BS/EN 900-2014 pdf download.Chemicals used for treatment of water intended for human consumption – Calcium hypochlorite.
C.5 Procedure
C.5.i Preparation of the apparatus
Connect the inlet of the reaction cell with the auxiliary purging gas controlled by a flow meter, If a drysng cell between the reaction cell and the atomizer is necessary, use only anhydrous CaCI2 and not CaSO4, because it can retain SeH2 Before using the hydride generation/analysis system, optimize operating parameters. Aspirate aqueous solutions of As. Sb and Se directly into the flame to facilitate atomizer alignment. Align quartz atomizers for maximum absorbance. Establish a purging gas flow, concentration and rate of addition of sodium borohydride reagent, solution volume, and stirring rate for optimum instrument response for the chemical species to be analysed. If a quartz atomizer is used, optimize cell temperature. If sodium borohydride reagent Is added too quickly, rapid evolution of hydrogen will unbalance the system. If the volume of solution being purged is too large, the absorption signal will be decreased. Recommended wavelengths are 193,7 nm, 196,0 nm and 217,6 nm for As. Se and Sb, respectively.
C.5.2 Preparation of calibration solutions
Transfer 0,00 ml; 1,00 ml: 2,00 ml; 5,00 ml; 10,00 ml; 15,00 ml and 20,00 ml of standard solutions of As(llI), Se(IV) or Sb to 100 ml volumetric flasks and make up to volume with water containing the same acid concentration used for sample preservation (commonly 2 ml to 5 ml nitric acid (C.3.5)).This yields calibrations solutions of 0 pg/I. 1 pg/I, 2 pg/i, 5 pgll, 10 pg/i, 15 pg/i and 20 pg/i As, Se or Sb. Prepare fresh daily.
C.5.3 Preparation of test solutions and standard solutions
Add 50 ml of the sample or As(Ill), Se(Vl) or Sb standard solution to 250 ml beaker. Alternatively, prepare standard solutions by adding aliquots of solutions containing 5 pg As, Se or Sb directly to the beaker and dilute to 50 ml in this beaker, thus achieving a concentration of 100 pg/i of the respective solutions. Add 7 ml sulfuric acid c(H2S04) = 9 mol/l (C.3.3) and 5 ml nitric acid (C.3.5). Add a small boiling chip or glass beads if necessary. Evaporate to SO3 fumes. Maintain oxidizing conditions at all times by adding small amounts of nitric acid, to prevent solution from darkening.
Maintain an excess of nitric acid until all organic matter is destroyed. Complete digestion is usually indicated by a light-coloured solution. Cool slightly, add 25 ml of water and I ml of perchioric acid (C.3.6) and again evaporate to SO3 fumes to expel oxides of nitrogen.
Monitor the effectiveness of the digestion procedure used by adding 5 ml of a standard arsenic solution, 5 ml of a standard selenium solution or 5 ml of a standard antimony solution to 50 ml of the sample and measuring recovery. Average recoveries shall be greater than 90 %. Alternatively, use 100 ml micro-Kjeldahl flasks for the digestion of total recoverable arsenic, selenium or antimony, thereby improving digestion effectiveness. After the final evaporation of the SO3 fumes, dilute to 50 ml for arsenic measurements or 30 ml for selenium and antimony measurements.
C.5.4 Determination of arsenic with sodium borohydride
To 50 ml of the digested standard solution or test solution in a 250 ml beaker (see Figure C.1) add 5 ml hydrochloric acid (C.3.7) and mix. Add 5 ml sodium iodide pre-reductant solution (C.3.2), mix and wait at least 30 mm.
NOTE The sodium eothde has not been found necessary for certain hydride reaction cell designs If a 20 % to 30 % loss In instrument sensitivity Is not important and variables of solution acid conditions, temperatures, and volumes for production of As(V) and arsine can be strictly controlled. This might require an automated delivery system.
Attach one beaker the first time to the rubber stopper containing the gas dispersion tube for the purging gas. the sodium borohydride reagent inlet, and the outlet to the atomizer. Turn on strip-chart recorder and wait until the base line is established by the purging gas and all air is expelled from the reaction cell. Add 0,5 ml sodium borohydride reagent (C.3. 1). After the instrument absorbance has reached a maximum and returned to the base line, remove the beaker, rinse the dispersion tube with water, and proceed to the next test solution or standard solution. Periodically compare standard As(lll) and As(V) curves for response consistency. Check for the presence of chemical interferences that suppress instrument response for arsine by treating a digested sample with 10 pg/I As(lll) or As(V) as appropriate. Average recoveries shall be not less than 90 %.
C.5.5 Determination of selenium with sodium borohydride
To 30 ml of the digested standard solution or test solution, or to 30 ml of the undigested standard, or the sample in a 250 ml beaker, add 15 ml hydrochloric acid (C.3.7) and mix. Heat for a pre-determined period at a temperature between 90 °C to 100 °C. Alternatively autoclave at 121 °C in capped containers for 60 mm, or heat for a predetermined time in open test tubes using a 90 DC to 100 °C hot water bath or an aluminium block digester. Check the effectiveness of the selected heating by demonstrating equal instrument responses for calibration curves prepared either from standard Se(lV) or from Se(Vl) solutions. Effective heat exposure for converting Se(Vl) to Se(IV). with no loss of Se(lV), ranges between 5 mm to 60 mm when open beakers or test tubes are used. Do not digest standard Se(lV) and Se(Vl) solutions used for this check of equivalency. After pre-reduction of Se(Vl) and Se(lV) attach beakers, one at a time, to the purge apparatus.BS/EN 900-2014 pdf download.
BS/EN 900-2014 pdf download
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