Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 94

determination was 16µg L −1 glass vessels were only suitable for brief contact during
operations such as pipetting or dilution; all other operations should be performed in
polythene beakers or flasks.
Bilikova [31] executed microgram level determinations of boron in non saline waters
by two methods, namely the modified curcumin method with rosocyanin, and the
Azomethine method. Both methods allowed determination of boron in water at between
0.1 and 1.6µg in 50 and 100 ml volumes respectively. Dryssen et al. [32] also used
curcumin to determine boron in non saline waters.
Other chromogenic reagents that have been employed for the spectrophotometric
determination of borate include crystal violet which forms a complex with boron, having
an adsorption maximum of 600nm [33], ferroin [34], carmine [35], chromotropic acid
[36]-[39], various diketones [40], 1,8-dihydroxynaphthalene-4-sulphonic acid [41],
dianthrinamde [42], Azomethine H. Detection limits claimed are down to 10µg L −1
(dianthrimide method).
Spectrofluorometric reagents that have been used include 4 ′ chloro-2-hydroxy-4-
methoxybenzophenone [43,44].
Yoshimura et al. [39] determined boron in non saline waters after specific adsorption
on Sephadex gel.
Lussier et al. [45] determined borate in light and heavy water by a method based on
flow injection analyses with indirect ultraviolet-visible spectrophotometric detection.
2.9.2 Spectrofluorometric methods
Aznarez et al. [23] have described a sensitive fluorometric method based on molecular
fluorescence with dibenzoylmethane. In this method the boron is extracted into isobutyl
methyl ketone with methylpentanediol.
In this method a Pye Unicam SP8 100 spectrophotometer or equivalent with special
equipment for fluorescence measurements was used. Glass materials must be avoided in
order to eliminate boron contamination. PTFE, polyethylene or platinum materials are
recommended.
50ml of non saline water is diluted with hydrochloric acid (1+1) to 100ml in a
calibrated flask. A measured volume of sample solution containing 0.5-5µg of boron is
placed in a separating funnel and extracted three times with 10ml volumes of isobutyl
methyl ketone in order to eliminate any iron interference. 10ml of 20 vol %
methylpentanediol in methyl isobutyl ketone solution is added and the mixture shaken for
about 5min with a mechanical shaker. The organic phase is dried with 1g of anhydrous
sodium sulphate.
3ml of the organic extraction phase is placed into a polyethylene test tube with a
hermetic cap and 2ml of 0.1% w/v benzoylmethane in glacial acetic acid added and 2ml
of concentrated phosphoric acid. The sealed test tube is shaken for 2min and heated at
80±3°C for 30min in a thermostated bath. After rapid external cooling to room
temperature, the relative fluorescence intensity of the solution is measured at 400nm with
excitation at 390nm and quinine sulphate solution as reference, within 45min.
A calibration graph is prepared as follows. To different volumes of standard solution
containing 0.5-5µg of boron, add an equal volume of hydrochloric acid (1+1) and extract