Moisture-Free Storage: Nitrogen or Desiccant?

Desiccators, sometimes called dry boxes, provide a low-humidity atmosphere for storage of items and materials that would otherwise be damaged by moisture. Desiccators are used for a wide range of applications across several scientific disciplines.

在化学和生物学中，干燥剂通常用于储存吸湿试剂和化学物质。将这些化合物保持在低湿度环境中会大大提高其保质期。在半导体研究和制造中，通常采用干燥储存来防止晶粒和其他可能导致直接或潜在失败的氧化氧化。

In order to achieve a low relative-humidity (RH) atmosphere for storage within a desiccator, two storage techniques are commonly used: desiccant-based and nitrogen-purged.

Benefits of Desiccant

A desiccant is a hygroscopic material, often silica gel. We’ve all seen “pillow packs” in pill bottles and electronic packaging. The desiccant absorbs moisture within the desiccator chamber to reduce the humidity. Desiccant-based storage is often coupled with a vacuum pump. The moisture-laden ambient air present in the closed environment is removed, with moisture further reduced and maintained with the hygroscopic desiccant. This method of dry storage is an economical and simple solution for dry storage of reagents and chemicals where precise control of humidity is not required.

Desiccant-based storage has several advantages. First, this method can increase the shelf life of costly chemicals and reagents that are labile under even slightly humid conditions. Additionally, desiccant-based storage is less costly than more complex nitrogen-based storage (compare the price of nitrogen tanks with silica gel). Lastly, desiccant can be dried by applying heat in a laboratory oven and reused, which further reduces cost.

What are the drawbacks to desiccant-based storage? First, it does not allow for precise control of humidity levels within the chamber. Also, because removal of moisture from the environment is a passive process, a substantial amount of time is required to achieve a dry environment. If the chamber is opened and exposed to ambient conditions, moisture is reintroduced, increasing the amount of time required to reach the ideal environment.

由于这些缺点，在存储需要经常访问的材料时，不建议使用基于干燥剂的存储。在化学和生物学实验室中，干燥剂是储存吸湿试剂的经济和有效解决方案。病理和临床实验室通常还使用此技术来存档甲醛固定和石蜡包裹的组织样品。

Nitrogen-Based Storage

The use of desiccators purged with nitrogen provides a low-moisture climate for a wide range of applications. This process involves the introduction of pure nitrogen into the chamber from an external source. The addition of nitrogen effectively replaces a humid (containing H2O molecules) atmosphere with an inert, dry atmosphere (containing N2 molecules).

Nitrogen is fed into the chamber through a tube, and controlled by a simple flow-meter. It can also be managed through equipment that monitors the chamber’s relative humidity level and adjusts flow accordingly. Nitrogen-based desiccator storage is often adopted in high-tech semiconductor research and manufacturing facilities to precisely control the %RH during storage.

One notable advantage of nitrogen-based dry storage is the ability to rapidly lower the relative humidity the chamber. When stored materials need to be accessed frequently, this is of particular importance. The rapid recovery time minimizes the exposure of the material to moisture more efficiently compared to desiccant-based storage.

Using a combination meter/valve, humidity levels can be monitored, and nitrogen flow rate adjusted, to maintain the desired set-point. By following this method, labs may also notice a reduction in their use (waste) of process gas. Therefore, nitrogen-based dry storage is an ideal solution for applications in the semiconductor industry where components are accessed frequently and need to be kept at a tightly controlled %RH to prevent oxidative damage.

公平地说，使用氮来干燥材料的储存有一些缺点。首先，需要外部氮来操作干燥器。这些可以是由第三方提供的储罐，也可以是需要压缩空气来源的氮发生器。与基于干燥剂的存储相比，这将增加操作成本。为了帮助解决这一问题，实验室可以使用自动控制系统监测％RH水平并控制氮的流动。当湿度较低时，通过减少氮气的流量来最大程度地减少氮的使用，反之亦然。通过使此过程自动化，需要更少的工时才能达到所需的结果，并且很少使用氮。

While an in-house nitrogen generator requires an initial capital expenditure, the future savings may warrant the expense; pure nitrogen will be available quickly and cheaply. These generators feed pressurized air through a selective membrane to extract nitrogen. For these reasons, nitrogen-based dry storage is often used in labs with a large number of desiccator storage units, applications that require frequent access to stored materials or where precisely controlled humidity levels are critical.

To learn more aboutnitrogen generators, visit Terra’s website. Or, click here fordesiccator chamberoptions for moisture-free storage.