Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 104

where (vii) and (viii) are the binary and ternary complexes of morin, respectively, and
(ix) and (x) are the binary and ternary complexes of quercetin, respectively. All of these
compounds have a flavone-boric acid stoicheiometry of 1:1, except for the binary
quercetin-boric acid complex, which has a ratio of 2:1. The ternary complexes in acetic
acid decomposed to the binary complexes. The presence of about 1% of oxalic acid in the
solution prevents degradation of the ternary complexes and improves their solubility
considerably. Degraded ternary complexes can be reformed by addition of an excess of
oxalic acid. The fluorescence spectrum of the binary complex coincides exactly with that
of the ternary complex but the intensity is about 10 times lower. The fluorescence
maximum for all of the complexes occurs at 505nm. The preparation of these compounds
is based on the procedures of Hörhammer and Hänsel [105], and Hänsel and Strasser
[106].
2.9.3 Flow injection analysis
Lussier et al. [45] determined borate in light and heavy water by flow injection analysis
with indirect ultraviolet-visible spectrophotometric detection.
2.9.4 Atomic absorption spectrometry and emission spectrometry
Atomic emission spectrometry has been shown to be capable of determining down to 2µg
boron in non saline waters [107-109]. Castillo et al. [110] exploited the extractions
reaction between boric acid and methanol in a concentrated sulphuric acid medium to
determine boron as methyl borate by flame atomic emission spectroscopy. The methyl
borate formed was vaporised and introduced directly into the flame, so that no collection
system or carrier gas were required. The possible interferences by competing ions were
investigated and the results are tabulated, most ions caused no interference. Recoveries
were in the range 90-100% for samples containing 0.25µg L −1 boron.
Graphite furnace flameless atomic absorption spectrometry has been used [111] to
determine 20-250µg L −1 boron in water. The natural concentration of boron in river
water is about 100µg L −1 . Samples are acidified to pH 2.0 and a magnesium/calcium
solution is added before determination at 249.7nm, using a graphite furnace spectrometer.
Szydlowski [112] has described a method for determining down to less than 100µg L −1
boron in natural and well waters. The recoveries were excellent at low concentrations, but