条件

采用Waters BEH C18（3.0 mm×100 mm, 2.6 μm）色谱柱；流动相A：含0.1%甲酸的水溶液；流动相B：乙腈；柱温箱温度：40°C；流速：0.4mL/min；进样量：3μL；洗脱方式：梯度洗脱，梯度程序：0 ~ 0.5 min，10% B，0.5 ~ 3 min，10% ~ 90% B，3 ~ 4.5 min，90% B，4.5 ~ 4.6 min，90% ~ 10% B，4.6 ~ 5 min，10% B。

2.4．质谱条件

离子源：ESI；离子源温度：550°C；喷雾电压：5500 V；检测方式：多反应监测（MRM）；扫描方式：正离子扫描；5种BZDs质谱参数见表1。

表1 5种BZDs的质谱参数。

化合物	保留时间(min)	前体离子(m/z)	产物离子(m/z)	去簇电压(V)	碰撞电压(eV)
7-氨基氯硝西泮	3.12	285.9	222.0* 121.0	160	34,42
7-氨基氟硝西泮	3.25	284.0	135.0* 225.9	180	34,36
氯硝西泮	3.72	316.1	214.0* 240.9	130	51,47
氟硝西泮	3.74	314.0	268.1* 239.0	160	35,46
地西泮-D₅（内标）	3.99	290.0	198.0* 227.0	130	40,34

*: 定量离子

3．结果与讨论

3.1．温度对对硝基BZDs稳定性的影响

本研究为考察储藏温度对全血中4种BZDs及其主要代谢物稳定性的影响，以10 ng/mL和100 ng/mL两个添加浓度水平的全血基质样本为研究对象，分别将添加的全血置于4°C和-20°C条件下储存不同的时间，来模拟实际法医毒物案件检验中血液检材样本的保存环境。为避免硝基苯二氮卓类药物标准溶液在实验进行过程中因自身降解引起浓度变化而导致各目标物定量结果产生偏差，本研究选用稳定性良好的地西泮-D₅作为内标参照物

[12]

，通过测定不同保存时间点目标药物与内标地西泮-D₅峰面积的比值变化，作为各药物在样本中的相对含量变化趋势，结果如图1所示。

a: 10ng/mL血添加4°C, b: 10ng/mL血添加-20°C, c: 100ng/mL血添加4°C, d: 100ng/mL血添加-20°C

Download: Download full-size image

Figure 1. 图1 温度对4种BZDs稳定性影响。

实验结果表明，在不同储藏温度和不同BZDs添加水平下，全血样本中BZDs及其代谢物的含量均呈现不同程度的下降趋势，提示该类化合物在全血基质中总体上具有相对的不稳定性。具体而言，在4°C条件下保存12周后，全血中氟硝西泮和氯硝西泮的含量分别下降至初始浓度的42.67%~48.06%和38.08%~53.54%；而在-20°C条件下保存相同时长后，两者的残余含量分别为初始值的52.49%~60.28%和43.77%~55.56%。上述数据表明，-20°C低温冷冻保存较4°C冷藏条件更有利于延缓氟硝西泮和氯硝西泮的降解进程，为实际案件中血液样本的长期保存提供了重要的条件选择依据。随着冷冻时间的进一步延长，两类药物的降解趋势持续加剧，在保存至48周时，全血样本中氟硝西泮和氯硝西泮的含量已分别降至初始水平的33.74%~49.04%和41.50%~47.34%，显示出显著的时间依赖性降解特征。

值得关注的是，全血样本中氟硝西泮和氯硝西泮的含量并非在整个储存周期内呈现单一的持续下降趋势，而是在储存初期出现一定程度的含量回升现象。该现象可能与BZDs在血液基质中的蛋白结合特性密切相关

[16, 17]

。文献表明，此类药物在进入全血体系后，可与血浆蛋白发生可逆性结合，从而形成结合态储库，在一定程度上延长药物在血液中的半衰期并维持其药理效应的持续性。在初始加标制备过程中，部分药物分子迅速与血液中的特定蛋白组分结合，导致初始提取检测所得游离态药物含量低于实际添加总量；随着储存时间的不断延长，蛋白结合态药物逐渐发生解离，释放出游离态药物，从而造成检测初期药物浓度在表观上出现一定程度的升高。与此同时，两个主要代谢物7-氨基氟硝西泮和7-氨基氯硝西泮的回升趋势更为显著。除前述蛋白解离机制外，这一现象还与全血中还原性微生物酶活性有关，在适宜的保存条件下，部分母体药物可在微生物酶催化作用下发生硝基还原反应，进一步转化为相应的7-氨基代谢产物，与原已存在的代谢物共同构成代谢物库，在蛋白解离和新生代谢的双重作用下，使得两类代谢物的表观含量在储存早期呈现明显的先升后降动态变化规律

[18]

。这一特征对实际案件中代谢物与母体药物比值的时间依赖性解读具有重要警示意义，提示在法医毒物分析中应充分考虑储存条件对药物分布与代谢动态的干扰效应。

3.2．冻融循环次数对硝基苯二氮卓类药物稳定性的影响

为考察反复冻融对全血中氟硝西泮、氯硝西泮及其代谢物稳定性的影响，本研究进一步设计了冻融循环实验。为避免长时间低温储存的降解效应对实验结果产生干扰，所有反复冻融样本于-20°C条件下保存5天后，同批次内完成提取与检测，结果如图2所示。实验数据显示，在经历1~5次冻融循环后，4种目标物在全血中的含量均未呈现单向下降趋势，各时间点测定值呈现小幅波动，总体保持动态平衡状态，且未见显著的显著性差异（P>0.05），与相关研究结果一致

[12]

。该结果表明，在短期储存条件下（-20°C，5天），反复冻融循环次数（≤5次）并非影响上述苯二氮䓬类药物及其代谢物稳定性的关键因素。

a: 10ng/mL血添加, b: 100ng/mL血添加

Download: Download full-size image

Figure 2. 图2 -20°C反复冻融4种BZDs稳定性影响。

4．结论

在法庭科学毒物分析领域，血液、肝组织等生物基质样本因在保存过程中温度的变化和反复冻融等因素，目标药物及其代谢产物可能发生一定程度的降解与破坏，进而造成初检与复检结果的不一致，给案件定性及结果解释带来较大困难。为评估上述因素对BZDs稳定性的具体影响，本研究以全血基质中氯硝西泮、氟硝西泮及其代谢物7-氨基氯硝西泮、7-氨基氟硝西泮为研究对象，考察储藏温度（4°C与-20°C）及冻融循环次数（≤5次）两种因素对上述4种目标物含量变化的影响规律。研究结果表明，储藏温度对BZDs稳定性的影响显著，温度越高，全血中目标BZDs的降解速率越快，相对含量下降趋势越显著；而在-20°C条件下短期保存并经历反复冻融循环（1~5次）后，全血中4种药物含量未出现明显的降低，相对含量保持相对稳定。基于上述发现，在实际案件处理中，建议案发后采集的生物检材应尽快安排定性定量检验，并在送检及储存过程中尽可能维持低温条件，以最大限度减缓药物降解；对于需长期保存的样本，在最终结果解释时应充分考虑储存时间对药物含量的潜在影响，审慎作出结论。本研究所揭示的稳定性变化规律，可为实际案件中因初检与复检结果存在差异时的合理解释提供实验数据支撑，有助于提高法医毒物鉴定意见的科学性和可信度。

致谢

本文为中央级基本科研业务费项目《氯硝西泮在不同生物检材中的稳定性研究》(2020JB021)的阶段性成果之一。

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Zhao, P., Wu, X., Zhang, Y. (2026). Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood. Science Research, 14(5), 280-285. https://doi.org/10.11648/j.sr.20261405.13

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Zhao, P.; Wu, X.; Zhang, Y. Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood. Sci. Res. 2026, 14(5), 280-285. doi: 10.11648/j.sr.20261405.13

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Zhao P, Wu X, Zhang Y. Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood. Sci Res. 2026;14(5):280-285. doi: 10.11648/j.sr.20261405.13

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@article{10.11648/j.sr.20261405.13,
  author = {Peng Zhao and Xiaojun Wu and Yunfeng Zhang},
  title = {Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood},
  journal = {Science Research},
  volume = {14},
  number = {5},
  pages = {280-285},
  doi = {10.11648/j.sr.20261405.13},
  url = {https://doi.org/10.11648/j.sr.20261405.13},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.sr.20261405.13},
  abstract = {This study investigated the effects of storage temperature and freeze-thaw cycles on the stability of flunitrazepam, clonazepam, and their 7-amino metabolites in whole blood, and clarified the patterns of concentration changes of the four target analytes in the whole-blood matrix over storage time, thereby providing scientific data support for interpreting discrepant results between initial and re-testing in actual cases arising from different storage conditions. In the experiments, blank whole blood was used as the matrix and spiked with reference standards to prepare samples at two concentration levels (10 ng/mL and 100 ng/mL). The samples were stored under refrigeration at 4°C and frozen at –20°C. At various time points, aliquots were taken to determine the relative peak?area ratios of each target analyte to the internal standard diazepam-D5. In parallel, the changes in relative content of the four drugs after 1 to 5 freeze?thaw cycles under short-term storage conditions were also evaluated. The results demonstrated that storage temperature significantly influenced drug stability; higher temperatures accelerated the degradation rate and led to more decreases in the concentrations of the target analytes in whole blood. Notably, at the early stage of storage, flunitrazepam and clonazepam showed a slight increase in concentration, which could be attributed to protein?binding effects. However, under short?term storage at –20°C with 1–5 repeated freeze-thaw cycles, the concentrations of the four target analytes did not exhibit any significant decline and remained relatively stable overall. Based on these findings, it is recommended that biological specimens collected after an incident should undergo qualitative and quantitative testing as soon as possible, and that low?temperature conditions be maintained throughout transportation and storage to minimize drug degradation. For samples requiring long-term preservation, the potential impact of storage duration on drug concentrations should be fully considered when interpreting the final results, and conclusions should be drawn cautiously to avoid misinterpretation.},
 year = {2026}
}

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TY  - JOUR
T1  - Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood
AU  - Peng Zhao
AU  - Xiaojun Wu
AU  - Yunfeng Zhang
Y1  - 2026/09/04
PY  - 2026
N1  - https://doi.org/10.11648/j.sr.20261405.13
DO  - 10.11648/j.sr.20261405.13
T2  - Science Research
JF  - Science Research
JO  - Science Research
SP  - 280
EP  - 285
PB  - Science Publishing Group
SN  - 2329-0927
UR  - https://doi.org/10.11648/j.sr.20261405.13
AB  - This study investigated the effects of storage temperature and freeze-thaw cycles on the stability of flunitrazepam, clonazepam, and their 7-amino metabolites in whole blood, and clarified the patterns of concentration changes of the four target analytes in the whole-blood matrix over storage time, thereby providing scientific data support for interpreting discrepant results between initial and re-testing in actual cases arising from different storage conditions. In the experiments, blank whole blood was used as the matrix and spiked with reference standards to prepare samples at two concentration levels (10 ng/mL and 100 ng/mL). The samples were stored under refrigeration at 4°C and frozen at –20°C. At various time points, aliquots were taken to determine the relative peak?area ratios of each target analyte to the internal standard diazepam-D5. In parallel, the changes in relative content of the four drugs after 1 to 5 freeze?thaw cycles under short-term storage conditions were also evaluated. The results demonstrated that storage temperature significantly influenced drug stability; higher temperatures accelerated the degradation rate and led to more decreases in the concentrations of the target analytes in whole blood. Notably, at the early stage of storage, flunitrazepam and clonazepam showed a slight increase in concentration, which could be attributed to protein?binding effects. However, under short?term storage at –20°C with 1–5 repeated freeze-thaw cycles, the concentrations of the four target analytes did not exhibit any significant decline and remained relatively stable overall. Based on these findings, it is recommended that biological specimens collected after an incident should undergo qualitative and quantitative testing as soon as possible, and that low?temperature conditions be maintained throughout transportation and storage to minimize drug degradation. For samples requiring long-term preservation, the potential impact of storage duration on drug concentrations should be fully considered when interpreting the final results, and conclusions should be drawn cautiously to avoid misinterpretation.
VL  - 14
IS  - 5
ER  -

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Author Information

Peng Zhao

Institute of Forensic Science, Ministry of Public Security, Beijing, China

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Xiaojun Wu

Institute of Forensic Science, Ministry of Public Security, Beijing, China

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Yunfeng Zhang

Institute of Forensic Science, Ministry of Public Security, Beijing, China

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Figure 1

Figure 1. 图 1 温度对4种BZDs稳定性影响。
Figure 2

Figure 2. 图 2 -20°C反复冻融4种BZDs稳定性影响。

Table 1

表1 5种BZDs的质谱参数。

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APA Style

Zhao, P., Wu, X., Zhang, Y. (2026). Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood. Science Research, 14(5), 280-285. https://doi.org/10.11648/j.sr.20261405.13

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ACS Style

Zhao, P.; Wu, X.; Zhang, Y. Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood. Sci. Res. 2026, 14(5), 280-285. doi: 10.11648/j.sr.20261405.13

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AMA Style

Zhao P, Wu X, Zhang Y. Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood. Sci Res. 2026;14(5):280-285. doi: 10.11648/j.sr.20261405.13

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@article{10.11648/j.sr.20261405.13,
  author = {Peng Zhao and Xiaojun Wu and Yunfeng Zhang},
  title = {Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood},
  journal = {Science Research},
  volume = {14},
  number = {5},
  pages = {280-285},
  doi = {10.11648/j.sr.20261405.13},
  url = {https://doi.org/10.11648/j.sr.20261405.13},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.sr.20261405.13},
  abstract = {This study investigated the effects of storage temperature and freeze-thaw cycles on the stability of flunitrazepam, clonazepam, and their 7-amino metabolites in whole blood, and clarified the patterns of concentration changes of the four target analytes in the whole-blood matrix over storage time, thereby providing scientific data support for interpreting discrepant results between initial and re-testing in actual cases arising from different storage conditions. In the experiments, blank whole blood was used as the matrix and spiked with reference standards to prepare samples at two concentration levels (10 ng/mL and 100 ng/mL). The samples were stored under refrigeration at 4°C and frozen at –20°C. At various time points, aliquots were taken to determine the relative peak?area ratios of each target analyte to the internal standard diazepam-D5. In parallel, the changes in relative content of the four drugs after 1 to 5 freeze?thaw cycles under short-term storage conditions were also evaluated. The results demonstrated that storage temperature significantly influenced drug stability; higher temperatures accelerated the degradation rate and led to more decreases in the concentrations of the target analytes in whole blood. Notably, at the early stage of storage, flunitrazepam and clonazepam showed a slight increase in concentration, which could be attributed to protein?binding effects. However, under short?term storage at –20°C with 1–5 repeated freeze-thaw cycles, the concentrations of the four target analytes did not exhibit any significant decline and remained relatively stable overall. Based on these findings, it is recommended that biological specimens collected after an incident should undergo qualitative and quantitative testing as soon as possible, and that low?temperature conditions be maintained throughout transportation and storage to minimize drug degradation. For samples requiring long-term preservation, the potential impact of storage duration on drug concentrations should be fully considered when interpreting the final results, and conclusions should be drawn cautiously to avoid misinterpretation.},
 year = {2026}
}

Copy | Download

TY  - JOUR
T1  - Influence of Temperature and Freeze-thaw Cycles on the Stability of Flunitrazepam and Clonazepam in Blood
AU  - Peng Zhao
AU  - Xiaojun Wu
AU  - Yunfeng Zhang
Y1  - 2026/09/04
PY  - 2026
N1  - https://doi.org/10.11648/j.sr.20261405.13
DO  - 10.11648/j.sr.20261405.13
T2  - Science Research
JF  - Science Research
JO  - Science Research
SP  - 280
EP  - 285
PB  - Science Publishing Group
SN  - 2329-0927
UR  - https://doi.org/10.11648/j.sr.20261405.13
AB  - This study investigated the effects of storage temperature and freeze-thaw cycles on the stability of flunitrazepam, clonazepam, and their 7-amino metabolites in whole blood, and clarified the patterns of concentration changes of the four target analytes in the whole-blood matrix over storage time, thereby providing scientific data support for interpreting discrepant results between initial and re-testing in actual cases arising from different storage conditions. In the experiments, blank whole blood was used as the matrix and spiked with reference standards to prepare samples at two concentration levels (10 ng/mL and 100 ng/mL). The samples were stored under refrigeration at 4°C and frozen at –20°C. At various time points, aliquots were taken to determine the relative peak?area ratios of each target analyte to the internal standard diazepam-D5. In parallel, the changes in relative content of the four drugs after 1 to 5 freeze?thaw cycles under short-term storage conditions were also evaluated. The results demonstrated that storage temperature significantly influenced drug stability; higher temperatures accelerated the degradation rate and led to more decreases in the concentrations of the target analytes in whole blood. Notably, at the early stage of storage, flunitrazepam and clonazepam showed a slight increase in concentration, which could be attributed to protein?binding effects. However, under short?term storage at –20°C with 1–5 repeated freeze-thaw cycles, the concentrations of the four target analytes did not exhibit any significant decline and remained relatively stable overall. Based on these findings, it is recommended that biological specimens collected after an incident should undergo qualitative and quantitative testing as soon as possible, and that low?temperature conditions be maintained throughout transportation and storage to minimize drug degradation. For samples requiring long-term preservation, the potential impact of storage duration on drug concentrations should be fully considered when interpreting the final results, and conclusions should be drawn cautiously to avoid misinterpretation.
VL  - 14
IS  - 5
ER  -

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