According to current USP specifications, "absorbent gauze" is cotton or a mixture of cotton and rayon (not more than 53% by weight) that is in the form of a plain woven cloth conforming to the standards set forth in the monograph.

Testing includes general characteristics [thread count (warp and filling), length, width and weight] followed by several chemical and physical tests [water extract of gauze examined for dried and ignited residue, the presence of acid, alkali, dextrin and starch]. The gauze itself is analyzed directly for residue on ignition, fatty matter, alcohol-soluble dyes, cotton and rayon content.

The chloride ion, one of the major inorganic anions found in the environment, is an integral component, in the form of a "salt," of many isotonic and physiological solutions. The ubiquitous chloride ion is also a major inorganic contaminant of water and wastewater.

This test determines the chloride level colorimetrically, using mercuric thiocyanate.

Conductivity is a physical test that measures the ability of an aqueous solution to carry an electric current. Conductivity is normally expressed in microSiemens per centimeter, m S/cm. The conductivity of a water sample results from the presence of positive and negative ions. Water molecules tend to dissociate into ions as a function of pH and temperature, resulting in a very predictable conductivity. Extraneous ions (chloride, sodium, carbonates, ammonia, etc.) also affect the conductivity and have significant impact on the water’s chemical purity and suitability for use in pharmaceutical and other applications.

Water conductivity is a requirement for Purified Water and Water for Injection under current USP specifications.

In the USP monograph, the tests for conductivity are divided into three stages.

Stage I requires conductivity to be measured in an uncompensated temperature mode against a standard conductivity solution, with a calibrated conductivity meter. By using the following chart, the measured conductivity of the water sample is compared to the chart value corresponding to the temperature range in which the conductivity was measured.

If the measured value is lower than the chart value, the sample passes the test for water conductivity. If not, Stage 2 is applied. 

Stage 2 involves stirring the sample at 25 ± 0.1° C until the drift in conductivity (due to the uptake of atmospheric carbon dioxide) is less than 0.1 m S/cm over a 5-minute period. In order to pass this stage, the final conductivity must not be greater than 2.1 m S/cm. Stage 3 is applied if this specification is not met.

Stage 3 compares the conductivity with the pH of the water sample. If the conductivity of the sample at its actual pH is less than the allowed conductivity at the same pH listed in the following chart, then the sample passes the requirement for water conductivity.

An infrared spectrum can therefore be used to characterize or identify organic compounds (i.e., polymers, solvents, etc.), establish a reference spectrum for future comparison, and determine functional groups of minor polymer components (i.e., organic additives, preservatives).

The Sadtlerâ IR database is also available, which allows performance of an IR search of over a 1,000 compounds and functional groups. It is also possible for the laboratory to set up a client sample IR database for quality control and comparison.

This is an analytical process in which the components of a mixture are separated from one another by volatilizing the sample into a carrier gas stream, which is passed through an analyte-specific column. Different components move through the column bed at different rates and appear separately at the effluent end, where they are detected and measured by thermal conductivity changes, density differences, or ionization detectors.

Gas chromatography (GC) is typically used for the analysis of minute quantities of complex mixtures from industrial chemicals, biological fluids and pharmaceutical preparations.

Glutaraldehyde is used as a liquid chemical sterilant in the medical device industry. It is often used in a hospital environment for the sterilization of reusable devices, such as endoscopic instruments, clinical thermometers, dental instruments, etc., because of its efficacy and timesaving ability. It contains two active aldehyde groups (compared with one for formaldehyde) and is sporicidal in the pH range of 7.5 to 8.5. Aqueous solutions of glutaraldehyde are mildly acidic in reaction and usually require a buffer or activator to raise the pH to its peak antimicrobial activity range.

The reagent 3-methyl-2-benzothiazolinone hydrazone hydrochloride in the presence of ferric chloride produces a blue color if glutaraldehyde is present. The intensity of the blue color is then determined colorimetrically from a standard plot.

This USP semi-quantitative test determines whether the total level of metallic impurities that react with the sulfide ion, under test conditions, exceeds the heavy metals limit specified in the individual USP monograph. Results are reported as weight percent (wt%) lead, based on color-comparison.
Note: The laboratory will determine the USP method to be used, based on the type of sample.

USP Method I
For substances that yield clear, colorless preparations under specified test conditions.

USP Method II
For substances that do not yield clear, colorless preparations under test conditions specified in Method I, or for those that interfere with sulfide precipitation, or for fixed and volatile oils.

Should results exceed the heavy metals limit, it may be necessary to test for the elements that typically respond to this test (i.e., antimony, arsenic, bismuth, cadmium, copper, lead, mercury, molybdenum, silver and tin) by atomic absorption (AA) or inductively coupled plasma (ICP) spectroscopy.

This series of tests is designed to provide information about the physical and chemical characteristics of elastomeric (rubber) closures. Prepared test samples (of a specific surface area) are extracted with purified water in an autoclave for 2 hours at 121° C.
[Sample requirements = 100 cm².] 
The extract is then subjected to the following tests:

• Reducing Agents
A 50-mL aliquot of the extract is titrated with 0.01 N iodine using starch as an indicator. The difference between the blank and sample titration is expressed in ml of 0.01 N iodine.

• Heavy Metals
The heavy metals content is determined by color comparison after reacting with the sulfide ion. The difference between the sample and the blank is the heavy metals content, as lead.

• pH Change
The difference between the pH of the blank and extract, determined potentio-metrically, is the pH change.

• Total Extractables
A 100-mL aliquot of the extract is evaporated and dried in a tared evaporating dish and the residue weight, in mg, is recorded. This same procedure is then performed on the blank. The difference in the residue weight of the extract and blank is the amount of total extractables.

These tests, designed to determine the physical and chemical properties of plastics and their extracts, are based on the aqueous extraction of the polymer. Prepared test samples are extracted in purified water for 24 hours at 70°C. 
[Sample requirements = 600 cm².] 
The extract is then subjected to the following tests:

• Non-Volatile Residue
A 50-mL aliquot of the extract is evaporated to dryness and the residue weight is determined. The difference between the amounts obtained from the sample and blank may not exceed 15 mg.

• Residue on Ignition
The residue from the non-volatile residue test is ashed, with the addition of sulfuric acid. The difference in the amounts of ignited residue for the sample and blank may not exceed 5 mg.

• Heavy Metals
The heavy metals content is determined by color comparison with a 1 ppm lead standard. The color is measured after pH adjustment and the reaction with the sulfide ion. The final sample color should not be darker than the 1 ppm lead standard.

• Buffering Capacity
A 20-mL aliquot of the extract and the blank are titrated potentiometrically to a pH of 7.0 with either 0.010 N acid or base. If the same titrant is used for both sample and blank, the difference in the amount of titrant may not exceed 10 ml. If different titrants are used, then the combined volume of the titrants may not be greater than 10 ml.

The current USP requirements for purified water include water conductivity and total organic carbon. Following is a comparison of the new and old requirements:

The test for water conductivity in the current monograph for purified water was introduced because it represents the cumulative conductivity values associated with the presence of chloride, sulfate, ammonia, calcium, carbon dioxide, heavy metals, and total solids. Each of these parameters, directly or indirectly, influences the electrical conductivity of water to a certain degree.

The total organic carbon test was originally introduced to the pharmaceutical industry as a valid check for trace organics in the water purification and distribution process. A sophisticated and numerical test, it is listed by the current monograph as an alternative to the test for oxidizable substances.

Total organic carbon (TOC) is a measure of the organic compounds (reported as carbon) present in water. It is an excellent method for measuring water purity because it is non-specific, highly sensitive, and theoretically capable of quantitating any carbon-containing compound. TOC analysis can be used to quantify nearly all of the commonly encountered organic contaminants (feedwater impurities, biofilm, etc.) expected from any water purification and distribution system.

The total organic carbon test was originally introduced to the pharmaceutical industry as a valid check for trace organics in the water purification and distribution process.

Atomic absorption spectroscopy is used to determine the presence of trace metals in a variety of samples. Most samples cannot be analyzed directly unless they are water or aqueous extracts. Most solid samples, if applicable, must undergo sample preparation techniques in order to completely dissolve the sample or to dissolve the elements of interest. Ashing and acid digestion are examples of common sample preparation techniques. The sample matrix usually dictates which sample preparation technique is followed.

Following are the elements typically analyzed by atomic absorption:

If the trace metal is unknown, it is recommended that an elemental scan be performed using ICP (Inductively Coupled Plasma) spectroscopy. This technology allows the simultaneous determination of 35–40 elements in a single sample run without the time-consuming modifications for each element required by atomic absorption.

Sample preparation techniques are the same as those for the Trace Metals test (by atomic absorption) described above.

The current USP requirements for water for injection include water conductivity and total organic carbon.

The test for water conductivity in the current monograph for purified water was introduced because it represents the cumulative conductivity values associated with the presence of chloride, sulfate, ammonia, calcium, carbon dioxide, heavy metals, and total solids. Each of these parameters, directly or indirectly, influences the electrical conductivity of water to a certain degree.

The total organic carbon test was originally introduced to the pharmaceutical industry as a valid check for trace organics in the water purification and distribution process. A sophisticated and numerical test, it is listed by the current monograph as an alternative to the test for oxidizable substances.

ECH and EG determined by water extraction. 1 extraction

Water extraction.
(24 hr., 37°C or specify time/temperature)