The Laboratory Notebook

Answering important questions about quality.

By Robert Green

This month we discuss the intricacies of alpha lipoic acid and the analysis of lycopene, which leads to a further discussion of the potential degradation of a sample in the laboratory.

Q. I purchase large amounts of alpha lipoic acid. I have read that there are two forms of this compound (an “R” form and an “S” form) and that the R form is better. I asked my supplier which one I was getting and he said a combination of both, but that there was no way to determine how much of each form was present. Is this true?

A. No. But before we dive into that a little background is in order. This requires a short dissertation on chemical nomenclature; if you hang in there you will be versed in the details of lipoic acid and able to dazzle your friends and colleagues.

Lipoic acid is a metabolite of the human body, meaning that it is not initially present but is produced through a chemical reaction. It is credited with playing an important role in metabolism and energy production. It has also been characterized as a scavenger of dangerous free radical molecules, and as such, is considered an important antioxidant. Lipoic acid is also used or researched in the treatment of various diseases, including diabetes, HIV/AIDS and Parkinson’s and Alzheimer’s diseases.

Now for the chemistry. Stereoisomers are compounds made up of the same atoms connected by the same sequence of bonds, but having different three-dimensional structures. So they are very closely related but not identical. A major type of stereoisomer is called an enantiomer, which is a mirror image stereoisomer. When an object is not super imposable on its mirror image, the object is called “chiral.” A great example of this is your hands. If you put one on top of the other they are very similar (each has a thumb and four fingers) but they are not super imposable (one has the thumb on right side of your fingers and the other has the thumb on the left side).

Chirality has become critically important for pharmaceuticals. The differences, which make compounds chiral, can produce very different pharmacological effects in biological systems.

Enantiomers are also known as optical isomers because they rotate a plane of polarized light in different directions. Optical isomers that rotate plane polarized light clockwise are denoted as (+). Optical isomers that rotate counter clockwise are denoted as (-).

The last chemical understanding we need involves the nomenclature used to describe the spatial arrangement of the atoms of a chiral entity. Suffice it to say that if under the chemical convention we move in a clockwise direction, we use the designator “R,” or if we move counter-clockwise we use “S.”

If you are still with us, you now have the tools necessary for a full understanding of the lipoic acid situation. Lipoic acid is a stereoisomer (it has two closely related but not identical forms), an enantiomer (the two forms are mirror images) and is chiral (the two mirror images are not super imposable). In the body, lipoic acid consists of one form, designated as R+. When lipoic acid is synthesized in the laboratory, it naturally consists of equal amounts of both the R+ and S - forms. The body recognizes and can absorb the R+ form since it is familiar with it. The body cannot absorb the S - version, and some even claim this version is detrimental.

Synthetic techniques now exist to emphasize the production of the R+ form and inhibit the production of the S- version, although it is difficult and expensive. Fortunately, analytical techniques for the separation and analysis of these two versions have been known and documented for some time. A quality analytical lab, which keeps itself current, will be able to perform this analysis for you.

Q. I had identical lycopene samples tested at two analytical labs with widely differing results. Any ideas why?

A. It could be any one of a number of reasons, but there is one thought, which is peculiar to lycopenes and a few other materials. But first, let’s briefly review lycopenes.

Lycopene is the pigment principally responsible for the characteristic deep red color of ripe tomato fruits and tomato products. It has attracted attention due to its biological and physicochemical properties, especially related to its effects as a natural antioxidant. In particular, it ap­pears lycopenes provide protection against a broad range of epithelial cancers.

Lycopenes are very sensitive and thus subject to degradation, which not only affects the sensory quality of the final products but also the health benefits. Lycopene degradation can occur during processing. Post-production exposure to heat can also cause degradation.

But there is something else that can cause lycopene to degrade post-production, and it is present in every laboratory—light. Lycopenes are photosensitive and degrade in light. If left in light, particularly during analytical processing when they are immersed in solvents, the lycopene degrades on the laboratory bench. The longer it sits, the worse it gets. We maintain a separate area in one of our analytical labs for photosensitive compounds where all lights are yellow and special procedures are employed.

Laboratory sample degradation is a critical and often overlooked issue. Just about every sample degrades when exposed to one or more environmental conditions. Temperature is an obvious one. Exposure to heat or cold could adversely affect a sample. Many samples require refrigeration for storage. Obviously, we cannot test samples in a refrigerator, so they are manipulated at room temperature. In these cases, it is critical to bring the sealed samples to room temperature before opening them; otherwise they attract moisture and no longer represent the original product. Once opened, they must be handled rapidly.

Extreme care must also be taken when selecting the solvents to use in the analysis process. The sample and solvent must be a perfect fit to insure the sample does not deteriorate during processing. But just selecting the solvent is not enough. Many solvents contain stabilizers. While these stabilizers are generally “invisible,” we have found that some actually affect the analytes we are measuring.

Once again we see that analytical chemistry is a very detailed and exacting science, which can never be taken for granted. Whether you are doing testing in-house or outside, be certain the analytical personnel not only have the required instrumentation, but that they are skilled in analyzing nutritional supplements. NW