Biomedical Engineering Reference
In-Depth Information
8
System Suitability Sample
CS and QC
Incurred Sa
m
ples
6
4
2
0
0
20
40
60
80
100
120
140
Sample Sequence No.
Fig. 16
Variable internal standard responses due to multiple sample processing steps (liquid-
liquid extraction, derivatization, and solid-phase extraction). Analyte: gestodene; internal standard:
norethindrone
incurred samples and CS/QC, because some analyte and IS in the organic solvent
layer have been soaked into the rubber and were retained, which reduced recovery.
On the other hand, the internal standard responses of the nonextracted system suit-
ability samples injected at the beginning and the end of the run were high and stable
(Fig.
17
).
Another example is an almost linear increase of IS responses with regard to the
injection sequence for all the extracted samples (incurred samples, CS and QC sam-
ples) while the IS responses of the system suitability samples injected at the begin-
ning and the end of the run were normal (Fig.
18
). The root cause was identified as
the inadequate mixing of the 100 mL aliquot of supernatant transferred from protein
precipitation with the 400 mL of reconstitution solution prefilled at the bottom of
wells (96-well plate). As the autosampler needle loaded a sample near the bottom of
a well, the loaded and later injected sample did not contain its “share” of the super-
natant because homogeneous mixing had not been reached. Apparently, the mixing
continued over the course of the run injection through diffusion, which resulted in
the gradual increase in IS responses observed in this example.
Sometimes, the root-cause might be difficult to identify due to timeline or
unavailability of incurred samples (e.g., not enough volume or no authorization
from the client). For example, during the initial sample analysis, variable and ran-
domly low IS responses were observed for incurred samples only (Fig.
19
). Despite
similar pattern as in the case of autosampler malfunctioning, the root cause was
unlikely related to autosampler issue because no CS or QC samples were affected in
this case. In addition, since all the CS and QC were accepted, there should be no
