Chemistry Reference
In-Depth Information
expand the 30-50% transmission interval to full scale by using the X 4 range-
Fig.2.21
Auto analyser manifold
Source: Reproduced with permission from the Royal Society of
Chemistry [345]
expansion facility. Allow the baseline to settle at 5% apparent transmission and then
introduce samples and standards at the rate of 50 per h. Read off the peak height, relative
to the base line, of the standards and construct a calibration graph. Remove arsenic and
cerium reagents and pump out the manifold with the deionised distilled water and wash
for a few minutes. When reducing agents are suspected to be present in the samples,
introduce the cerium reagent used for blank determinations and re-establish a base line at
5% apparent transmission as described above. Aspirate samples at the rate of 50 per h.
Read off the peak heights of the sample blanks and substract these from the peak heights
returned for the samples. By using the calibration graph and the blank-corrected peak
heights, determine the total iodine concentration of each sample.
Determination of iodine
Pipette a 20ml aliquot of sample into a clean glass separating funnel. Add 0.1ml of the
tetraphenylarsonium hydroxide reagent from an Eppendorf pipette. (Tetraphenylarsonium
hydroxide solution, 0.2mol L
−1
. Dissolve 4.55g of solid AnalR-grade
tetraphenylarsonium chloride hydrochloride (Koch-Light Laboratories) in 50ml of
distilled water. Add 2.0g of silver oxide and stir overnight, using an automatic stirrer.
Filter through a Whatman GF/C glass-fibre filtre before use and store in a dark glass
bottle.) Shake, add 4.0ml of chloroform and shake for 2min. Allow the two phases to
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