ISO-13395-1996.pdf

INTERNATIONAL STANDARD IS0 13395 First edition 1996-07-I 5 Water quality - Determination of nitrite nitrogen and nitrate nitrogen and the sum of both by flow analysis (CFA and FIA) and spectrometric detection Qua/it see 5.1 and 5.2). 4.13 lmidazole stock solution, c = 0,25 mol/l. 4 Reagents If not stated otherwise, only reagents of recognized analytical grade and water according to grade 1 of IS0 3696 shall be used. The blank value of the re- agents shall be checked regularly (see 9.3). 4.1 Phosphoric acid (HsPO,), p = 1.71 g/ml. 4.2 Sulfanilamide (4-aminobenzenesulfonamide, C,H,N,O,S). Dissolve, in a beaker of nominal capacity 1 litre, 17,0 g of imidazole (4.6) in approximately 900 ml of water. While stirring with a magnetic stirrer, add hydrochloric acid I (4.7) and adjust, with the help of a pH electrode, the pH to 7.5. Transfer to a volumetric flask, of nominal capacity 1 000 ml, and dilute to volume with water. The solution is stable for 4 weeks if kept in a brown glass bottle at room temperature. 4.3 /V-(1-naphthyl)ethylenediaminedihydrochloride N-(1 -naphthyl)-1,2-diaminoethanedihydrochloride), W, this solution is stable. 4.10 Copper sulfate solution II, p(CuSO,.5H,O) = 20 g/l; this solution is stable. Prepare the solutions, containing the surfactant (4.111, freshly before use. Prior to use, solutions C and B for FIA shall be degassed, for example by membrane filtration (vac- uum). Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 05:51:17 MDTNo reproduction or networking permitted without license from IHS -,-,- Q IS0 IS0 13395:1996(E) 1 rable 1 - Options for preparing the solutions C and B in figures A.l, B.l and C.l Method Parameter Content of Content of solution C solution B isee figures (see figures A.l, B.l and A.1, B.l and C.1) C.1) FIA Nitrite Water WaterI) Buffer (4.14) ) No solution Bl) CFA Nitritelnitratc Buffer (4.14) Buffer (4.14) Nitrite “C” is not Waterl),2) necessary Buffer (4.14) ),2) No solution Bl),Z) Nitrite/ this interference can be pre- vented by a dialysis of the sample, if need be in the online process. (See 9 in annex D.) 9 Procedure 9.1 Preparation, activation and checking of the cadmium reductor 9.1.1 Cadmium column with granulate Place a sufficient quantity of the cadmium granulate (4.12) to fill the column (see 5.1) in a beaker (5.5) of nominal capacity 25 ml. Stir with hydrochloric acid II (4.8) until the surface of the granulates shows a met- allic shine. Remove the acid by washing with water. Decant the water and stir the granulate twice for ap- proximately 2 min with copper sulfate solution II (4.10). The surface of the granulate will turn black. Decant and carefully wash with water. Fill the column with the granulate, avoiding air bubbles and large cavities, and stopper the ends of the column (e.g. with glass wool). Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 05:51:17 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 13395:1996(E) Assemble the column in the flow system, and activate the reductor by applying nitrate(N) solution I (4.21) or II (4.22) three times. Repeatedly measure the calibration solution (4.23) which has, for the respective working range, the highest permissible nitrite/nitrate(N) concentration (2 mg/l or 20 mg/l, respectively), until stable results are obtained. NOTE 8 The cadmium column can be stored, free from air bubbles, in the imidazole stock solution (4.13). Prior to re-use, the column should be stabilized and activated as described above. 9.1.2 Cadmium tube Using the syringe (5.61, aspirate approximately 5 ml of the buffered copper sulfate solution (4.16) into the cadmium tube (see 5.2) and allow to react for 5 min. Repeat the procedure, avoiding air bubbles. Using the syringe, aspirate approximately 20 ml of imidazole stock solution (4.13) through the tube and allow to react, avoiding air bubbles. Assemble the column in the flow system, activate and stabilize as described in 9.1 .I. NOTE 9 The cadmium tube can be stored, free from air bubbles, in the imidazole stock solution (4.13). Prior to measurement, stabilize or treat, if required, (see 9.1.3) with buffered copper sulfate solution (4.16). 9.1.3 Checking the reduction capacity applies to the nitrate(N) or the nitrite/nitrate(N) determination only1 Sequentially analyse a nitrate(N) and a nitrite(N) sol- ution with a nitrogen mass concentration of 2 mg/l each for the nitrite/nitrate(N) working range II, or of 20 mg/l each for the nitrite/nitrate(N) working range I, and compare the measured values obtained. Transport reagent solutions (4.17) through the flow system with a built-in cadmium reductor and allow the baseline to stabilize. For example, to check the nitrite/nitrate(N) working range I, use the nitrite(N) solution I (4.19) and the nitrate(N) solution II (4.22). If the measured value for nitrate(N) is less than 90 % of the measured nitrite(N) value, appropriate meas- ures according to 9.1 .I and 9.1.2 shall be taken to obtain a reduction capacity of at least 90 %. Check the reduction capacity again, prior to the analysis of each series of samples. 9.2 Preparation for measurement Assemble the flow system according to the method of determination desired (FIA or CFA, determination of nitrite/nitrate(N) or nitrite(N); see figures A.l, B.l and Cl). Prior to measurement of nitrite, continuously run the reagent solutions for approximately 10 min through the flow system. For the determination of nitrite/nitrate(N), run the reagent solutions through the system for approximately 10 min without the Cd reductor and after that for approximately 10 min with the Cd reductor. Record and zero the base absorbance. The system is ready when the baseline no longer shows any drift. A satisfactory signal-noise relation should be obtained. Then perform the reaction steps in the sequence of 9.3 to 9.5. 9.3 Monitoring the blank of the reagents Allow the baseline to stabilize Instead of the buffer solution B (4.15) and the reagent solution R1 (4.17) transport water for 2 min and record changes in the measuring signal. If the absorbance changes by more than 0,015 per 10 mm path length, either the water being used or the reagent solutions may be contamined. Take ap- propriate measures to eliminate the interference. Then transport the reagent solutions again. 9.4 Calibration Select the respective working range for nitrite(N) or nitrite/nitrate(N) and prepare the calibration solutions (4.23) for the selected working range. Each working range requires its own calibration. Calibrate by sequentially adding the calibration sol- utions and the blank solution. Prior to the calibration, zero the instrument, if necessary following the manufacturer s instructions. Determine the measured values from the calibration solutions used while following the manufacturer s in- structions, as long as they do not contradict the specifications of this International Standard. The test conditions for the calibration and the measurement of samples (9.5) are the same. The magnitude of the measuring signal is proportional to the mass concentration of nitrite(N) or 7 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 05:51:17 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 13395:1996(E) 0 IS0 nitrite/nitrate(N). Establish the regression line for the measuring series obtained. The following general equation is satisfied: y = b*pN + a (1) where Y is the measured value, in terms of instrument-related units (e.g. peak height in millimetres or millivolts); b is the slope of the calibration function, in instrument-related units litre per milligram; PN is the mass concentration, in milligrams per litre, of nitrite(N) or nitrite/nitrate(N); a is the ordinate intercept of the calibration function, in terms of instrument-related units. 9.5 Sample measurement Analyse the samples, pretreated according to clause 7, in the same manner as the calibration sol- utions (4.231, with the flow system (FIA, see 5.1 and figureA.l; CFA, see 5.2 and figures B.l and Cl). If the mass concentrations to be determined exceed the validity range of the selected working range, dilute the sample or analyse it using the other working range. Check the validity of the calibration function in the respective working range after each sample series, but at the latest after the measurement of 10 to 20 samples, using one calibration solution each for the lower and upper third of the respective working range. Check the reduction capacity (9.1.3) again or make a new calibration (9.41, if necessary. After measurement, store the cadmium reductor in an imidazole solution that is free from oxygen (see notes 8 or 9). 10 Evaluation Determine the mass concentration of the determinand in the measuring solution using the measured value obtained as described in 9.5, from the calibration function equation (I 1, 9.41. For the evaluation use the appropriate function. Do not extrapolate beyond the working range selected. calculate pN using equation (2): PN= y-a b where PN is the mass concentration, in milligrams per litre, of nitrite(N) or nitrite/nitrate(N) in the sample; y, a and b are as defined in equation (1). 11 Expression of results Report the results to a maximum of two significant figures. EXAMPLES Nitrite(N): Nitrate(N): Nitrite/nitrate(N) 2,9 x 1 O- mg/l 3,O w/l 4.1 ms/l 12 Precision The statistical data in tables 4 to 7 were established in an interlaboratory trial, carried out in November 1991Illl: Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 05:51:17 MDTNo reproduction or networking permitted without license from IHS -,-,- CJ IS0 IS0 13395:1996(E) Table 4 - Statistical data for the determination of nitrite(N) with flow injection analysis (FIA) Sample Type 1 n * X Corr x RR 4 vc, SR VCR No. of matrix 96 w/l mg/l % w/l % w/l % 1 15 55 0 0,030 0,030 101 0,000 8 2,67 0,001 6 5,41 2 15 49 11 Potable water ) 2) 0,090 0,089 99,l 0,000 8 0,90 0,001 5 1.73 3 15 54 5,3 0,300 0,301 100 0,004 1 1.36 0,015 0 4,98 4 15 49 11 0,900 0,898 99.8 0,006 5 0,72 0,033 8 3,76 5 15 55 0 0,030 0,033 109 0,002 0 6.06 0,004 4 13,6 6 Industrial waste 15 54 1,8 0,090 0,092 102 0,003 0 3,26 0,005 4 5,88 7 waters) 2) 15 53 3,6 0,300 0,296 98.8 0,005 2 I,76 0,025 1 8,48 8 15 53 3,6 0,900 0,912 101 0,006 1 0,67 0,084 6 9.28 9 15 50 9.1 0,030 0,030 101 0,000 6 2,00 0,001 2 3,92 10 Standard 15 55 3,5 0,090 0,091 102 0,001 6 1.76 0,004 3 4,73 11 soIutions4) 2) 15 55 3,5 0,300 0,302 101 0,004 1 1.36 0,014 0 4.65 12 15 48 13 0,900 0,900 100 0,007 2 0.80 0,028 1 3,13 / is the number of laboratory sets n is the number of outlier-free individual analytical values n is the relative portion of the outliers X CDrr is the correct value, by convention X is the total mean RR is the recovery rate s,. is the repeatability standard deviation VC,. is the repeatability coefficient of variation s, is the reproducibility standard deviation VC, is the reproducibility coefficient of variation 1) Drinking water, spiked with nitrite or nitrate solution. 2) Drinking water, waste water, as well as the spiked solutions, were stabilized with 2 ml/l each of chloroform and were shipped in separate bottles to the participants of the interlaboratory trial. 3) Industrial waste water, spiked with nitrite or nitrate solution in the participant s laboratory. In addition, the waste water contained 14 g/l of chloride and a COD of 1 400 mg/l. 4) Water as in 2), spiked with nitrite or nitrate solution in the participant s laboratory. 9 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 05:51:17 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 13395:1996(E) 0 IS0 Table 5 - Statistical data for the determination of nitrite(N) with continuous flow analysis (CFA) Sample Type 1 n 0 X cow x RR 4 vc, sR VCR No. of matrix % v/l mg/l % m/l % msil % 1 11 42 0 0,030 0,031 102 0,001 7 548 0,002 6 8,43 2 11 42 0 Potable water11 2) 0,090 0,092 102 0,002 3 2.50 0,005 6 6,12 3 11 39 2,5 0,300 0,307 102 0,005 5 1.79 0,035 4 1 I,6 4 11 30 25 0,900 0,910 101 0,006 4 0,70 0,017 3 I,90 5 11 33 21 0,030 0,035 117 0,001 5 4,29 0,003 8 IO,8 6 Industrial waste 11 41 0 0,090 0,104 115 0,008 9 8,56 0,014 2 13,7 7 waters) 2) 11 36 10 0,300 0,327 109 0,005 1 I,56 0,023 4 7.16 8 11 40 0 0,900 0,969 108 0,014 4 I,49 0,094 0 9,70 9 11 39 7,l 0,030 0,031 102 0,001 8 5,81 0,002 5 8.21 10 Standard 11 42 0 0,090 0,090 100 0,005 0 5,56 0,007 6 8,46 11 solutions4) 2) 11 40 0 0,300 0,307 102 0,004 0 I,30 0,029 8 9,73 12 11 36 10 0,900 0,907 101 0,014 3 I,58 0,055 0 6,07 is the number of laboratory sets r is the number of outlier-free individual analytical values 7 is the relative portion of the outliers r toll is the correct value, by convention F is the total mean RR is the recovery rate sT is the repeatability standard deviation V,. is the repeatability coefficient of variation F is the reproducibility standard deviation VR is the reproducibility coefficient of variation 1) Drinking water, spiked with nitrite or nitrate solution. 2) Drinking water, waste water, as well as the spiked solutions, were stabilized with 2 ml/l each of chloroform and were shipped in separate bottles to the participants of the interlaboratory trial. 3) Industrial waste water, spiked with nitrite or nitrate solution in the participant s laboratory. In addition, the waste water contained 14 g/l of chloride and a COD of 1 400 mg/l. 4) Water as in 2). spiked with nitrite or nitrate solution in the participant s laboratory, 10 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 05:51:17 MDTNo reproduction or networking permitted without license from IHS -,-,- Q IS0 IS0 13395:1996(E) Table 6 - Statistical data for the determination of nitrite/nitrate(N) with flow injection analysis (FIA) Sample Type 1 n 0 X mrr x RR S, vc, sR VCR No. of matrix 96 mg/l w/l % w/l % w/l % 1 15 56 0 3,230 3,295 102 0,039 1 I,19 0,149 1 4,52 2 15 56 Potable water ) 2) I,8 3,790 3,888 103 0,041 1 1.06 0,144 7 3,72 3 15 57 0 6,000 6,155 103 0,085 0 I,38 0,250 0 4.06 4 15