The three most common contaminants that affect chromatographic applications are oxygen, water vapor, and hydrocarbons, which
all can infiltrate the gas supply from the general atmosphere during filling by the supplier or at the point of use. Oxygen
can accelerate column bleeds, reduce column life, and change retention times, as well as cause "ghosts" (unexpected peaks).
Moisture can reduce column life as well as shift retention times and increase baseline noise levels. Hydrocarbons also can
elevate baseline noise, degrade analyte quantification, and cause ghost peaks. There are a host of other contaminants that
can affect performance. For example, some mass spectrometry applications are sensitive to inert gases like krypton, although
these gases do not affect many other detectors. Also, consider impurities similar to analytes that the detectors are seeking.
Electron capture detectors (ECDs) are sensitive to halogen contamination because ECDs are designed to find halogens.
After understanding the impurities that will affect the equipment, determine the lowest purity level the system can tolerate.
Since, in general, the higher the purity, the higher the cost, this will enable users to produce the desired results at the
ENSURING GAS QUALITY
Users must safeguard purity to the point of use by verifying gas quality at every step of the process — from the supplier's
raw materials to bulk transfers, cylinder filling, delivery, and most importantly, the gas supply system at the laboratory
that carries the product to the point of use.
The most important verification is the final delivered product. Many applications, such as calibration of equipment, require
product that includes a certificate of analysis provided by the supplier. Without this certificate, a user may not know if
the gas meets specifications. In other cases, the gas does not have to be individually analyzed if it conforms to certain
standards. In such cases, the gas may come with a certificate of conformance. Users should be wary of any supplier who tries
to represent a certificate of conformance (a promise to meet a specification) as a certificate of analysis (an actual result).
Conversely, dictating a certificate of analysis where it is not required may lead to unnecessary custom work by the gas supplier
— work that the supplier will build into the customer's cost. Factors that determine whether a certificate of analysis or
certificate of conformance is needed include the nature of the work. For example, would Good Manufacturing Practice (GMP)
or Good Laboratory Practice (GLP) guidelines call for individual analysis?
Check that the certificate of analysis is for the end-use product in the cylinder, not the raw material. While raw materials
are sometimes the source of contamination, most problems are related to cylinder hygiene and the process of filling the cylinder.
The three most troublesome contaminants — oxygen, moisture, and hydrocarbons — are contaminants with the greatest potential
to enter a cylinder during filling. One of the best ways to check this process is to observe it through a quality audit of
the supplier's fill operations and analytical laboratory.
If buyers are sure of the purity of the gas they purchased, the quality of the filling and cylinder cleaning processes, and
the supplier's analytical processes, yet are still not getting the results they want, an investigation into their internal
gas system is in order. In other words, they may be "drinking clean water through a dirty straw." It is possible that impurities
are being introduced by leaks and contamination in the regulators, piping, and other equipment from the gas supply to the
point of use.
MANAGING THE GAS SUPPLY CHAIN
Managing the gas supply chain itself — from procurement to onsite cylinder handling to return of the "empty" cylinders after
use — often creates added headaches. Biotechnology laboratories that streamline the procurement and use of gas and cryogens
can maximize efficiency and minimize hidden costs.
The first step towards managing gas use in the laboratory is to effectively manage cylinder rentals. Gas is one of the few
supplies that comes in returnable, rented containers. Most laboratories assign flat rental allocations in which each user
is allocated a set portion each month. Because this in-house charge is a flat fee and a relatively low expense, many end-users
do not actively monitor cylinder balances. They simply want the gas available when it's needed. This results in overstocking
the supply, with users keeping more than a few months' inventory onsite even though their supplier is capable of making several
deliveries a week.