Chemistry Reference
In-Depth Information
preconcentration, and detection are performed simultaneously, increasing the sensitivity and the selectivity
of the analytical procedures and reducing the reagents consumed. The advantages of using automated solid
phase extraction (SPE, in- and on-line approaches) or microextraction (SPME) in combination with FIA (and
all of the rest FI techniques) as a way of replacing toxic reagents have been experimentally demonstrated
[20-25]. The extraction procedure accomplishes two goals: separation of the analyte from interfering species
in the sample; and, preconcentration of the analyte to increase the sensitivity. The great advantage of SPE is
that both organic compounds and inorganic species can be extracted. Among multiple examples, a time-
based multi-syringe flow injection (MSFI) approach was proposed for automated disk-based sorbent
extraction of three nitro-substituted phenol isomers followed by on-line simultaneous determination of
individual species by diode-array spectrophotometry [26]. The MSFI manifold was coupled to a multi-
position selection valve to an analyzer that ensured minimum operational maintenance via exploitation of
membrane switching protocols. As compared with other previously reported methods, the proposed flow-
through disk-based system could be considered as an environmentally friendly approach because the use of
harmful organic solvents was avoided. Circumventing the generally used cadmium filings and carcinogenic
reagents or by reaction with phenolic compounds in highly concentrated sulfuric acid medium for the
determination of nitrate in waters, a green analytical procedure for nitrate determination in natural waters
based on direct spectrophotometric measurements in ultraviolet, using a flow-injection system with an anion-
exchange column for separation of nitrate from interfering species, allowing selective nitrate determination
without employing toxic reagents [27]. Also, an environmentally friendly methodology was developed for
quality control analysis of commercial pesticide formulations containing Malathion, using flow injection
analysis (FIA) - Fourier transform infrared (FTIR) spectrometry, without any pre-treatment of samples,
saving time and reducing the volume of harmful chlorinated solvents employed in the analysis (2 ml) [28].
A flow injection spectrophotometric method was proposed for the determination of chloride ion in natural
waters by reaction with Hg(SCN)
2
immobilized in an epoxy resin bead [29]. The manifold allowed a
throughput sample of 100 determinations per hour. The main advantage of the developed method was the
400
reduction of the Hg waste solution generated when compared to conventional methods for chloride
determination based on the same spectrophotometric reaction. In addition, the retention of reagents in solid
supports was proposed for the monitoring of sub-nanogram amounts of chlorpyrifos in fruit based on
immobilizing luminol or periodate on an anion-exchange column [30]. A reagentless process and reduced
background noise was achieved. Low reagent consumption and the use of water as eluent are some of the
'green' advantages of the proposed method. In this 'green' sense, a procedure for determination of carbaryl
pesticide in natural waters was recently developed [31]. The flow system was designed with solenoid micro-
pumps in order to improve mixing conditions and minimize reagent consumption as well as waste generation.
The degradation of the generated waste yielded a colorless residue with 94
%
reduction in total organic
carbon after 5 min of exposure to UV radiation. Toxicity tests with marine bacteria
Vibrio fischeri
classified
the waste as non-toxic and the cost of the waste degradation as very low. This research group also developed
a methodology to determine free chlorine in natural waters using similar approaches and pursuing the same
environmentally-friendly aims [32].
Increasing numbers of publications reveal researchers interest in waste management [33]. A highly concern
situation is laboratory wastes. They are not discarded directly into the environment but are treated off-line.
However, this practice increases the running costs of analytical laboratories and creates a problem through
the accumulation of toxic residues. A green alternative to waste storage is therefore on-line recovery of
solvents and toxic or expensive reagents [3]. A useful way of recovering reagents on-line is to incorporate a
cation exchange mini-column after a flow-through cell. In this way, the main reagent can be regenerated
on-line and heavy-metal ions can be removed from the waste, thus reducing both reagent consumption and
waste generation [34]. The method involved spectrophotometric determination of Pb with chromogenic
reagent arsenazo(III), the accumulation of lead onto the cationic exchanger, and subsequent regeneration of
%
