Brazilian Journal of Analytical Chemistry - BRJAC - Brazilian Journal ...

a m u l t iC o m m u t a t e d flow system f o r peraCetiC a C i d determination
The sample consumption was 600 times lower for
the flow system than for the reference method. The
sampling throughput was 80 injections per hour, for
the proposed system, which indicates that laboratory
productivity would be enhanced by 3.6 or 18 times,
compared to the Vacu-vials ® Kit and to the reference
method, respectively.
The performance of the multicommuted flow injection
analysis process (MCFIA) in real sample analysis
was evaluated using three disinfectant samples that
were assayed using both the proposed procedure and
the reference permanganate titration [12] method. The
results are presented in Table III.
taBlE iii. PEraCEtiC aCid C o n C E n t ra t i o n s (g l -1 ) in s a m P l E
d i s i n fE C t a n t s o B t a i nE d By thE P ro P o s E d ProCEdurE (mCfia) a n d
thE rEfErEnCE m E t h o d [12].
sa m P l E s
Pro P o s E d m E t h o d
(g l -1 )
rEfErEnCE m E t h o d
(g l -1 )
rE l a t i v E Er r o r
(%)
1 166.9 ± 16.4 163.4 ± 13.2 - 2.14
2 169.8 ± 18.2 162.1 ± 4.8 - 4.75
3 77.4 ± 6.4 101.3 ± 21.9 23.6
The data reported indicate the presence of peracetic
acid concentrations between 77 and 170 g L -1 with a
RSD between 6.4 and 18.2 % using the method under
study, compared with 4.8 to 21.9% for the reference
method. The values of relative errors were both positive
and negative, indicating that both procedures provide
comparable results without systematic errors.
In the reference method, the hydrogen peroxide
present is first titrated under cold conditions with a
standard solution of potassium permanganate. This
titration eliminates the peroxide. Potassium iodide is
then rapidly added and the iodine liberated by the
peracid is titrated with standard thiosulphate solution
[12]. In the proposed method there is no step to eliminate
peroxide. As mentioned, the proposed method
is based on the reaction of PAA with I - solution. The
concentration of I - in the sample solution should be
high enough to dissolve the I 2 resulting from the reaction
of PAA (and H 2 O 2 ) with I - (reference 3). Probably,
in sample 3, there was a high concentration H 2 O 2 and
this reacted with I - generating a larger amount of I 2 .
Thus, the excess of I - was not enough to solubilize I 2 ,
so that the analytical signal was smaller, resulting in a
lower PAA concentration.
The standard addition method was also used to test
the accuracy of the assessment samples, yielding the
results showed in Table IV. As seen, the recoveries obtained
are within the range of 95 to 106 %, which is
considered acceptable for this type of sample.
sa m P l E s
taBlE iv. rECovEriEs o f PEraCEtiC aCid in w a t E r samPlEs.
rEsults ExPrEssEd in m g l -1
Co n C E n t r a t i o n
162 Br J Anal Chem
A n = 3
a d d E d
st a n d a rd a d d i t i o n
mE t h o d a
rECovEry (%)
1 1.00 1.01 ± 0.04 101 ± 4
2 1.69 1.79 ± 0.16 106 ± 9
3 1.35 1.32 ± 0.05 97 ± 3
4 1.22 1.17 ± 0.09 95 ± 7
5 2.00 1.94 ± 0.12 97 ± 5
4. co n c l u s Io n s
The proposed methodology (MCFIA) with spectrophotometric
detection showed robustness and versatility
and offers several advantages over the reference
method for routine analyses of peracetic acid samples
(permanganate titration) [12] and the Vacu-vials ® kit,
such as higher analytical frequency and lower cost.
The reaction and detection are integrated in the same
manifold and all operations can be controlled from
the computer, providing simplicity and reliability when
compared to permanganate titration. Considering the
advantages presented, it is feasible to employ this procedure
for the analysis of peracetic acid in any water
treatment laboratory.
ac K n o w l e d g e m e n t s
The authors thank the CNPq (Proc. 472358/2006-5)
and CNPq/FACEPE/PRONEX (Proc. 0333-3.07/06) for financial
support and Microbiana Descontaminações Ltda
(São Paulo, SP – Brazil) for samples of peracetic acid.
references
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