SIST EN 16318:2013+A1:2016
(Main)Fertilizers and liming materials - Determination of chromium(VI) by photometry (method A) and by ion chromatography with spectrophotometric detection (method B)
Fertilizers and liming materials - Determination of chromium(VI) by photometry (method A) and by ion chromatography with spectrophotometric detection (method B)
This European Standard specifies two methods for the determination of the content of soluble chromate in fertilizers and liming materials.
Method A specifies the determination of chromate after extraction with water by photometry. This method can be used to determine Cr(VI)-mass fractions in solids higher than 1 mg/kg.
Method B specifies the determination of chromate by alkaline digestion and ion chromatography with spectrophotometric detection. This method can be used to determine Cr(VI)-mass fractions in solids higher than 0,1 mg/kg.
NOTE 1 In case of reducing or oxidizing fertilizer matrix, no valid Cr(VI) content can be reported.
NOTE 2 The term fertilizer is used throughout the body of this European Standard and includes liming materials unless otherwise indicated.
Düngemittel und Kalkdünger - Bestimmung von Chrom (VI) mit Photometrie (Verfahren A) und mit Ionenchromatographie mit spektrometrischer Detektion (Verfahren B)
Diese Europäische Norm legt zwei Verfahren zur Bestimmung des Gehalts an löslichem Chromat in Düngemitteln fest.
Verfahren A legt die Bestimmung von Chromat nach Extraktion mit Wasser durch Photometrie fest. Dieses Verfahren ist anwendbar für die Bestimmung von Chrom(VI)-Massenanteilen von mehr als 1 mg/kg in Feststoffen.
Verfahren B legt die Bestimmung von Chromat durch alkalischen Aufschluss und Ionenchromatographie mit spektrometrischer Detektion fest. Dieses Verfahren ist anwendbar für die Bestimmung von Chrom(VI)-Massenanteilen von mehr als 0,1 mg/kg in Feststoffen.
ANMERKUNG Bei Vorliegen einer reduzierenden oder oxidierenden Düngemittelmatrix kann der Chrom(VI)-Gehalt nicht zuverlässig ermittelt werden.
Engrais et amendements minéraux basiques - Dosage du chrome (VI) par spectrophotométrie (méthode A) et chromatographie ionique avec détection spectrophotométrique (méthode B)
Cette norme européenne spécifie deux méthodes de détermination de la teneur en chromate soluble dans les engrais.
La méthode A présente la détermination du chromate après extraction avec de l’eau par spectrophotométrie. Cette méthode peut être utilisée afin de déterminer les fractions massiques de Cr(VI) supérieures à 1 mg/kg dans les solides.
La méthode B présente la détermination du chromate par digestion alcaline et chromatographie ionique avec détection spectrophotométrique. Cette méthode peut être utilisée afin de déterminer les fractions massiques de Cr(VI) supérieures à 0,1 mg/kg dans les solides.
NOTE En cas de matrice d’engrais oxydante ou réductrice, aucune teneur en Cr(VI) valide ne peut être énoncée.
Gnojila in sredstva za apnjenje - Določevanje kroma (VI) s fotometrijo (metoda A) in z ionsko kromatografijo s spektrofotometrijsko detekcijo (metoda B)
Ta evropski standard določa dve metodi za določevanje vsebnosti topnega kromata v gnojilih in sredstvih za apnjenje.
Metoda A določa določevanje kromata po vodni ekstrakciji s fotometrijo. Ta metoda se lahko uporablja za določevanje masnih deležev Cr(VI), višjih od 1 mg/kg, v trdnih snoveh.
Metoda B določa določevanje kromata z alkalnim razklopom in ionsko kromatografijo s spektrofotometrijsko detekcijo. Ta metoda se lahko uporablja za določevanje masnih deležev Cr(VI), višjih od 0,1 mg/kg, v trdnih snoveh.
OPOMBA 1: V primeru zmanjšanja ali oksidacije matrice gnojila ni mogoče poročati o veljavni vsebnosti Cr(VI).
OPOMBA 2: Izraz »gnojilo« se uporablja v celotnem glavnem delu tega evropskega standarda in vključuje sredstva za apnjenje, če ni navedeno drugače.
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Düngemittel und Kalkdünger - Bestimmung von Chrom (VI) mit Photometrie (Verfahren A) und mit Ionenchromatographie mit spektrometrischer Detektion (Verfahren B)Engrais et amendements minéraux basiques - Dosage du chrome (VI) par spectrophotométrie (méthode A) et chromatographie ionique avec détection spectrophotométrique (méthode B)Fertilizers and liming materials - Determination of chromium(VI) by photometry (method A) and by ion chromatography with spectrophotometric detection (method B)71.040.50Fizikalnokemijske analitske metodePhysicochemical methods of analysis65.080GnojilaFertilizersICS:Ta slovenski standard je istoveten z:EN 16318:2013+A1:2016SIST EN 16318:2013+A1:2016en,fr,de01-julij-2016SIST EN 16318:2013+A1:2016SLOVENSKI
STANDARDSIST EN 16318:20131DGRPHãþD
SIST EN 16318:2013+A1:2016
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 16318:2013+A1
February
t r s x ICS
x wä r z r Supersedes EN
s x u s zã t r s uEnglish Version
Fertilizers and liming materials æ Determination of chromatography with spectrophotometric detection Engrais et amendements minéraux basiques æ Dosage t chromatographie ionique avec détection
Düngemittel und Kalkdünger æ Bestimmung von Chrom Ionenchromatographie mit spektrometrischer This European Standard was approved by CEN on
s w September
t r s u and includes Amendment
s approved by CEN on
s { December
t r s wä
egulations which stipulate the conditions for giving this European Standard the status of a national standard without any alterationä Upætoædate lists and bibliographical references concerning such national standards may be obtained on application to the CENæCENELEC Management Centre or to any CEN memberä
translation under the responsibility of a CEN member into its own language and notified to the CENæCENELEC Management Centre has the same status as the official versionsä
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t r s x CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Membersä Refä Noä EN
s x u s zã t r s u ªA sã t r s x ESIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 2 Contents Page European foreword . 4 1 Scope . 5 2 Normative references . 5 3 Terms and definitions . 5 4 Sampling and sample preparation . 5 5 Method A: Determination by water extraction and spectrophotometric detection . 6 5.1 Principle . 6 5.2 Reagents . 6 5.3 Apparatus . 7 5.4 Procedure. 7 5.4.1 Preparation of the test solution . 7 5.4.2 Preparation of the blank test solution . 8 5.4.3 Spectrophotometric measurement . 8 5.5 Calculation and expression of the results . 8 5.5.1 Calibration . 8 5.5.2 Calculation of the element content in the sample . 8 6 Method B: Determination by alkaline digestion and ion chromatography with spectrophotometric detection . 9 6.1 Principle . 9 6.1.1 Digestion . 9 6.1.2 Determination . 9 6.1.3 Interferences and sources of error . 10 6.2 Reagents . 10 6.3 Apparatus . 12 6.4 Alkaline digestion procedure . 13 6.4.1 General . 13 6.4.2 Preparation of test solutions using a hotplate or heating block . 13 6.5 Procedure. 13 6.5.1 Instrumental set-up . 13 6.5.2 Calibration . 13 6.5.3 Test solution measurement . 14 6.6 Quality control . 14 6.6.1 General . 14 6.6.2 Blank test solution . 14 6.6.3 Verification of method . 14 6.6.4 Duplicate samples . 14 6.6.5 Cr(VI) spiked samples . 15 6.6.6 Cr(III) spiked samples . 15 6.6.7 Interpretation of Quality Control data . 15 6.7 Calculation and expression of results . 15 6.7.1 Calculation . 15 6.7.2 Expression of results . 16 7 !Precision— Inter-laboratory tests" . 16 8 Test report . 16 SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 3 Annex A (informative)
Results of the inter-laboratory test performed by VDLUFA on method A . 17 A.1 Inter-laboratory tests . 17 A.2 Statistical results for the determination of chromium(VI) by photometry (method A) . 17 Annex B (informative)
Results of a validation study on spiked water samples . 18 Bibliography . 19
SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 4 European foreword This document (EN 16318:2013+A1:2016) has been prepared by Technical Committee CEN/TC 260 “Fertilizers and liming materials”, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 2016, and conflicting national standards shall be withdrawn at the latest by August 2016. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document includes Amendment 1 approved by CEN on 2015-12-19. This document supersedes !EN 16318:2013". The start and finish of text introduced or altered by amendment is indicated in the text by tags !". This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association. !deleted text" !WARNING — Avoid any contact with the skin, ingestion or inhalation of Cr(VI) compounds. Cr(VI) compounds are genotoxic and potentially carcinogenic to humans." According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 5 1 Scope !This European Standard specifies two methods for the determination of the content of soluble chromate in fertilizers and liming materials." Method A specifies the determination of chromate after extraction with water by photometry. This method can be used to determine Cr(VI)-mass fractions in solids higher than 1 mg/kg. Method B specifies the determination of chromate by alkaline digestion and ion chromatography with spectrophotometric detection. This method can be used to determine Cr(VI)-mass fractions in solids higher than 0,1 mg/kg. !NOTE 1" In case of reducing or oxidizing fertilizer matrix, no valid Cr(VI) content can be reported. !NOTE 2
The term fertilizer is used throughout the body of this European Standard and includes liming materials unless otherwise indicated." 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 1482-2, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample preparation EN 12944-1:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 1: General terms EN 12944-2:1999, Fertilizers and liming materials and soil improvers — Vocabulary — Part 2: Terms relating to fertilizers !EN 12944-3:2001, Fertilizers and liming materials — Vocabulary — Part 3: Terms relating to liming materials" EN 15192:2006, Characterisation of waste and soil — Determination of Chromium(VI) in solid material by alkaline digestion and ion chromatography with spectrophotometric detection EN ISO 3696, Water for analytical laboratory use — Specification and test methods (ISO 3696) 3 Terms and definitions !For the purposes of this document, the terms and definitions given in EN 12944-1:1999, EN 12944-2:1999 and EN 12944-3:2001 apply." 4 Sampling and sample preparation Sampling is not part of the methods specified in this European Standard. A recommended sampling method is given in EN 1482-1 [2]. Sample preparation shall be carried out in accordance with EN 1482-2. Reasonable precautions have to be taken to prevent oxidation of chromate present in the sample. Samples shall be taken using appropriate devices and placed in containers that do not contain stainless steel (e.g. plastic, glass). After digestion, the sample shall be analyzed as soon as possible. SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 6 5 Method A: Determination by water extraction and spectrophotometric detection 5.1 Principle Chromate is extracted from the sample with water at room temperature. The chromate concentration in the extract is measured by colorimetry using 1,5-diphenylcarbazide. When chromate reduces the 1,5-diphenylcarbazide a magenta coloured complex of 1,5-diphenylcarbazone and chromium is formed which can be measured colorimetrically at 540 nm. 5.2 Reagents Use only reagents of recognized analytical grade and water conforming to 5.2.1. 5.2.1 Water, according to EN ISO 3696, grade 2 (electrical conductivity max. 0,1 mS × m-1 equivalent to resistivity greater than 0,01 „m at 25 °C). It is recommended that the water used is obtained from a purification system that delivers ultrapure water having a resistivity greater than 0,18 „m. 5.2.2 Hydrochloric acid, c(HCl) = 12 mol/l; 37 % volume fraction,
³
sá s z g/ml. 5.2.3 Hydrochloric acid, diluted, c(HCl) approximately 6 mol/l. Mix equal volumes of hydrochloric acid (5.2.2) and water (5.2.1). 5.2.4 Diphenylcarbazide solution. Dissolve 1,0 g Diphenylcarbazide [CO(NHNHC6H5)2] in 100 ml acetone and add one drop of acetic acid. If this solution is stored in a glass bottle in the dark at 4 °C, it may be used for approximately two weeks. This solution shall be clear without colour. If the diphenylcarbazide solution has become coloured, it shall be discarded and freshly prepared before use. 5.2.5 Chromate standard stock solution, (chromate) = 1 000 mg/l. Dissolve 2 829 mg potassium dichromate (K2Cr2O7) in 1 000 ml water (5.2.1) using a volumetric flask. This solution may be used for two weeks if stored in the dark at 4 °C. 5.2.6 Chromate standard stock solution, (chromate) = 50 mg/l. Dilute 5 ml chromate stock solution (5.2.5) to 100 ml with water (5.2.1) using a volumetric flask. This solution shall be freshly prepared on the day of use. 5.2.7 Standard solutions. Prepare the standard solutions by diluting aliquots of the 50 mg/l chromate standard stock solution (5.2.6) with water (5.2.1) in 100 ml volumetric flasks. The aliquots and final concentrations of chromate are given in Table 1. Other volumes and concentrations may be used for the preparation of standard solutions if appropriate. See 5.4.3 for further instructions on how to prepare the standard solutions. SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 7 Table 1 — Aliquots and final concentrations for the preparation of chromate standards from a 50 mg/l chromate standard stock solution in 100 ml volumetric flasks Aliquot Final concentration of chromate ml mg/l 0 0 (calibration blank) 0,05 0,025 0,20 0,10 0,50 0,25 1,00 0,50 1,50 0,75
A blank solution shall be prepared in a separate volumetric flask by adding water (5.2.1) only. The standard solutions shall be prepared freshly on the day of use. 5.3 Apparatus 5.3.1 Common laboratory glassware. 5.3.2 Analytical balance, capable of weighing to an accuracy of 1 mg. 5.3.3 Membrane filters and vacuum filtration apparatus. The filters should be made of cellulose nitrate, pore size 5 µm and fit into the vacuum filtration apparatus. 5.3.4 Mechanical shaker. 5.3.5 Pipettes and/or dilutor, pipettes with fixed or variable volume and volumetric glassware to perform dilutions. Alternatively, a dilutor may be used, which is an instrument used for automated volumetric dilutions. The precision and accuracy of this equipment for volumetric dilutions shall be proved, controlled, and documented regularly. 5.3.6 Spectrophotometer, capable to measure transmitted light at 540 nm. 5.3.7 100 ml bottles, made from PE or PP, equipped with watertight caps. 5.4 Procedure 5.4.1 Preparation of the test solution Weigh approximately 10 g, to the nearest 0,01 g, of the prepared sample and transfer to a suitable extraction vessel (5.3.7). Add 40 ml of water (5.2.1). If the sample material (e.g. organic material) absorbs a high amount of water, add additionally water (5.2.1) to obtain a fluid suspension. Record the amount of additional water added. It may be necessary to use larger extraction vessels in such cases. Close the cap tightly and SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 8 shake vigorously for 15 min on a mechanical shaker (5.3.4). Filter the suspension immediately through membrane filters with 5 µm pore size using the vacuum filtration apparatus (5.3.3). Pipette 20 ml of the test solution to a 100 ml volumetric flask and continue immediately with the colorimetric measurement. If the test solution shows a yellow colour, the aliquot should be reduced to minimize interferences by the colour of organic substances. The test solution may not be stored. The chromate content shall be analyzed on the day of preparation. 5.4.2 Preparation of the blank test solution Carry out a blank test at the same time as the extraction, with only the reagents and follow the same procedure as for the samples. 5.4.3 Spectrophotometric measurement Add approximately 40 ml of water (5.2.1) to all volumetric flasks containing the standard solutions (5.2.7), the blank test solution (5.4.2) and the sample test solutions (5.4.1). Then add 2 ml diluted hydrochloric acid (5.2.3). The pH-value of the resulting solution should be between pH 1 and pH 2. Add more diluted hydrochloric acid (5.2.3) if the pH-value is higher until a pH-value between pH 1 and pH 2 is reached. Add 2 ml diphenylcarbazide solution (5.2.4) to each volumetric flask and fill up to the mark with water (5.2.1). Wait 15 min and measure the extinction of the solutions on a spectrophotometer at 540 nm. 5.5 Calculation and expression of the results 5.5.1 Calibration In the case of a linear calibration curve, the calibration function can be described according to Formula (1). Scba=×+ (1) where S is the net signal for Cr(VI) in a solution; c is the concentration of Cr(VI) in this solution, in milligrams per litre or in micrograms per litre; b is the slope of the linear calibration function; a is the intersection of the linear calibration function.
Calculate the analyte concentration, cf, in the filtrate of the test portion using the slope b and the intersection a according to Formula (2): ffSacb−= (2) where Sf
is the net signal of the test solution.
5.5.2 Calculation of the element content in the sample Calculate the analyte concentration in the sample or the mass fraction of the analyte, wE, expressed in milligrams of analyte per kilogram of fertilizer according to Formula (3). SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 9 ()1000fblEtccwVm−=×× (3) where cf is the concentration, in milligrams per litre, of the filtrate of the test portion, as determined according to Formula (2); cbl is the concentration, in milligrams per litre, of the blank solution; m is the mass of the sample, in grams, taken for the extraction, and corrected for water content; Vt is the total volume, in litres, of water added to the test portion for extraction.
6 Method B: Determination by alkaline digestion and ion chromatography with spectrophotometric detection 6.1 Principle 6.1.1 Digestion Cr(VI) is digested from the sample by an alkaline solution. To quantify the content of Cr(VI) in a solid matrix, the following three criteria shall be satisfied: a) the digestion solution shall solubilize all species of Cr(VI); b) the conditions of the digestion shall not induce reduction of native Cr(VI) to Cr(III); c) the method shall not cause oxidation of native Cr(III) contained in the sample to Cr(VI). The alkaline digestion described in this document meets these criteria for a wide spectrum of solid matrices. Under the alkaline conditions, neglect able reduction of Cr(VI) or oxidation of native Cr(III) is expected. The addition of Mg2+ in a phosphate buffer to the alkaline solution prevents air oxidation of trivalent chromium (see [7], [8] and [9]). NOTE Background on methods for the determination of Cr(VI) in solid samples is given in EN 15192:2006, Annex D and [10], [11], [8]. 6.1.2 Determination The quantification of Cr(VI) in the alkaline digestion solution should be performed using a suitable technique with appropriate accuracy. For this purpose, ion chromatography is used to separate Cr(VI) from interferences. Following this ion chromatographic separation, Cr(VI) is measured spectrophotometrically either at 365 nm (direct UV detection) or after post-column derivatization with 1,5-diphenylcarbazide in acid solution at 540 nm. Post-column derivatization involves reaction of 1,5-diphenylcarbazide with Cr(VI) to produce trivalent chromium and diphenylcarbazone. These then combine to form a trivalent chromium-diphenylcarbazone complex containing the characteristic magenta chromagen (max = 540 nm). NOTE The choice of detection method is based upon the required sensitivity. Direct UV detection is less sensitive than detection after post-column derivatization with 1,5-diphenylcarbazide. Hyphenated methods with ion chromatographic separation and detection techniques, such as inductively coupled plasma-mass spectrometry (ICP-MS) or inductively coupled plasma-atomic SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 10 emission spectroscopy (ICP-AES), may be used once validation of the chosen analytical method has been performed. 6.1.3 Interferences and sources of error Use of ion chromatography is necessary for the separation of Cr(VI) from possible interferences in the alkaline digestion solution from solid material [12] (see also EN 15192:2006, D.3). For waste materials or soils, where the Cr(III)/Cr(VI) ratio is expected to be high, Cr(VI) results may be biased due to method-induced oxidation. This can be particularly expected in soils high in Mn content and amended with soluble Cr(III) salts or freshly precipitated Cr(OH)3 [10] (see also EN 15192:2006, D.2). Cr(VI) can be reduced to Cr(III) during digestion from the sample due to reaction with reducing agents such as e.g. divalent iron. This problem is minimized in the described procedure using alkaline digestion solution [8] (see also EN 15192:2006, D.2). Cr(III) can be oxidized to Cr(VI) in hot alkaline solutions. This problem is minimized in the described procedure by adding magnesium to the alkaline digestion solution [8], [9], [10], [13] (see also EN 15192:2006, D.2). Overloading the analytical column capacity with high concentrations of anionic species (e.g. chloride) may cause underestimation of Cr(VI) [6]. 6.2 Reagents Use only reagents of recognized analytical grade, and water as specified in 6.2.1. 6.2.1 Water, according to EN ISO 3696, grade 2 (electrical conductivity max. 0,1 mS × m-1 equivalent to resistivity greater than 0,01 „m at 25 °C). It is recommended that the water used is obtained from a purification system that delivers ultrapure water having a resistivity greater than 0,18 „m. 6.2.2 Sulfuric acid, concentrated, (H2SO4 g/ml, w(H2SO4 %. 6.2.3 Sodium carbonate, anhydrous, w(Na2CO3) > 99,9 %. 6.2.4 1,5-Diphenylcarbazide, !w((C6H5NHNH)2CO) > 98 %". 6.2.5 Acetone. 6.2.6 Methanol. 6.2.7 Potassium dichromate, w(K2Cr2O7) > 99,9 %. Dry to constant weight at 110 °C, cool and store in a desiccator. 6.2.8 Sodium hydroxide, w(NaOH) > 99 %. 6.2.9 Magnesium chloride hexahydrate, w(MgCl2.6H2O) > 99 %. 6.2.10 Dipotassium hydrogenphosphate, w(K2HPO4) > 99 %. 6.2.11 Potassium dihydrogenphosphate, w(KH2PO4) > 99 %. 6.2.12 Lead chromate, w(PbCrO4) > 99 %. SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 11 6.2.13 Diphenylcarbazide reagent solution. Dissolve 0,125 g of 1,5-diphenylcarbazide (6.2.4) in 25 ml of acetone (6.2.5) or methanol (6.2.6) in a 250 ml volumetric flask. Fill 125 ml of water (6.2.1) into a separate container, slowly add 7 ml of concentrated sulfuric acid (6.2.2), swirl to mix and allow to cool. Degas with, e.g. helium or argon, for 5 min to 10 min prior to adding to the 1,5-diphenylcarbazide solution. After combining the solutions, fill up to the mark with water (6.2.1) and degas additionally for 5 min to 10 min. The reagent solution is stable for five days. 6.2.14 Eluent solution. Use an eluent solution appropriate to separate chromate over the ion chromatographic column (6.3.7). 6.2.15 Alkaline digestion solution, sodium hydroxide, c(NaOH) = 0,5 mol/l, sodium carbonate, c(Na2CO3) = 0,28 mol/l. Dissolve 20,0 g of sodium hydroxide (6.2.8) in approximately 500 ml of water (6.2.1). Add 30,0 g of sodium carbonate (6.2.3) and swirl to mix. Quantitatively transfer the solution into a 1 l volumetric flask. Dilute to the mark with water (6.2.1). The pH-value of the digestion solution shall be checked before use. The pH-value shall be 11,5 or higher. Store in a polyethylene bottle at room temperature and prepare fresh monthly. 6.2.16 Calibration solutions of Cr(VI). 6.2.16.1 Cr(VI) standard stock solution, 1 000 mg/l Cr(VI). Dissolve 0,282 9 g of potassium dichromate (6.2.7) in 75 ml of water (6.2.1) in a 100 ml volumetric flask. Dilute to the mark with water (6.2.1), close and mix thoroughly. Store the solution in a polypropylene bottle for a maximum period of one year. Alternatively, a commercial standard solution with a certified Cr(VI) concentration traceable to national standards may be used. Observe the manufacturer's expiration date or recommended shelf life. 6.2.16.2 Cr(VI) working standard solution, 10 mg/l Cr(VI). Accurately pipette 10,0 ml of the Cr(VI) standard stock solution (6.2.16.1) into a 1 l volumetric flask, dilute to the mark with water (6.2.1), close and mix thoroughly. Prepare this solution fresh monthly. 6.2.16.3 Cr(VI) calibration solutions. Prepare a set of at least five calibration solutions by diluting the Cr(VI) working standard solution with a 1 + 1 diluted alkaline digestion solution (6.2.15). Add 25 ml of the alkaline digestion solution (6.2.15) into a 50 ml volumetric flask, pipette accurately the appropriate volume of Cr(VI) working standard solution (6.2.16.2) into the volumetric flask and dilute to the mark with water (6.2.1), close and mix thoroughly. Prepare these calibration solutions fresh daily. 6.2.16.4 Cr(VI) spiking solutions. The Cr(VI) working standard solution (6.2.16.2) may be used to spike samples. 6.2.17 Phosphate buffer solution, 0,5 mol/l dipotassium hydrogenphosphate (K2HPO4)/0,5 mol/l potassium dihydrogenphosphate (KH2PO4), pH 7. Dissolve 87,09 g K2HPO4 (6.2.10) and 68,04 g of KH2PO4 (6.2.11) in approximately 700 ml of water (6.2.1) and swirl to mix. Transfer the solution into a 1 l volumetric flask. Dilute to the mark with water (6.2.1). SIST EN 16318:2013+A1:2016
EN 16318:2013+A1:2016 (E) 12 6.2.18 Magnesium chloride solution. Dissolve 85,4 g MgCl2.6H2O (6.2.9) in a 100 ml volumetric flask, dilute to the mark with water (6.2.1), close and mix thoroughly. 6.2.19 Chromium chloride hexahydrate, w(CrCl3.6H2O) > 96 %. 6.2.20 Cr(III) spiking solution. Use a commercial standard solution with a certified Cr(III) concentration, e.g. 1 000 mg/l Cr(III) traceable to national standards. Observe the manufacturer's expiration date or recommended shelf life. Alternatively, dissolve 512 mg of chromium chloride hexahydrate (6.2.19) in water (6.2.1) in a 100 m
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