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

An early approach to PAA determination involves a
two-step titration. The H 2 O 2 present is titrated at a low
temperature with a standard solution of potassium permanganate
(KMnO 4 ) in the first step. Potassium iodide
is then rapidly added and the iodine liberated by the
PAA is titrated with a standard thiosulfate solution. This
procedure is called the potassium permanganate – thiosulfate
titration method and has been used as the reference
method for monitoring industrial PAA applications
[6,11,12].
There are other methods to determine PAA in disinfectant
samples [2], in synthetic samples [3], in brewery
cleaning-in-place disinfection processes [4,11,13], in tap
water [6] and in wastewater samples previously treated
with PAA [14] using spectrophotometry [2,4,6,14-16],
potentiometry [3], gas chromatography [17] and highperformance
liquid chromatography [11,13].
An analytical method for the analysis of PAA requires
high selectivity and little cross-reaction with the
coexistent H 2 O 2 . The coexistence of PAA with H 2 O 2 is
unavoidable owing to the synthesis of PAA from H 2 O 2
and acetic acid, as mentioned above, and its continuous
decomposition [3]. A rapid analytical technique is
also desirable for the analysis of PAA, since diluted solutions
are unstable and they have to be recalibrated
frequently using titration or other absolute determination
methods [3,11]. But, a rapid analytical technique is
difficult using a manual procedure.
By employing automatic procedures, however, these
goals may be attained using those based on a sequential
injection analysis (SIA) [18] or a multicommuted
flow injection analysis process (MCFIA) [19-21].
Solenoid micro-pumps were introduced to replace
peristaltic pumps as an alternative for fluid propulsion
in a flow system [22]. A flow system based on micropumps
has been designed employing one propelling
device for each solution, controlled by a microcomputer,
thus permitting solution flow rates that can be
individually varied by the software [23].
The inherent features of the MCFIA, such as versatility,
low reagent consumption, and robustness, are also
enhanced using a solenoid micro-pump to propel sample
and reagent solutions [18, 24-28].
In this work, we describe the development of a multicommuted
flow injection procedure for the spectrophotometric
determination of peracetic acid in disinfectants
employing solenoid micro-pumps to propel
reagent solutions contained in Vacu-vials ® ampoules
(CHEMetrics, Calverton, VA, U.S.). The detection was
measured at 565 nm.
2. experImental
2.1. safety n o t e
PAA is strong oxidizer, is incompatible with easily oxidized
substances and forms explosive mixtures. These
www.brjac.com.br
Silva et al.
solutions are severely irritating to eyes, skin and mucous
membranes.
2.2. re a g e n t s a n d s o l u t Io n s
All the solutions were prepared from analytical reagent
grade chemicals using ultrapure water (18 MΩ
cm -1 ) obtained by means of a Milli-Q (Millipore Corp.,
USA) water purification system.
The PAA solutions were prepared from their stock solutions
(15 %, w/v). The concentration of the PAA stock
solution, obtained from Microbiana Descontaminações
Ltda (São Paulo, SP – Brazil), was analyzed to be 169.7
± 2.2 g L -1 using the conventional method proposed by
Greenspan and Mackellar [12]. An aqueous stock solution
of 100 mg L -1 peracetic acid was prepared. The concentrations
of calibration solutions varied from 0.5 to 5.0
mg L -1 of PAA. Sample solutions of PAA were prepared
by diluting the appropriate volume of PAA with water.
Vacu-vials ® ampoules (CHEMetrics, Calverton, VA,
U.S.) containing approximately 2 mL of DDPD solution
were used as the reagent. The DDPD solution is
a methyl-substituted form of DPD (N, N-diethyl-p-phenylenediamine)
which is kept in a sealed glass tube under
vacuum.
The activator solution was 15 g L -1 potassium iodide.
Three drops of the activator solution were added to 25
mL of the calibration and PAA sample solutions.
All disinfectant samples contained peracetic acid (approximately
15%, v/v), acetic acid (16%, v/v) and hydrogen
peroxide (23 %, v/v), although the package label
did not specify a PAA concentration. The disinfectant
samples were diluted to the desired concentration with
water prior to analysis.
fi g u rE 1. fl o w diagram o f thE m u l t iC o m m u t E d f l o w systEm. a) diagram o f
thE f l o w systEm. P 1 , P 2 a n d P 3 : s o l E n o i d m iC r o-PumPs; s: s a m P l E; r: rE a g E n t
s o l u t i o n; C: CarriEr s o l u t i o n (h 2 o), rC: rE a C t i o n C o i l, 0.8 m m i.d., 100
Cm; x: C o n f l u E n C E; dEt: dEtECtor, 565 n m; w: w a s t E. B) sw i tC h t i mE C o u rs E
o f m iC r o-PumPs, rEsPECtivEly t 1 , t 2 a n d t 3 . st: s a m P l i n g stEP; wt: washing
stEP. thE shadow arEas BEnEath o f l i nE s indiCatE that thE s o l E n o i d m iC r o-
PumPs w E r E switChEd on.
159