In addition to measuring pH value, weighing, and acid-base titration, moisture determination is also a very common laboratory measurement item. Moisture measurement is crucial for various industries, such as:

• Excessive moisture in lubricating oil can accelerate machine wear;
• Food and feed need to maintain a certain moisture content so that they do not feel too dry or stale to eat, and do not provide a breeding ground for bacteria and fungi that can cause spoilage;
• The pharmaceutical industry also needs to closely monitor the moisture content of tablets and freeze-dried powder products, as regulations stipulate that the moisture content of freeze-dried powder products should not exceed 2%.

Classic moisture determination method - Karl Fischer titration method

The Karl Fischer titration method for determining moisture content was introduced in the 1930s and is a widely used and reliable method to this day. It is a fast and commonly used method for determining moisture content.

• The Karl Fischer titration method can determine the moisture content of various types of samples, including liquids, solids, slurries, and even gases.
• For samples with moisture content ranging from 0.1% to 100%, volumetric Karl Fischer titration can be used for moisture determination, while for samples with moisture content ranging from 0.001% to 1%, Coulombic Karl Fischer titration can be used for moisture determination.
• Depending on the type, moisture content, and solubility of the sample in the Karl Fischer reagent, direct injection or dissolution in a suitable reagent (not reacting with the Karl Fischer reagent) can be chosen before injection.
• Samples that are insoluble or easily hygroscopic can be heated and extracted for moisture using a Karl Fischer furnace, and then brought into a titration cell by a carrier gas for moisture determination.

New Choice for Moisture Determination - Near Infrared Spectroscopy

Since the 1980s, near-infrared spectroscopy technology has been widely used in fields such as food and feed, polymers, and textiles. Ten years later, this technology was gradually applied in fields such as pharmaceuticals, personal care, and petrochemicals.

Near infrared spectroscopy is used to detect the harmonics and combined spectral bands of molecular vibrations. In the typical vibrations of organic molecules with functional groups such as - CH, - NH, - SH, and - OH, the - OH portion is a particularly strong near-infrared absorber. This is also why moisture quantification is one of the key applications of near-infrared spectroscopy technology.

Near infrared spectroscopy is a supplementary method used for conventional moisture quantification. Similar to high-performance liquid chromatography, near-infrared spectroscopy requires the establishment of an initial model.

• Near infrared spectroscopy can be used for quantitative analysis of moisture in solid, liquid, and slurry samples.
• The moisture detection limit for solid samples is approximately 0.1%; The liquid sample is within 0.02% (200 mg/L), however, there are some special cases (such as moisture in chemical materials) where the moisture detection limit can reach 40-50 mg/L.
• After successfully establishing the initial model, near-infrared spectroscopy can be used to determine the moisture content of the modeled sample. No sample preparation or chemical reagents are required, and measurement results can be obtained in less than 1 minute, making it easy to use even without a chemical background.
• Near infrared spectroscopy allows for direct measurement without the need for sample preparation. Solid samples are measured in sample bottles, while liquid samples are measured in colorimetric dishes.

Moisture determination - Karl Fischer titration, near-infrared spectroscopy, or together?

Karl Fischer titration and near-infrared spectroscopy have their own advantages, which can be summarized as follows:

Karl Fischer titration and near-infrared spectroscopy are both powerful tools for determining the moisture content of large quantities of samples. You can choose a very economical and efficient moisture determination method based on your actual application and measurement requirements.

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