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Analytical Chemistry Chemical Cytometry Quantitates Superoxide

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Table 1. Intraday Precision and Accuracy for the<br />

Determination of MK-2662 in Different Lots of Human<br />

Plasma<br />

method<br />

nominal<br />

concn<br />

(nM)<br />

mean<br />

measured<br />

concn (nM)<br />

(n ) 6) a<br />

accuracy<br />

(%) b<br />

precision<br />

(%) c<br />

PPT (n ) 6) 1.00 1.01 101.00 2.97<br />

2.00 1.98 99.00 3.03<br />

10.00 9.93 99.30 2.92<br />

50.00 49.86 99.72 3.43<br />

200.00 201.30 100.65 2.93<br />

500.00 503.99 100.80 2.92<br />

800.00 801.50 100.19 3.05<br />

1000.00 998.47 99.85 2.93<br />

IAP (n ) 3) 2.00 1.97 98.6 9.76<br />

5.00 5.29 105.8 2.56<br />

10.00 9.48 94.8 3.44<br />

50.00 51.22 102.4 3.17<br />

100.00 96.73 96.7 4.24<br />

160.00 162.42 101.5 4.12<br />

200.00 200.14 100.1 1.98<br />

a Back-calculated by interpolation from the calibration curve, constructed<br />

by weighted (1/x 2 ) linear regression of peak area ratios<br />

(analyte over ISTD) vs concentrations of the calibration standards in<br />

plasma. b Expressed as [((mean observed concentration)/(nominal<br />

concentration)) × 100] (%). c Coefficient of variation of back-calculated<br />

concentration.<br />

the analytical recovery of the two methods, determined to be<br />

greater than 90% for the PPT method and approximately 30% for<br />

the IAP method (data not shown). The low recovery of IAP might<br />

be the result of relatively low binding affinity of anti-PEG antibody,<br />

which consequently leads to incomplete analyte capture during<br />

the binding step and partial analyte loss during the washing steps.<br />

However, since the stable-isotope-labeled PEGylated MK-2662 was<br />

used as the IS, the low recovery of IAP, as expected, did not have<br />

significant impact on the assay precision and accuracy.<br />

Application of PPT 2D LC-MS/MS and IAP 2D LC-MS/<br />

MS to Clinical Sample Analysis. The protein precipitation<br />

followed by 2D LC-MS/MS was initially applied to analysis of<br />

the clinical plasma samples to support the first in-human study<br />

after subcutaneous (sc) administration of MK-2662. The interday<br />

QC data collected during seven daily sample analysis runs showed<br />

accuracy ranging from 104.72% to 106.33% with

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