Wet Chemistry Testing

Colorimetric Tests

Colorimetric tests are a category of tests in which the concentration of the compound to be examined is determined at a particular wavelength of light using a UV/Vis spectrometer. In most cases, the concentration of the material is determined based on a linear calibration prepared using certified standard materials. Results are reported in concentration (µg/mL, %) or other unit depending on the specifications listed in the individual method. UV/Vis scans are also available using USP <857> Ultraviolet-Visible Spectroscopy. 


Gravimetric Tests

Gravimetric tests are a general category of testing in which the final product is weighed to provide the result. For most gravimetric tests, the sample either undergoes a thermal process or a dissolution and precipitation process. The final result may be reported as the total mass of residue found (such as in mg) or as a function of the mass of sample (weight/weight basis). For some tests, the final result is compared to a limit and a determination of Pass/Fail is made. Common gravimetric tests performed at Galbraith Laboratories are listed below:

Residue on Ignition by USP <281>

Loss on Drying by USP <731>

Loss on Ignition by USP <733>

Total and Sulfated Ash

Solubles and Insolubles




Qualitative Tests

Qualitative tests are a broad category of tests in which no quantitative value is produced as the result. These tests are often reported as a pass/fail, less than a specified limit, or as a description of the specification. Qualitative testing is commonly a part of individual monographs found in various pharmacopoeial compendia, such as USP, EP, JP, FCC, and ACS. Examples of qualitative tests include limit tests, identification tests, physical characteristic tests (such as color and appearance), and other various tests that do not produce a quantitative value.


Identification Tests

Identification tests are a broad category of tests intended to verify the presence of a specific element, functional group or compound. Galbraith Laboratories commonly provides identification testing from various compendial monographs such as USP <191> Identification Tests – General, USP <197> Spectrophotometric Identification, and USP <201> Thin-Layer Chromatography. These results are often reported as a pass/fail result, or occasionally in different formats as listed in the individual monograph.


Limit Tests

Limit tests are a category of impurity tests in which a solution of an unknown sample is compared to a standard that contains the impurity at the specified limit. Generally, this definition applies to limit tests that are in widespread use in various pharmacopoeial compendia, such as USP, EP, JP, FCC and ACS. These tests do not give quantitative results, only qualitative “pass/fail” results based on the specified limit.


Volumetric Tests

Volumetric tests are a category of test in which known volumes of a standardized solution are added incrementally to an unknown solution in order to determine the concentration of a component in an unknown sample. Methods may be developed by Galbraith Laboratories, or compendial methods may be used, such as USP, EP, JP, FCC and ACS. Galbraith Laboratories can provide manual or automated titrations to an indicator or potentiometric endpoint. Results are generally reported as the percentage of the component in the sample (weight/weight basis).


Karl Fischer Tests

Karl Fischer is a specific method of determining water content in a product. The Karl Fischer instrument determines the amount of water directly from the number of coulombs required for the electrolysis of iodide to iodine. Both coulometric and volumetric testing is available. Galbraith Laboratories offers various methods including internally developed procedures and USP <921> Water Determination.