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

developmenT o f e n v i ro n m e nT a l l y susTainable
proCedures f o r The d e T e r m i n aT i o n o f orThophosphaTe
a n d ToTal i ro n in fresh w a T e r, e m p l o y i n g a h o m e m a d e
led-based p h o T o m e T e r a n d a m u l T iC o m m u T e d approaCh
mário al m i r feres a , an d ré f. la v o ra n T e b , bo a v e n T u ra f. reis a *
a) Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, 13400-970, Piracicaba, SP, Brazil
b) Universidade Federal Rural de Pernambuco, Departamento de Química, 52171-900, Recife, PE, Brazil
*Corresponding author:
Phone 55 19 3424 2946;
Email: reis@cena.usp.br
1.In t ro d u c t Io n
AbstrAct
In this article, a flow system designed to allow photometric determination of
orthophosphate and total iron in fresh water while generating a low volume of waste is
described. The procedures for the determination of orthophosphate and iron were based
on the molybdenum blue and 1,10-phenanthroline methods, respectively. Accuracy was
assessed by comparing results with those achieved using independent procedures. No
significant differences at 95% confidence level were observed. Other useful features,
including linear responses ranging from 0.1 to 5.0 mg L-1 3- PO (R = 0.999) and from
4
0.1 to 2.0 mg L-1 Fe (R = 0.999), detection limits of 20 µg L-1 3- -1 3+ PO and 50 µg L Fe ,
4
3- relative standard deviations of 0.6 % (n = 11) and 0.9 % (n = 11) for PO and Fe,
4
respectively, and analytical throughput of 76 determinations per hour, were also achieved.
Reagent consumption of 0.2 mg ammonium molybdate, 0.12 mg 1,10-phenanthroline
and 0.53 mg ascorbic acid per determination, and a waste volume of 0.264 mL per
determination were also achieved.
Ke y w o r d s : Multicommuted flow analysis, LED-based photometer, orthophosphate,
iron, water, Green chemistry
Nowadays, attention has been given to the quality of
fresh water, which has been accomplished by monitoring
the presence of several chemical species, including iron
and phosphate. Iron is considered essential for living
organisms. Nevertheless, high concentrations cause
tissue damage as a result of free radical formation [1,2].
Thus, the World Health Organization (WHO) established a
guideline value of 0.3 mg L -1 of iron in drinking water [3].
Phosphorus present in rivers and lakes generally results
from fertilization of arable land, industrial activities and
municipal sources, causing eutrophication, which has
been considered as a serious environmental problem
[4,5]. For this reason determination of phosphate levels
is a requirement when monitoring water quality.
The determination of iron and phosphate in water by
spectrophotometry has been carried out by employing
analytical procedures based on the flow injection
analysis (FIA) process [6,7], presenting as an advantage
high throughput, which could be considered a common
feature of FIA systems [8,9]. Because reagent solutions
are pumped continuously through the flow system, part
of them is discarded as waste without mixing with the
sample solution, resulting in misuse of this part of the
reagent solution. Because of this, the ability to reduce
waste generation must be included as a requirement to
reduce the pollution caused by the analytical procedure,
in accordance with the principles of Green Analytical
Chemistry [10].
Sequential injection analysis (SIA) [11,12] and
multicommuted flow analysis (MCFA) [13,14] processes
present as a common feature low reagent consumption,
resulting in reduction of waste generation [15,16,17].
Generally, the carrier solution does not participate in
the chemical reaction, but it can be considered as a
major contributor to waste generation. For this reason,
a strategy to reduce the use of this solution will be
incorporated within the current analytical procedure, in
order to improve environmental sustainability.
Photometric procedures for the determination of iron
and orthophosphate in fresh water will be developed
employing a MCFA process designed to use an air stream
as carrier. The procedures will be implemented using the
molybdenum blue method and the 1,10-phenanthroline
method for orthophosphate and iron determination,
42 Br J Anal Chem