Biomedical Engineering Reference
In-Depth Information
QCs preparation, two additional lots of blood were used to prepare two matrix effect
(ME) samples at low and high concentrations. All ME samples, QCs and calibration
standards in blood carrying six compounds were spotted on three types of paper/
cards at the same time. The spotting volume was either 15 or 5 mL. The spot centers
(3 mm i.d.) were punched for the samples prepared with 15 mL of blood but full spots
(6 mm i.d.) were punched for the samples prepared with 5 mL of blood. The punches
were extracted and analyzed with the procedure described earlier. QCs and ME sam-
ples were quantified against calibration standards that were prepared, spotted, and
analyzed in the same fashion. Mean bias (%) was calculated for all evaluation sample
lots (QCs or ME samples) and all concentration levels of each of the five compounds.
Standard deviation error bars are used to reflect the variation of the individual bias
among all concentration levels. Compounds A, B, C, E, and F on FTA Elute Cards
and VWR 237 paper are presented in Fig.
6a-d
showing the paper/card impact on the
matrix effect. Compound D is not presented here because the analyte was eluted at
the zone when severe compound-specific matrix ionization suppression was observed
(chromatogram not shown). The acceptance criteria used was ±15 % for bias in
matrix effect evaluation. Figure
6a, b
indicate that FTA Elute cards have significant
matrix effect compared to VWR 237 paper spot center punches for all analytes tested.
However, when using accurate low volume spotting and a full punch, the overall
matrix effects generated on FTA Elute cards and VWR 237 paper are similar. In other
words, plain paper with either partial or full punch of the spot generates less matrix
effect than treated paper/cards.
4
Conclusion
The paper/cards used for dried blood spot sampling can affect the accurate quantita-
tive determination of analytes for pharmacokinetic evaluations. Various factors were
evaluated using six analytes over a wide log
D
range. These were related to impreg-
nated chemicals on the cards, variable volume, viscosity, and compound dependent
distribution of the analytes. The widely used treated paper/cards generally showed
a more complex and significant impact than the plain filter paper/cards. Chemicals
on the treated paper/cards in conjunction with the specific properties of the analytes
may cause variations in the analyte distribution that could provide a challenge, so
evaluations of the sampling paper/card should be carefully conducted before a DBS
method can be applied for accurate measurement of analytes in DBS-LC-MS or if
pharmacokinetics is the end point of a study. The level of acceptable variation needs
to be evaluated and decided before implementing such a method for quantitative
work. Spotting on uniform plain filter paper was shown to reduce the variability
with regard to matrix effects, thus resulting in a more accurate analyte determina-
tion. However, the most accurate matrix and paper/card independent values were
derived from accurate volume spotting with full cut of the spots. In addition to the
factors presented, hematocrit effect or any other components that lead to varying
blood viscosity, the paper/card type, media evenness, and paper lot-to-lot variation
should be considered as critical impact factors.
