Document 70M5qG8ya5wookNZLxBNZQv8e
AR226-2036
PECKSR
07/28/98 11:53 AM
To:
cc: Subject:
SZAKATBK, MILLERSR, HALBERRM PLAYTIS , MILLERW , PARSONMA, MAYLESM , ZIPFEL pathforward and problems with detemiination of C8 In air
Based on high reported C8 results for -the air samples collected on and due to erratic 6C results, I recommend resareples be taken
from these locations. If possible, duplicate samples should be
collected. This will help ensure accurate results and allow for
some analytical development as described below.
7/24/98,
Several problems ware observed in the analysis of the samples. Meet significantly, there was an abnormally large variation in the response of the C10 internal standard (42%) which is not understood. This certainly influenced calculation of the results reported 7/25 since
the C8 response is normalised for C10. Additionally, the linearity of the calibration plot (R"2^0.908) was very poor (a much wore linear response
was seen if the correction for C10 was ignored). Another
abnormality was the samples were mistakenly left in the hot block, for
an excessive time; the impact of this is unknown.
The calibration was repeated on 7/27 with excellent results. Variation in C10 peak heights was less than 4%. a series of standards without addded C10 was also analyzed, and the GC response was extremely linear with C8 (R~2=0.995). .
tn the table below, C8 results from different calibration plots are shown. Results above the RBL of 0.5 mpb are in bold. Different calculations
are as follows:
1. The first column ("w/CIO") shows the original results calculated
per the method where the C8 peak heights are corrected (normalized) based on the C10 peaks. Calibration samples from 7/24.
2. The second column of results were based on the uncorrecfced C8 peak heights using the calibration samples which were analyzed on 7/24.
3. The third column of results were based on the uncorrected C8 peak heights using the calibration samples which were analyzed on 7/27.
4. The fourth column of results ("no C10") were based on a series of calibration samples which were prepared without C10.
Table; Calculated C8 in Air (moles per billion)
SAMPLE
LOCATION
A
smoking area? 162 roof
ignore C10
w/CIO
7/24 cal
0.710
0
no C10
7/27 cal 0.195
7/27 cal 0.303
EID086170
\
B
blank
0.456
0.141
0.407
0.523
C top of SW stairs, unit side
0.859
0.420
0.763
0.863
D
SB rail
0.808
0
B mid-rail, North
0.152
0.120
0
0.170
0.252 0.282
Several comments are in order:
& Column 1 (original) results are invalid due to excessive variation in ClO response.
o Column 2 results are significantly lower than column 3 due to differences in the slopes and offsets of the 2 calibration plots.
o
Calibration plots for column 2 and 3 results showed good
linearity (R''2=0.984-0.985) even though the impact of the added ClO
(which contains some C8 impurity) was ignored.
0 Results in the fourth column are higher since the standards were prepared without ClO. The air samples contained extra C8 (from the ClO impurity) which was not subtracted in this calculation.
o
Standards prepared on the same day (7/27) showed quite similar
calibration plots.
o Response for standards prepared on different days (7/23 vs 7/27) was quite different.
In this series of samples, the ClO added standard seriously complicated the calculations. We observed linear GC response with NO ClO (a "classical" source of variation, injected volume, has effectively been eliminated with the use of autosamplers). I am hoping to demonstrate that the method can give reliable determination of C8 in air when no ClO ie added. This would streamline the assay and allow roore rapid turnaround, we are requesting duplicate air samples so one set can be analyzed w/o ClO.
added
One area that still concerns roe is the day-to-day variation in GC
response for the standards, analysis of standards is being performed today in
duplicate. This will give more information to help quantify
day-to-day variance as well as ensuring quality of reagents for use
with additional air samples.
Comments are welcome.
SP
EID086171