University of Kentucky College of Agriculture Division of Regulatory Services

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1 University of Kentucky College of Agriculture Division of Regulatory Services Comparison of Manual and Automatic Titrametric Analysis of Potassium in Fertilizer using AOACI Method C. Wayne Ingram, Dr. Melton Bryant, Dr. David Terry* - Presenter * - Retired University of Kentucky John Griffiths Mettler Toledo Inc. AAPFCO Midyear Meeting Charleston, SC February 23, 2010

2 Regulatory Services Potash Analysis Flow Analyzer Method Routine and quality samples are analyzed with the Automated Flame Photometric Method (AOAC Official Method , Phosphorus (Available) in Fertilizers, Direct Extraction Method and AOAC Official Method , Potassium in Fertilizers Automated Flame Photometric Method). Titration Method Routine and quality samples as well as any sample outside the investigational allowance are analyzed by titration (AOAC Official Method , Potassium in Fertilizers Volumetric Sodium Tetraphenylboron Method I).

3 Objective of Investigation Comparison of a new automated titration method to the standard manual titration method for determining the amount of potassium (as soluble potash, K 2 O) in fertilizer. Manual Method Brinkman Metrohm dispenser with visual observation Automated Method Mettler Toledo T-50 auto-titrator with DP5 phototrode probe (T-50 loaned to UK Regulatory Services)

4 Potash Analysis Method The fertilizer samples were analyzed using the Official Methods of Analysis of AOAC International 18th ed. AOAC Official Method Potassium in Fertilizers Volumetric Sodium Tetraphenylboron Method I

5 Reagents: Volumetric Sodium Tetraphenylboron Method I Ammonium oxalate solution (4%) Tributyl Citrate Sodium hydroxide solution (20%) Formaldehyde, 37% W/W Sodium Tetraphenylboron Solution (STPB) (1.2%) STPB binds soluble K Benzalkonium chloride (BAC) solution-approximately 0.625% Used to back titrate for excess STPB Clayton Yellow (Titan Yellow) indicator (0.12%) In titration - yellowish brown turns to pink color

6 Sample List Table 1 Description of Sample % Guarantee UKRS Report Sample Source N:P:K Commercial (liq) Commercial (liq) Commercial (organic) Commercial Commercial (organic) Commercial (liq) Commercial Magruder Check Sample Magruder Check Sample Commercial Commercial Commercial Commercial Commercial Commercial Commercial 10-10: Magruder Check Sample Magruder Check Sample Commercial (liq) Commercial Commercial Custom Mix Magruder Check Sample Commercial Commercial Magruder Check Sample Custom Mix Commercial Magruder Check Sample Magruder Check Sample Magruder Check Sample Magruder Check Sample Custom Mix SOP MOP MOP MOP Sample Source Number of Samples Specialty 14 Specialty (liquid) 4 Specialty (Organic) 2 Custom Mixture 3 Fertilizer Ingredient 4 Magruder Check Sample 10 Total Sample 37 The samples represent the typical range of fertilizers that UK Regulatory Services (UKRS) analyzes on a routine basis with guarantees ranging from low (3%) to high (60%) levels of soluble potash in the fertilizer.

7 STPB Procedure Review The percent guarantee determines the amount sample used for analysis. Potash Guarantee (%) Sample Weight (g) Weight Range (g) Sample Digestion Weigh samples into a 250 ml volumetric flask (add charcoal if sample is organic) Add approximately 175 ml of Ammonium Oxalate Boiling chips and 2-3 drops of Tributyl Citrate (defoaming agent) Swirl solution in flasks, place onto hotplate 450 F (232.2 C) When all samples have started boiling (some flasks may take longer than others to start boiling), turn temperature back to 400 F (204.4 C) Let samples boil for 20 minutes Cool samples in a water bath Bring to volume with deionized water Mix and let settle for 2 hours

8 Procedure (continued) Routinely, the sample aliquot is taken from the 250 ml volumetric flask and transferred into a 50 ml volumetric flask. 10 ml for the manual method Add 2 ml sodium hydroxide Add 5 ml formaldehyde Add STPB to complex potash Calculated based on sample weight and guarantee (added in excess) Bring to volume with deionized water (50 ml) (Use 25 ml for analysis)

Procedure (continued) Modification for replicates: Make a 5X sample volume using a 250 ml volumetric flask 50 ml sample for comparison analyses Add 10 ml sodium

9 Procedure (continued) Modification for replicates: Make a 5X sample volume using a 250 ml volumetric flask 50 ml sample for comparison analyses Add 10 ml sodium hydroxide Add 25 ml Formaldehyde Add STPB to complex potash Calculated based on sample weight and guarantee (added in excess) Bring to volume with deionized water (250 ml)

10 Procedure (continued) Filter the samples into another 250 ml flask Pipette 25 ml samples from the filtration flask into the titration vessels for the manual and automated analyses.

11 Procedure: Titration Solution 25 ml of solution + 6 drops of Clayton Yellow (indicator) Manual Method 125 ml erlenmeyer flask 3 replicates Automated Method 80 ml titration cup 3 replicates

12 Manual Analysis The manual analysis using Brinkman Metrohm with electronic dispenser (not a manual burette) used as the basis for the comparison of the two titration methods. Three replicates analyzed for each sample analysis. Manual delivery of titrant. Use Potassium Dihydrogen Phosphate ( KH 2 PO 4 ) from National Institute of Standards and Technology (NIST) (SRM 200a), as the reference sample.

Manual Analysis Manual Electronic Dispenser (25 ml sample) Add a magnetic stirring bar Back titrate excess STPB with BAC to a light pink endpoint that holds for at

13 Manual Analysis Manual Electronic Dispenser (25 ml sample) Add a magnetic stirring bar Back titrate excess STPB with BAC to a light pink endpoint that holds for at least 20 seconds Record titrant volume onto the spreadsheet (Visual observation of pink color on the white particles) Note: Potash calculations via electronic spreadsheet

Automated Analysis Automated Titration (25 ml sample) Back titrate excess STPB with BAC to a point of inflection on the T-50 auto-titrator (pink color formation).

14 Automated Analysis Automated Titration (25 ml sample) Back titrate excess STPB with BAC to a point of inflection on the T-50 auto-titrator (pink color formation). (The phototrode is set at 555 nm) Rinse probe and stirrer between samples with Triton X-100 solution (0.1% surfactant) The titrant volume is recorded by the computer and printed as a permanent record. Note: Potash calculations via electronic spreadsheet 80 ml 100 ml Preliminary Data 100 ml vessel Additional 20 ml water required to cover the phototrode Investigation Data 80 ml vessel No additional water

Titration: Preliminary and Investigation Data Investigation Data from 80 ml vessel used with a direct comparison of manual (25 ml) and automated (25 ml) methods based on absorption of the

15 Titration: Preliminary and Investigation Data Investigation Data from 80 ml vessel used with a direct comparison of manual (25 ml) and automated (25 ml) methods based on absorption of the indicator on solution particles Preliminary Data from the 100 ml vessel (25 ml sample + 20 ml water) was done to investigate the DP5 Phototrode probe and absorption of indicator on solution particles

16 Automated Analysis The DP5 Phototrode probe is routinely used for the automated determination of metal ions (Fe 2 O 3, Al 2 O 3, MgO) with EDTA. The light transmission of the solution is measured during the titration. DP5 Phototrode

Automated Analysis Normal Phototrode Application The

it is reflected back to the photo sensor by a mirror.

in solution at the titration endpoint allowing the

17 Automated Analysis Normal Phototrode Application The DP5 Phototrode directs light into the solution where it is reflected back to the photo sensor by a mirror. In this transmission mode, the indicator color changes in solution at the titration endpoint allowing the determination of the metal ion concentration. DP5 Phototrode

18 Automated Analysis of Potassium In the potassium analysis, STPB develops a turbid solution with particles that reduces the light being detected. The analysis can not be performed using the DP5 Phototrode in the transmission mode, since the light is reduced and an endpoint is not detected. To deal with this issue, our idea was to remove the mirror and measure the reflected light from the particles, thus using the DP5 Phototrode in a reflection mode. In this reflection mode, the light absorbed by the indicator on the surface of the particles at the endpoint results in a reduction of the reflected light making it possible to measure an endpoint.

Operation of the instrument in the reflection mode is a novel application

19 Automated Analysis This modified configuration of the instrument provides a measurable endpoint for the potassium method. Operation of the instrument in the reflection mode is a novel application of the DP5 Phototrode and T-50 Titrator that was developed for this application. Phototrode Mirror

Automated Analysis DP5 Phototrode directs light into the

reflected from At the endpoint, light is absorbed by the

20 Automated Analysis DP5 Phototrode directs light into the solution and light is reflected back to photo sensor from the particles. The millivolt signal is determined by the amount of light reflected from the particles. At the endpoint, light is absorbed by the indicator on the particles reducing the millivolt signal. Particle color Endpoint color

21 Comparison: Manual vs. Automated Methods Manual: BAC is added to the sample until the eye recognizes a pink endpoint that holds at least 20 seconds. Automated: Endpoint intensities BAC is added to the sample and the T-50 with DP5 Phototrode will record the data and calculate the endpoint. Sample + STPB + indicator Sample + STPB + BAC Particles develop Sample + STPB + BAC Color on particles

22 Results: Graph of Automated Titration BAC Volume Used by the T-50 for Titration Endpoint Absorption of light from indicator on particles Endpoint * Signal Strength (mv) Reflecting light from particles Begin with initial titrate volume 0.5 ml Add ml increments 18.7 minutes to reach endpoint Long analysis time BAC (ml)

23 Signal Strength (mv) Results: Graph of Routine Automated Titration BAC Volume Used by the T-50 for Titration Endpoint Absorption of light from indicator on particles Endpoint * Reflecting light from particles Begin with initial titrant volume 4.0 ml Add ml increments 3.0 minutes to reach endpoint Shorter analysis time BAC (ml)

24 Results: Average K 2 O Manual vs. Automated Sample # Guar (%) Manual Avg % K 2 O 3 replicates Automated Avg % K 2 O 3 replicates Rel % Diff (Auto-Manual) Manual % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % Average %K 2 O ( 3 replicates) Relative Percent Difference for Manual and Automated Methods

25 Manual, K2O (%) Results: Comparison Manual and Automated Method Comparison of the Percent K 2 O from the Manual and Automated Methods (70,70) Theoretical Results Automated = Manual Automated, K 2 O (%)

26 2 Rel % Difference K2O Results: Comparison of Relative Percent Difference Using Manual Method as the Basis 7.00 ((Automated avg - Manual avg) / Manual avg) x Automated > Manual Automated < Manual Guarantee (%K 2 O) Aumated

27 Rel Std Dev (%) Results: Comparison of Relative Standard Deviation of Manual and Automated Methods Manual 2 Automated 2.50 %RSD = (Std Dev Avg from Replications) x The RSD of 95% of all the samples was 1.0% Guarantee (%)

28 Statistical Analysis SAS was used to compare the manual and automated data sets. Conclusions of Statistical Analysis of the Analytical Data Method Condition Precision Accuracy Manual 25 ml Sample Automated (80 mlvessel) 25 ml Sample No Significant Difference No Significant Difference Preliminary Data Manual 25 ml Sample Automated (100 ml vessel ) 25 ml + 20 ml H 2 O Sample Automated More Precise No Significant Difference Statistical Analysis with SAS/STAT Software Statistical analysis Dr. David Terry

29 Results: Particles on the stirring blades Titration Particles Cleaning Required Use Surfactant Rinse

30 Results: Automated Titration when Over Titrated 12.0 Initial Titrant Volume > Endpoint Volume Over Titration with BAC for Titration Endpoint Signal Strength ( mv) Begin with initial titrant volume 4.6 ml Add ml increments Initial BAC application beyond Endpoint The Endpoint was ml BAC (ml)

31 Conclusions: Advantages and Disadvantages Advantages of Automated Does not rely on human eye and color perception to determine the endpoint. Allows analyst to perform other task while the T-50 is unattended and processing the 18 samples on the sample carousel. Gives a permanent record of BAC volume with less probability of transposing the data. Removes bias from the analyst adding or subtracting BAC drops. Disadvantages of Automated Cleaning particles from stirring blades. Added expense to the potassium (potash) analysis (Instrument).

32 Conclusions Automated method and manual method give equivalent potash results. Excellent automated analysis with definitive endpoint. Automated method and manual method have equivalent precision. Future plans: 1. Implement Metter Toledo T-50 system for potassium analysis. 2. Evaluate its application for the analysis of various fertilizer products

33 John Griffiths Acknowledgments Mettler Toledo Inc. Instrument Sales Specialist Titration, Density, Refractometry & Automation Systems Tore Fossum Mettler Toledo Inc. Director of Research and Development Mettler Toledo Inc. Loan of the T50 Auto-Titrator

34 QUESTIONS?

Chemistry 119: Experiment 4. Titrimetric Determination of Acetic Acid Samples And Preparation of Youden Plot

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