Chemistry Reference
In-Depth Information
individual contaminants cannot be identified or quantitated. In addition, residues
must be at least somewhat water soluble to be detected. Colorimetric assays, while
still classified as residue nonspecific, are more specific than TOC assays. Assays
such as the Biuret, Bradford, and Lowery tests can quantify proteins in the pres-
ence of other organic residues. UV/VIS absorbance testing is usually used to detect
compounds in final rinse water samples. Conductivity testing, sometimes performed
on-line, is useful for measuring inorganic or ionic residues. Many buffer and media
components and cleaning agents can be easily detected by this technique.
Residue-specific methods include USP purified water assays, endotoxin test-
ing, bioassays, and TLC or HPLC. USP purified water assays include testing for
chloride, sulfates, ammonia, carbon dioxide, calcium, heavy metals, oxidizable
substances, total solids, pH, conductivity, and TOC. Water assays are commonly
performed on rinse samples and are quite useful in assessing the efficacy of a clean-
ing regimen. The main disadvantage of USP purified water testing is that it only
detects a limited number of inorganic compounds that must be water soluble. Also,
USP purified water testing is usually a limit test and therefore does not provide
quantitative data. Endotoxin testing, also performed on rinse water samples, is used
to detect and quantify bacterial cell wall fragments. It can be quite accurate and
precise to low levels, but is susceptible to interferences. Bioassays are used to assess
the specific biological activity of a given molecule. This is the least commonly used
method to assess equipment cleanliness due to time, expense, and a high experi-
mental error. Also, it is unlikely that many biologically active compounds remain
so even after a cursory cleaning. On the other hand, HPLC is one of the more com-
monly used residue specific assays. HPLC can detect and quantitate a broad range
of compounds, from proteins and peptides to smaller molecules and detergents. It
provides the required specificity, accuracy, and repeatability required for cleaning
validation testing.
7.7.4 S
ettIng
r
eSIdue
l
ImItS
The calculation of cleanliness for a piece of equipment is based on the assumption
that all surfaces are uniformly contaminated. However, in reality, this is not always
the case. Residue limits should be practical, achievable, verifiable, and based on the
most deleterious component [52]. Limits may be established based on the minimum
known pharmacological or physiological activity of the active ingredient and must
be scientifically justifiable.
There are several methods (formulas) used to calculate cleaning effectiveness.
These formulas include the 10 PPM formula, the Acceptable Daily Intake formula,
and the 1/1000 of Therapeutic Level formula [44,51]. The 10 PPM formula allows
for no more than 10 PPM of cross-contamination between successive products. The
Acceptable Daily Intake formula allows no more cross-contamination than what the
acceptable daily intake indicates. The 1/1000 of Therapeutic Level formula allows
no more than 1/1000 of product A's minimum daily therapeutic dose into product B's
maximum daily dose. Cleaning criteria are usually based on the formula that results
in the lowest number. Obviously, the more potent a given compound, the lower
the cleaning criteria. The low levels that often must be measured during cleaning
