| method | Nitrate is reduced to nitrite on a copper coated cadmium reductor. Nitrite forms a red complex which is detected photometrically at 535 nm using an auto-analyzer. | ||
| solutions | |||
| buffer | 15 g NH4Cl /L solution adjusted to pH 8.5 using a 25% ammonia solution | ||
| reagent 1 |
0.29 M/L sulfanilamid(C6H8N2O2S)
in 1.5% HCl: dissolve 12.5 g sulfanilamid in 12.5 ml HCl conc. and fill up to 250 ml |
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| reagent 2 | 19,3
mM/L Naphthyl-ethylen-diamin-dihydrochlorid (C12H14N2*2HCl,
Merck # 106237) in 0.01% Triton (Merck # 112298): 0,125 g N,1,-Naphthylethylendiamindihydrochlorid is dissolved in 250 mL pure water. Add 250 µL Triton 10% |
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| standard stock | 1000 ppm Nitrate Standard Merck #119811 | ||
| 1000 ppm Nitrite Standard Merck #119899 | |||
| reductor
column (for nitrate analysis) |
Sieve granulated cadmium Merck # 2001 to a size fraction of approx. 40-60 mesh (0.425 - 0.250 mm). Granulate is washed using 2M HCl and copper-coated with a 10 g/L coppersulfate (CuSO4) solution: Put washed granulate into beaker and add copper sulfate solution. Shake for 3 min. (Copper sulfate solution should loose color). Repeatedly wash with pure water until solution is clear. Dry and fill into 120x5 mm glass column. Keep granulated cadmium in place by quartz wool. Connect column to peristaltic pump and fill with pure water from bottom to top to get a bubble-free column. Activation of reductor with 8 to 15 mM/L (500 to 1000 ppm) nitrate solution for ten minutes | ||
| analysis conditions | 4cm flow-through cuvette, linear range up to approx. 1ppm nitrate | ||
| pump | peristaltic pump Ismatec | ||
| detection | ME flow-through Photometer with green LED (535 nm) | ||
| recording | strip chart recorder 5V | ||
| analysis time | approx. 90 sec.per sample | ||
| setup scheme |  |
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| pump tubes |
sample
buffer air reagent 1 reagent 2 |
white-white |
1.02
mm I.D. 1.52 mm I.D. 0.64 mm I.D. 0.64 mm I.D. 0.64 mm I.D. |
| rinse | Rinsing
the system between samples with pure water instead of sample. Rinsing the system after analysis only through buffer /reagent1/reagent2 tubes with 0.025 % Triton solution. |
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| tips + tricks | Never let reductor column run dry. Stop pump when changing from one sample to another. Do not try to measure nitrate in samples, if you can smell hydrogen sulfide (column blocking). Iron precipitates will also block the quartz wool at the column entrance. Changing the quartz wool stoppers frequently reduces the problem. | ||