SmartChem Method Summaries - NASA



SmartChem 170 Method Summaries, adapted from Westco Unity SmartChem Methods

I. METHOD SW-NH3-3: Ammonium in Fresh and Sea Water

1.0 SCOPE AND APPLICATION

This method covers the determination of ammonium in surface and saline waters. The working range of this method is from 0 to 140 μmol/L NH4+. This method is based on Standard Methods 4500-NH3-G (19th, 20th, and 21st Edition) and 4500-NH3-H (18th Edition).

2.0 METHOD SUMMARY

The method is based on the formation of the indophenols-blue complex. Ammonia reacts with alkaline phenol and hypochlorite to form indophenols-blue (Berthelot reaction). The intensity of the color developed is proportional to the ammonia concentration. The reaction kinetics and intensity of the blue color produced is pH dependent. The blue color developed during the reaction is intensified by the addition of sodium nitroprusside.

Application of the indophenol-blue method for the analysis seawater samples poses some “unique”problems related to the sea water sample matrix/salinity/alkalinity. The optimal reaction pH is high (optimum range is 10.5 to 11.5, and the reaction rate increases at a pH > 12.0), and at high pH cations can be precipitated that will interfere in the analysis. Therefore the use of low-nutrient sea water to prepare a calibrants, control, and spikes solutions is “strongly” recommended.

The working range of this method is from 0 to 140 μmol/L NH4+. The range of the

method can be extended by varying the sample and reagent volumes. The method may require need minor adjustments in reagent volumes, and in the compositions and concentrations of the complexing reagent based on the sample matrix and analyte concentration requiring

analysis.

3.0 REAGENTS AND STANDARDS

3.1 Reagent water: Distilled or de-ionized water, free of the analyte of interest. ASTM type I or II; Ammonia may be absorbed from the atmosphere. Avoid prolonged exposure of open containers of reagent water to the laboratory atmosphere.

3.2 Stock Complexing Reagent 1: In a 250 mL flask, dissolve 35 g of sodium citrate dihydrate,

[Na3C6H5O7·2H2O] (CAS: 6132-04-3) in approximately 230 mL of reagent water. Add and dissolve 2.5 grams of ethylene diaminetetraacetic acid (EDTA) (CAS: 60-00-4) and 2.5 grams of sodium hydroxide (NaOH) (CAS: 1310-73-2). Dilute to volume and store at room temperature. Can store for up to 2 weeks.

3.2.1 Reagent 1- Working Complexing Reagent Solution: Add 0.35 mL of concentrated Probe Rinse Solution (Westco Part Number 3AS-RN00-21) to a clean and dry SmartChem reagent bottle and then add 35.0 mL of the stock complexing reagent (Section 3.2). Gently swirl the solution to mix the solution. Cap the SmartChem reagent bottle with Parafilm and allow the solution to stand approximately 30 minutes before beginning the analysis. Prepare this solution fresh daily.

3.3 Reagent 2 - Alkaline Phenol Reagent: Add and dissolve 2.0 grams sodium hydroxide (CAS: 1310-73-2) to approximately 75 mL of reagent water in a 100 mL volumetric flask and then chill the solution by placing in an ice bath for 5 minutes. While the solution is in the ice bath, slowly add 4.25 mL of crystaline phenol C6H5OH (CAS: 108-95-2). Cap and remove the volumetric flask from the ice bath and allow it to reach room temperature and then dilute to the mark with reagent water. Store this solution in a dark glass or dark plastic bottle and refrigerate the solution when not in use. Prepare this solution fresh weekly.

3.4 Reagent 3 - Sodium Nitroprusside (Sodium Nitroferricyanide) Solution: Dissolve 0.0875 g of sodium nitroprusside dihydrate, (sodium nitroferricyanide dihydrate) Na2Fe(CN)5NO·2H2O (CAS: 13755-38-9) in approximately 80 mL of reagent water in 100 mL flask. Add 0.5 mL concentrated Probe Rinse Solution (Westco Part Number 3AS-RN00-21), dilute to volume, and invert mix five times. Store the solution in a dark glass container at room temperature. Solution should be prepared fresh weekly.

3.5 Reagent 4 - Sodium Hypochlorite, Solution. Add 10 mL of a bleach solution containing 5.25% NaOCl (CASRN 7681-52-9) (such as "Clorox") to approximately 35 mL of reagent water

in a 50 mL volumetric flask, and then add 0.5 mL of concentrated Probe Rinse Solution (Westco Part Number 3AS-RN00-21) and dilute to the mark with reagent water. Invert five times to mix. Prepare this solution fresh daily.

3.6. Stock Solution, 1000 mg/L: Dissolve 0.3819 g anhydrous ammonium chloride NH4Cl (CASRN 12125-02-9), dried at 105˚C, in reagent water and dilute to 100 mL (1.0 mL= 1.0 mg N). Store in a glass, capped bottle in the refrigerator. Make fresh every month.

3.6.1. Working Standard Solution, 0.5 mg/L: Transfer 0.05 mL of Stock Solution (Section 3.6) to a volumetric flask and dilute to 100 mL with reagent water. Refrigerate solution when not in use. Solution should be prepared fresh every two to three days.

3.6.2. Spike Solution, 1.0 mg/L: Transfer 0.10 mL of Stock Solution (Section 3.6) to a volumetric flask and dilute to 100 mL with reagent water. Refrigerate solution when not in use. Solution should be prepared fresh every two to three days.

3.7. Cuvette cleaning solution: Add 15 mL of Cuvette Cleaning Solution and dilute to 1 L with reagent water. Store the solution at room temperature.

3.8. Probe rinse solution: Add 0.5 mL of Probe Rinse Solution (Unity Part Number 3AS-RN00-21) to 1 L of reagent water. Store the solution at room temperature.

4.0 PROCEDURE

4.1. The 630 nm filter is used in this method.

4.2. Parameter file details: The Sample Blanking Option may be used after the addition of Reagent 1- sample blanking option is not used for this project.

|Method Code: SWNH |Volume |Delay Time |Read Time |Rinse Volume |Reagent |

| |μL |Sec. |Sec. |μL |Code |

| | | | | | |

|Sample |256 | | | | |

|Reagent 2- Na-Phenolate |30 |108 |0 |0 |SWPH |

|Reagent 3- Nitroprisside |25 |0 |0 |0 |SWNI |

|Reagent 4- Hypochlorite |10 |0 |540 |0 |SWHY |

II. Method NO3-001-A: Nitrate-Nitrite in Water, Waste Water and Soil Extracts and Other Aqueous Samples

1. SCOPE AND APPLICATION

This method is applicable to surface, drinking, ground, and saline waters, and domestic and industrial wastes. The applicable range of this method is 0.01 – 2 mg N/L (nitrate-nitrite nitrogen). This method is based on EPA Method 353.2 Revision 2.0 (1993) and Standard Methods 4500 NO3F, 18th and 19th Editions.

2. SUMMARY OF METHOD

This method determines the combined nitrate (NO3)1- + nitrite (NO2) 1- present in the sample. This sum is also known as total oxidized nitrogen (TON) and also referred to as (NOx) 1-.

Nitrate is reduced to nitrite by passage of a sample through an open tubular copperized cadmium redactor (OTCR). The resulting nitrate plus any nitrite originally present in the sample is then determined as NO2 by diazotizing with sulfanilamide followed by coupling with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a highly colored azo dye, which is measured colorimetrically at 520 or 550 nm.

Nitrate concentrations can be determined by subtracting the nitrite concentrations determined by SMARTCHEM® 170/200 Method NO2-001-A (Rev: May 2011) from the TON-(NOx) determined by this method.

3. REAGENTS AND STANDARDS

3.1. Reagent Water: Distilled or de-ionized water, free of the analyte of interest, ASTM type I or type II.

3.2. Color Reagent: To approximately 150 mL of reagent water add 25 mL concentrated phosphoric acid H3PO4 (CASRN 7664-38-2). Cool to room temperature and then add and dissolve 10.0 g of sulfanilamide 4-NH2C6H4SO2NH2 (CASRN 63-74-1). Add 0.5 g of N-(1-napthyl)ethylenediamine dihydrochloride C10H7NHCH2CH2HN2∙2HCl (CASRN 1465-25-4) and dissolve. Add 2.0 mL of concentrated Probe Rinse Solution (Unity Part Number 3AS-RN00-21) and dilute to 250 mL with reagent water. Invert five times to mix. Store in a dark glass or plastic container and away from heat (in the refrigerator). This buffer solution is used as Reagent 2 in this method. This solution is stable for several months.

3.3. Ammonium chloride-EDTA buffer solution: Dissolve 85 g of reagent grade ammonium chloride NH4Cl (CASRN 12125-02-9) and 0.1 g of disodium ethylenediamine tetraacetate C10H14N2Na2O8∙2H2O (CASRN 6381-92-6) in approximately 900 mL of reagent water in a beaker. Adjust the pH to 8.5 with concentrated ammonium hydroxide NH4OH (CASRN 1336-21-6), transfer to 1000 mL volumetric flask and dilute to one liter. Invert five times to mix. This buffer solution is used as Reagent 1 in this method. Store at room temperature and make fresh every 2 months.

3.3.1. Nitrate module reservoir buffer solution (30%): Dilute 300 mL of the ammonium chloride-EDTA buffer solution (Section 3.3) to 1 liter with reagent water in a 1000 mL beaker. Adjust the pH of this diluted buffer solution to 8.5. This solution is used to flush the OTCR between sample analysis and is not used in the reaction chemistry.

3.4. Stock Nitrate solution (1000 mg/L NO3-N): Dissolve 0.7218 g of potassium nitrate KNO3 (CASRN 7757-79-1), oven dried at 100-105°C for 24 hours, in reagent water and dilute to 100 mL. Keep under refrigeration when not in use (1.0 g/L NO3-N; 1 mL = 1.0 mg NO3-N).

3.4.1. Working Standard Solution (0.5 mg/L NO3-N): Transfer 0.05 mL of Nitrate Stock Solution (Section 3.4) to a volumetric flask and dilute to 100 mL with reagent water. Refrigerate solution when not in use. Solution should be prepared fresh every two to three days.

3.5. Stock Nitrite solution (1000 mg/L NO2-N): Dissolve 0.4926 g of sodium nitrite NaNO2 (CASRN 7632-00-0) in 90 mL of reagent water and dilute to 100 mL. Keep under refrigeration when not in use (1.0 g/L NO2-N; 1 mL = 1.0 mg NO2-N).

3.5.1. Working Standard Solution (0.5 mg/L NO2-N): Transfer 0.05 mL of Stock Solution (Section 3.5) to a volumetric flask and dilute to 100 mL with reagent water. Refrigerate solution when not in use. Solution should be prepared fresh every two to three days.

3.6. Cuvette cleaning solution: Add 15 mL of Cuvette Cleaning Solution and dilute to 1 L with reagent water. Store the solution at room temperature.

3.7. Probe rinse solution: Add 0.5 mL of Probe Rinse Solution (Unity Part Number 3AS-RN00-21) to 1 L of reagent water. Store the solution at room temperature.

4. PROCEDURE

4.1. The 550 nm filter is used in this method.

4.2. This method does not use Sample Blanking.

4.3. The total volume of sample+ Reagent 1(buffer solution) used for Nitrate Reduction must be 304 μL.

4.4. Parameter file details:

|Method Code: LNOX |Volume |Delay Time |Read Time |Rinse Volume |Reagent |

|(low range modification) |μL |Sec. |Sec. |μL |Code |

|NO3 volume |304 | | | | |

|Reagent 2- Color Reagent |78 |0 |342 |0 | |

III. Method PHO-001-A: Phosphorus, All Forms, Orthophosphate, Hydrolyzable, and Total in Water, Waste Water and Soil Extracts and Other Aqueous Samples

1. SCOPE AND APPLICATION

This method covers the determination of specified forms of phosphorus in drinking, surface and saline waters, domestic and industrial wastes. The method is based on reactions that are specific for the orthophosphate ion. Although this method is designed for the determination of orthophosphate only, other phosphorus compounds can be converted to the reactive forms by various sample pretreatments described in Standard methods 18th and 19th Edition, Sections 4500-P.B.1, 2 , and 5. The working range for this method is 0.01 to 1.00 mg P/L. This method is based on EPA Method 365.1, Revision 2.0 (1993).

2. SUMMARY OF METHOD

Ammonium molybdate and antimony potassium tartrate react in an acid medium with dilute solutions of phosphorus to form an antimony-phospho-molybdate complex. This complex is reduced to an intensely blue-colored complex by ascorbic acid. The color measured at 880 nm is proportional to the phosphorus concentration.

Only orthophosphate forms a blue color in this test. Polyphosphates (and some organic phosphorus compounds) may be converted to the orthophosphate form by manual sulfuric acid hydrolysis. Organic phosphorus compounds may be converted to the orthophosphate form by manual persulfate digestion.

3. REAGENTS AND STANDARDS

PREPARE AND STORE ALL REAGENTS IN ACID WASHED CONTAINERS!

3.1. Reagent Water: Distilled or de-ionized water, free of the analyte of interest, ASTM type I or type II.

3.2. Sulfuric acid solution, 5N: Slowly add 70 mL of concentrated H2SO4 (CASRN 7664-93-9) to approximately 400 mL of reagent water. Cool to room temperature and dilute to 500 mL with reagent water. Can store indefinitely; store under fume hood.

3.3. Potassium antimonyl tartrate solution (0.3%): Dissolve 0.3 g potassium antimonyl tartrate hemihydrate K(SbO)C4H4O6 ∙1/2H2O (CASRN 28300-74-5) in approximately 50 mL reagent water in a 100 mL vometric flask, dilute to volume. Store under refrigeration in an amber glass bottle.

3.4. Ammonium molybdate solution (4 %): Dissolve 4 g ammonium molybdate tetrahydrate (NH4)6Mo7O24∙4H2O (CASRN 12054-85-2) in reagent water in a 100 mL flask; bring up to volume. Store under refrigeration in an acid washed plastic bottle.

3.5. Sodium dodecyl sulfate (SDS) 15% w/w: Use only purest grade. Phosphate concentration in the SDS reagent should be ≤0.0001%. Dissolve 15 g SDS CH3(CH2)11OSO3Na (CASRN 151-21- 3) in 85 mL reagent water. DO NOT make to 100 mL; use only 85 mL of water to make this. Store in a glass bottle at room temperature.

3.6. Color reagent for Orthophosphate Determination: Mix the above reagents in the following proportions for 100 mL of the mixed reagent: 50 mL 5N H2SO4 (Section 3.2), 5 mL antimony potassium tartrate solution (Section 3.3), 15 mL ammonium molybdate solution (Section 3.4), and 5 mL 15% w/w SDS (Section 3.5) and 25 mL reagent water (Section 3.1). Mix after addition of each reagent. Store in an acid washed amber plastic bottle at room temperature. Do not refrigerate the mixed color reagent solution containing SDS. It is recommended that this solution be prepared fresh monthly. This solution will serve as Reagent 2.

3.7. Ascorbic acid (0.1M): Make this solution in a 50 mL centrifuge plastic tube. Dissolve 0.9 g ascorbic acid C6H8O6 (CASRN 50-81-7) in approximately 40 mL reagent water; dilute to volume. Add 0.5 mL 15 % SDS (Section 3.5) and swirl gently to mix minimizing foaming. Prepare this solution fresh daily. This solution will serve as Reagent 3.

3.8. Stock phosphorus solution (100 mg/L): Dissolve 0.04393 g pre-dried (105°C for 1 hour) KH2PO4 (CASRN 7778-77-0) in reagent water and dilute to 100 mL in a volumetric flask. Store under refrigeration when not in use; can store up to 2 months.

3.9. Working standard solution (0.5 mg/L): Transfer 0.5 mL of the Stock Phosphorus solution (Section 3.8) to a clean 100 mL volumetric flask; dilute to volume with reagent water. Can store for 2-3 days, under refrigeration.

3.9.1. Phosphorus Spike Solution (1.0 mg/L): Transfer 1.0 mL of the Stock Phosphorus solution (Section 3.8) to a clean 100 mL volumetric flask; dilute to volume with reagent water. Can store for 2-3 days, under refrigeration.

3.10. Cuvette cleaning solution: Add 15 mL of Cuvette Cleaning Solution and dilute to 1 L with reagent water. Store the solution at room temperature.

3.11. Probe rinse solution: Add 0.5 mL of Probe Rinse Solution (Unity Part Number 3AS-RN00-21) to 1 L of reagent water. Store the solution at room temperature.

3.12. Reagent Diluent for Orthophosphate: Add 1.0 mL of 15% w/w SDS (Section 3.5) to 49 mL Reagent water (Section 3.1) in a plastic 50 mL centrifuge tube. Invert five times to mix. This reagent should be prepared fresh daily. This solution will serve as Reagent 1.

4. PROCEDURE

4.1. The 880 nm filter is used in this method.

4.2. This method does not use Sample Blanking.

4.3. Parameter file details:

|Method Code: WP2W |Volume |Delay Time |Read Time |Rinse |Code |

| |μL |sec. |sec. |μL | |

|Sample |310 | | | | |

|Reagent 2- Color Reagent |37 |0 |0 |0 |MOL1 |

|Reagent 3- Ascorbic Acid |16 |0 |306 |0 |ASC1 |

IV. SIL-001-1: Silica in Water, Waste Water and Soil Extracts

and Other Aqueous Samples (Low-Range Method Version)

1. SCOPE AND APPLICATION

This method covers the analysis of silica in drinking water, surface and saline waters, domestic and industrial waters, and soil extracts. The applicable range of the method is from 0.01 to 20 mg/L SiO2. Various analytical ranges can be used by modifying the reagents used. This method is based on USGS I-2700-85 and Standard Methods 4500-Si-F 18th and 19th Editions.

2. SUMMARY OF METHOD

Silica reacts with molybdate reagent in acid media to form a yellow silicomolybdate complex. Oxalic acid is added to destroy the molybdophosphoric acid, but not the molybdosilicic acid. The molybdosilicic complex is reduced by ascorbic acid to form the heteropoly blue complex. The color complex is then measured at 880 nm.

The possibility of having “un-reactive” silica is greater in waters containing high concentrations of silica than in waters containing low concentrations of silica. When significant amounts of un-reactive silica are known to be present, a 1-hour digestion of a 50 mL sample with 5.0 mL of 1.0 M NaOH is suggested as a means of making all the silica available for the reaction with the molybdate reagent.

3. REAGENTS AND STANDARDS

3.1. Reagent water: Distilled or deionized water, free of the analyte of interest, ASTM type I or type II.

3.2. Sulfuric acid, H2SO4, 0.2 N: Carefully add 5.6 mL of concentrated sulfuric acid H2SO4 (CASRN 7664-93-9) to approximately 500 mL of reagent water in a 1 L volumetric flask; allow the solution to cool, and then dilute to 1 L with reagent water. Store this solution in a plastic container.

3.3. Ammonium molybdate reagent: Dissolve 2.0 g ammonium molybdate tetrahydrate (NH4)6Mo7O24σ4H2O (CASRN 12054-85-2) in approximately 80 mL of 0.2 N H2SO4 (Section 3.2). Add 0.4 mL of 15 % (w/w) SDS solution (Section 3.7) and dilute to 100 mL with 0.2 N H2SO4. Gently invert 5 times to mix. Store this reagent in an amber plastic bottle. Make fresh every one to two weeks. This is reagent 1.

3.4. Oxalic acid solution: Dissolve 2.5 g oxalic acid dehydrate H2C2O4σ2H2O, (CASRN 6153-56-6) in approximately 40 mL of reagent water in a 50 mL centrifuge tube, and then dilute to the 50 mL mark with reagent water. Store this reagent in a plastic bottle. Make fresh weekly. This is reagent 2.

3.5. Ascorbic acid reducing agent: Dissolve 1.75 g of ascorbic acid C6H8O6 (CASRN 50-81-7) in approximately 40 mL of reagent water in a 50 mL centrifuge tube. Add 0.25 mL of 15 % SDS (w/w) solution (Section 3.7) and dilute to 50 mL with reagent water. Gently invert 5 times to mix. Prepare this reagent fresh daily. This is reagent 3.

3.6. Stock silica solution: Dissolve 0.473 g sodium metasilicate nonahydrate Na2SiO3σ9H2O (CASRN 6834-92-0) in approximately 90 mL reagent water. Dilute to 100 mL, mix, and transfer to plastic bottle for storage. Can store for up to 2 months under refrigeration.

3.6.1. Working silica standard (10 mg/L SiO2): Transfer 1 mL of the stock silica solution (section 3.6) to a clean 100 mL volumetric flask; dilute to volume with reagent water. Transfer and store to a plastic bottle. Make fresh every 2 to three days. This solution is also used as a spike.

3.7. Sodium dodecyl sulfate (SDS) 15% w/w: Use only purest grade. Phosphate concentration in the SDS reagent should be ≤0.0001%. Dissolve 15 g SDS CH3(CH2)11OSO3Na (CASRN 151-21- 3) in 85 mL reagent water. Store in a glass bottle at room temperature; can store up to one year.

3.8. Cuvette cleaning solution: Add 15 mL of Cuvette Cleaning Solution and dilute to 1 L with reagent water. Store the solution at room temperature.

3.9. Probe rinse solution: Add 0.5 mL of Probe Rinse Solution (Unity Part Number 3AS-RN00-21) to 1 L of reagent water. Store the solution at room temperature.

4. PROCEDURE

4.1. The 880 nm filter is used in this method.

4.2. This method does not use Sample Blanking.

4.3. Parameter file details

|Method Code: WSIL |Volume |Delay Time |Read Time |Rinse |Code |

| |μL |sec. |sec. |μL | |

|Sample Volume |128 | | | | |

|Reagent 2- Oxalic Acid |151 |144 |0 |0 |SIOX |

|Reagent 3- Ascorbic Acid |73 |0 |342 |0 |LSIA |

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