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Wet Chemistry Analysis an Introduction William Lipps OI Analytical Contents • Introduction • Laboratory Techniques • Titration • ISE • Manual Colorimetry • Automated Chemistry • CFA • Discrete Analyzers • Methods • Ammonia • Nitrate • Total Nitrogen • Phosphorus • TOC • Cyanide Treatment after the CWA Formation of inorganic nutrients from secondary treatment Carbohydrate CO2 + H2O Protein Amino Acid NH3 + PO4 + SO4 NH3 NO2 NO3 The release of nutrients has resulted in large “dead zones” Nitrogen in the environment 78% Atmosphere = N2 Organic Matter (OM) is ~ 5% N Fertilizer either NH4+, NO3-, Urea or OM > 90% Soil N is in the OM NH4+ adsorbs to clay NO3- readily leaches into water Nitrogen Reactions of Environmental Significance R-NH2 NH3 (NH2)2CO + H2O CO2 + NH3 NH4+ + 3 O2 2 NO2- + 4 H+ 2 NO2- + O2 2 NO3- Phosphorus in the environment Found in soil as insoluble compound Always in compound state (PO4-3, HPO4-2, H2PO4-) Organic P is not bioavailable Most stable as PO4-3 (or HPO4-2 and H2PO4-) Soluble P encourages algae growth Phosphorus in the environment • Polyphosphates improve soap quality • No federal ban • State bans Gathering of Data requires testing Laboratory techniques used for the determination of environmental contaminants • Titration • Ion Selective Electrode • Manual Colorimetry • Automated Wet Chemistry Neutralization Titration VC=VC Neutralization Titration Acid – Base Reactions Acid + Base = Salt + Water HCl + NaOH = NaCL + H2O Low pH + High pH = Neutral Solution For more information about titrations: http://preparatorychemistry.com/Bishop_Titration. htm http://www.dartmouth.edu/~chemlab/techniques/ti tration.html Ion Selective Electrodes (ISE) The importance of the Reference Electrode is often overlooked The silver/silver chloride reference is the most common for ISE measurements ISE measurements require calibration Must prepare stock solutions Must prepare a range of Calibrants Must dilute distillates to a known volume Routine operation of ISE direct potentiometry pH/ISE meter ± 0.2mV or better Stir at constant rate – no vortex Standards and samples at constant temperature Calibration with standards is necessary Cal 1 = 1 mg/L Cal 2 = 10 mg/L Cal 3 = 100 mg/L ISE Calibration Manual Colorimetry Derivation of Beer’s law A = abc, where: A = amount of intoxication a = alcohol type (beer, wine, liquor, etc) b = bottle size c = cups consumed Manual Colorimetry measurements use Beer’s law Change in slope as a result of a or b The real explanation of Beer’s Law A = abc A = Absorbance a = molecular absorptivity b = path length c = concentration Absorbance is a measurement of the decrease of light transmitted Relationship of Absorbance and % Transmission Spectrophotometers detect an absence of light Automating Wet Chemical Analysis Advantages to Automation Save Time Decrease Cost Improve Quality Decrease Waste Economic Advantage to Automation More Samples = More Money Common Laboratory Items are automation Magnetic Stirrers Auto-filling burettes Vacuum Filtration Bottle top dispensers Almost any method can be automated Ammonia Nitrate/Nitrite TKN Phosphate Total Phosphorus Automation minimizes error from manual methods Criteria for Automation Easy to Use Better Results Lower cost Less reagent/waste Reagent Use in milliliters Questions to ask yourself as you consider automation Will I have a lot of samples for the same test? Will I have a lot of tests on the same sample? In continuous flow, reagents are propelled by a pump through tubing and a detector Flow Injection Analysis, or FIA, injects sample into flowing reagent stream In FIA the sample and reagent never completely mix The sample disperses into and reacts with reagents as it travels down the tubing The longer the tubing, or slower the flow rate, the greater the dispersion Segmented Flow Analysis inserts air bubbles to decrease dispersion Segmented Flow Analysis, SFA, uses evenly spaced air bubbles to minimize dispersion Air segments prevent dispersion of sample allowing longer times for chemical reactions SFA results in higher throughput for analyses with long reaction times SFA completely mixes sample and reagent and makes it possible to bring reactions to completion Fast reacting chemistries are essentially equivalent whether SFA or FIA Slow chemical reactions have need longer dwell times to increase absorbance Heating can speed a slow reaction making FIA possible Reaction Time and Matrix Interference SFA determines sample volume by aspiration time; it is never absolute Comparison of SFA and FIA SFA FIA Startup time 15 minutes 15 minutes Non- Reagent System Segmented Segmented Conduits 0.034 – 0.050” 0.020 – 0.034” Sample Peristaltic Valve Introduction pump Summary of SFA and FIA SFA FIA Sample intro time loop Volume ~200 µL ~200 µL Max delay time 10 minutes 1 - 2 minutes Sample/hour 40 - 90 30 - 120 RSD < 2% < 2% Reagent (mL) 2 - 3 2 - 4 Interpreting an SFA Flow Diagram The Discrete Analyzer Discrete analyzers combine sample and reagents and move hardware to detector Discrete analyzers with flow-cells react sample and reagent in cuvette, then pump through a flow-cell Potential Carryover – not samples, but reagents from one test to next Test Reagent Phosphate, Nitrate-Nitrite Ammonia Phosphate/TP Ammonia TKN Phosphate Ammonia Phenol Comparison of Discrete and CFA Discrete CFA Continuously Reagents per test flowing Need wash Carryover None solution Function of # Determined by Throughput reagents peak width Comparison of Discrete and CFA SFA or FIA Discrete Continuous or Mode Batch batch Selective no yes Random no yes Fast yes no For more information on CFA or Discrete Analyzers Ewing’s Analytical Instrumentation Handbook, Second Edition Ewing’s Analytical Instrumentation Handbook, Third Edition Automatic Chemical Analysis by Peter B Stockwell Dissolved Nitrogen Compounds TDN – Total Dissolved Nitrogen Includes NO3, NO2, NH3 as DIN Includes soluble organics as DON TDN = DON + DIN TDN = DON + NO3+NO2+NH3 TDN = DIN (POTW effluents) DON = ~ 60 – 69 % of TDN (lakes, rivers, oceans)* * Worsfold, and others, Characterization and quantification of organic phosphorus and organic nitrogen components in aquatic systems: A review, Analytica Chimica Acta 624 (2008) 37-58 Analysis of Dissolved Nitrogen Compounds Filter preserved sample Analyze TDN Analyze DIN NO3 + NO2 NH4 DON = TDN - DIN Inorganic nitrogen analysis requires two methods Ammonia nitrogen Nitrate plus nitrite nitrogen Measured separately then added together The determination of Ammonia Nitrogen • Distillation • Titration • Manual Colorimetry • Automated Colorimetry • Diffusion Titration of Ammonia requires a preliminary distillation Distribution of Ammonia with pH 120 100 80 % 60 NH4+ NH3 40 20 0 pH 5 6 7 8 8.5 9 9.5 10 10. 11 12 13 14 5 Ammonia Titration NH3 + HCl NH4CL Excess HCL NaOH + HCl NaCl + H2O 5 NH3 + 10 HCL = 5 NH4CL + 5 HCl Titrations do not require knowledge of final volume or calibration curves Example Calculation: Sample Volume distilled = 50 Milliliters Normality of base = 0.02 ppm NH3-N = ((mL blank titration – mL sample titration)/ liter sample distilled) N base x 15 mg N ((10-5)/0.05) x 0.02 x 14 = 28 mg N/L What is an approximate detection limit for ammonia by titration? Example Calculation: Sample Volume distilled = 50 Milliliters Normality of base = 0.02 ppm NH3-N = ((mL blank titration – mL sample titration)/ liter sample distilled) N base x 15 mg N ((10-9.95)/0.05) x 0.02 x 14 = 0.28 mg N/L Things to remember about the Ammonia Titration No need for Standard Ammonia Solutions No calibration curve Final distilled volume not needed Need accurately standardized acid and base reagents Distillation required! Direct determination of Ammonia by ISE Routine operation of ISE direct potentiometry for Ammonia Accurate Stock Solution Calibration Standards = differ by factors of 10 Calibrate from low to high Immerse probe, then add ISA Best guess at low concentrations. Ionic Strength Adjustment (ISA) brings pH above 11 Measure 100 mL sample, add stir bar Immerse probe at 20° angle Add 2 mL ISA Readings > 0.5 ppm in 30 seconds Lower concentrations in 5 minutes Quality Control Requirements for Ammonia by ISE # Standards 3 or more Midrange CCV ± 15% LCS ± 15% Method Blank < 0.5 X lowest calibrant Routine operation of ISE direct potentiometry for Ammonia Membrane – must not be torn Ensure there is filling solution Volatile amines interfere For more information on direct potentiometry for Ammonia http://www.coleparmer.com/TechLibraryArticle/971 Ammonia Analysis – Manual Berthelot Reaction 2012 MUR includes Manual Phenate method Requires distillation Citrate buffer minimize precipitation of Ca & Mg Phenol dissolved in alcohol Reagents for the manual phenate ammonia method Phenol Reagent - 11 milliliters liquid phenol in 100 mL ethanol Prusside – 0.5 grams Sodium Nitroferricyanide in 100 mL Stock Complex Reagent – 200 g trisodium citrate + 10 gram NaOH per liter Oxidizing Reagent – 100 mL Stock Complex reagent and 25 mL 5% Hypochlorite Stability of the manual phenate ammonia reagents Phenol Reagent – weekly Prusside – 1 month Stock Complex Reagent – 1 year 5% Hypochlorite – 2 months Oxidizing Reagent - daily Order of Reagent addition and method steps 1. 25 milliliters of sample 2. 1 milliliter phenol reagent 3. 1 milliliter prusside 4. 2.5 milliliter Oxidizing reagent 5. Incubate at room temperature for 1 hour 6. Read absorbance at 640nm Quality Control Requirements for Ammonia by manual phenate # Standards 4 or more Midrange CCV ± 10% LCS ± 10% Method Blank Below MDL Ammonia Analysis – Automated Berthelot Reaction Requires distillation (2012 MUR) EDTA minimizes precipitation of Ca & Mg, no buffer Phenol dissolved in strong NaOH Reagents for the automated phenate ammonia method Phenol Reagent – 83 g phenol + 32 g NaOH in 1000 mL reagent water Prusside – 0.5 grams Sodium Nitroferricyanide in 1000 mL reagent water EDTA Reagent – 50 g disodium EDTA + 3 gram NaOH per liter Oxidizing Reagent – 50 mL 5% Bleach + 50 mL reagent water Stability of the automated phenate ammonia reagents Phenol Reagent – 1 month Prusside – 1 month EDTA Reagent – 1 year 5% Hypochlorite (Bleach) – 2 months Oxidizing Reagent - daily Order of Reagent addition and method steps for the automated phenate method 1. 1.2 ml/min EDTA 2. 0.42 ml/min sample 3. 0.42 ml/min phenate 4. 0.32 ml/min oxidizing reagent 5. 0.42 ml/min prusside 6. Heat at 50°C and read at 640nm EDTA, the complex reagent for EPA 350.1 interferes Overcoming EDTA interference with automated phenate (EPA 350.1) 50 grams disodium EDTA = 0.13 M 0.13 M x 0.8 ml/min divided by 1.22 ml/min sample + EDTA = 0.085 M EDTA 0.085 M EDTA x 40 g Ca /Mol x 1000 mg/g = 3,400 mg Ca / L (Hardness = 8,500 mg/L) 5 grams EDTA will complex 340 ppm Ca Overcoming EDTA interference with automated phenate (EPA 350.1) Replace EDTA with Sodium Citrate 0.5 M Citrate will complex more Ca + Mg Quality Control Requirements for Ammonia by automated phenate # Standards 3 or more Midrange CCV ± 10% LCS ± 10% Method Blank Below MDL Order of reagent addition – phenate ammonia methods Manual Automated 1 phenol EDTA 2 prusside phenolate Combined 3 oxidizer and oxidizer citrate 4 prusside Preliminary distillation or diffusion is required for ammonia 40 CFR Part 136.3 and 136.6 allows modifications that can improve EPA 350.1 Diffusion in place of Distillation Citrate in place of EDTA Salicylate in place of Phenol Completely automated and Part 136.3 approved The May 18, 2012 40 CFR Part 136 Method Update approves diffusion Diffusion = Distillation Gas Diffusion equally replaces distillation in all methods requiring distillation Passive Micro Diffusion using Conway diffusion cells is allowed Manual pervaporation is allowed Automated Diffusion using continuous flow analysis is allowed Automated gas diffusion selectively passes uncharged molecules through a membrane Donor and acceptor solutions travel through channels separated by a membrane Diffusion separation and chemical determination combined in one step EPA 350.1 Ammonia Nitrogen by Gas Diffusion Colorimetry EPA Modified Manual distillation Automated Diffusion Phenolate Salicylate EDTA Citrate 0.01 – 2.0 ppm 0.01 – 20 ppm Order of reagent addition – phenate ammonia methods including gas diffusion Manual Automated GD 1 phenol EDTA Citrate 2 prusside phenolate oxidizer Combined Combined prusside 3 oxidizer and oxidizer and citrate salicylate 4 prusside Important facts on ammonia phenate methods NH3 + HOCL H2NCL + H2O (pH 11) Phenolate reaction pH 11 Salicylate reaction pH 12.8 Troubleshooting automated ammonia analysis Symtom Possible cause Contaminated wash Negative peaks or samples too acid Poor peak shape Check pump tubes No peaks Check reagents Low spike recovery Metals in matrix Comparison of NH3-N methods demonstrates better precision by automation Technique % RSD @ 0.4 ppm N Titration 50 ISE 30 Manual Spectrometry 2 SFA/FIA 1 Techniques for the analysis of Nitrate Nitrogen Nitrate + Nitrite MDL (mg/L) Manual Cadmium Reduction 0.01 Auto-Cadmium Reduction 0.001 Auto-hydrazine Reduction 0.01 Systea (ATP) 0.01 Reductase 0.01 Nitrate Manual Brucine 0.1 Ion Selective Electrode 0.14 Ion Chromatography 0.002 Direct determination of Nitrate by Ion Selective Electrode Routine operation of ISE direct potentiometry for Nitrate Accurate Stock Solution Calibration Standards = differ by factors of 10 Calibrate from low to high Immerse probe, then add ISA Best guess at low concentrations. Ionic Strength Adjustment (ISA) brings pH below 3 Measure 10 mL sample, add stir bar Immerse probe Add 10 mL ISA Low concentration = long response time Ionic Strength Adjustment (ISA) contains: AgSO4 to remove Cl-, Br-, I-, S-2, CN- Sulfamic acid to remove NO2- pH 3 adjusts to remove HCO3- Al2(SO4)3 to complex organic acids The nitrate ISE requires a double junction reference electrode (NH4)2SO4 Quality Control Requirements for Nitrate by ISE # Standards 3 or more Midrange CCV ± 10% LCS ± 15% Method Blank < 0.5 X lowest calibrant Suggested QC requirements Routine operation of ISE direct potentiometry for Nitrate Membrane – must not be torn Calibrate from low to high Keep probe tips moist The manual determination of Nitrate +Nitrite Reduce NO3-N to NO2-N Measure NO2-N Nitrate Nitrogen is calculated by difference NOx-N – NO2-N = NO3-N Methods for the determination of nitrate plus nitrite Method Technique MDL (mg/L) Cd 353.2 0.01 Reduction Cd 4500 NO3 E 0.01 Reduction Hydrazine 4500 NO3 H 0.01 Reduction Nitrate + Nitrite by Cadmium Reduction NO3- + Cd0 + 2H+ NO2- + Cd+2 + H2O Chemistry of Reaction = reduction by cadmium Nitrite measured by Greiss Reaction Nitrate + Nitrite by manual Cadmium Reduction Interferences for the manual nitrate plus nitrite by cadmium reduction method Suspended solids Oil & Grease Residual Chlorine Metals (Cu+2, Fe+2, Mn+2) S-2 Activation of the Cadmium Granules 1. Rinse with 1+1 HCL 2. Rinse with water 3. Swirl with 2% CuSO4 solution 4. Decant and repeat till colloidal copper develops 5. Rinse with buffer until all copper is gone 6. Keep metal in buffer Preparation of sample solutions 1. Dilute 25 mL sample with 75 mL Buffer 2. Pass ½ through column to waste 3. Collect next half 4. Add 2 mL color reagent to the 50 mL sample 5. Read abs at 540 nm Quality Control Requirements for Nitrate by manual cadmium reduction # Standards 5 or more Midrange CCV ± 10% LCS ± 10% Reduction Efficiency > 75% Method Blank Below MDL Nitrate + Nitrite by Automated Cadmium Reduction Interferences for the automated nitrate plus nitrite by cadmium reduction method Suspended solids Oil & Grease Residual Chlorine Metals (Cu+2, Fe+2, Mn+2) S-2 Dissolved Oxygen Activation of the Cadmium Coil 1. Rinse with 0.5M HCL 2. Rinse with water 3. Pass 10 mL 1+ 1 2% CuSO4 solution and Imidazole Buffer through coil at 1 mL per minute 4. Rinse with Imidazole Buffer till all blue color is gone 5. Store with Imidazole buffer in tube Order of Reagent addition and method steps for the automated cadmium reduction method 1. 1.2 ml/min Buffer 2. 0.32 ml/min sample 3. 0.32 ml/min color reagent 4. Read at 540nm Differences between reduction columns OTCR PBCR Requires segments No segments Low surface area High surface area SFA – no debubble SFA - debubble FIA - bubble FIA – no bubble Quality Control Requirements for Nitrate by automated cadmium reduction # Standards 5 or more Midrange CCV ± 10% LCS ± 10% Reduction Efficiency > 90% Method Blank Below MDL Examples of approved modifications that can be made to improve performance Item Purpose Alternative Buffer and Ammonium complex Imidazole Chloride/EDTA reagent pH 7.5 minimize Minimize over- pH 8.5 Cd(OH)2, no reduction over-reduction Reduce NO3 to Cd granules Cd coil NO2 Cadmium also Reacts with Oxygen 2Cd° + O2 + 4H+ 2Cd+2 + 2H2O Cadmium reacts with dissolved oxygen faster than with nitrate Dissolved oxygen in samples and reagents the major source of Cd in waste Up to 220 ppm Cd+2 when not degassed* (decreased to ~ 2 ppm when degassed) * Gal, Frenzel, and Moller, Re-examinationof the cadmium Reduction Method and Optimization of the Conditions for the Determination of Nitrate by Flow Injection Analysis, Microchim Acta 146, 155-164, 2004 Nitrate reductase is a potential alternative to cadmium reduction Selective Benign Homogeneous reaction List of abbreviations for environmental nitrogen DIN – Dissolved Inorganic Nitrogen DON – Dissolved Organic Nitrogen TON – Total Organic Nitrogen PN – Particulate Nitrogen PON – Particulate Organic Nitrogen TDN – Total Dissolved Nitrogen TN – Total Nitrogen TIN = DIN Total Nitrogen Compounds TN – Total Nitrogen Includes NO3, NO2, NH3 as DIN Includes soluble organics as DON Includes particulate nitrogen as PN TN = DON + DIN + PN PN = PON TN = DON + PON + NO3+NO2+NH3 TKN = PON + DON + NH3 EPA definition of total nitrogen Measuring organic nitrogen requires a TKN and ammonia analysis TKN is a “classical” analysis of total nitrogen TKN includes Organic Nitrogen Ammonia Nitrogen (NH3-N) TKN does not include Nitrate Nitrogen (NO3-N) Nitrite Nitrogen (NO2-N) Must use 40 CFR Part 136 methods The “classical” Kjeldahl Reactions distilled and titrated ammonia Present Day TKN methods can either distill (diffuse) or measure NH4+ in the matrix The block digester methods for TKN do not require distillation Sodium Citrate is a better complexing agent Salicylic acid method Blue color measured at 640 – 660 nm Continuous Flow or Discrete Analyzer methods. Digest multiple samples on a block and analyze them automatically Faster than titration Results in minutes Easy repeat of questionable results Dilute off scale samples No distillation Operational Comparison of TKN methods Manual Digestion Require final Require final & Distillation digest volume distillate volume Followed By: Titration no no Ion Selective no yes Electrode Manual Phenate no yes Automated no yes Phenate Block Digestion Automated yes N/A Salicylate Techniques for the analysis of Total Nitrogen (EPA only approves TKN) Manual Digestion & MDL (mg/L) Distillation Followed By: Titration 1.0 Manual Phenate 0.05 ? Ion Selective Electrode 0.03 Automated Phenate 0.01 Block Digestion Automated Salicylate 0.1 Auto-GD/pH colorimetry 0.2 Auto-GD/Salicylate 0.02 Tips for a successful TKN digestion Acid wash all glassware Digest calibrants Minimize sample/reagent volumes Minimize digestion time Rinse sample cups with sample Problem -TKN does not measure nitrate, and total nitrogen includes nitrate plus nitrite Low Recovery of TKN in presence of NO3-N 120 100 % Recovery of 2.5 ppm TKN 80 60 40 20 0 0 5 20 50 ppm NO3-N Schlueter 1977 Typical N in influent and effluent Influent Effluent TKN (mg/L) 30 2 NO3-N (mg/L) 0 17 TN (mg/L) 30 19 Minimize digestion time to maximize recovery when nitrate is present 1. 25 mL sample 2. 10 mL digestion reagent 3. 5 stones 4. 160° C for 1 hour 5. 380° C for 30 minutes 6. Cool, rinse sides, cool 7. Dilute to 25 mL (or 50 mL) Tips for a successful TKN analysis by direct colorimetry Connect buffer line prior to color reagent Make sure pH exiting flow-cell is >12 Connect color reagent and watch baseline rise Closely match carrier or wash matrix to sample With EPA allowed method modifications, both ammonia and TKN can be determined with the same CFA method EPA 351.2 TKN by Gas Diffusion Colorimetry EPA Modified Direct Colorimetry Automated Diffusion Salicylate Salicylate Tartrate Citrate 0.01 – 2.0 ppm 0.01 – 20 ppm There is a need for methods that measure TN directly Low Level Organic Nitrogen Requires a TN analysis, not TKN NOx-N = NO3-N + NO2-N Analysis of Total Nitrogen Compounds Filter preserved sample for DIN Do Not filter preserved sample for TN Analyze TN Analyze DIN (DIN=TIN) NO3 + NO2 NH4 TON = TN - DIN HTCO Total Nitrogen Bound (TNb) Use TOC Analyzer 720° C reactor TOC & TNb Total Nitrogen Bound, or TNb is measured on a TOC analyzer Comparison of TNb to TKN (QC samples) Use TOC Analyzer Advantages and disadvantages of TNb Use TOC Analyzer Alkaline Persulfate Digestions for TN do not require specialized equipment Use TOC Analyzer Manually digest Determine NO3-N Measures all TN Manual Alkaline Digestion for TN can be done in an autoclave or with test tubes Comparison of TN to TNb illustrates equivalent results on samples tested Use TOC Analyzer Doyle 2004 Comparison of TN to TKN + NO3/NO2 -N Use TOC TOC Analyzer TKN + NOx TN (mg/L) (mg/L) (mg/L) Cecil 17.5 2.9 2.9 Greenville 1 36.0 3.1 3.5 Hiwassee 2 59.0 8.8 8.9 Irwin 108 17.7 16.0 Cabrera 1993 Comparison of TN to TKN with % RSD Use TOC Analyzer TKN TKN TN TN (mg/L) (%RSD) (mg/L) (%RSD) Bear Creek 0.18 10.65 0.22 5.72 Silver Fork 0.36 19.29 0.41 6.49 Salt River 0.59 25.31 0.76 3.23 Ted Shanks 0.61 25.25 1.05 6.04 Smart 1981 Advantages and disadvantages of manual TN persulfate methods Use TOC Analyzer Automated Alkaline UV Persulfate Digestions increase throughput Use TOC Analyzer Automated digest Determine NO3-N Measures TDN Comparison of Automated TN with TKN Use TOC Analyzer Unknowns regarding the efficiency of Automated UV Alkaline Digestion Particulates? Advantages and disadvantages of automated TN persulfate methods Use TOC Analyzer What samples for Total Nitrogen may look like Organic matter consumes persulfate too (NH2)2CO + 8 S2O8-2 + 18 OH- 2 NO3- + CO2 + 16 SO4-2 + 11 H2O About 100 ppm C upper limit A Humic acid molecule Particulates consume persulfate and are hard to sample ~ 15 - 20% N attached to particulates Particulates > ~ 30 ppm TSS N/A by CFA Non quantitative transfer of particulates to HTCO Fe+2 to Fe+3 = 1 e- Total Phosphorus Digestion Methods Acid Persulfate (beaker or autoclave) Kjeldahl (block digestion) Both convert inorganic and organic phosphorus to orthophosphate Acid persulfate digestion for total P can be done in a beaker, autoclave, or test tubes Comparison of Dry Ashing and Acid Persulfate for Total P Outlier data on persulfate and wet oxidation comparison for TP digestion Dry Ash Persulfate Material tested uMol P uMol P Montmorillonite 1.44 1.00 Kaolinite 22.0 3.04 Suzamura, Limnol. Oceanogr. Methods 6 2008, 619-629 Potential problems with acid persulfate digestions for total phosphorus Too much acid High chloride Organic Matter Excess particulates Contamination Advantages and disadvantages of manual acid persulfate methods for TP Use TOC Analyzer “Kjeldahl” Digestion for TP Comparison of persulfate and Kjeldahl for TP Potential problems with Kjeldahl digestions for total phosphorus High Acid Concentration Hazardous Digestion Catalyst May require dilution of acid Advantages and disadvantages of manual acid persulfate methods for TP Use TOC Analyzer Using USGS I-4690-91 to overcome problems with normal Kjeldahl phosphorus methods Uses Dialysis includes On-line dilution Includes On-line filtration Controls acid concentration Low Detection Limit Alkaline Persulfate Digestions for Total P Use TOC Analyzer Manually digest Determine PO4-3 Measures TP Manual Alkaline Persulfate Digestion for TP Comparison of Alkaline Persulfate and Acid Persulfate Total Phosphorus Alkaline Acid Compound (mg/L P) (mg/L P) Adenosine tri- 0.166 0.176 phosphate (ATP) Glycerophosphate 0.196 0.204 Phenyl Phosphate 0.168 0.179 Phytic Acid 0.177 0.180 USGS Water Resources Investigative Report 03-4174 (2003) Comparison of TKP and Alkaline Persulfate Kjeldahl and Alkaline Persulfate Phosphorus 0.35 0.3 0.25 0.2 Alkaline P 0.15 0.1 0.05 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Kjeldahl P Advantages and disadvantages of manual Alkaline persulfate method for TP Use TOC Analyzer Automated Alkaline UV Persulfate Digestions Use TOC Analyzer Automated digest Determine PO4-3 Measures TDP Advantages and disadvantages of automated persulfate method for TP Use TOC Analyzer Tips for a successful phosphorus digestion Acid wash glassware Digest standards Use disposable tubes for digestion Contamination For more information on total phosphorus digestions see: http://nwql.usgs.gov/WRIR-03-4174.shtml http://www.caslab.com/Test-Methods- Search/PDF/USGS-Method-I-2610-91.pdf Determinative Steps Ammonia Nitrate + Nitrite Nitrogen Phosphate List of abbreviations for environmental phosphorus DIP – Dissolved Inorganic Phosphorus DOP – Dissolved Organic Phosphorus FOP – Filterable Organic Phosphorus FRP – Filterable Reactive Phosphorus TOP – Total Organic Phosphorus PIP – Particulate Inorganic Phosphorus POP – Particulate Organic Phosphorus TDP – Total Dissolved Phosphorus TP – Total Phosphorus TPP – Total Particulate Phosphorus TRP – Total Reactive Phosphorus Steps for the analysis of phosphorus fractions Total P Filter Liquid Solid TDP TPP FRP Weak acid Strong Weak Acid Acid/oxidant DIP DOP POP PIP TRP TOP Calculation of the phosphorus species TP = TDP + TPP TRP = FRP DIP = hydrolysis (aq) DOP = oxidizing(aq) – DIP PIP = hydrolysis(s) POP = oxidizing(s) TIP = DIP + PIP TOP = DOP + TOP Speciation of phosphorus by digestion Compound Soluble Digestion PO4-3, HPO4-2, yes none H2PO4- [P3O10]-5 yes hydrolysis Ca5(PO4)3OH no hydrolysis Organic P yes/no Oxidizing Analytical speciation of phosphorus according to methods Soluble and Particulate filterable non-filterable Reactive Measure PO4-3 Hydrolysis Acid digestion Measure PO4-3 Total Digestion Oxidizing digestion Measure PO4-3 A simplified scheme for Phosphorus analysis based on reality Almost no one does hydrolysable P EPA permits are total P or orthophosphate EPA permits do not require speciation Analysis of Dissolved Phosphorus Compounds Filter sample Analyze Orthophosphate Manually or auto digest an aliquot Analyze orthophosphate Report as TDP Analysis of Total Phosphorus Compounds Filter sample for orthophosphate FRP = TRP Analyze orthophosphate Do Not filter preserved sample for TP Manually digest an aliquot Analyze orthophosphate Unless TP = TDP you cannot auto-digest Methods for the determination of phosphate Antimony-phosphomolybdate Reduced to Blue color (w/ ascorbic acid) A representation of the molybdenum blue reaction 7 H3PO4 + 12(NH4)6Mo7O24 + 51H+ 7(NH4)3PO412MoO3 + 51NH4+ + 51 H2O (NH4)3PO412MoO3 + Ascorbic Acid = Molybdenum Blue Complex A representation of the molybdenum blue complex Use a surfactant A key to optimum performance of your phosphate method [H+] / [Mo+6] = 74 [H+] = 0.4 to 0.7 Calculate [Mo+6] from Ammonium Molybdate (NH4)6Mo7O24 1163.9 grams per mol (NH4)6Mo7O244H2O 1235.86 grams per mol Calculate [Mo+6] from Ammonium Molybdate tetrahydrate (NH4)6Mo7O244H2O 1235.86 grams per mol g/ L X 7 [Mo+6] / 1235.86 g/L X 0.0057 = [Mo+6} in stock Molybdate Solution Calculate [Mo+6] in Ammonium Molybdate Stock Solution EPA 365.1 or SM4500 Ammonium Molybdate Stock 40 grams /L x 0.0057 = 0.228 [Mo+6] = 0.228 Calculate [H+] in Sulfuric Acid Stock Solution EPA 365.1 70 mls H2SO4 per 500 mL 70 x 36 / 0.5 L = 5.04 [H+] = 5.04 Calculate [H+] and [Mo+6] in mixed color reagent 50 ml H2SO4 x 5.04 / 100 ml = 2.52 15 ml Mo+6 x 0.228 / 100 ml = 0.0342 Calculate [H+] and [Mo+6] ratio in final solution 8 milliliters of color reagent is added to 50 milliliters of sample 8 x 2.52 / 58 = 0.347 8 x 0.0342 / 58 = 0.0047 0.347 / 0.0047 = 73.8 A suggested possibility to improve SM 4500 manual phosphate 155 ml H2SO4 /L = 5.58 M 44 g Moly / L = 0.251 M Mixed Color Reagent [H+] = 2.79 [Mo+6] = 0.0376 Ratio = 73.8 Final acid = 0.384 Chemistry is like cooking Fundamentals of all TOC analyzers Oxidize Carbon Measure CO2 All TOC analyzers have a similar operation Definitions for TOC Analysis Non specific NOM = Naturally Occurring Organic Matter Total Carbon = Inorganic Carbon + Organic Carbon Inorganic Carbon = bicarbonate and carbonate Organic Carbon = NOM Discovery of Organic Carbon and CO2 CxHx + O2 + heat CO2 + H2O CaCO3 + heat CaO + CO2 (LOI) Organic Matter and Dichromate OM + Cr2O7-2 2 Cr+3 + CO2 6 Fe+2 + Cr2O7-2 6 Fe+3 + 2 Cr+3 Combustion and Coal/Steel 1000C O2 CO2 Sample First Combustion analyzer for water samples Sample injected with syringe 1000C O2 CO2 2 – 500 ppm TOC Heated Persulfate Digestion of Water (NH2)2CO + 8S2O8-2 CO2 Break Ampoule and Measure CO2 Autoclave Ampoule Auto-sampler breaks ampoule CO2 swept into IR MDL = 0.2 mg/L TOC UV Persulfate TOC on Technicon Auto- Analyzer 4O2 + UV 8O- (NH2)2CO + 8O- CO2 (NH2)2CO + 8S2O8-2 CO2 High Temperature Catalytic Oxidation 2(NH2)2CO + 7O2 + catalyst CO2 Differences in Oxidation Techniques Speciation of TOC Organic Carbon = NPOC TOC = TC – TIC TC-TIC = NPOC Subtraction? Problems with Subtraction TOC = TC – TIC 100 ppm TC – 100 ppm TIC = 0 ppm TOC 110 ppm TC – 90 ppm TIC = 20 ppm TOC 90 ppm TC – 110 ppm TIC = - 20 ppm TOC Wet Oxidation compared to HTCO on samples containing particulates 100 90 80 70 Wet HTCO 60 mg TOC / L 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 How to really measure TOC in samples containing particulates Calculated TOC compared to Direct Injection of samples with particulates non Filtered versus Calculated HTCO 100.000 90.000 80.000 non filtered calculated 70.000 60.000 mg TOC / L 50.000 40.000 30.000 20.000 10.000 0.000 1 2 3 4 5 6 7 8 9 10 Potential problems with each TOC technique Use TOC Analyzer Cyanide Chemistry and Analysis Contents :C≡N Free Cyanide is the most toxic cyanide species Total CN is regulated because it can generate free cyanide [Fe(CN)6]-3 + H+ 6 HCN + Fe+3 You cannot manually distil Free Cyanide You cannot auto-distil Free Cyanide You cannot titrate Free Cyanide You cannot measure Free Cyanide by ISE You cannot measure Free Cyanide by Direct Colorimetry Fundamental CN Chemistry Distribution of the Industrial Uses of CN %, Other, 8, 8% %, Vitamins, 6, 6% %, Coatings, 6, 6% %, Mining, 8, 8% %, Plastics, 60, 60% %, Chemicals, 12, 12% Who is measuring cyanide? NPDES Pretreatment SDWA Industrial hygiene foods Beverages A generalized summary of cyanide and it’s metal – cyanide species Transition metals - strong bonds Alkali metals - ionic bonds Free Cyanide is the CN ion and HCN, generate HCN at pH 6 Available CN is a tetragonal coordination complex with CN ligands plus free CN Zn, Cd, Cu, Ni, Ag, Hg Total CN is a Hexagonal coordination complex with CN ligands plus available CN Cyanide methods measure the various cyanide “species” Free CN is the concentration of HCN at a defined pH The Hydrogen Cyanide Molecule = Free CN Sampling and sample preservation Store samples at 2 – 6 °C in the dark at pH 11 Sulfide reacts with free cyanide lowering its concentration Holding Time Study – Sulfide Bearing Samples 120 100 80 60 40 20 0 2 hours 24 hours 48 hours 200 ppm S + 200 ppb CN 20 ppm S + 20 ppb CN Cannot use Cadmium to Treat Sulfide % Recovery 120 100 80 60 40 20 0 Fe(III) Hg Ni Free CN % Recovery Using Headspace to Treat Sulfide % Recovery 89 84 79 74 69 64 Hg Ni Free CN Using Bismuth to Treat Sulfide prior to distillation % Recovery 120 100 80 60 40 20 0 Fe(III) Free CN Recovery of 100 ppb CN in up to 50 ppm Sulfide using on-line sulfide abatement Recovery 110 105 100 95 90 0.1 1 10 30 50 Oxidizers react with free cyanide lowering its concentration Loss of 200 ppb CN due to ascorbic acid addition 250 200 150 100 50 0 0 24 48 72 Ascorbic Acid (0.05 g/ 100ML) Sodium Arsenite (0.05 g / 100ML) Free Cyanide analysis Method Number Description Measurement Micro-diffusion at ASTM D 4282 Colorimetry pH 6 Auto-diffusion at ASTM D 7237 pH 6 Amperometry Auto-diffusion at OIA-1677-09* Amperometry pH < 2 * Use if sulfide is present Chemical reactions used to selectively analyze free cyanide NaCN + H+ Na+ + HCN HCN + OH- CN- + H2O ASTM D 4237 Micro-diffusion is a manual extraction ASTM D 4282 is an approved method for free cyanide Calibration Range 10 – 150 ppb RSD 32 ppb 3% 80 ppb 6% 144 ppb 13 % Measure absorbed cyanide by pyridine- barbituric acid colorimetry ASTM D7237 is flow injection method that automates the gas diffusion step Buffer ASTM D 7237 is an approved method for free cyanide Calibration Range 2– 500 ppb RSD 5 ppb 21 % 110 ppb 7% 500 ppb 12 % ASTM D7237 combines sample processing and analysis Comparison of D 4282 and D 7237 data shows that data is equivalent Free cyanide is toxic to aquatic life and needs to be measured ASTM D 7237 = lower detection and faster analysis times D 4282 D 7237 PQL (ppb) 10 2 Analysis time 6 hours 2 minutes diffusion manual automated detection colorimetric amperometric Available and Total Cyanide Chemistry and Analysis Methods and Interferences Manual “distillation” is used to dissociate as HCN Macro Distillation MIDI Distillations Distillation can be automated on a continuous flow analyzer Distillation and condenser Distillate Many cyanide interferences result from distillation Destroy CN Create CN UV distillation colorimetry - worst These compounds are in almost every sample and interfere significantly ASTM D7365 Challenge Matrix demonstrates positive bias of cyanide methods ppb CN detected (none in sample) 700 600 500 400 300 200 100 0 Micro dist Midi dist Macro Dist Kelada Cyanide loss from distillation with thiocyanate present % Recovery 100 90 80 70 60 50 40 30 20 10 0 20 ppm SCN- 200 ppm SCN- Cyanide loss from distillation with thiosulfate present % Recovery 70 60 50 40 30 20 10 0 20 ppm S2O3-2 200 ppm S2O3-2 Cyanide loss from distillation with sodium sulfite present % Recovery 45 40 35 30 25 20 15 10 5 0 20 ppm SO2-2 200 ppm SO2-2 Interferences with Determinative Step Titration by silver ion S -2 Cl- Ion Selective Electrode (ISE) Cl- Br- S-2 Ag+ Colorimetric methods SC N- 2 S- SO 3- C olor TDS Turbidity Gas diffusion - Amperometry CN- Membrane HCN Sulfide > 50 ppm Available Cyanide Analysis Amenable Cyanide—CATC methods measure “available cyanide” Method Description Measurement Number Alkaline Chlorination/ SM 4500-CN G Colorimetry Manual Distillation Colorimetry, Alkaline Chlorination/ ASTM D 2036 Gas Diffusion - Manual distillation Amperometry WAD Cyanide methods measure “available cyanide” Method Description Measurement Number Buffered pH 4.5 SM 4500-CN I manual Colorimetry Distillation Buffered pH 4.5 Colorimetry, manual ASTM D 2036 distillation Gas Diffusion - Amperometry Ligand Exchange methods measure available cyanide Method Description Measurement Number Ligand Exchange Gas Diffusion - OIA 1677 / Flow Injection Amperometry Analysis Ligand Exchange / Flow Injection Gas Diffusion - ASTM D 6888 Analysis Amperometry GD-amperometry methods do not require distillation Ligand Exchange GD-amperometry methods get better recovery WAD CATC OIA 1677 OIA 1677 or ASTM D6888 flow diagram Acid Reagent Ligand Exchange GD-amperometry methods have fewer interferences CATC WAD OIA 1677 Excessive N-organics None Iron Cyanide Concentration SCN,NH3,NO2 — Dependent S2O3, H2O2 — — Concentration — — Dependent Ligand Exchange GD-amperometry methods give you results in minutes CATC WAD OIA 1677 2 Sample distillations 1 distillation No distillation Preparation 2 – 3 hours 2 – 3 hours 1 – 2 Analysis minutes 1 – 2 minutes 1 – 2 minutes Total Time 3 – 4 hours 3 – 4 hours 1 – 2 minutes Total Cyanide Analysis Manual Distillation Methods Total cyanide methods using manual distillation Descriptive Method Description Measurement Name Number Midi Distillation – Automated EPA 335.4 MgCl2 Colorimetry Midi / Micro/macro Colorimetry/ISE/a Total Cyanide ASTM D2036 Distillation – mperometry/IC MgCl2 Midi / Micro Gas Diffusion - ASTM D 7284 Distillation – Amperometry MgCl2 Most total cyanide analyses are by EPA 335.4 or similar Prolonged heating strong acid (pH <2) Purging into base Colorimetry Semi-automated colorimetric cyanide analysis flow diagram Semi-Automated GD-amperometric by ASTM D7284 Automated total cyanide methods use UV to liberate HCN from Fe Descriptive Method Description Measurement Name Number High power UV- ASTM D4374 Auto distillation Automated (Kelada 01) colorimetry Alkaline pH Low power UV- Auto distillation Automated Total Cyanide EPA 335.3 Colorimetry pH <2 Low power UV- Gas Diffusion - ASTM D7511 pH <2 Amperometry hv [Fe(CN)6 ]-3 + H+ 6 HCN + Fe+3 A sample diagram of the Kelada 01 automated cyanide method A sample diagram of the EPA 335.3 automated cyanide method A sample diagram of ASTM D7511 Comparison of Kelada and ASTM D7511 Kelada 01 ASTM D7511 Pump Tubes 15 5 Reagents Pyridine No Pyridine Distillation Yes No SCN 0.25 – 0.5 % 0.01 – 0.03 % Interaction ASTM D7511-09 has fewer interferences than distillation Interfering Species 20 mg/L 335.4 D7511-09 Nitrite 0.203 0.198 Sulfite 0.08 0.199 Chlorine 0.120 0.118 Thiosulfate 0.124 0.196 Thiocyanate 0.174 0.208 Sulfide 0.120 0.189 * Cyanide added at 0.200 mg/L (EPA MCL SDWA) ASTM D7511 recovers less CN from the ASTM “challenge matrix” ppb CN detected (none in sample) 700 600 500 400 ppb CN 300 200 100 0 D7511 Micro dist Midi dist Macro Dist Kelada Thank You!! William Lipps OI Analytical William.email@example.com
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