Safety of Windows and Prisms Used in FTIR

Window and Prism Materials

The window and prism materials mainly used in FTIR analysis include those given in Table 1. Here, we will take a look at KRS-5, zinc selenide (ZnSe), and barium fluoride (BaF₂), materials that require particular care.

KRS-5

KRS-5 is a mixed crystal consisting of thallium bromide (TlBr) and thallium iodide (TlI).
As KRS-5 contains thallium, inhaling the powder produced when a KRS-5 window or prism is polished may cause intoxication. Users must not attempt to polish KRS-5 by themselves.
It is specified as a Class 2 Designated Chemical Substance by Japan's Law for Pollutant Release and Transfer Register (PRTR).

Zinc Selenide (ZnSe)

Zinc selenide is often used as a prism material. It reacts with acidic samples to produce toxic hydrogen selenide and it should only be used in the analysis of samples with pH values in the range of 6.5 to 9.5. Also, if ignited by fire or some other means, it decomposes to produce harmful fumes of selenium oxides.
It is designated as a poisonous substance (selenium compound) by Japan's Poisonous and Deleterious Substances Control Law and it is specified as a Class 1 Designated Chemical Substance by the PRTR Law.

Barium Fluoride (BaF₂)

Barium fluoride is often used as the window material in analysis performed with a microscope. If it is heated or comes in contact with acid, it produces harmful hydrogen fluoride gas.
It is designated as a deleterious substance (barium compound) by the Poisonous and Deleterious Substances
Control Law and it is specified as a Class 1 Designated Chemical Substance by the PRTR Law.

Poisonous and Deleterious Substances Control Law (Japan)

Among the materials listed in Table 1, zinc selenide (poisonous substance) and barium fluoride (deleterious substance) are subject to control. I will leave interpretations of the law to more specialized documents. Here, I will describe some points related to purchase, storage management, use, and disposal that users must be careful to observe.

[Purchase Control]

• Be sure to create registers for purchased chemicals, and clearly indicate the current amounts and usage status.

• Ascertain the physical and chemical properties, particularly the toxicity, of poisonous and deleterious substances. Regarding items that require immediate action in the event of an accident, obtain all the relevant information in advance, and maintain a state of readiness.
• Store poisonous and deleterious substances in robust medicine cabinets and chemical closets, keep these containers locked, and take any steps necessary to ensure that the substances are not stolen or lost.
• In places where stored poisonous or deleterious substances are on display, label them "not for medicinal purposes". Additionally, label poisonous substances "poisonous substances" with white letters on a red background and label deleterious substances "deleterious substances" with red letters on a white background.

• Store chemicals in clearly visible locations.
• Store poisonous or deleterious substances in locked containers specifically designed for this purpose.
• Clearly identify the administrators of keys, periodically check the numbers of keys, and take any other steps necessary to ensure comprehensive key management.
• Create an administrative ledger, and periodically check stocks. Perform the storage management required to prevent loss.

• Poisonous and deleterious substances cannot be disposed of without being treated.
• Either dispose of poisonous or deleterious substances using the legally specified method, such as decomposition, combustion, or neutralization, or have them disposed of by a disposal subcontractor authorized by the local authority.

• Periodically train personnel handling poisonous and deleterious substances with regard to the handling methods used.

Although crystalline materials such as windows and prisms are themselves subject to the Poisonous and Deleterious Substances Control Law, in cases where they are incorporated into holders or form part of the equipment in some other way, they are not. There is still the same level of danger, however, so handle such parts with due care.

Other Laws and Regulations

There are window and prism materials that are regulated by laws and regulations other than the Poisonous and Deleterious Substances Control Law and the PRTR Law. Be sure to use these materials safely with reference to the MSDSs described later and other appropriate documentation.

MSDS

An MSDS (Material Safety Data Sheet) is a document that summarizes information about a material that includes chemical and physical properties, dangers and hazards, emergency measures for dealing with intoxication, points to note in handling, storage, and disposal, and applicable laws and regulations. If you read this, you will know how to store, use, and dispose of the applicable material.
An MSDS for a material can be obtained from the place of purchase. It can also be searched for and accessed via the Internet.

Summary

Most of the window and prism materials used in FTIR analysis are crystalline, so they do not have an immediate effect on the human body. With some materials, however, swallowing a broken fragment or inhaling abrasion powder after polishing with deficient equipment may result in intoxication. In some cases, a material may react with a chemical to produce toxic gas. In addition, there are materials for which strict management of storage and disposal is demanded by laws and regulations.
We ask that you use materials properly with reference to the applicable MSDSs and other documentation.

Table 1 Common Infrared Transmissive Materials