NO SUCH THING AS THE BEST TECHNIQUE
and/or metabolites, extra precautions may be needed.
“ In the case of instability of the analyte ”
and tubes. It was observed that the use of soft push caps may reduce the recovery of some analytes, while the use of polypropylene closures (screw caps) did not have an influence at all (Table 1). It is therefore advisable to stay away from soft closures, unless testing has proven that adsorption is not an issue for the analyte being evaluated.
Table 1: Recovery (%) compared to freshly spiked plasma: collection after 5 min and 2h incubation in the tube at room temperature and cooled with melting ice.
Tube & cap MicronicTM 28 tube
with TPE cap (blue)
MicronicTM tube with EVA cap
Temperature Time (min) Cpd 1 RT RT
5
Ice RT RT
FluidX screw cap (no liner)
Ice RT RT
Ice
120 120 5
120 120 5
120 120
103 101 102 96
103 107 103 103 110
Cpd 2 90 61 85 95 85 94
100 104 100
Cpd 3 94 74 89 95 85 97 98
100 103
Cpd 4 90 54 80 97 84 99 99 96
107
Although the above described techniques will work in the majority of cases, there are situations that adaptation of the method might be necessary. These include but are not limited to instability, sensitivity and metabolites.
INSTABILITY
In the case of instability of the analyte and/or metabolites, extra precautions may be needed. By default, blood is cooled on melting ice to allow centrifugation without any risk of losing the wax plug. However, because of the small volumes and manual actions to transfer the plasma to another capillary, the sample may warm too fast to ensure sufficient analyte stability. Subsequent cooling is not immediately effective as the capillary is separated from melting ice by an air volume in the tube. In those situations a non-CMS approach is more effective. It allows for immediate addition of a stabilizer, while with the Vitrex technique this would require an immediate wash-out after sampling. Both Vitrex and Drummond techniques have the disadvantage that warming of the sample may be too quick to be controlled, because of the high surface/volume ratio of capillaries compared to a volume in a small tube.
www.bioanalysis-zone.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48
