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1、INTERNATIONAL STANDARD IS0 5961 Second edition 1994-01-l 5 Water quality - Determination of cadmium by atomic absorption spectrometry Qua/k4 de Ieau - Dosage du cadmium par spectrom 2,0 ml; 4,0 ml; 6,0 ml; 8,0 ml and 10,O ml respectively of the cadmium standard sol- ution (2.3.4) into 100 ml one-mar
2、k volumetric flasks. Add 1 ml of nitric acid (2.3.1) to each of these sol- utions. Dilute to volume with water and mix. The calibration solutions contain 0,05 mg/l; 0,2 mg/l; 0,4 mg/l; 0,6 mg/l; 0,8 mg/l and I,0 mg/l of cadmium respectively. Copyright International Organization for Standardization P
3、rovided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:11 MDTNo reproduction or networking permitted without license from IHS -,-,- Q IS0 IS0 5961:1994(E) 2.3.6 Blank test solution 2.4.8 Heating device, for example a hotplate. Pipette 1
4、ml of nitric acid (2.3.1) into a 100 ml one- mark volumetric flask, and dilute to volume with water (2.3.4). If the sample requires a pretreatment by digestion, the blank shall be given the same pretreatment (see 2.5.2). 2.4.9 Membrane filtration device with filters, of pore size 0,45 km, washed tho
5、roughly with dilute nitric acid and rinsed with water. 2.5 Sampling and sample pretreatment 2.3.7 Solution for zero-setting the instrument See IS0 5667-3. Use water (2.3.4) as a zero-setting solution. The blank solution (2.3.6) may also serve for zero-setting pro- vided its cadmium concentration is
6、negligibly low. 2.5.1 Sampling Collect the samples in polyethylene or borosilicate glass containers which have previously been cleaned 2.4 Apparatus with nitric acid and water. Immediately before use, clean the glassware with warm, dilute nitric acid, approximately 2 mol/l (e.g. by soaking for 24 h)
7、, followed by a thorough rinsing with water (2.3). Verify that each lot of pipette tips and single-use plastics vessels is free from potential cad- mium contamination by carrying out blank measure- ments (see 2.6.1). 2.5.2 Pretreatment and preparation of the sample solutions 2.5.2.1 Pretreatment for
8、 the determination of the content of dissolved cadmium Usual laboratory apparatus and Filter the water sample as soon as possible after sampling (2.5.1) through a membrane filter of pore 2.4.1 Atomic absorption spectrometer, equipped with background correction and a radiation source for the determin
9、ation of cadmium, operated according to the manufacturers instructions. size 0,45 pm. To stabilize the filtrate, add, for example, 10 ml of nitric acid (2.3.1) per litre of water sample to achieve a pH of less than 2; add more acid, if necessary, to ensure a pH of less than 2. 2.4.2 Gas supply for a
10、ir and acetylene. It is es- sential that the manufacturers safety instructions be observed. The residual gas pressure for acetylene cylinders shall be at least 5 x 1 O5 Pa. 2.4.3 Air-acetylene burner. 2.5.2.2 Pretreatment for the determination of cadmium after mineralization Acidify the water sample
11、 as soon as possible after sampling by adding 1 ml of nitric acid (2.3.1) per litre of sample; add more acid, if necessary, to ensure a pH of less than 2. 2.4.4 One-mark volumetric flasks of capacity 10 ml, 100 ml and 1 000 ml. Completely mix the sample, for example by thorough shaking. 2.4.5 One-ma
12、rk pipettes, of nominal capacity 1 ml, 2 ml, 3 ml, 4 ml, 5 ml, 6 ml, 8 ml, 10 ml, 20 ml, 30 ml and 40 ml. 2.4.6 Microlitre pipettes or diluters. 2.4.7 Beakers, of capacity 250 ml. Place 100 ml of the homogenized sample in a 250 ml beaker. Add 1 ml of nitric acid (2.3.1) and 1 ml of hydrogen peroxide
13、 (2.3.2). Heat the beaker on a hotplate until about 0,5 ml re- mains. It is essential that the sample is not reduced to dryness. 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007
14、 22:08:11 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 5961:1994(E) 0 IS0 If there is heavy organic contamination of the water sample, consider a repeated addition of hydrogen peroxide (Caution). Dissolve the residue in 1 ml of nitric acid (2.3.1) and some water, tra
15、nsfer quantitatively to a 100 ml one- mark volumetric flask and dilute to volume with water. a mid-range calibration solution to check whether the calibration curve is still valid. If the cadmium content of the measuring solution ex- ceeds the range of validity of the calibration curve, dilute the m
16、easuring solution accordingly with blank solution. If sample volumes other than those specified are used, the apparatus and reagents shall be adjusted to the respective ratio of volumes. 2.7 Evaluation It is not necessary to carry out a digestion in cases where cadmium is quantitatively determinable
17、 with- out this treatment. In such circumstances, only acidify the water sample. 2.6 Procedure Prior to measurement, adjust the instrumental par- ameters of the spectrometer (2.4.1) in accordance with the manufacturers operating instructions. Optimize flame conditions, Zero the spectrometer by aspir
18、ating the zero-setting solution (2.3.7) into the flame. 2.6.1 Blank test Carry out a blank test with the blank solution (2.3.6) at the same time as the determination, using the same procedure and the same quantities of all the reagents as in the sampling and determination, but replacing the test por
19、tion with water (2.3). 2.6.2 Calibration To establish the calibration curve, spray in the cali- bration solutions (2.3.5) successively, in ascending order of concentration, and record the absorbance. 2.7.1 Calculation Establish the calibration function by linear regression using the data obtained fr
20、om the measurement of the calibration solutions. Calculate the mass concentration p(Cd) of cadmium, expressed in milligrams per litre, in the water sample using the equation p(W = (4 -4) x v, b x V, where A, is the absorbance of the blank solution; A, is the absorbance of the measuring solution; b i
21、s the slope of the calibration curve, in litres per milligram, according to 2.6.2; V, is the volume, in millilitres, of the measuring solution; V, is the volume, in millilitres, of the water sample applied to prepare the measuring solution. Dilution steps which differ from those specified above shal
22、l be taken into account during the calculation. Check the zero with the zero-setting solution (2.3.7) after the measurement of each calibration solution. 2.7.2 Expression of results 2.6.3 Test portion measurement Continue by measuring the blank solution (2.6.1) and the measuring solutions (2.5.2) an
23、d record the absorbances. After each measuring series, but at least after 10 to 20 measurements, re-analyse the blank solution and The values shall be rounded to the nearest 0,Ol mg/l. EXAMPLES Cadmium (Cd): 0,07 mg/l Cadmium (Cd): 0,41 mg/l 4 Copyright International Organization for Standardization
24、 Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:11 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 5961:1994(E) 2.8 Test report The test report shall contain the following information: d) deta
25、ils of sample pretreatment, if applicable; e) any deviations from this procedure and all the cir- cumstances which may have affected the results. a) a reference to this International Standard; b) complete identification of the water sample; c) expression of the results, according to 2.7.2; 2.9 Preci
26、sion See table 1. Table 1 - Precision data Sample No. n 2 x x I, K =I3 VCR WFR f-w/l w/l r-w/l % w/l % 96 Suitable for Al) 21 23 63 0 0,113 0,118 0,009 7 8.2 0,005 8 5,0 104,l 81, 2) 23 60 5 0,563 0,587 0,030 9 5,3 0,009 2 1.6 104,3 Cl, 3) 23 63 0 0,968 1,008 0,073 3 7,3 1 0,012 I,2 104,l % La w/l I
27、d % WI 46 90 D4) 2) 52 133 2 0,91 1,292 0,319 6 24,7 0 0,083 6,4 141,9 all methodssj 22 55 2 0,91 1,148 0,270 4 23,5 0,048 3 4,2 126,2 method 3.6.2.1 17 45 0 0,91 1,363 0,356 8 26,2 0,115 9 8,5 149,8 addition: manual 13 31 11 0,91 I,39 0,171 8 12,4 0,064 3 4,6 152.7 addition: automatic E4) 2) 52 136
28、 0 2,70 2,96 0,639 9 21.6 0,266 3 9,0 109,6 all methodss) 22 56 0 2,70 2,78 0,631 8 22,8 0,1994 7,2 102,9 method 3.6.2.1 17 40 11 2,70 2,99 0,344 5 11,5 0,195 1 6,5 110,7 addition: manual 13 35 0 2.70 3,22 0,559 2 17.4 0,158 3 4,9 119,2 addition: automatic F41 6) 53 135 7 16,2 18,34 3,348 7 18.3 1,4
29、20 8 787 113,2 all methodssj 23 56 11 16,2 17,14 2,232 8 13,0 0,756 7 4,4 105,8 method 3.6.2.1 17 43 7 16,2 18,33 3,969 7 21,7 1,497 6 8.2 113,l addition: manual 13 33 8 16,2 20,17 3,107 7 15,4 1,309 6 6,5 124.5 addition: automatic 1 is the number of participating laboratories 01 is the repeatabilit
30、y standard deviation n is the number of values VC, is the repeatability variation coefficient n, is the percentage of outliers bfl is the reproducibility standard deviation x is the true value VC, is the reproducibility variation coefficient 2 is the total mean WFR is the recoven/ rate 1) AAS method
31、 in an air-acetylene flame. 2) Industrial waste water with a low level of pollution. 3) C: spiked drinking water. 4) Electrothermal atomization MS method. 5) “All methods” means that both the manual and the automated addition have been included in the calculation. 6) F: spiked distilled water. 5 Cop
32、yright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:11 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 5961:1994(E) 6 IS0 Section 3: Determination of
33、 cadmium by electrothermal atomization atomic absorption spectrometry 3.1 Interferences The following ions will not, if present individually, in- terfere with the method as long as their mass con- centrations do not exceed 100 mg/l: iron, copper, nickel, cobalt and lead. No interferences could be ob
34、served up to mass con- centrations of 1 000 mgll for sodium, potassium, calcium, magnesium, sulfate and chloride. Combinations of the above-mentioned ions, even if present in much lower concentrations, can lead to depression or enhancement of the measured signals. Some other ions, if present in low
35、concentrations, can cause interferences. The method of standard ad- ditions should therefore be given preference to the normal calibration. Samples of unpredictable matrix behaviour need to be analysed using the method of standard additions. Interferences caused by back- ground absorption can be eli
36、minated to a large extent by the application of a background compensating system. 3.2 Principle Injection of the acidified sample into an electrically heated graphite tube of an electrothermal atomization atomic absorption spectrometer. Measurement of the absorbance at a wavelength of 228,8 nm. If n
37、ecess- ary, application of the standard additions technique. 3.3 Reagents The requirements for the purity of the reagents are given in 2.3. 3.3.1 Nitric acid, p = 1,40 g/ml. 3.3.2 Hydrogen peroxide, w(HOJ = 30 % (m/m). 3.3.3 Cadmium stock solution I, p(Cd) = 1 000 mg/l. See 2.3.3. 3.3.4 Cadmium stoc
38、k solution II, p(Cd) = 10 mg/l. See 2.3.4. 6 3.3.5 Cadmium standard solution II, p(Cd) = 100 pg/l. Pipette 10,O ml of the cadmium stock solution II (3.3.4) into a 1 000 ml one-mark volumetric flask, add 10 ml of nitric acid (3.3.1) and dilute to volume with water. Store the solution in a polyethylen
39、e or borosilicate glass container. Prepare the solution immediately be- fore use. 3.3.6 Cadmium standard solution Ill, p(Cd) = 5 idI. Pipette 50 ml of the cadmium standard solution II (3.3.5) into a 1 000 ml one-mark volumetric flask, add 10 ml of nitric acid (3.3.1) and dilute to volume with water
40、(2.3). Store the solution in a polyethylene or borosilicate container. Prepare the solution immediately before use. 3.3.7 Cadmium calibration solutions Prepare at least five calibration solutions using the cadmium standard solution II (3.3.5) and matching the expected cadmium concentrations. As an e
41、xample, proceed as follows for the range from 0.3 w/l to 3 kg/l. Pipette 0,3 ml; 1,0 ml; 1,7 ml; 2,4 ml; and 3,0 ml re- spectively of the cadmium standard solution II (3.3.5) into five 100 ml graduated flasks. Add 1 ml of nitric acid (3.3.1) to each of these sol- utions. Dilute to volume with water
42、and mix. The calibration solutions contain 0,3 pg/l; 1,0 pg/I; 1,7 pg/l; 2,4 pg/l; and 3,0 pg/l of cadmium, respec- tively. Prepare the calibration solutions immediately before use. 3.3.8 Blank test solution Pipette 1 ml of nitric acid (3.3.1) into a 100 ml one- mark volumetric flask and dilute to v
43、olume with water. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 22:08:11 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 5961:1994(E) If the
44、 sample requires a pretreatment by digestion, the blank shall be given the same pretreatment (see 2.5.2). 3.4.4 Gas supply for argon. 3.4.5 Other apparatus (see 2.4). 3.3.9 Zero-setting solution Use water (2.3) as a zero-setting solution. The blank solution (3.3.8) may also serve for zero-setting, p
45、ro- vided its cadmium concentration is negligibly low. 3.3.10 Matrix-matching solutions (see 2 in annex A) Dissolve 1.0 g of palladium powder in 3 ml of nitric acid (2.3.1) and 20 ml of hydrochloric acid (p = 1,19 g/ml) whilst gently warming, and dilute to 100 ml with water. Dissolve 10 g of ammoniu
46、m nitrate (NH,NO,) in water and dilute to 100 ml with water. 3.3.10.1 Solution for waters of high salinity Mix equal volumes of the palladium solution and the ammonium nitrate solution (see 3.3.10). 10 1 of this solution contain 50 pg of Pd and 500 pg of NH,NO,. 3.3.10.2 Solution for water with a lo
47、w level of pollution Mix 15 ml of the palladium solution and 15 ml of the ammonium nitrate solution in a 100 ml measuring flask, and dilute to volume with water. 10 PI of this solution contain 15 pg of Pd and 150 Kg of NH,NO,. 3.4 Apparatus For cleaning of glassware see 2.4. Usual laboratory apparat
48、us and 3.4.1 Atomic absorption spectrometer, equipped with background correction and a radiation source for the determination of cadmium. 3.4.2 Graphite furnace, equipped with a control unit. 3.4.3 Pyrolytically coated graphite tube with a platform. NOTE 2 If no interference is expected, normal tube
49、s may be used. NOTE 3 For optimum precision an automatic sample injector is recommended. 3.5 Sampling and sample pretreatment Proceed as specified in 2.5. 3.6 Procedure Prior to measurement, adjust the instrumental par- ameters of the spectrometer (3.4.1) in accordance with the manufacturers operating instructions. Zero the spectrometer using the zero-setting soluti