Water quality

BS EN 12260-2003 pdf free.Water quality一 Determination of nitrogen Determination of bound nitrogen (TN), following oxidation to nitrogen oxides.
Oxidation of the sample containing nitrogen by catalytic combustion in an oxygen atmosphere at > 700 °C, to nitrogen oxides. Quantification of nitrogen concentration is carried out by chemiluminescence detection (after reaction with ozone).
4 Interferences
Depending on the instrument in use. interferences may arise from memory effects. These may occur either from samples or standard solutions with high amounts of bound nitrogen.
NOTE Potential problems can arise with samples containing significant total organic carbon (TOG) concefitrations. The analysis of samples containing large amounts of TOG will lead to the reporting of lower results for nitrogen. Suspected problems can be identified by determining nitrogen before and after suitable dilution, or by using standard addition techniques.
Not all organic nitrogen compounds are quantitatively converted to nitrogen oxides by the oxidation procedure used (see recovery rates in table 81).
If a homogenized sample containing suspended material produces results (obtained from replicate measurements) which deviate by more than 10 %, the sample needs to be filtered through a 0,45 um filter,free of nitrogen containing compounds. In this case, only the dissolved portion of the bound nitrogen will be determined and reported.
5.4.1 Dissolve (4,717±0,001)g of ammonium sulfate, (NH4)2S04, previously dried at (105±2)°C to constant weight, in a 1 000 ml volumetric flask, and make up to volume with water.
5.4.2 Dissolve (7,219 ± 0.001) g of potassium nitrate, KNO3, previously dried at (105 ± 2) °C to constant weight, in a 1 000 ml volumetric flask, and make up to volume with water.
5.4.3 Mix equal volumes of the above solutions (see 5.4.1 and 5.4.2) to produce a mixed standard solution.
Stored in a refrigerator at (4 ± 2) °C, the standard solution can be used for about one month.
5.5 Nicotinic acid, C6H5N02, > 99,5 %.
5.6 Nitrogen stock solutions for system check, N) = 1,000 gIl.
5.6.1 Prepare separately stock solutions corresponding to 5.4.1 and 5.4.2.
5.6.2 Dissolve (8.793 ± 0,001) 9 of nicotinic acid (5.5), previously dried at (105 ± 2) °C to constant mass. transfer to a 1 000 ml volumetric flask and make up to volume with water (5.2).
Store in a refrigerator at (4 ± 2) °C, the standard solution can be used for about one month.
5.7 Oxygen, 02, with a volume fraction of > 99.7 %.
6 Apparatus
6.1 Apparatus suitable for the determination of total bound nitrogen by oxidation
This apparatus will be instrument dependant and comprises for example reaction vessel, automatic sample injection device, sample homogenizing equipment, suitable detectors or sensors and computing system. A manual injection system may also be used. For requirements for a suitable system see clause 10.
When sampling, ensure that a representative sample Is obtained (tIn Is particularly important for samples containing any undissolved matte), and that the sample is not contaminated, In ackition, see EN ISO 5667-3.
Withdraw samples In suitable containers consisting of glass or suitable plastics, appropriately sealed.
Analyze samples as soon as possible.
NOTE Delay may reseAt m the reporting of low van leepeciaty in the case of bciocaby active sarrçIea)
Samples may be stabilized by the addttion of hy&ochlonc acId (5.3) to achieve a pH value of less man 2. and stored In a refrigerator at (4 a 2) ‘C. Staleed samples may be stored for a period of up to 8 days. Alternatively store smaller sample volumes (e.g. 50 ml 10 100 ml) at -15 C to 20 C up to 14 days.
If nacessary. homogenize the sample at order to obtain a representative aliquol for the determination (see dame 4). H this is impracticable. 111cr (twough a 0,45 pm fer (6.3)
8 Procedure
Folow the instrument manufacturer’s instructions.
Prior to the determination of bound rdrogen, ensure that instrument operational tests arid the verification of the responses to blank and standard solutions are camed out within the tntervals specified by the manufacturer.
Adjust the Instrument according to the manufacturers wistrudtions for each series of measuremeves
It an instrument is fitted with an automated qection system. ensure that tile sample is urcely to cause sy interference with the inecflon procedure by, br example, homogenizing the sample (see also clause 4).
lrqect ideriticat vanes of blai* solutions and samples into the aistrument according to the manutaciurer’s instructions arid measure me responses obtained tor aaquots of each sokitlon at least tiwee times.
Reect the first and uee the mean response from at least two ecttons taking into accoent any memory elf ects likely to occur (see clause 4) Use the calibration greph (see clause 9)10 determIne the concentration of total bound nitrogen in the sample.
9 Establishment of the calibration curve
Use the mixed standard solution (5.4.3) to prepare calibration solutions in accordance with the range of corcentratiomw of total bound ratrogen expected ci the samples to be determined.
Use the calibration solutions on the day of preparation only. Catrate within one decade & concentration. For the concentraticn range ottO mgIl to too mgi. proceed. for example, as follows:
Into 7 separate volumetric tOO ml flasks, pipette 0. (blank) 1,0 ml 2,0 ml: 3.0 ml; 6.0 ml; 8.0 ml or 10.0 ml of the mixed standard sokitlon (5.4.3) arid make up to vobame with water: these quantities correspond to mass concentrations of nitrogen of 0mg/I, 10,0mg/I; 20,0 mg/I; 30,0 mg/I; 60,0 mg/I; 80,0 mg/I or 100,0 mg/I respectively.
Use identical injection volumes for each solution, blank and sample measurement.
Inject at least three times and use the mean response taking into account any memory effects likely to occur (see clause 4). The number of replicate measurements shall be identical to those used for the blank and sample measurements.
Use the data obtained to calculate the regression graph according to ISO 8466-1 or ISO 8466-2, respectively.
10 System check
Carry out system check determinations using dilutions of each nitrogen stock solution (5.6) in the appropriate range to identify any deviations of the response values obtained during the oxidation stage. Using a stock solution of 50 mg/I N, deviations of up to ± 5 % of the theoretical value may be tolerated.
11 Calculation
Calculate the mass concentration, p, in milligrams per litre, of nitrogen in the solution using the data obtained (e.g. response value, see clause 9) according to ISO 8466-1. Take into account all of dilution steps. In case of a non-linear calibration function, proceed according to ISO 8466-2.
NOTE It is possible to use less than the required number of calibration points provided there is a linear relationship and all data are within the confidence interval of the basic calibration.BS EN 12260 pdf free.Water quality