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5.3.4 Quantification of PCAs
5.3.4.1 Applied methods
Tomy et al. (1997) was the first, who described a detailed quantification method based
on ECNI. The concentrations of formula/congener groups and as a sum of total PCA
were calculated via the total signal area in the mass chromatograms. A correction of the
PCA molecular weight deviation between sample and reference standard was made.
Quantification was also based on the internal standard method.
Tomy et al. (1997) remarked that the overall response factor is strongly dependent on
the degree of chlorination of the PCA. Therefore, it was recommended, that the chlorine
content of sample and quantification reference should match as closely as possible to
avoid systematic errors. Table 13 shows that the systematic error for ECNI
quantification increases dramatically with an increasing deviation between the degree of
chlorination of sample and reference. The newly developed techniques CH4/CH2C12-
NICI-LRMS and EI-MS/MS are much less susceptible to this problem.
Table 13: Quantification of three sPCA solutions (overall amount 1500 ng) with variable chlorine content
with a sPCAs reference standard of 55 % Cl and 63 % Cl content using ECNI, CH4/CH2C12-NICI-LRMS
and EI-MS/MS. Relative deviations are given in parenthesis.
Standard
sPCA 51 %C1
sPCA 55 % Cl
sPCA 63 % Cl
Sample
sPCA 55 %
sPCA 63 %
sPCA 51 %
sPCA 63 %
sPCA 51 %
sPCA 55 %
Cl
Cl
Cl
Cl
Cl
Cl
ECNI-LRMS
4300
15600
522 (65 %)
5440
143 (90 %)
413 (72 %)
(190 %)
(940 %)
(260 %)
CH 4 /CH 2 C1 2 -
1770(18 %)
1210(19 %)
1270(15 %)
1030(31%)
1860 (24%)
1980 (32 %)
NICI-LRMS
EI-MS/MS
1590 (6 %)
1450 (3 %)
1430 (5 %)
1323 (12 %)
1700(14%)
1750(17 %)
Consequently, it is essential for ECNI quantification to determine the PCA chlorine
content in the sample first and to select a corresponding reference standard. Only
synthetic reference standards of 51 %, 55 % and 63 % are commercially available, and
the use of technical mixtures should be avoided due to possible interferences by
additives.
