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Fertilizers R. A. Sweeney,* C. W. Gehrke, and P. R. Rexroad University of Missouri, Columbia, Missouri 652 1 1
X-ray fluorescence, and also with flame atomic absorption spectrometry. Automated flow injection methods were described by Hansen et al. (86) for the determination of NO3 , P, K, and NH3 in fertilizer. Methods described employed potentiometric and spectrophotometric detection. Sample solutions were analyzed at rates of 85 120 samples per h with high reproducibility and low reagent consumption reported. Results were found to agree well with those by conventional techniques. Weber and Blanc (228) described a new apparatus for the automated thermometric analysis of fertilizer for K, P, and NH?. The apparatus contained a micro-scale flow-through measuring cell fitted with a mechanical stirrer for vigorous mixing. They described this system as universal, since heats of reaction from redox, precipitation, neutralization, and dilution reactions could all be measured. The determination of K 2 0 by measuring the heat of reaction of K with perchlorate was shown as an example of how interferences from competing reactions such as NH3 with perchlorate were overcome. Flow diagrams for K, P, and NH, determinations were given. Errors in the analysis of synthetic fertilizer mixtures were found negligible when the system was calibrated with standards having approximately the same sample matrix. Thermometric analysis of fertilizers using a direct injection enthalpimetric technique was reported by Iipinska and Sipos-Kawecka (124). Detailed descriptions for the determination of P205in phosphates, superphosphate, and mixed fertilizers, K,O in mixed fertilizers. and N in ammonium phosphates, ",NO3, and urea were given. The relationship between the specific gravity and the composition of fertilizer solutions was used by Palgrave (253) as a preliminary indication of fertilizer quality. Nomograms constructed from the relationship were used. Procedures for constructing them were given with reference to a 9 9 9 grade composed of ( N H J 2 H P 0 4 ,urea, and KC1. Two-component fertilizers were analyzed by Firsov (63)by measuring the resistance of sample solutions. An apparatus specifically constructed for this purpose consisted of a slide-wire bridge and a resistance-measuring unit. Correction factors were used to adjust readings resulting from various impurities The procedure was reported simple, fast, and relatively accurate. A detailed description of laboratory equipment and instrumentation for high-volume analyses of soils, plants, fodders, and fertilizers was presented by Tselikov et al. (211). Included were automated systems and computerized data handling schemes. Jain and Sarkar (98) assembled a test kit for assessing fertilizer quality. The kit consisted of the necessary reagents and equipment used to perform tests for KH4+,Sod2 , C1 , Na+, urea, NO1 , CO1' , K+, and CaL+. Standard fertilizer samples were also provided.
This review covers the literature reported from January 1, 1977, to December 31, 1978, and includes procedures recorded in readily available journals, in Chemical Abstracts, and in Fertilizer Abstracts (62). Some selectivity has been exercised to include only those procedures especially pertinent for direct application to fertilizers, easily adapted to fertilizers, or containing information related to research in fertilizer methodology. In the Literature Cited section of this review, Fertilizer Abstracts (62) are abbreviated as Fert. A.
GENERAL Rund (I 7 4 ) , in his annual report to the AOAC on fertilizer methods, reported the results of collaborative studies on new methods for the analysis of N and P. These methods were given official first action status a t the 91st Annual AOAC Meeting in October 1977. Further description of these methods is presented in the nitrogen and phosphorus sections of this review. The literature of analytical chemistry for 1975 and 1976 was reviewed by Gehrke et al. ( 7 2 ) . Presented were those procedures directly applicable to fertilizer analysis for the major (N, P, K) secondary and minor nutrients. One hundred and thirty-eight references were cited. Johnson (105) compiled a reference of fertilizer methods in the form of abstracts selected from those previously published in Fertilizer Abstracts between July 1972 and June 1977. T o facilitate its use. abstracts were grouped into categories by subject and cross-referenced at the end of each section. An author index is also provided. The advent of sophisticated computer-controlled instrumentation for chemical analyses has made simultaneous multielement analysis an attractive pursuit. A number of papers reviewed in this section describe such methods. Three investigators described multielement analysis of fertilizers using neutron-activation analysis. Srapenyants and Savel'ev (196) reported an output of 250-500 samples (1250-2500 actual determinations) per 8-h shift from their automatic computer-based system. The elements N, P, K, Ca, Mg, and Si were determined with reported accuracies of 1 3 % for N, 15-1070 for P, K, Mg, and C1, and k l 5 % for Ca. Bodart and Deconninck (25) determined P, K, C1, Mg, and Si. They described a technique used to resolve the Si-P interference, which they report is applicable to all fertilizers containing 0.75 w/w presented a problem. Three samples with high C1:N03 ratios had recoveries of 94.1-99.1% when compared to results by CNM. Excluding the three samples with the high Cl:N03
Contribution of the Missouri A ricultural Experiment Station. .Journal Series No. 8284. Approve{ by t h e Director. 0003-2700/79/0351-091R$O 1 OO/O
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ratio, the average relative standard deviations were 0.68% for SAM and 0.65% for CNM. The ml thod was reported as simple, accurate, precise, flexible, and rapid and required a minimum of laboratory space. Rexroad and Krause (169) conducted an AOAC collaborative study comparing two modified Hg-free methods for nitrogen in fertilizer with the official comprehensive nitrogen method (CNM). Eleven samples were studied. The modified Raney power method with no metallic oxidative catalyst gave significantly lower results on two samples, one containing nitric phosphates and nonsulfate S, the other tryptophan. The modified comprehensive N method (MCMN) using 0.4 g of CuSO, in place of Hg gave comparable results with the official method. This study led to AOAC adoption of the MCNM method as official first action. Marecek (132)presented a review on techniques for NH4+, NO3-, urea-N, and total N determination in inorganic synthetic fertilizers. A critical evaluation of some methods and their error sources were emphasized. The direct determination of ammoniacal and some other N forms in fertilizers by molecular emission cavity analysis was reported by Belcher (12). The determination was achieved by conversion of the N forms to NH,, and subsequent volatilization and transport via an O2 stream into the molecular emission analysis cavity, wherein a wide band emission (arnm 500 nm) was produced. A reproducibility of 1 2 % a t the 100-ppm level and a detection limit of 1 ppm were reported. T h e stated analysis time was 5 min. Sosin and Matenko (195) described two methods for the determination of nitrogen in nitrogenous fertilizers, both involving titration in nonaqueous media. ",NO, was titrated as an acid in Me,CO, MezSO with NaOMe in the presence of thymol blue. NaN0, was decomposed by HC02H and evaporated to dryness, and the residue dissolved in HOAc. The resulting NaOAc was titrated as a base with HC10, using Me violet indicator. Nagai et al. (146) reported a method for identifying slow-release components in nitrogen fertilizers by paper chromatography. Urea, isobutylidene, ureaform, methylenediurea, dimethylenetriurea, trimethylenetetraurea, and crotonylidenediurea were separated on Toyo No. 50 filter paper when sprayed with p - [(CH3),N]C6H4CHO. A combination electrode was used by Barbera ( 8 ) for the determination of NO3- nitrogen in compound fertilizers. The reliability of the electrode wap reported to be better than 2 % , and the results obtained were reported not to differ from those provided by the Devarda method for NO, reduction to NH, and by the Kjeldahl method for NH, determination. Murty et al. (244) presented a method for reductimetric determination of nitrate, nitrite, and other compounds in concentrated phosphoric acid with iron(I1). The method was reported useful in the estimation of the NO? content of fertilizers. Sloan and Veales (193) used physical measurements to determine the composition of liquid fertilizer containing ",NO?, urea, and H 2 0 . Under controlled conditions they measured the specific gravity and refractive index of the samples and developed plots from these data. The total N content was interpolated from these plots. Schindler et al. (184)developed an ammonium ion-selective enzymatic flowthrough system for the measurement of urea concentrations. A selective disk electrode was used to measure the NH4+liberated by urease. The active component of the electrode membrane was the carrier-antibiotic nonactin, which was incorporated in a poly(viny1 chloride) matrix. Lug0 and Rossi (126) reported the results of an interlaboratory study on three methods used to determine urea-N in samples of pure urea, mixed fertilizer, urea plus ",NO3, and a n organic mixture. Eight European laboratories participated. The determinations were made colorimetricallv with p-dimethylaminobenzaldehyde, volumetrically with urease, and gravimetrically with xanthydrol. The volumetric method gave results that varied greatly within and between laboratories. The other two methods were reported to give accurate results with good reproducibility. Barbera and Canepa (9)described a method for determining free, unreacted urea-N in mixed compounds containing condensation products of urea and formaldehyde. TJsing an NH, gas-sensing electrode, free urea was determined potentiometrically by measuring the NH i produced before and
following exhaustive hydrolysis by urease. Abramova et al. ( 1 ) reported a spectrophotometric method for the determination of urea in fertilizers based on the formation of the colored urea-p-dimethylaminobenzaldehyde complex. The presence of mineral acids tended to decrease absorbance readings, while aliphatic acids (HCOOH and HOAc) tended to increase absorbance readings. I t was reported that the presence of Pod8-,Ni, Co, Cu, and Mn did not interfere with the urea determination. Szorad-Rusz and Halasz (199) described thermometric titration methods for the determinations of ammonium N content in ammonium nitrate and ammonium and urea N content in various fertilizer samples. Experiments carried out with a modified Directhermon-D instrument equipped with a new small volume measuring cell showed that hypobromite can be readily used for the titration. A precision pulse buret was used to add titrant a t a feed rate of 1 mL/min. Hansen et al. (85) reported a simple, reliable, and precise automated method for the determination of NO3-. The method, based on the flow injection principle, used a NO3sensitive electrode situated in a flow-through cell as the detecting device. Application of the method to the analysis of NO< in soil extracts, waste waters, fertilizer solutions, and air samples was described. Sampling rates of 90 samples/ h and standard deviations of 1-2% were reported typical with this system. A mechanical apparatus was patented by Aegidius ( 2 ) for the sequential determination of nitrogen by the classical Kjeldahl method. Four to seven flasks were mounted on a circular rotating device which turned at regular intervals to succeeding positions where heating, cooling, diluting, neutralizing, steam distilling, and titrating station were provided. An AutoAnalyzer I1 was evaluated by Eastin (54) for the automated determination of NH4+in plant tissues following semi-micro Kjeldahl digestion. Digesting was accomplished in a Folin-Wu digestion tube with a mixture containing K SO,, CuSeO?, and pumice. Automated detection of NH,+'was reported to compare well with classical distillation-titration measurement for the determination of 1.32-7.92% N. Carlson (35) developed an automated continuous flow instrument for the automated separation and conductimetric determination of ammonia or dissolved carbon dioxide. Evaluation of the instrument was made using Kjeldahl digests of 39 leaf samples. The sample solution stream was mixed with NaOH for NH3 determination or HC10, for C 0 2 determination. A stream of deionized H 2 0 picked up NH3 or C 0 2 diffusing from the sample stream through silicone rubber hollow fibers. As the H 2 0 stream emerged from the hollow fibers, it passed through an electrical conductivity cell. The conductivity response was related t o NH, or COP in the sample. Good agreement was reported between the new method and the distillation titration of Kjeldahl digests. A modification of an AOAC method for determining urea uith urease was reported by Falls et al. (61).The modification included direct titration to the end point instead of back titration, and titration with 0.3 N H 2 S 0 4rather than 0.1 N HC1. because the stronger acid yielded a much sharper end point. Also, jack bean meal was directly added to the sample flask instread of using a neutral urease solution. The modified method allowed the end point of the titration to correspond to the break point of ammonium carbonate (pH 4.2), which was the compound being titrated in the urea analysis. Denney (50) developed a method for urea determination that was reported to be well suited for automated systems. The sample was reacted with an acidic reagent solution of o-phthaldehyde and a chromogenic compound. The mixture was incubated at 37 "C for 10 min and the absorption of the complex was measured in a spectrophotometer. Stephenson (197) further developed Lang's modified Kjeldahl technique for nitrogen determination in water, wastewater, and sludge. Samples were digested with sulfanilic acid for low N concentrations and with diethanolamine for high N concentrations. The method was found to be both rapid and accurate with no measurable interference from compounds found in domestic wastewater sludge. Perepelitsa and Myadelets (158) studied the performance of the distillation affecting the rate of NH3 distillation in nitrogen determination. Kardasz and Roszyk (108) presented a modification of the method of wet rnineralizatioii for organic substances. Two
",+,
ANALYTICAL CHEMISTRY, VOL. 51, NO. 5, APRIL 1979
Charles W. Gehrke is Professor of Biochemistry and Manager of the Experiment Station Chemical Laboratories at the University of Missouri. I n addition to teaching and research in the field of analytical biochemistry. his duties include those of State Chemist for the M W Fertilizer Control Law. He received his B.A. degree from the Ohio State University in 1939, a B.S. degree in Education in 1941, and a M.S. degree in 1941. From 1941 to 1945, he was Chairman of the Department of Chemistry and Professor of Chemistry at Missouri Valley College. He returned to Ohio State University in 1946 as an instructor in acriahral b&mktrv and received his FhD.
He is active In &e Amerl&n Chemical Society, AOAC, IFT, and is now serving as Chahnan of the MaCommittee for the AAPFCO. His research interests include the development of quantitative gas and high-performance liquid chromatographic methods for amino acids, purines, pyrimidines, nucleosides, fatty acids, and biological markers in the detection of cancer; characterization and interaction of proteins; and automation of analytical methods for nitrogen, phosphorus, and potassium in fertilizers, and for other biologically important molecules. Automated spectrophotometric methods have been developed for lysine, methionine, and cystine. He is author of over 175 scientific publications in analytical and biochemistry. Professor Gehrke has been an invited scientist on gas-liquid and high-performance liquid chromatography, amino acids, and biologic markers, in cancer, in Japan and many universities and institutes in the United States and Europe. He participated in the analyses of Apollos 11, 12, 14, 15, 16, and 17 for amino acids and extractable organic compounds with Professor Cyril Ponnamperuma, University of Maryland, and a consortium of scientists with the National Aeronautics and Space Administration. In 1971, he received the annual AOAC Harvey W. Wiley Award in Analytical Chemistry, and was the recipient of the Senior Fawity Member Award, college of Ayicukwe, in 1973. In August 1974, he was invited to the Soviet Academy of Sciences to make the summary presentation on organic substances in lunar fines. In 1975, he was a member of the American Chemical Society Charter Review Board for Chemical Abstracts. As an invited teacher under the sponsorship of the five Central American Governments, he taught chromatographic analysis of amino acids at the Central American Research Institute for Industry (March 1975). He was elected to "Who's Who in Missouri Education" in 1975, was the recipient of the facuity Alumni Goid Metal Award from the Alumni Associabon, University of Missouri---Columbia in 1975, and a Mid States honor lecturer in 1978-79. Paul R. Rexroad is Associate Manager, Experiment Station Chemical Laboratories, and Instructor, Biochemisw, University of Missouri. These positions include work in the state fertilizer control laboratories. He received his B.S. (1948) and M.S. (1950) degrees from the Ohio State University. He worked in the laboratories of the feed and fertilizer divisions of the Ohio Farm Bureau Cooperative for over 10 Years before ioinincl the staff of the
ticipth in the AOAC and the AssociaW of American Plant Food Contrd officials. He is the Associate Referee for nibogen in fertilizers for the AOAC and the author of a number of papers in the field of analytical chemistry. He was named a Fellow of the AOAC in 1977.
Rose A. Sweeney is Supervisor-Fertilizer Laboratory, Experiment Station Chemical Laboratories, University of Missouri. She received her B.A. (1969) from the University of Missouri and has been a member of the Experiment Station staff for nine years.
wet digestion methods for the Kjeldahl determination of N in organic materials such as plants were described. Two milliliters of 30% H 2 0 and 3 mL of H 8 O 4 were added to 0.25 g of crushed, air-dried ground plant material. The mixture turned dark brown after heating and then either 50 mg of
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Se-containing catalyst or an additional 1 mL of 30% H202was added. The solution was then boiled until a clear, colorless solution was obtained. The digestion time was approximately 15 min. Kumazawa (118) reported a method for total N determination applicable to samples too small for the Kjeldahl method. Samples were sealed in a container along with CaO and CuO and heated until combustion occurred and N was generated. The container was then opened and the volume and pressure of the N released were measured. Lekova (122) developed an apparatus for the automatic determination of 0.00!+100% N by a modified Dumas method. Alferov et al. (3)published a study of the conditions for the spectrophotometric ammonia determination using obenzenesulfonamido-p-benzoquinone.The relative error was reported to be lo0 times that for Na and 10 times that for Rb. The K combined with H L in the organic phase to form a KHL, complex, the absorption of which was measured at ,560 nm. The procedure was used to determine solutions containing 1ci--400 ppm of K without interference from the presence of
