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Fluid Journal : Early Spring 2011
6 The Fluid Journal Early Spring 2011 A typical chromatographic fingerprint of a Triazone fertilizer solution (UTS) shows the presence of untreated urea, Triazone six-member ring, and ureaform constituents. A typical high-performance liquid chromatographic (HPLC) fingerprint of a Triazone fertilizer solution (UTS) is shown in Figure 6. The two larger adsorption peaks at around 3 min and 6 min are due to free urea and Triazone, respectively. The smaller peaks are the urea-formaldehyde adducts (ureaforms). The N from free urea shall not be claimed as CRN/SRN and an accurate method is needed to account for these. Questionable techniques AOAC International currently has two official methods--959.03 (Urease Method) and 983.01 (Liquid Chromatographic Method). Both methods suffer from interference of these co-products. One or more of these substances makes Method 959.03 unreliable by hampering action of the urease enzyme. The liquid chromatography in Method 983.01 suffers from co-elution of some of these substances in some occasions. No suitable method currently exists for regulatory analyses of urea (or urea N) in these products. Urea-formaldehyde. It also has long been determined that 959.03, the method most commonly used for regulatory urea determination in fertilizers, is not reliable for the determination of urea in a certain class of urea-containing fluid fertilizers that also contain a substantial component of water soluble urea-formaldehyde reaction products. Test data indicate that one or more substances from this UF-derived component inhibit the action of the urease enzyme upon which action These three terms have been used synonymously. Urea-formaldehyde condensation products, commonly known as "ureaforms," have been used for many years as the source of controlled-release N fertilizers for plants. In commercial fluid fertilizers derived from reaction of urea and formaldehyde, unreacted urea is always a substantial component of such products and is quantitatively claimed on the registration labels. These classes of products also contain a substantial component of water-soluble urea- formaldehyde reaction products. Due to the presence of these co-products, quantitative determination of the claimed urea content is important. Urea and formaldehyde react with each other under acidic or basic conditions to produce ureaform products, including dimethylolurea (DMU), methylenediurea (DMU), and dimethyltriurea (DMTU). A based catalyzed reaction of urea and formaldehyde is shown in Figure 2. Under acidic conditions, urea and formaldehyde react according to the chemical reaction shown in Figure 3. Ureaforms have been used as CRN Figure 2. A based catalyzed reaction of urea and formaldehyde. Figure 3. Reaction of urea and formaldehyde under acidic conditions. fertilizers. Controlled reaction of urea, formaldehyde, and ammonia forms a six-member ring that contains a high percentage of CRN (Figure 4). Triazone. According to the definition by AAPFCO (Official Publication No. 63, 2010), Urea-Triazone Solution (UTS) is a stable solution resulting from controlled reaction in an aqueous medium of urea, formaldehyde, and ammonia, which contains at least 25 percent N. The solution shall contain no more than 40 percent, no less that 5 percent of total N from unreacted urea and not less than 40 percent from Triazone. All other N shall be derived from water-soluble, dissolved reaction products of the above reactants. It is a source of slowly available N. Figure 5 shows the N release pattern from urea and Triazone. Due to the presence of some unreacted urea in Triazone products, not all of the N content of these fertilizer solutions is slow release. Accurate reporting of the urea from N (fast release) and other available N contents (control-release/slow release) should be accounted for and conform to the label. MDU DMTU