Plasma and serum are blood matrices used in equine doping analysis. Additives in blood collection tubes will influence analytical performance. This study evaluated four collection tubes on screening for 176 analytes and confirmation of 19 analytes. Three serum tube types—Red top (silicone-coated), Tiger top (serum separator tube 1), and Clear Gel (serum separator tube 2)—were compared with Gray top plasma tubes (sodium fluoride potassium oxalate).
The Gray top tube provided approximately 15% more sample volume than the serum tubes for analysis. When used for screening, all 176 compounds were detected with the highest average signal intensity of the 4 tube types. In contrast, 2 to 5 analytes were not detected in serum from the three tube types investigated. Signal intensity rankings were: Gray top > Red top > Clear Gel > Tiger top, with serum from the Tiger top tube at 80% of the average signal intensity of the Gray top tube. Among the 176 analytes, 42.5% of drugs had significantly lower signal intensity (< 85%) in serum from the Tiger top tube compared to the Gray top tube.
MRM confirmation revealed substantial interference caused by the Tiger top tube for analytes such as testosterone and methamphetamine, whereas no such interference was observed with other tubes. The average signal intensity of 19 drugs shows the same trend as the screening study. Matrix effects, rather than extraction recovery, were identified as the primary cause of signal intensity drop by the Tiger tube. Further investigation revealed that analytes, such as dexamethasone could be absorbed by the materials in the Tiger top tube, leading to a significant decrease in concentration after storage.
This study suggests that in the doping control analysis, the performance ranking of tubes is as follows: Gray top tube > Red top > Clear gel > Tiger tube.