1、Designation: D4517 04 (Reapproved 2009)D4517 15Standard Test Method forLow-Level Total Silica in High-Purity Water by FlamelessAtomic Absorption Spectroscopy1This standard is issued under the fixed designation D4517; the number immediately following the designation indicates the year oforiginal adop
2、tion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of total silica in water.1.2 T
3、his test method is applicable in the range from 25 to 250 g/L of silica as SiO2. Higher concentrations may be determinedby decreasing the aliquot volume (see Note 6). Concentration range should not be extended by dilution.1.3 This test method determines total silica, and does not distinguish between
4、 soluble and insoluble forms.1.4 This test method was tested on reagent water only. It is the users responsibility to assure the validity of the test method forwaters of other matrices.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in thi
5、s standard.1.6 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of theuser of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitationsprior to use.2. Referenced
6、 Documents2.1 ASTM Standards:2D859 Test Method for Silica in WaterD1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Steam in Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2777 Practice for Determination of Pr
7、ecision and Bias of Applicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3919 Practice for Measuring Trace Elements in Water by Graphite Furnace Atomic Absorption SpectrophotometryD4453 Practice for Handling of High Purity Water SamplesD5810 Guide
8、for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis3. Terminology3.1 DefinitionsDefinitions: For definitions of terms used in this test method, refer to Terminology D1129.3.1.1 For definitions of terms used in this st
9、andard, refer to Terminology D1129.4. Summary of Test Method4.1 Total silica is determined using an atomic absorption spectrophotometer in conjunction with a graphite furnace. A sampleis placed in a graphite tube, evaporated to dryness, charred, and atomized. Since the graphite furnace uses the samp
10、le much moreefficiently than flame atomization, the detection of low concentrations of elements in small sample volumes is possible. Finally,1 This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.03 on Sampling Water andWater-
11、Formed Deposits, Analysis of Water for Power Generation and Process Use, On-Line Water Analysis, and Surveillance of Water.Current edition approved Oct. 1, 2009Aug. 1, 2015. Published November 2009September 2015. Originally approved in 1985. Last previous edition approved in 20042009as D4517 04.D451
12、7 04 (2009). DOI: 10.1520/D4517-04R09.10.1520/D4517-15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The
13、last approved version of this historical standard is referenced on www.astm.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequa
14、tely depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
15、n, PA 19428-2959. United States1the absorption signal during atomization is recorded and compared to standards.Ageneral guide for the application of the graphitefurnace is given in Practice D3919. Pretreatment of the graphite tube may be used to enhance the sensitivity and repeatability, orboth, of
16、the test.44.2 Total silica is determined using a freshly ultrasonically treated and shaken aliquot of sample.4.3 This test method determines low-level total silica in high purity water. Refer to Test Method D859, Test Method B, fordetermination of molybdate-reactive silica.5. Significance and Use5.1
17、 Control of silica in boiler feedwater and boiler water is necessary to minimize the formation of scale-forming silicates thatdecrease heat transfer in the boiler. Volatilization and carryover of silica with the steam may cause hard, glassy siliceous depositsto form on turbine blades that reduce tur
18、bine efficiency.5.2 Colloidal silica that is not removed by boiler water pretreatment processes may be solubilized in the boiler and thuscontribute to the dissolved silica concentration in the boiler. Both dissolved and total silica are of interest.6. Interferences6.1 For a complete discussion of ge
19、neral interferences with furnace procedures, the analyst is referred to Practice D3919.6.2 Relatively pure waters such as demineralizer effluent, condensate, or high-pressure boiler feedwater are of sufficient purityto minimize potential interferences such as sodium, orthophosphate, or sulfate.6.3 G
20、raphite tube pretreatment with the calcium/lanthanum reagent has been found to improve the silica response with somegraphite tube materials or designs. Since response problems may include memory effects as well as poor sensitivity, the followingprocedure must be used to determine whether pretreatmen
21、t is needed.6.3.1 Following instrument set-up and blank determination as described in 10.1 10.3, inject 10 to 12 replicates of a standardcontaining 100 to 150 g/L of SiO2. Treat the tube in accordance with 6.4, and repeat. Note whether the response of the two setsis constant, indicating no memory ef
22、fect, or whether the first set shows increasing response. Note also whether the response of thesecond set is greater than that of the first. If either sensitivity of repeatability is improved, tube pretreatment is recommended.6.4 Pretreatment may be accomplished as follows:6.4.1 Inject into the furn
23、ace the diluted calcium/lanthanum reagent using the maximum aliquot recommended by themanufacturer of the tube, and start the atomization program. Repeat three times, or more if necessary. Run blank atomization cyclesuntil the furnace blank is constant.6.4.2 Proceed to calibrate the furnace and anal
24、yze samples in accordance with Sections 10 and 11. The absorbance enhancementmay deteriorate after numerous injections, in which case retreatment will be required. Refer to Practice D3919.7. Apparatus7.1 Atomic Absorption Spectrophotometer , Spectrophotometer, for use at 251.6 nm.NOTE 1A wavelength
25、other than 251.6 nm may be used if it has been determined to be equally suitable.NOTE 2The manufacturers instructions should be followed for all instrument parameters.7.2 Silicon Light Source, silicon hollow cathode lamp.7.3 Graphite Furnace, capable of reaching temperatures sufficient to atomize th
26、e element of interest. Atomization temperaturemust be reached as rapidly as possible for maximum sensitivity.NOTE 3Special furnace accessories are commercially available to provide a means of accelerating atomization temperature.7.4 Graphite Tubes, compatible with furnace device. Standard graphite t
27、ubes are preferred, particularly when tube pretreatmentis practiced. Pyrolytic graphite tubes may be used if it has been determined by the analyst that the precision, bias, and sensitivityof the determination are not compromised.7.5 Pipets:7.5.1 Microlitre, with disposable, polypropylene tips. Sizes
28、 may range from 1 to 1000 L, as required.7.5.2 Millilitre, 50.0 mL.7.6 Data SystemFast transient signal data are collected and processed using an internal microprocessor or external desktopcomputer systems. Data can be stored on disks, transmitted to central servers, or printed in hard copy. Data ma
29、y be evaluated andprocessed using the instruments dedicated systems to determine analyte concentrations. Users of this practice may use a strip chartrecorder to obtain sample and calibration data, if desired.4 Rawa, Judith A. and Earl L. Henn, “J. A., and Henn, E.Determination of Trace Silica in Ind
30、ustrial Process Waters by Flameless Atomic Absorption Spectrometry,” L.,“Determination of Trace Silica in Industrial Process Waters by Flameless Atomic Absorption Spectrometry,” Analytical Chemistry, Vol 51, March 1979.D4517 1527.7 Ultrasonic Cleaner, operable at 20 KHz.7.8 Flasks, volumetric, 100 a
31、nd 1000-mL polyethylene.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society wheresuc
32、h specifications are available.5 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently highpurity to permit its use without lessening the accuracy of the determination.8.2 Purity of WaterAll references to reagent water in this method shall be understood to co
33、nform to Specification D1193, forreagent water Type II. In addition, the reagent water shall be made silica-free and determined as such in accordance with thismethod. The collecting apparatus and storage containers for the reagent water must be made of suitable materials that will notcontaminate the
34、 reagent water with silica (see Section 9).NOTE 4Silica-free water may be prepared by distillation, demineralization, and passage through a 0.22 m filter. Total removal of colloidal silica maybe done by treating the above water with hydrofluoric acid, letting it stand for 24 h, and then processing i
35、t through strong base ion-exchange resin in thehydroxide form.8.3 Calcium/Lanthanum ReagentWet 2.90 g of lanthanum oxide (La2O3 99.99 % pure) with about 50 mL of water in a 100mL volumetric flask. Carefully add 5.5 mL of concentrated nitric acid (HNO3 sp gr 1.42) and swirl to dissolve. Add 0.100 g o
36、fcalcium oxide (CaO) and swirl to dissolve. Dilute to volume with water. This solution contains 100 mg/L CaO and 2500 mg/L La.Dilute 1:100 for injection. The diluted reagent is needed only for pretreatment of the graphite tube as described in 6.4.8.4 Silica Stock Solution (1 mL = 1 mL = 1 mg SiO2)Di
37、ssolve 4.7 g of sodium metasilicate (Na2SiO39H2O) and dilute to 1L with water. Determine the silica concentration of this solution in accordance with Test Method D859, Test Method A.8.5 Silica Working Solution (1 mL = 0.05 mL = 0.05 mg SiO2)Dilute 50.0 mL of the silica stock solution (see 8.4) to 1
38、L withwater in a volumetric flask. The concentration of this diluted standard is calculated after confirming the concentration of the stocksolution.8.6 Argon, standard, welders grade, commercially available.9. Sampling9.1 Collect the sample in accordance with the applicable ASTM standards: Practice
39、D1066, SpecificationGuide D1192, andPractices D3370. , and Practice D4453.9.2 Since silica is such a ubiquitous material, meticulous sample collection, handling, and injection into the furnace arenecessary to avoid contamination.9.2.1 Collect samples only in plastic or TFE-fluorocarbon containers. P
40、olystyrene, polypropylene, linear polyethylene, andTFE-fluorocarbon have been found to be generally suitable, but tests should be conducted on sample containers before use todetermine their suitability.9.2.2 Sample containers must be ultrasonically cleaned before use. Fill the sample containers with
41、 water and immerse in anoperating ultrasonic cleaner for at least 1 min. Remove, shake vigorously, and drain. Additional cycles of cleaning may be foundnecessary.9.2.3 Before actual sample collection, rinse sample container with the sample it is to contain three times with vigorous shaking,then fill
42、 Do not allow any object to touch the inside of the bottle or cap.10. Calibration10.1 Prepare standards for test calibration containing about 0, 50, 100, 150, and 250 g/L of SiO2 by diluting 0, 100, 200, 300,and 500 L of the silica working solution (see 8.4) to 100 mL with water in separate volumet
43、ric flasks.NOTE 5The exact concentration of the prepared silica standards is determined from the result obtained by the gravimetric standardization of the stocksolution in 8.4.10.2 Zero the instrument without making an injection or initiating an atomization program.10.3 Set the atomization program (
44、drying, charring, atomizing) according to the manufacturers instructions.NOTE 6While sample size and furnace programming vary among instruments, the following analytical conditions have generally been found to besuitable. It is up to the analyst to optimize analytical conditions for the instrument u
45、sed.AliquotAn aliquot size of 10 to 100 L, depending on tube size and concentration of sample. The same aliquot size must be used for all standard,sample, and blank injections.5 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on
46、 the testing of reagents not listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.D4517 153Function Temperature, C Tim
47、e, sDry 100 1 s/LChar 1000 30Atomize 2800 7Function Temperature, C Time, sDry 100 1 s/LChar 1000 30Atomize 2800 710.4 Determine the furnace blank by initiating the atomization program without making an injection. Repeat until the furnaceblank reproduces within 10 %.NOTE 7Determination of the furnace
48、 blank is a mechanism for evaluating the acceptability of the graphite tube for silica determination.10.5 Inject a measured aliquot of the 100 g/L of SiO2 standard solution (see 10.1) into the furnace, and initiate the presentatomization program. Repeat this analysis until the response reproduces wi
49、thin 10 %.10.6 Determine the acceptability of the water by injecting a measured aliquot of the “0” standard solution into the furnace andinitiating the preset atomization program. Repeat this analysis until the response reproduces within 10 %.10.7 Inject a measured aliquot of each of the remaining standard solutions as described in 10.5.10.8 Prepare a calibration curve by plotting absorbance or peak height versus concentration as micrograms per litre of SiO2 onlinear paper if direct readout in terms of concentration is not possible with the i
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