1. Phosphorus Measurements ä The Technique ä Detection Limits ä Wallastonite ä The Technique ä Detection Limits ä Wallastonite 

2. Ascorbic Acid Technique ä Ammonium molybdate and antimony potassium tartrate react in an acid medium with orthophosphate-phosphorus to form an antimony-phospho-molybdate complex. ä This complex is reduced to an intensely blue-colored complex by ascorbic acid. ä The reaction is slow and the complex is not stable and thus analysis must be performed after 10 minutes and before 30 minutes. ä Ammonium molybdate and antimony potassium tartrate react in an acid medium with orthophosphate-phosphorus to form an antimony-phospho-molybdate complex. ä This complex is reduced to an intensely blue-colored complex by ascorbic acid. ä The reaction is slow and the complex is not stable and thus analysis must be performed after 10 minutes and before 30 minutes.

3. Interference ä Barium, lead, and silver interfere by forming a precipitate. ä The interference from silica, which forms a pale-blue complex is small and can usually be considered negligible. ä Arsenate is determined similarly to phosphorus and should be considered when present in concentrations higher than phosphorus. ä Barium, lead, and silver interfere by forming a precipitate. ä The interference from silica, which forms a pale-blue complex is small and can usually be considered negligible. ä Arsenate is determined similarly to phosphorus and should be considered when present in concentrations higher than phosphorus.

4. Sample Preparation ä No pretreatment ä Measures orthophosphates ä Sulfuric acid treatment ä Measures hydrolyzable and orthophosphates ä Persulfate digestion (strong oxidant) ä All phosphorus converted to orthophosphates ä Measures total phosphorus ä No pretreatment ä Measures orthophosphates ä Sulfuric acid treatment ä Measures hydrolyzable and orthophosphates ä Persulfate digestion (strong oxidant) ä All phosphorus converted to orthophosphates ä Measures total phosphorus

5. Detection Limits ä What controls our ability to measure small concentrations of phosphorus? ä How could we determine if the answer we get is meaningful?  Expected analytical range is 10  g/L to 1 mg/L as phosphorus ä What controls our ability to measure small concentrations of phosphorus? ä How could we determine if the answer we get is meaningful?  Expected analytical range is 10  g/L to 1 mg/L as phosphorus

6. Types of Detection Limits ä Instrument detection limit (IDL) ä instrument noise ä Method detection limit (MDL) ä instrument noise ä sample preparation ä Practical quantitation limit (PQL) ä routinely achievable detection limit with reasonable assurance that any reported value greater than the PQL is reliable ä 5 times MDL ä Instrument detection limit (IDL) ä instrument noise ä Method detection limit (MDL) ä instrument noise ä sample preparation ä Practical quantitation limit (PQL) ä routinely achievable detection limit with reasonable assurance that any reported value greater than the PQL is reliable ä 5 times MDL Which dominates?

7. Instrument Noise for a Spectrophotometer ä What measurements are involved in obtaining a concentration reading from a spectrophotometer? ä _____________ ä _________________________________ ä _____________ ä What measurements are involved in obtaining a concentration reading from a spectrophotometer? ä _____________ ä _________________________________ ä _____________ Reference (P 0 ) Lamp intensity Absorbance of cuvette Standards Sample Absorbance of reference solution sample preparation

8. What are the limitations at low concentrations? Reference P0P0 P0P0 Photons strike diode and produce a voltage response Voltage is digitized Digital Calculations → absorbance ä Po - _________ light intensity ä P light intensity after passing through sample ä As C  0 P  __ ä Describe the journey after light leaves sample to computer ä ______________________________________ ä ___________________ ä ________________________________ ä Po - _________ light intensity ä P light intensity after passing through sample ä As C  0 P  __ ä Describe the journey after light leaves sample to computer ä ______________________________________ ä ___________________ ä ________________________________

9. Minimum Detectable Absorbance ä Suppose a 12 bit Analog to Digital Converter is used. What is the smallest absorbance that can be measured? What if P 0 is digitized into 200 intervals? 12 bit ( ) means _____ intervals 4096

10. Additional Instrument Limitations ä Differences in ___________ ä Fluctuations in ______ intensity ä Power supply ä Warm up time ä Repeatability of Cuvette ___________ ä Sample carryover if using sipper cell ä Differences in ___________ ä Fluctuations in ______ intensity ä Power supply ä Warm up time ä Repeatability of Cuvette ___________ ä Sample carryover if using sipper cell Cuvettes Lamp alignment

11. Method Detection Limit ä "Method detection limit" is the smallest concentration that can be detected above the noise in a procedure and within a stated confidence level. ä What is C such that I can be 99% confident that C > 0? ä "Method detection limit" is the smallest concentration that can be detected above the noise in a procedure and within a stated confidence level. ä What is C such that I can be 99% confident that C > 0?

12. Measuring the MDL ä Make a standard that is near the MDL ä Divide it into at least 7 portions. ä Process each portions through all sample preparation and analysis steps ä Calculate the MDL using the equation ä Make a standard that is near the MDL ä Divide it into at least 7 portions. ä Process each portions through all sample preparation and analysis steps ä Calculate the MDL using the equation n is the sample size, s is the standard deviation,  =0.01 is generally the required confidence, t is the student t distribution n is the sample size, s is the standard deviation,  =0.01 is generally the required confidence, t is the student t distribution

13. Is the MDL > IDL? ä Are sample preparation errors significant? ä Variability in reagent blank (reference sample) ä Results in a calibration curve with nonzero intercept ä Sample contamination ä Ultra pure water ä Acid washed plastic or glass ware ä Airborne contamination ä Are sample preparation errors significant? ä Variability in reagent blank (reference sample) ä Results in a calibration curve with nonzero intercept ä Sample contamination ä Ultra pure water ä Acid washed plastic or glass ware ä Airborne contamination

14. Decreasing the IDL ä May or may not decrease the MDL ä How can you improve an estimate of a parameter? ä Use more ________! ä How could you use a section of the spectrum? ä Use standards to determine _________ ________ ______ ä Take an average of all the predicted concentrations? ä May or may not decrease the MDL ä How can you improve an estimate of a parameter? ä Use more ________! ä How could you use a section of the spectrum? ä Use standards to determine _________ ________ ______ ä Take an average of all the predicted concentrations? diodes extinction coefficient array Arrays!

15. Maximum Detection Limit ä Chemistry ä reagent limitations (stoichiometry) ä reaction by-products ä Instrument limitations ä Maximum detection limits are easily surmounted by __________ ä Chemistry ä reagent limitations (stoichiometry) ä reaction by-products ä Instrument limitations ä Maximum detection limits are easily surmounted by __________ dilution

16. Wallastonite ä Wallastonite (calcium metasilicate mixed with ferrous and aluminum metasilicate) tailings can be used to effectively remove phosphorus from solution. ä These tailings are waste products generated during wallastonite ore mining in Northern New York. ä Wallastonite (calcium metasilicate mixed with ferrous and aluminum metasilicate) tailings can be used to effectively remove phosphorus from solution. ä These tailings are waste products generated during wallastonite ore mining in Northern New York.

17. Wallastonite Column Results ä Why are long retention times needed? ä What is the mechanism? ä Why are long retention times needed? ä What is the mechanism? 5 mg phosphorus/L influent

18. Wallastonite Research (Proposal) ä Quantify phosphorus removal as a function of time in batch tests  Phosphorus concentration (100  g/L) ä Wallastonite concentrations (0, 10, 30, 100, 300, 1000) mg per 7 mL phosphorus solution ä Batch contact times (1, 5, 15, 30, 60, 90) minutes ä Quantify phosphorus removal as a function of time in batch tests  Phosphorus concentration (100  g/L) ä Wallastonite concentrations (0, 10, 30, 100, 300, 1000) mg per 7 mL phosphorus solution ä Batch contact times (1, 5, 15, 30, 60, 90) minutes

19. Expectations

20. Prelab  You will be creating 1 mL standards by diluting a stock of 100  g P/L (1, 3, 10, 30, 100  g P/L) ä Reagent dilution problem  You will be creating 1 mL standards by diluting a stock of 100  g P/L (1, 3, 10, 30, 100  g P/L) ä Reagent dilution problem

21. Spectral Analysis  The initial extinction coefficient arrays are obtained from the slope of the linear regression line for A( ) = f(c) ä Uses general least squares regression to add multiples of extinction coefficient arrays for each component to obtain the best curve fit for the sample ä A better estimate of the extinction coefficient is obtained by interpolating between adjacent standards ä Repeat least squares regression analysis  The initial extinction coefficient arrays are obtained from the slope of the linear regression line for A( ) = f(c) ä Uses general least squares regression to add multiples of extinction coefficient arrays for each component to obtain the best curve fit for the sample ä A better estimate of the extinction coefficient is obtained by interpolating between adjacent standards ä Repeat least squares regression analysis