The TGS method is only described in the previous version of this manual (EMEP/CHEM 3/77). The recommended method for NO2 is sampling with iodide impregnated glass sinter filters followed by the nitrite determination described below.
This method is applicable to the determination of nitrite in extracts from iodid impregnated glass sinter filters (see Section 3.3.1) in the range 0.02–3 µg NO2--N/ml. Samples containing higher concentrations must be diluted prior to the analysis and the impregnation matrix have to be added in the dilution step to match the matrix of the calibration standards.
Nitrite (NO2-) and sulphanilamide form a diazo compound in acid solution which by a coupling reaction with NEDA, N-(1-naphthyl)-ethylenediamine-dihydrochloride, gives a red azo dye. The concentration in the solution is determined spectrophotometrically at 540 nm. The calibration standards must match the sample solutions by addition of an iodide matrix.
Spectrophotometer or filter photometer capable of measuring at 540 nm.
Optical glass cells, 10, 20 or 50 mm.
Bulb pipettes, micropipette (adjustable) and dispenser (adjustable).
Capped vials or reagent tubes, 10ml.
Volumetric flasks.
All reagents must be of recognized analytical grade. The water used for dilution should be deionized. The water should have a resistance > 10 M/cm. The sample, calibration standards and reagent solution bottles should be made of borosilicate glass, polyethylene or polypropylene.
Phosphoric acid (H3PO4), conc.
Sulphanilamide (NH2C6H4SO2NH2)
NEDA,
N-(1-naphthyl)-ethylenediamine-dihydrochloride (C10H7NHCH2CH2NH2*2HCl)
Sodium iodide (NaI)
Sodium carbonate (Na2CO3)
Sodium nitrite (NaNO2)
Iodide matrix solution
(10x concentration of leachate): 9.8 g NaI, 1.46 g Na2CO3 and 133 µl
triethanolamine dissolved and diluted to 100 ml with deionized water.
Mixed reagent
(Sulphanilamide-NEDA solution): To a 1000 ml volumetric
flask add about 500 ml deionized water, 8 ml phosphoric acid, 8 g
sulphanilamide and 0.2 g NEDA. Dissolve and dilute to 1000 ml with deionized
water.
Sodium nitrite stock solution, 1000 µg NO2-N/ml
Dissolve 4.927 g NaNO2 which has been dried 1 hour at 105 C in some deionized water and
dilute to 1000 ml with deionized water. This solution can be stored for several
months if stored in a borosilicate bottle in a refrigerator.
Nitrite working standard, 10 µg NO2-N/ml
10 ml of the sodium nitrite stock standard is diluted to
1000 ml with deionized water. This solution can be used for 1 month if stored
in a borosilicate bottle in a refrigerator.
Nitrite calibration standards
To 100 ml volumetric flasks add 0, 0.5, 1.0, 5.0, 10.0 and
30.0 ml nitrite working standard, 10 µg NO2-N/ml and 10 ml iodide matrix
solution. Dilute to the mark with deionized water. These calibration standards
contain 0, 0.05, 0.10, 0.50, 1.0 and 3.0 µg NO2-N/ml and have the same iodide
concentration as the samples. The range of the calibration solutions may be
different if only low concentrations occur, but five calibration standards in
addition to a blank should be used. These calibration standards should be made
new every day.
Transfer 0.5 ml sample leachate to a 10 ml vial or test tube
and add 3.0 ml mixed reagent. Close the vial or test tube, shake well and read
the absorbance at 540 nm after at least 15 min. Treat 0.5 ml of the nitrite
calibration solutions the same way and plot the calibration curve. The
concentration of the samples in µg NO2-N/ml are found from the calibration
curve. Leachates from field blanks are also treated in the same way, and a
representative value for the field blank in µg NO2-N/ml should be subtracted
before the calculation in Section 3.3.1.10.