Essential considerations in moisture determination by Karl Fischer titration

Karl Fischer Titration  method

Karl Fischer titration method is highly specific and selective to water and gives the total water present ,i.e, surface absorbed water as well as water of crystallization.

The method is based on a potentiometric determination involving quantitative reaction of water with iodine in presence of an alcohol, a base and sulphur dioxide. Pyridine or less toxic imidazole is used as base along with methanol or ethanol as the alcohol. The Karl Fischer titration method being highly specific and selective to water is free from interference of residual solvents as well as other limitations of the Loss on drying method. Further it is useful for determinations ranging from percentage to ppm levels. The only limitation of the method is the limited solubility of some products in alcohol or their reactivity with Karl Fischer reagent.

Karl Fischer Titrator (Image Courtesy : http://www.darshtechnologies.com)

Presence of moisture plays a vital role in deciding characteristic properties and stability of pharmaceutical and food products. Merits and demerits of water determination methods have been covered earlier. Karl Fischer is the preferred method adopted by most laboratories due to its high specificity and selectivity towards water present even in traces levels in a product.

The results of Karl Fischer titration are highly reliable and at same time the analysis does not require large investments. However, required precautions should be taken in handling of samples as well as the Karl Fischer reagent.

Essential Considerations

Reaction Cell

The reaction cell and electrodes should be cleaned properly to remove traces of earlier samples and residual moisture. After rinsing with high purity grade solvent the cell should be dried in hot air oven to ensure removal of any residual moisture. The sample port should be opened only briefly for sample introduction and the jacket on lid should be packed with silica gel to prevent moisture from atmosphere interfering with the estimations.

Sample Homogeneity

The sample must be stored in water resistant packs or sealed vials to minimize contamination during storage and transportation. It is essential to homogenize it to a fine powder if it is in granular or crystalline state. The measured samples should be introduced into the cell with minimum exposure.

Residual Water

It is necessary to determine the water factor in the blank methanol solvent every time. This factor depends on the amount of water present in the pure methanol solvent taken in the reaction vessel and depends on volume of Karl Fischer reagent required to neutralize it.

Use of Buffers

Karl Fischer titrations are best carried out in neutral solutions, commonly between pH 5-5 to 8.0. Moisture content in acidic and basic samples should be determined after buffering the solvent in reaction vessel before sample introduction. Commonly imidazole is used for acidic samples and salicylic acid is used for bases.

Calibration

Calibration is commonly carried out using disodium tartrate dihydrate as a primary standard. The standard contains 15.66% water. It dissolves in methanol slowly (2-3 minutes) so it should be allowed to dissolve completely after introduction and starting the titration.

Safe use of Karl Fischer Reagent

Karl Fischer reagent contains potentially hazardous and corrosive constituents. Care should be exercised to prevent contact with eyes or skin. It can prove fatal if accidentally swallowed. It can also catch fire easily as it is flammable. It is advised that you should familiarize yourself with its MSDS before handling Karl Fischer reagent so that you are aware of its hazardous properties.

Importance of Material Safety Data Sheets in Laboratories and Warehouses

Access to MSDS is important for all (Image Courtesy : http://www.huffinsurance.com/)

The safety of workers in laboratories and warehouses storing chemicals is a joint responsibility of all. This statement is often boldly displayed in concerned departments. However, every laboratory or warehouse worker cannot be expected to know the properties and hazards of all materials and therefore it is important to realize that safety can be implemented only when awareness on the hazards posed by chemicals and other materials is shared between all those concerned.

A material safety data sheet or MSDS, as it is often referred to, is a document that serves this purpose. It lists out details of physical and chemical properties, technical data, trade and common names, hazards, remedies on exposure and safe handling practices on chemicals to users and those involved in their handling and transportation.

Information available in MSDS

A material safety data sheet provides details that should not be overlooked or ignored by anyone involved in handling, transportation or laboratory usage of chemicals. It becomes all the more important to familiarize yourself with MSDS before you decide to use or handle a new chemical. Before proceeding further it is necessary to familiarize with the type of information available in the MSDS.

Chemical Properties

• Class of chemical, chemical name and trade name(s)
• Physical description of material along with its characteristic physical properties
• The decomposition behaviour and release of dangerous decomposition products, if any
• Common chemical properties and reactivities with incompatible materials
• Hazard properties and flammable limits of volatile and explosive materials
• Guidelines on safe disposal
• Recommendations on use of safe packaging materials.

Handling and Storage

Each material requires precautions in its handling and storage. MSDS lists out:

• Special handling procedures
• Recommended storage conditions such as air conditioning, humidity, temperature and exposure to light
• Safety practices in case of spills, accidental release, fires, etc
• Requirement of safety gear and special material handling tools

Toxicological Properties

The effects of exposure to a material may not be evident immediately but long-term effects can prove to be detrimental to health. MSDS lists out such effects, particularly:

• Short-term and long-term exposure hazards
• Safe limits of exposure
• Entry routes into the body and resulting damages to different body organs
• Recommendations on protective safety gear and how to prevent exposure
• Safe disposal practices to prevent adverse effects on environment

Transportation Guidelines

Transportation staff is also susceptible to dangers when transporting hazardous substances. Even the onlookers in event of accidents can suffer severe damages in case of accidents during transportation. MSDS provides the required guidelines for safe transport of such materials

• Need for hazard warning information and prominent display of hazard sign on transport vehicle
• Precautions during loading and unloading of containers
• Special packaging requirements for safe transport
• Need for protection against natural elements such as sunlight and rain during transportation

Fire Hazards

Fires resulting from chemicals can lead to widespread damage inside warehouse or a laboratory. Information on fire hazards of a product must be known to all concerned. MSDS lists out the following:

• Type of fire resulting from a product and requirement of class of fire extinguisher
• Personal fire protection for firefighting staff especially if toxic or corrosive fumes result from such fires
• Storage conditions and practices to prevent fire accidents

First aid measures

• First aid remedies in case of injuries or poisoning resulting from mild or high exposure
• Immediate first aid steps to be adopted before seeking expert medical attention
• Steps to be taken to handle emergencies
• Information on contacting for expert advice in case of exposure to special chemicals

The MSDS provides highly valuable information on safe handling of materials used in laboratories. It is therefore necessary that all should be made aware of the importance of MSDS sheets and should have easy access to them at all times.