SKALAR METHODS ANALYSIS: NITRATE + NITRITE RANGE: µg N/liter SAMPLE: SEA WATER

Transcription

1 SKALAR METHODS ANALYSIS: NITRATE + NITRITE RANGE: µg N/liter SAMPLE: SEA WATER Catnr issue /MH/ SAN ++ PRINCIPLE The automated determination for the determination of Nitrate and Nitrite is based on the cadmium reduction method; the sample is buffered at ph 8.2 and is passed through a column containing granulated copper cadmium to reduce the nitrate to nitrite. The nitrite (originally present plus reduced nitrate) is determined by diazotizing with sulfanilamide and coupling with N (1 naphthyl)ethylenediamine dihydrochloride to form a highly coloured azo dye which is measured at 540 nm. LABORATORY FACILITIES 1. Maximum power consumption depending on the analyser configuration, 2000 VA. Check voltage at the back of the instrument before installation. 2. Facilities for chemical wastes. Check environmental regulations for proper disposal of waste. 3. Cadmium granules sieve twice, first aperture 0.3 mm and secondly aperture 1.0 mm. PROCEDURE SAMPLE PREPARATION Water no Field of application Sample preparation for the determination of total alkalinity, aluminium, amino acids, ammonia, anionic surfactants (MBAS), bromide, calcium, C.O.D., chromium, conductivity, D.O.C., ethanol, hardness, magnesium, manganese, methanol, nitrate + nitrite, nitrite, nonionics, ortho phosphate, potassium permanganate, potassium, total N (UV digestion), protein, silicate, sodium, volatile acids and urea in water. Principle The sample is not preserved and analysed as soon as possible, at least within 24 hours after collection. Store the sample at 4 C till analysis. Note : The sample preparation in this method is only meant to be an example procedure. It requires validation on its correct procedure for all types of samples to be analyzed, which is the responsibility of the user. catnr of 7

2 REAGENTS A. Buffer solution (1 liter) Required chemicals: Imidazole g. C 3 N 4 N 2 Hydrochloric acid... x ml. HCl (1M) Brij 35 (30%)... 1 ml. B. Colour reagent (1 liter) Required chemicals: o Phosphoric acid ml. H 3 PO 4 (85%) Sulfanilamide g. C 6 H 8 N 2 O 2 S N (1 Naphthyl)ethylene diamine dihydrochloride g. C 12 H 16 Cl 2 N 2 C. Rinsing liquid sampler Preparation: Dissolve the imidazole in ± 800 ml distilled water. Adjust the ph to 8.2 ± 0.1 with the hydrochloric acid solution. Add the Brij 35 and mix. Fill up to 1 liter with distilled water and mix. Solution is stable for 1 week. Store at 4 C when the solution is not used. Preparation: Dilute the o phosphoric acid in ± 700 ml distilled water. Add the sulfanilamide and the N (1 naphthtyl)ethylene diamine dihydrochloride and dissolve. Fill up to 1 liter with distilled water and mix. Solution is stable for 2 weeks. Store in a dark coloured bottle. Required chemicals: For sea water samples, adjust the salinity of the rinsing water sampler to the same level as the salinity of the sea water samples when matrix peaks reach the same level as the detection limit. Use ultra pure sodium chloride or zero seawater for adjustment. Solution is stable for 1 week. STANDARDS Stock solution 100 mg N/liter (1 liter) Required chemicals: Sodium nitrate mg. NaNO 3 Preparation: Dissolve the sodium nitrate in ± 800 ml distilled water. Fill up to 1 liter with distilled water and mix. Solution is stable for 4 weeks. Store at 4 C when the solution is not used. catnr of 7

3 Working standards 1500 µg N/liter: Dilute 1.5 ml stock solution 100 mg N/liter to 100 ml with rinsing liquid sampler µg N/liter: Dilute 1.2 ml stock solution 100 mg N/liter to 100 ml with rinsing liquid sampler. 900 µg N/liter: Dilute 0.9 ml stock solution 100 mg N/liter to 100 ml with rinsing liquid sampler. 600 µg N/liter: Dilute 0.6 ml stock solution 100 mg N/liter to 100 ml with rinsing liquid sampler. 300 µg N/liter: Dilute 0.3 ml stock solution 100 mg N/liter to 100 ml with rinsing liquid sampler. 1. Prepare the working standards fresh daily. 2. The water used for the reagents and standards must be degassed properly before making up the reagents and standards. Especially water produced by reverse osmosis or ion exchange equipment contains a lot of gasses, which must be removed by degassing (degassing procedure see operational remarks and trouble shooting). CATALOGUE NUMBERS REQUIRED CHEMICALS Product Supplier and catnr. Danger classification Imidazole Merck harmful, corrosive, toxic for reproduction Brij 35 (30%) Skalar SC ortho Phosphoric acid (85%) Merck corrosive Sulfanilamide Merck N (1 Naphthyl)ethylenediamine dihydrochloride Merck irritant Sodium nitrate Merck oxidising, harmful Hydrochloric acid (32%) Merck corrosive Copper(II) sulfate pentahydrate Merck harmful, irritant, dangerous for the environment Cadmium granules Merck carcinogenic, harmful Activated cadmium Skalar SC carcinogenic, harmful Sodium hypochlorite solution (13% active chlorine) Acros corrosive REAGENTS ACTIVATION PROCEDURE D. Hydrochloric acid solution (4M) Required chemicals: Hydrochloric acid ml. HCl (32%) ml. E. Copper(II) sulfate solution (2%) (1 liter) Preparation: Dilute the hydrochloric acid in 600 ml distilled water. Required chemicals: Copper(II) sulfate g. CuSO 4.5 Preparation: Dissolve the copper(ii) sulfate in ± 800 ml distilled water. Fill up to 1 liter with distilled water and mix. catnr of 7

4 F. Cadmium Required chemicals: Cadmium granules...± 4.5 g. size mm (sieved) ACTIVATION AND FILLING PROCEDURE Cadmium is very toxic, procedure mentioned below must be carried out under the following safety conditions; - in fumehood - use gloves and dust mask - use safety glasses This activation and filling procedure can be avoided by ordering a packed Cadmium column SA 5358 or Sieve strongly, minimal 10 minutes the cadmium with aid of 18 Mesh and 40 Mesh sieves. 18 Mesh 40 Mesh closed catchpot 2. Put the cadmium which is on the 40 Mesh sieve in a beaker. 3. Add the 4M hydrochloric acid (HCl) solution in the beaker until the cadmium is completely under the acid solution, and stir strongly with aid of glass rod the cadmium. 4M HCl 4. Remove the 4M hydrochloric acid (HCl) solution layer from the beaker. 5. Add distilled water to the cadmium until the cadmium is completely under the distilled water solution, and stir strongly with aid of glass rod the cadmium. H2O 6. Repeat procedure 5 at least another 10 times. 7. Step 5 is the most critical step, no acid may be left 8. Check the ph from the distilled water after 10 times washing the cadmium. When it is neutral continue with step 7. When it is not neutral, continue washing the cadmium with distilled water. 9. Add the copper(ii) sulfate solution 20g/liter to the cleaned cadmium until the cadmium is completely under the CuSO 4 solution and stir strongly the cadmium with aid of the glass rod. 10. The cadmium colour changes to black. CuSO4 11. Remove the CuSO 4 layer and wash 2 times with distilled water the cadmium. catnr of 7

5 12. Dry the cadmium on filter paper and heating plate (± 60 C). 13. The cadmium is now activated and ready for use. 14. Add with aid of a funnel, the granules to a dry column, with now and then vibrating to pack the column on both sides. 15. Fill up to ± 5 mm from the top. 16. Place a small piece of polyethylene tube (cat.no. SA 5144) which is sharpened at the inlet, into the column to avoid granules coming out of the column. 17. Fill, with aid of a syringe containing buffer solution (reagent A), the column. Prevent air coming in the column. 18. Place the column into the system. Avoid air entering the column. Activated cadmium granules can be stored dry, in a well closed bottle. RECOMMENDED OPERATIONAL SETTINGS 1. System sample time: 60 sec., wash time: 60 sec., air time: 0 sec. 2. Module sample time: 60 sec., wash time: 60 sec., air time: 0 sec. 3. Calibration type: 1 st order ISO Sampler settings normal: 2, extra 4 OPERATIONAL REMARKS AND TROUBLE SHOOTING 1. The stabilising time of the system is approximately 15 minutes. 2. The sensitivity of the highest standard 1500 µg N/liter is ± AU. 3. Persons using this Skalar method should be familiar with normal laboratory practice. This Skalar method does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions. 4. The connection between the sampler and the sample pump tube is made of 5175 tube. 5. If a digital matrix photometer , is in use, a correction interference filter of 620 nm ± 10 nm is advised. 6. The reagent bottles must be rinsed thoroughly with distilled water before refilling with fresh reagents. This is done to remove precipitation of micro organism and other interferences. 7. If solvents or high concentrated acids (> 2M) must be controlled by a rinsing valve, use the solvent/acid resistant type. 8. To check the reduction capacity of the cadmium column, run a nitrite standard with the same concentration (expressed in N) as the highest nitrate standard. If the results differs more then 10% replace the column. The life time of a cadmium column, in normal use, approximately 1 month. 9. Avoid any turbidity in the reagents, filter if necessary. 10. After 6 months the amount of Brij 35 can be reduced to 1 ml/liter. 11. Degassing procedures; a) Good: degas the water with a helium gas flow of approximately 20 liter/hour with aid of a sparger. Degas 5 liter water for 15 minutes. This procedure removes all dissolved air or, degas the water by boiling the water for 10 minutes. Cool down to room temperature before usage. b) Medium: degas the water with a nitrogen gas flow of approximately 20 liter/hour with aid of sparger. Degas 5 liter water for 15 minutes. This procedure will remove most of the dissolved gasses. c) Bad: degas the water by ultrasonic waves. This procedure will remove a small part of the dissolved gasses. catnr of 7

6 INTERFERENCES 1. Iron, copper and other metals present in the sample give negative results on the nitrate values. Add 1 g of EDTA Na 2 / liter buffer solution. 2. Sample turbidity may interfere with this method, when no dialyser is used. Remove by filtration before analysis. Sample colour (that absorbs in the photometric range used for analysis) will also interfere. GENERAL REMARKS 1. In most analyses, the first peak coming from the baseline is lower than it should be. The first peak coming from the baseline is rejected and will not be included in the calculation of the CV value. 2. If the sample take up volume is less than 1.00 ml/min, a bypass is required to increase the sample stream to approximately 1.00 ml/min. For 5210 debubbler, when the sample is 1.00 ml/min and higher use 0.23 ml/min debubble tube. MAINTENANCE 1. Daily; when daily analysis is finished rinse all reagent lines with distilled water for 30 minutes. 2. Weekly; to decontaminate the system, rinse 30 minutes with 1% hypochlorite solution and another 30 minutes with distilled water, but disconnect the cadmium column before rinsing. 3. Monthly; replace all pump tubing (or shift pump tube one colour bridge on pump). MODULE CONSUMABLES silicone tube catnr sleeves catnr polyethylene tube catnr sleeves catnr polyethylene tube catnr pump tube 1.40 ml/min. catnr polyethylene tube catnr pump tube 0.16 ml/min. catnr tube for valve SA 5290 catnr pump tube 0.42 ml/min. catnr sleeves catnr MODULE COMPONENTS manifold holder catnr debubbler catnr module catnr valve catnr end block catnr Cd column catnr inlet connector catnr mounting clamps catnr inlet connector catnr x clamps small catnr x glass coil catnr sinkers catnr glass coil catnr flow cell 30 mm catnr connector catnr x filter 540 nm catnr REFERENCES Chemical method (no. 461) 1. Standard method for examination of water and waste water, 15 th edition, catnr of 7

7 2. Navone, R., 1964, Proposed method for nitrate in potable waters, Amer. J., Water works Ass. 56:781, Walinga, I., van Vark, W., Houba, V.J.G., van der Lee, J.J., Plant Analysis Procedure, Part 7, Department of Soil Science and Plant Nutrition, Wageningen Agricultural University, Syllabus 1989, page ISO 13395:1996, Determination of nitrite nitrogen and nitrate nitrogen and the sum of both by flow analysis (CFA) and spectrometric detection. 5. ISO 3696:1987, Water for analytical laboratory use. Specification and test methods. 6. ASTM, D1193, Standard Specification for Reagent Water. Sample preparation (water 1.1.3) 1. Environmental Protection Agency, methods for chemical analysis of water and wastes, Standard Methods for the determination of water and waste water, 17 th edition, ASTM, International Organisation for Standardisation, ISO FLOW DIAGRAM ml/min waste 5323 Flow cell 30 mm Filter 540 nm Colour reagent Ai r waste Cadmium column Air Buffer solution Sample waste Sampler Revision: Rev 1 Rev 2 Rev 3 Method: Date: Analysis: Nitrate + Nitrite Chemists Range: µg N/liter Authorization Sample: Sea water First issued: catnr of 7