Aluminium
1.1 Chrome azurol S spectrophotometry
1.1.1 Scope
This standard specifies the determination of aluminium in drinking water and its source water by chrome azurol S spectrophotometry.
This method is applicable to the determination of aluminium in drinking water and its source water.
The minimum detectable mass of this method is 0.20μg; if 25mL of water sample is taken for determination, the minimum detectable mass concentration is 0.008 mg/L.
Interference determination of copper, manganese and ferrum in water. 1mL of ascorbic acid (100g/L) can suppress the interferences of 25μg of copper and 30μg of manganese. 2mL of mercaptoacetic acid (10g/L) can suppress the interference of 25μg of ferrum.
1.1.2 Principle
With pH ranges from 6.7 to 7.0, in the presence of octyl phenoxy poly ethoxy (OP) and cetyl pyridine bromide (CPB), glaucous quaternionic micelle, generated from the reaction of aluminium with chrome azurol S, which then is subjected to colorimetric assay.
1.1.3 Reagents
1.1.3.1 Chrome azurol S solution (1g/L): weigh 0.1g of chrome azurol S (C23H13O9SCl2Na3), dissolve in 100mL of ethanol solution (1+1), and mix well.
1.1.3.2 Emulsifier OP solution (3+100): pipet 3.0mL emulsifier OP and dissolve in 100mL pure water.
1.1.3.3 Cetyl pyridine bromide (CPB for short) solution (3g/L): weigh 0.6g of CPB (C21H36BrN), dissolve in 30mL of ethanol [φ(C2H5OH)=95% ], and dilute to 200mL with water.
1.1.3.4 Ethylenediamine-hydrochloric acid buffer solution (pH 6.7~7.0): take 100mL of anhydrous ethylenediamine (C2H8N2), add 200 mL of pure water, after cooled, slowly add 190mL of hydrochloric acid (ρ20=1.19g/mL), and mix well. If the pH is above 7 or below 6, respectively add hydrochloric acid or diethylamine solution (1+2) and adjust with acidometer.
1.1.3.5 Ammonia water (1+6).
1.1.3.6 Nitric acid solution [c(HNO3)=0.5mol/L].
1.1.3.7 Aluminium standard stock solution [ρ(Al)=1mg/mL]: weigh 8.792g of aluminium potassium sulfate [KAl(SO4)2•12H2O], dissolve in pure water, scale the volume to 500 mL; or weigh 0.500g of pure aluminum sheet, dissolve in 10mL of hydrochloric acid (ρ20=1.19g/mL), put in a 500mL volumetric flask, and scale to the volume with pure water. This solution shall be kept in polytetrafluoroethylene or polyethylene bottle.
1.1.3.8 Aluminium standard working solution [ρ(Al)=1μg/mL]: prepare with diluted aluminium standard stock solution (1.1.3.7) immediately before use.
1.1.3.9 Paranitrophenol-ethanol solution (1.0g/L): weigh 0.1g of paranitrophenol and dissolve in 100mL of ethanol [φ(C2H5OH)=95%].
1.1.4 Instruments
1.1.4.1 Colorimetric tube with stopper: 50mL; prior to use, it shall be soaked in nitric acid (1+9) to remove aluminium.
1.1.4.2 Acidometer.
1.1.4.3 Spectrophotometer.
1.1.5 Analytical procedure
1.1.5.1 Take 25.0mL of water sample and put into a 50mL colorimetric tube with stopper.
1.1.5.2 Take another eight 50mL colorimetric tubes, add 0mL, 0.20mL, 0.50mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL and 5.00mL of aluminium standard working solution (1.1.3.8) respectively, and dilute with pure water to 25mL.
1.1.5.3 Add one drop of paranitrophenol solution (1.1.3.9) respectively into each tube and mix well; add ammonia water (1.1.3.5) until pale yellow; add nitric acid solution (1.1.3.6), and once the yellow disappears, add another two more drops.
1.1.5.4 Add 3.0 mL of chrome azurol S solution (1.1.3.1), after well mixed, add 1.0 mL of emulsifier OP solution (1.1.3.2), 2.0mL of CPB solution (1.1.3.3) and 3.0mL of buffer solution (1.1.3.4), dilute with pure water to 50mL, mix well and stand for 30 min.
1.1.5.5 Measure the absorbance with 2cm cuvette at 620nm wavelength by taking the reagent blank as reference.
1.1.5.6 Plot the standard curve and search out the mass of aluminium in the sample tube from the standard curve.
Note: in the case of copper or manganese present in water, 1mL of ascorbic acid (100g/L) can suppress the interferences of 25μg of copper and 30μg of manganese. In the case of ferrum present in water, 2mL of mercaptoacetic acid solution (10g/L) can suppress the interference of 25μg of Fe.
1.1.6 Calculation
The mass concentration of aluminium in water sample is calculated according to Formula (1):
(1)
Where,
ρ(Al) - the mass concentration of aluminium in water sample, mg/L;
m - the mass of aluminium in water sample tube obtained from the standard curve, μg;
V - the water sample volume, mL.
1.1.7 Precision and accuracy
With 5 laboratories having performed determinations respectively on 20μg/L and 160μg/L water sample, all the relative standard deviations are below 5% and the recovery ranges from 94% to 106 %.
1.2 Salicyl fluorone-hexadecylpyridinium chloride spectrophotometry
1.2.1 Scope
