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1、INTERNATIONAL STANDARD IS0 11437-I First edition 1994-l 2-01 Nickel alloys - Determination of trace-element content by electrothermal atomic absorption spectrometric method - Part 1: General requirements and sample dissolution Alliages de nickel - Dosage des 616ments-traces - M F is a dilution facto
2、r given in the relevant part of IS0 11437; m is the mass, in grams, of the test portion. 8.2 Precision 8.2.1 Laboratory tests The methods in the subsequent parts of IS0 11437 have been subjected to interlaboratory testing. 8.2.2 Statistical analysis 8.2.2.1 Results from the interlaboratory test pro-
3、 gramme were evaluated according to IS0 5725. The data were tested for statistical outliers by the Cochran and Dixon tests given in IS0 5725. 4 8.2.2.2 The principle of the Cochran test is that a set of results is an outlier if the within-laboratory variance is too large in relation to the others. D
4、ixon s tests is to determine if the mean from a laboratory is too far from the other laboratory means. Both tests were applied at the 95 % confidence level. 8.2.2.3 Repeatability and reproducibility were calcu- lated according to IS0 5725 at the 95 % confidence level. Results of the statistical anal
5、ysis, including the within-laboratory and between-laboratory standard deviations are given for each element in the relevant part of IS0 11437. 9 Test report The test report shall include the following information: a) a reference to the method used; b) the results of the analysis; c) the number of in
6、dependent replications; d) any unusual features noted during the analysis; e) any operation not included in this part of IS0 11437 or regarded as optional. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 N
7、ot for Resale, 04/22/2007 20:56:01 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11437-1:1994(E) Optimization and checking of spectrometer performance criteria A.1 Introduction Table A.1 - Programme for graphite tube conditioning Annex A (normative) To obtain the best
8、 results when using the graphite furnace technique, the instrument settings, particu- larly the furnace programme, shall be optimized. Once the instrument settings are optimized, it is essential that the instrument meets certain performance re- quirements before it is used in the method specified in
9、 the relevant part of IS0 11437. A.2 Initial instrument checks and adjustments A.2.1 Switch on the power, cooling water, gas supplies and fume extraction system. 8.2.2 Open the furnace and inspect the tube and contacts, Replace the graphite components if wear or contamination is evident. Inspect the
10、 windows and clean if necessary. If a new tube or graphite contacts are fitted, condition these using the heating programme recommended by the manufacturer. NOTE 2 In the absence of the manufacturer s rec- ommendations, the conditioning furnace programme shown in tableA. should be used. A.3 Radiatio
11、n source Both single-element hollow cathode lamps or electrodeless discharge lamps are suitable. These should be installed and operated as recommended by the manufacturer. After the warm-up time specified by the manufac- turer, the signal from each radiation source should not deviate by more than 0,
12、5 % from the maximum value (i.e. by not more than 0,002 absorbance units) over a period of 15 min. Significantly greater fluctuations are usually indicative of a faulty lamp. NOTE 3 The use of multi-element lamps is not generally recommended. A.4 Spectrometer parameters A.4.1 Wavelength Select the w
13、avelength specified in the relevant part of IS0 11437. A.4.2 Slit Select the slit width recommended by the manufac- turer. Where two slit settings are available, ensure that the type provided for use with the graphite fur- nace is selected. A.4.3 Background correction A.4.3.1 Deuterium background co
14、rrection systems. Select the background correction option and allow the lamps to stabilize for 30 min. Check that the energies of the analyte radiation source and the deuterium radiation source are balanced within the tolerances recommended by the manufacturer. A.4.3.2 Zeeman background correction s
15、ystems. Ensure that the poles of the magnet are clean. 5 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:56:01 MDTNo reproduction or networking permitted without license from
16、IHS -,-,- IS0 11437-1:1994(E) 0 IS0 A.4.3.3 Test of background correction system. Measure the atomic and background absorbances of 20 pl of a 0,2 % (m/V) magnesium nitrate solution at a wavelength between 200 nm and 250 nm (e.g. Bi 223,l nm) using a charring temperature of 950 “C and an atomization
17、temperature of 1 800 “C. A large background signal should be observed, with no over or under correction of the atomic signal. NOTE 4 In general, the deuterium correction system should be able to correct for broad band background absorbances of up to 0.5 to 0.6 absorbance units. Zeeman systems should
18、 cope with levels as high as I,0 to I,5 absorbance units. A.5 Autosampler The operation of the autosampler should be checked. Particular attention should be paid to the condition of the pipette tip and the position of the tip during sample deposition. The manufacturer s instructions regarding the ad
19、justment of the autosampler should be followed. A.6 Optimization of the furnace heating programme Optimization of the furnace heating programme is essential if good results are to be obtained using this technique. Furnace programmes recommended by manufacturers are often concerned with samples compl
20、etely unrelated to nickel alloys. Consequently, the analyst shall optimize the furnace programme for use with the nickel alloy matrix in the manner de- scribed in A.6.1 to A.6.4. The furnace programme for the nickel alloy matrix being considered here consists of four basic steps: drying, charring, a
21、tomization and cleaning. A.6.1 Drying A.6.1.1 For most samples a drying temperature of 120 “C is satisfactory. To avoid spattering, the tem- perature should be increased to 120 “C in 20 s and then held at that temperature for a time depending on the volume of sample introduced. The following hold ti
22、mes are typical. Injected volume, 1 Hold time, s IO 15 40 30 A.6.1.2 When samples are deposited on the L vov platform, a two-stage drying process is beneficial in preventing spattering. The first stage involves heating the sample rapidly to 80 “C in 1 s and then holding the temperature at 80 “C for
23、a short time. The time during which the temperature is maintained at 80 “C depends on the volume of solution injected. The following hold times are typical. Injected volume, 1 Hold time, s 10 15 40 30 The temperature is then increased over a period of 20 s to 30 s, to a value 20 “C to 40 “C above th
24、e boiling point of the solvent. This higher temperature is held for 15 s to 40 s depending on the volume of sample injected. The following hold times are typical. Injected volume, 1 Hold time, s 10 15 40 40 A.6.1.3 In A.6.1.1 and A.6.1.2, once suitable drying conditions have been selected, the dryin
25、g process can be monitored visually with the aid of a dental mirror to ensure that it proceeds smoothly without spattering. WARNING - Do not view the tube directly during the charring, atomization or cleaning steps. A.6.2 Charring During this step, volatile components of the matrix are driven off an
26、d precursor reactions occur, for example reduction of the analyte oxide to the elemental state and the formation of matrix refractory oxides and car- bides. NOTE 5 Because of the low volatility of the nickel alloy matrix, most of it will remain in the furnace after charring. The analyst shall first
27、select the combination of graphite tube, normal or L vov platform, and measuring mode, peak height or peak area to be used. The analyst shall then determine the optimum charring temperature experimentally as described in A.6.2.1 to A.6.2.10. 6 Copyright International Organization for Standardization
28、 Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:56:01 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 IS0 11437-1:1994(E) A.6.2.1 Use the optimum drying conditions as de- termined in A.6.1. NOTE 6 At
29、 this stage, both the optimum charring and atomization settings are unknown. Estimates for suitable atomization settings should be made and the charring con- ditions optimized first. A.6.2.2 Consult the manufacturer s literature and set the atomization temperature accordingly. Select the GAS STOP op
30、tion. Select an atomization integration time of IO s. This ensures that the whole of the analyte peak will be measured. A.6.2.3 Select a charring time comprising a 30 s in- crease and a 30 s hold. A.6.2.4 Select a calibration solution which will give an absorbance reading of 0,2 to 0,4. A.6.2.5 Vary
31、 the charring temperature, in steps of 100 “C, throughout the range 500 “C to 1 400 “C taking three measurements for the calibration solution (A.6.2.4) at each step. A.6.2.6 Calculate the mean of the three measure- ments attained for each temperature step. Plot a graph relating the charring temperat
32、ure to the mean absorbance. Note the temperature at which the absorbance starts to decline. Subtract 50 “C from this value to obtain the optimum charring temperature. NOTE 7 The 50 “C allowance is to accommodate any day-to-day variations in the working of the temperature measuring system. A.6.2.7 Us
33、e the optimum charring temperature found in A.6.2.6 and vary the hold time over the range 15 s to 60 s in steps of 15 s. Take three measure- ments for the calibration solution (A.6.2.4) during each step. Monitor the background signal during this pro- cess. Note the time at which the background signa
34、l returns to the baseline. A.6.2.8 Calculate the mean of the three absorbance measurements. There shall be no evidence of analyte loss (indicated by lower absorbances for the longer hold times). A.6.2.9 Provided the condition in A.6.2.8 is satisfied, select the shortest time in which the background
35、sig- nal returns to the baseline (A.6.2.7). Add 10 s to this value to obtain the optimum hold time. A.6.2.10 If the condition in 8.6.2.8 is not satisfied, repeat actions A.6.2.7 to A.6.2.9 using a charring temperature which is 50 “C less than that originally selected in A.6.2.6. NOTE 8 A slow time o
36、f 30 s and a hold time of 30 s is usually sufficient for all pretreatment reactions to occur. Short increase times may provoke loss of sample from the tube caused by explosive splatter. A.6.3 Atomization This step involves the production of gaseous analyte atoms inside the graphite tube. As far as i
37、s possible, matrix atoms should be absent to minimize inter- ference. The analyst shall determine the optimum atomization temperature and integration time experimentally using the same GAS STOP, graphite tube and measuring mode combination selected before the optimization of the charring step. NOTE
38、9 Although it is possible to optimize the L vov platform using the peak height measurement mode to achieve its full potential, the analyst should optimize the atomization step in such a manner that the conditions re- quired for the Stabilized Temperature Platform Furnace (STPF) operation are satisfi
39、ed. In addition to the use of GAS STOP and matrix modification (inherent in the procedure), the following additional conditions should be satisfied. The temperature difference between the charring step and the atomization step should be as small as possible (less than 1 000 “C). This allows the furn
40、ace to ap- proach conditions which are nearly isothermal more quickly, and reduces the amount of matrix volatilized. The peak area integration measurement mode should be used. There shall be zero time increase between the charring and atomization steps. A.6.3.1 Use the optimum drying and charring co
41、n- ditions determined in A.6.1 and A.6.2, respectively. A.6.3.2 Select an atomization temperature of 1 200 “C and an integration time of 20 s. A.6.3.3 Using the same calibration solution (A.6.2.41, obtain three absorbance measurements at this atomization temperature. A.6.3.4 Vary the atomization tem
42、perature by in- creasing it up to 2 000 “C in 100 “C steps. Measure the absorbance of the calibration solution during each step as directed in A.6.3.3. A.6.3.5 Plot the mean of the three measurements obtained for each step against the atomization tem- perature. 7 Copyright International Organization
43、 for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/22/2007 20:56:01 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 11437-1:1994(E) 0 IS0 A.6.3.6 Examine the graph and determine the low- est atom
44、ization temperature where maximum absorbance is obtained. Add 200 “C to this value to obtain the optimum atomization temperature. NOTES IO At the lowest atomization temperature giving maxi- mum absorbance when using the peak area integration measurement mode, the peaks are broad with considerable ta
45、iling. The extra 200 “C will overcome these problems. 11 If the L vov platform is to be used under STPF con- ditions, check that the difference between the optimum charring temperature and optimized atomization tempera- ture does not exceed 1 000 “C. A.6.3.7 Duration of the atomization step Use the
46、optimum temperature found in A.6.3.6 and a hold time of 10 s. 8.6.3.7.1 instruments equipped with a VDU or fast recorder Measure the calibration solution (A.6.2.4) and observe the atomic signal during the atomization stage. De- termine the optimum hold time by adding 1 s to the time taken for the tr
47、ace to return to the zero-axis of the absorbance scale. A.6.3.7.2 Instruments without a VDU or fast re- corder Make three measurements of the calibration solution used in A.6.2.4. Calculate the mean absorbance. Re- peat these measurements using progressively shorter hold times (1 s intervals) until
48、the mean of the three measurements starts to decrease. Add 1 s to the hold time at this point to obtain the optimum hold time. A.6.4 Cleaning step Heat the furnace at 2 650 “C for 5 s to remove as much of the residual matrix as possible. NOTE 12 In practice, the matrix elements that form refractory
49、oxides and carbides cannot be completely re- moved, even at high temperatures. A.7 Instrument performance criteria The following tests shall be performed after opti- mization of the instruments described in A.2 to A.6, using the calibration solutions identified in 5.1, table 1 of the relevant part of IS0 11437. A.7.1 Determination of characteristic mass, 4 A.7.1.1 Measure the absorbance of calibration sol- uti