The focus of the swimming world will be on a laboratory in Barcelona today as the representatives of Irish swimmer Michelle de Bruin inspect and supervise the opening of the B sample portion of the urine sample she submitted to testers last January.

The analysis of the B sample will have a significant influence on the outcome of the case. If it confirms the finding of the A sample it will add considerable weight to FINA's assertion that de Bruin tampered with the sample before it entered the chain of custody.

Of equal importance but still not known yet are the results of the long-term analysis being performed on several of de Bruin's samples. The laboratory report from the January 10th sample suggested the administration of a testosterone precursor designed to promote the production of testosterone within the body.

This morning's testing is expected to take at least three hours but it is as yet uncertain as to whether or not results will be announced before the weekend.

Dr Jordi Sedura, head of the Barcelona laboratory, said this week that he was satisfied that all storage procedures and chain of custody procedures for the sample had been adhered to. He added that he had never known a case where the B sample differed from the A sample.

This morning the first task of de Bruin's solicitor, Peter Lennon, and the biochemist accompanying him to Barcelona will be to inspect the conditions in which the sample has been held and then to examine the seals on the Versapak canister in which the urine sample resides.

Any detectable breach of the seals or signs of tampering would be a key issue in later proceedings.

Testers in the laboratory will then test the specific gravity and protein levels of the sample using machinery which gives a more precise reading than the dipstick method used by sampling officers in the field.

Much was made in the early days of the controversy regarding the difference in the specific gravity measure taken by the sampling officers in Kilkenny on January 10th and that taken using different instruments in Barcelona the following week.

Analysts suggest, however, that a difference in measurements is not significant and the discrepancy is extremely unlikely to have any bearing on the outcome of the case.

Today, the remaining 30 millilitres of the sample provided on January 10th will be analysed using a technique called gas cromatography - mass spectrometry.

Small amounts of the sample will be poured into four test tubes, each portion of which is chemically worked up to make it pure enough for analysis. Lennon has speculated publicly that the test tubes used at this stage of the process may have been cleaned using industrial alcohol. An opportunity will be afforded this morning to examine all equipment.

The work-up process is achieved by dripping the urine slowly through a resin which will catch steroids but allow other chemicals to pass through.

The steroids are then chemically removed from the resin to be centrifuged. The result is a two layered liquid, the bottom layer of which contains the steroid conjugates.

This is reacted with chemicals, thus changing their molecular structure so that they may be passed through a 25-metre long glass tube called a capillary column. During this process the molecules are heated to 200 degrees celsius.

The molecules interact with the various components of the sample, retarding some more than others. The time that any substance takes to pass through the column is particular to that substance and helps to identify it.

The mass spectrometer is attached to the end of the gas cromatographic column to detect the substances passed into it by bombarding the molecules with a beam of electrons which fragment the molecules into ionic pieces.

The end result will be a specific graph which can be compared with the graph readouts of known substances. The result is comparable to fingerprinting in its conclusiveness. Every substance will have fragmented in a specific and unique manner.

In Barcelona today the two key elements of the procedure from the de Bruin perspective will be examining the security and storage of the samples and overseeing the testing procedure.

Any subsequent appeals are likely to be fought on the minutiae of the test tubes and phials.

Although the charge of adulteration has grabbed most of the headlines with its lurid mention of whiskey odours, the alleged presence of a testosterone precursor in the sample could have equally catastrophic effects for de Bruin's career.

Testosterone has always been problematic for testers in that it is an endogenous substance which occurs naturally within the body. Science has struggled to come up with an accurate way of measuring testosterone levels, settling eventually on the technique of using the ratio of testosterone to its epimer, epitestosterone, as the criterion.

The naturally occurring ratio was set at 1:1 and, due to the possibility of natural fluctuations, the legal limit for sports-people was set at 6:1 - meaning that an athlete could have more than five times the natural level of testosterone and still stay within the rules.

The area of detecting testosterone precursors is virtually virgin territory for the sports world and several of these products were added to the banned list last Autumn.

If de Bruin's B sample matches the A sample, she will be granted a hearing before the FINA doping panel sometime in late June. If banned, she has said that she will appeal the decision to the Court of Arbitration for Sport in Lausanne.

Meanwhile, it has been learned that de Bruin will not compete in the French national championships in Paris at the weekend despite the fact that she has not yet received an interim suspension from FINA. De Bruin had been scheduled to swim in two events at the meeting.