determination of srn in liquid (water soluble) urea...

Determination of SRN in Liquid (water soluble) Urea-Formaldehyde Fertilizers

Method Forum February 24, 2016

Albuquerque, New MexicoTessenderlo Kerley, Inc. | tkinet.com | www.cropvitality.com | 1

SRN Fertilizers

Slow Release Fertilizers (SRN):

Slow Release Fertilizers ‐are solid or liquid fertilizer products that release (convert to a plant available form) their nutrients at a slower rate relative to a “reference soluble” product. This may be accomplished by biodegradation and/or by limited solubility and/or by hydrolysis or other recognized chemical or biochemical means. Some examples include solid fertilizers such as: methylene urea (MU), Magnesium Potassium Phosphate and bio‐solids, and liquid fertilizer such as triazone. The product may provide longevity claims when compared to an appropriate reference material.

Solid: IBDU, CDU, NutraleneLiquid: N-Sure, NBN 30, Clear N, Last N

Tessenderlo Kerley, Inc. | tkinet.com | www.cropvitality.com | 2

Manufacturers of Liquid Water soluble SRN Fertilizers

Helena

Koch

Yara

Tessenderlo Kerley

Arclin

Advachem

Sadepan

Agrium


Production

• From Urea, Formaldehyde, Formalin (or UFC)

• Or from Urea, Formaldehyde, Formalin (or UFC) and ammonia.

• under controlled conditions to form a liquid urea-formaldehyde condensate product.


Urea Formaldehyde Condensate Reaction

• Base Catalyzed


Urea

NH2H2N

O

HH

O

NHH2N

O

CH2OH

NHHN

O

CH2OHCH2OH

Base

MMUDMU

+

+

Urea Formaldehyde Condensate Reaction

• Acid Catalyzed


NH2H2N

O

NHH2N

O

HH

O

NHH2N

O

NH2HN

O

CH2

NHHN

O

NH2HN

O

CH2CH2

MDU

DMTU

+

Acid

+

Urea + Formaldehyde + Ammonia (gas or aqua)


HPLC Chromatogram


(28-0-0) UF Liquid product Composition?

• Monomethylol urea (MMU) ≈ 2%

• Dimethylol urea (DMU) ≈ 0.3%

• Methylene diurea (MDU) ≈ 1.00%

• Biuret ≈ 0.02-0.3%

• HMT ≈ 1-2%

• Free Urea 14-15%

Overall, 22% of N is from urea & 78% of N is from SRN

The minor components are about 5-8%

70% of the composition is a major component

What is this major component?


1H‐NMR Spectra in DMSO

D2O Added H‐NMR Spectra

13C‐NMR Spectra in DMSO

Major component of crystal. Green is unaccounted for electron density (error in structure)

Proposed Mechanism for the Formation of the Major Component


NH 2H2N

O

N

N

N

O

HH

CH 2OH

NH 2H2N

ON

N

N

O

N

HH

HC

O

NH 2

5-Hydroxymethyltriazine Urea

N-Sure

+ Formaldehyde + AmmoniaUrea

++ Ureaforms

Slow Release Pattern

15

SRN Determination

• SRN is coming from cyclic compound or chained compounds (MMU, DMU, etc).

• Free Urea does not provide SRN

• To accurately report the SRN one has to determine the Free Urea accurately.

• SRN is determined by subtracting the total Nitrogen present from the amount of free Urea


Aqueous Urea-Formaldehyde Fertilizer Products

Each of existing products in the market claim certain

Percent of SRN from 50-80%.

Existing Method of Analyses

• AOAC Methods 959.03 (Urease, 1960)

• AOAC Method 983.01 (Liquid Chromatography, 1984)1

• AOAC Method 2003.14 (Liquid Chromatography, 2008)

1 Official Methods of Analysis (2000) 17th Ed., AOAC INTER NATIONAL, Gaithersburg, MD, Methods 959.03 and 983.01


Test products

1. LF3060 (30‐0‐0), Koch Agronomic Services, LLC, 4111 E. 37th St. N, Wichita, KS 67220, USA2. CoRoN (28‐0‐0), Helena Chemical Company, 225 Schilling Blvd., Collierville, TN 380173. Arclin 28‐0‐0, Arclin Resins, Research & Technology, 4754 28th St., Springfield, OR 974774. Greenfeed 27‐0‐0 (light Green liquid), Plant Food Company, 38 Hightstown‐Cranbury Station Road,

Cranbury, NJ 085125. Greenfeed 27‐0‐0 (Dark Green liquid), Plant Food Company, 38 Hightstown‐Cranbury Station Road,

Cranbury, NJ 085126. NDemand 30‐0‐0, Wilbur‐Ellis Agribusiness, 3300 S. Parker Road, Suite 500, Aurora, CO 80014,

USA7. NDemand 30L, Wilbur‐Ellis Agribusiness, 3300 S. Parker Road, Suite 500, Aurora, CO 80014, USA8. Gradual N (30‐0‐0), Winfield Solutions, LLC, 1080 County Road West, Shoreview, MN 551269. N‐28 clear Fertilizer (28‐0‐0), Advachem, Route de Wallonie, Darse d’Hautrage, BE 7334 Hautrage10. N‐Sure (28‐0‐0), Tessenderlo Kerley, Inc., 2255 N. 44th St., Suite 300, Phoenix, AZ11. Trisert NB (26‐0‐0), Tessenderlo Kerley, Inc., 2255 N. 44th St., Suite 300, Phoenix, AZ12. Formolene Plus (30‐0‐0), Tessenderlo Kerley, Inc., 2255 N. 44th St., Suite 300, Phoenix, AZ

18


Analyses of Twelve Fertilizer Samples for Urea by AOAC Method 2003.14

FertilizerSample

LabID

Total–N*

%Urea‐NMean Std.dev.Lab1 Lab2

1 26‐068‐03 29.89 12.04 12.45 12.25 0.212 26‐051‐01 28.54 8.63 8.51 8.57 0.063 26‐068‐02 28.44 8.68 8.57 8.63 0.054 26‐076‐07 28.33 8.45 8.45 8.45 0.005 26‐076‐06 28.47 8.58 8.60 8.59 0.01 6 26‐076‐08 24.95 16.08 15.70 15.89 0.19 7 26‐079‐01 30.78 12.55 12.70 12.63 0.078 26‐086‐04 30.06 12.56 12.07 12.32 0.25 9 26‐103‐02 28.01 12.09 11.36 11.73 0.37 10 26‐103‐03 28.13 6.85 6.83 6.84 0.0111 26‐100‐03 26.36 15.55 15.28 15.42 0.1412 26‐010‐02 29.87 9.37 9.51 9.44 0.07

Average X 10.95 10.84 ‐ ‐ Standard Deviation σx 2.97 2.87 ‐ ‐ Number of samples n 12 12 ‐ ‐ Variance σ2 8.80 8.21 ‐ ‐ Pearson Correlation 0.99 ‐ ‐ ‐ ‐ T Stat 1.30 ‐ ‐ ‐ ‐ P(T<t) one‐tail 0.11 ‐ ‐ ‐ ‐ t Critical one‐tail 1.80 ‐ ‐ ‐ ‐ P(T<=t) two‐tail 0.22 ‐ ‐ ‐ ‐ T Critical two‐tail 2.20 ‐ ‐ ‐ ‐

*Note: Total‐N includes other forms of nitrogen in addition to unreacted (free) urea


Schematically comparisons of HPLC Results by two Labs

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12

% Urea‐N

Sample #

Comparison of Urea analysis by Labs 1 & 2

Lab 1

Lab 2


Urease Analyses of Twelve Fertilizer Samples & Comparisons with the HPLC Results for Urea

% Urea‐N % Urea‐N % Urea‐N

Total‐N Fertilizer Sample

Urease Method AOAC 959.03

HPLC Method AOAC 2003.14

(Means from two Labs)

Difference Urease‐HPLC

(Mean)

29.89 1 13.26 12.25 +1.02 28.54 2 9.87 8.57 +1.30 28.44 3 10.06 8.63 +1.44 28.33 4 9.33 8.45 +0.88 28.47 5 9.91 8.59 +1.32 24.95 6 15.44 15.89 ‐0.45 30.78 7 14.81 12.63 +2.19 30.06 8 14.08 12.32 +1.77 28.01 9 8.89 11.37 ‐2.48 28.13 10 8.94 6.84 +2.10 26.36 11 16.18 15.42 +0.77 29.87 12 11.86 9.44 +2.42


Comparisons of the Results by HPLC (2003‐14) and by UreaseMethod (Powdered Sample)

Product % Total N

%SRN Claimed

SRN Determination

Method

HPLC (2003-14) Urease 28-0-0 72 72 88

30-0-0 60 60 77

30-0-0 50 50 68

28-0-0 75 50 70

30-0-0 85 46 80

Difficulties with Existing Methods

Urease Method Problems

The Urease method is the method most commonly used in both industry and regulatory laboratories for urea in all types of fertilizers.

However, for UF-based fertilizers, one or more of the UF-derived components inhibit the action of Urease enzyme. Method 959.03 is dependent upon this quantitative action.

Method Condition:

• 20 ml of 1% Urease Solution

• Urease activity should at least hydrolyze 0.1 g of Urea



Analyses of Urea using Different Sources of Urease

0.1 g 0.3 g 0.6 g 1.0 g

1 20 ml (1% Sol.) 100.1 100.1 99.7 99.9

2 10 ml Glycerol Ext. 99.9 99.7 99.7 69.9

2 20 ml Glycerol Ext. 99.9 99.7 99.7 99.4

3 20 ml (1% Sol.) 99.6 99.7 97.6 62.7

4 20 ml (1% Sol.) 99.3 99.7 83.2 52.6

5 2 tablets 100 98.6 69.3 45.5

6 20 ml Glycerol Ext. 99.9 99.9 99.7 99.5

7 20 ml (1% Sol.) 100.3 100.1 99.9 99.6

% Hydrolysis of urea from the amount usedUrease AmountUrease

Source


AOAC 959.03 (Urease Method) vs. AOAC 2003.14 (HPLC) Results for Analyses of Unreacted Urea in Urea‐Triazone Liquid Fertilizers

Urease HPLC Urease HPLC Urease vs HPLC

1 A 0.20 0.34 20.2 33.7 6020ml 1% Solution B 0.11 0.16 10.9 16.1 68

C 0.24 0.32 23.5 32.1 73D 0.27 0.35 27.3 35.1 78

2 A 0.17 0.34 16.9 33.7 5010ml Glycerol Ext. B 0.08 0.16 7.5 16.1 47

C 0.14 0.32 14.2 32.1 44D 0.25 0.35 25.4 35.1 72

2 A 0.34 0.34 34.3 33.7 10220ml Glycerol Ext. B 0.17 0.16 17.0 16.1 106

C 0.32 0.32 32.4 32.1 101D 0.33 0.35 33.4 35.1 95

3 A 0.15 0.34 15.0 33.7 4520ml 1% Solution B 0.10 0.16 9.5 16.1 59

C 0.18 0.32 17.8 32.1 55D 0.32 0.35 32.4 35.1 92

4 A 0.18 0.34 18.1 33.7 5420ml 1% Solution B 0.11 0.16 11.0 16.1 68

C 0.18 0.32 18.4 32.1 57D 0.24 0.35 23.5 35.1 67

5 A 0.17 0.16 6.9 16.1 43Two Tablets B 0.13 0.32 13.0 32.1 40

6 B 0.17 0.16 16.9 16.1 10510 ml Glycerol Ext. C 0.33 0.32 33.1 32.1 103

6 B 0.17 0.16 17.1 16.1 10620 ml Glycerol Ext. C 0.33 0.32 33.2 32.1 103

7 A 0.34 0.34 34.0 33.7 10120ml 1% Solution B 0.16 0.16 16.2 16.1 101

C 0.32 0.32 32.3 32.1 101D 0.33 0.35 33.0 35.1 94

Sampleamount used

Urease Method Results

• Often Not Reproducible

• Type of Urease is important (powder, Tablet, Liquid form)

• Urease activities varies with different sources

• Interference from ureaform components


AOAC HPLC Method 983.01


Comparisons of results for sample #10, #11, and #12 by two HPLC Methods

Sample # 10 (28‐0‐0)

Sample # 11 (26‐0‐0)

Sample #12 (30‐0‐0)

% Free Urea

(AOAC 2003.14) (AOAC 983.1)

Lab 1 Lab 2 Lab 3

13.6 13.9 15.8 30.5 30.3 30.2 21.9 21.7 23.7

AOAC HPLC Method 983.01

Method 983.01 is not reliable for determination of urea inthe cited class of fertilizers because in most, if not all,

cases, there is co-elution of a non-urea peak withThe urea peak.

Mobile Phase: WaterColumn: ODSDetector: Refractive Index



Comparisons of the analytical results for Grade 26‐0‐0 by AOAC 983.1 & AOA 2003.14

Sample ID Samples

Analyzed by Lab‐1

Grade %

Biuret Test 1

% Biuret Test 2

% Biuret Test 3

% Biuret Test 4

Average% Biuret STDEV

By 2003‐14 Method 25‐012‐05 Sulfur coated urea 39‐0‐0 0.911 0.943 0.979 0.933 0.942 0.02525‐068‐06 Triazone Fertilizer 26‐0‐0 0.118 0.124 0.131 0.139 0.128 0.00825‐070‐01 Fertilizer “A” 15‐15‐15 0.668 0.689 0.762 0.708 0.707 0.03525‐070‐02 Fertilizer “B” 25‐11‐10 0.296 0.356 0.440 0.416 0.377 0.056

By 983.1 Method 25‐012‐05 Sulfur coated urea 39‐0‐0 0.795 0.795 0.794 0.791 0.794 0.00225‐068‐06 Triazone Fertilizer 26‐0‐0 5.793 5.854 5.856 5.814 5.829 0.02725‐070‐01 Fertilizer “A” 15‐15‐15 0.560 0.560 0.557 0.555 0.558 0.00225‐070‐02 Fertilizer “B” 25‐11‐10 0.299 0.302 0.303 0.300 0.301 0.002

By SRIC* Method (same as 2003‐14) 25‐012‐05 Sulfur coated urea 39‐0‐0 0.934 0.965 0.987 0.974 0.965 0.01925‐068‐06 Triazone Fertilizer 26‐0‐0 0.120 0.131 0.130 0.134 0.129 0.00525‐070‐01 Fertilizer “A” 15‐15‐15 0.663 0.711 0.734 0.727 0.709 0.02825‐070‐02 Fertilizer “B” 25‐11‐10 0.286 0.367 0.388 0.382 0.356 0.041

*Shanghai Research Institute of Chemical Industry Testing Center

AOAC Official Method 2003.14Liquid Chromatography

First Action 2003, Final Action 2008

HPLC Method

• UV absorption detector 195 nm• Mobile Phase: 85% Acetonitrile, 15% water

• Flow rate: 1.30 ml/min

• Mobile phase temp: Ambient

• Column temperature: 30-35 oC

• Injection volume: 10 l

• HPLC Column – A 250 x 4.6 mm amine (NH2) column with 5 packing is used for this separation We obtained the best results using Phenomenex .

• External Urea, Biuret, MMU, DMU, and HMTA Standards



Conclusions

The AOAC Official Methods 959.03 (Urease Method) and 983.01 (HPLCMethod) are frequently inaccurate and therefore not suitable formeasuring the amounts of free and unreacted urea in liquid urea‐formaldehyde condensate products. AOAC Official Method 2003.14consistently provides more accurate analytical results for measuring thecontents of free urea in these classes of fertilizers.

The results have been accepted as a manuscript for the publication inthe Journal of AOAC International and will appear in the next issue.

determination of srn in liquid (water soluble) urea...

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