Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 200

Reductant solution. Dissolve 0.218g of hydrazine sulphate in 400ml of deionised water.
Add 5 ml of copper II sulphate solution and 5 ml of zinc(II) sulphate solution. Make up to
500 ml. Prepare freshly as required.
Diazotisation reagent—dissolve 2.5g of sulphanilamide in 400ml of deionised water.
Add 25ml of concentrated phosphoric acid (check concentrated phosphoric acid for low
nitrite content prior to use). Dissolve 0.125g of N −1 -naphthylethylethylenediamine
dihydrochloride in the resulting solution and dilute to 500ml. Store in a refrigerator.

Apparatus
Pye Unicam URAS system (ACI) automatic chemistry unit with an SP6-550 ultraviolet
visible spectrophotometer and a Hewlett Packard 9815A calculator or equivalent. The
instrument settings were given as in Table 2.24.
Direct adaptation to the discrete analyser met with little success owing to a non-zero
intercept of approximately 50µg L −1 on the concentration axis, although nitrate and nitrite
standards of the same concentration gave the same absorbance. A possible cause of the
concentration axis

Table 2.24 Instrument settings for the Pye Unlearn AURA discrete analyser cycle time,
15s temperature, 33°C; path length 10mm, and wavelength, 540nm

Reagent Dispenser

colour

Position Reaction

time/min

Syringe
size /µL

Syringe
vol /µL

Stroke/
mm

Sample 47 450 400 32.0

Sodium
hydroxide

solution Blue 47 1.5 2000 800 13.8

Reductant
solution

Orange

41 a

1 1000 250 14.0

Diazorisation
reagent

Green

13 a

3.25 1000 400 22.5

a Stirrer
Source: Reproduced with permission from the Royal Society of Chemistry [400]

Table 2.25 Precision measurements of nitrate in standard solutions

Standard deviation a /µg L −1

Solution Mean absorbance

concn /µg L −1

S w S b S t

0 0.005 3(10) - -

200 0.101 5(10) 13(9) 14