Fertilizers C. W. Gehrke, L. L. Wall,
Sr.,and P. R. Rexroad
University of Missouri, Columbia, Mo 65201
This review covers the literature reported from January 1, 1971, to December 31, 1972, and includes procedures recorded in readily available journals, in Chemical A bstracts, and in Analytical A bstracts-Fertilizers (2). Some selectivity has been exercised to include only those procedures especially pertinent or those which in the authors’ judgement, could be adapted easily to fertilizer analytical problems.
hour. A newly developed sample-retrieval system removes digested samples from the helix. In comparing data for 458 samples analyzed by the Missouri Automated Nitrogen Method (MANM) and the C o r prehensive Nitrogen Method (CNM), 2.053-2.054, the aTrerage difference between the two methods (MANM-CNM) was +0.04% nitrogen. The average relative difference was 1.12%. The average value for 140 samples of KNO3 primary standard analyzed by the MANM was 13.84% nitrogen (theoretical SAMPLING nitrogen content 13.85%). The results of these standards ranged from 13.58 to The results of a survey regarding the specifications and 14.14% nitrogen and the standard deviation was 0.11. The details of sampling bagged fertilizers was reported by relative standard deviation was 0.80%. Less than 1% of Gehrke (30). Adherence to the recommended equipment the fertilizer samples received for analysis in the Missouri and procedures of the AOAC was quite good. No serious Laboratories contained insoluble organic nitrogenous masampling problems were reported. The recommended bag terial which were unsuitable for andysis by the MANM. sampler specifications, detailed in the study, based on the These few samples were not included in the statistical most widely used equipment were adopted as official first evaluation. action by the Association of Official Analytical Chemists. More new automation for the detwmination of nitrogen in fertilizers and foods was the subjc ct of a paper by Merz WATER et al. (61). The elimination of error3 found in the Dumas Duncan (22) found the results of a preliminary collabomethod was achieved by using pun? 0 2 to give explosive rative study of Karl Fischer titration methods for the decombustion in a tube suitable €or higher flow velocity. termination of free and total water in fertilizers to be in The combustion gases were passed with COz over CuO wide disagreement. It was recommended that the proand Cu into a n automatic azotometer and the nitrogen posed methods of the AOAC be rewritten in explicit dewas determined volumetrically. An electronic balance and tail. a n electromagnetic charging valve were essential for comA study was also made by Duncan to determine the efplete automation of the method. Total analysis time, infect of grinding during preparation for analysis on the cluding flushing time with COz, was 2.5 minutes. moisture content of triple superphosphate (23). The findFiedler and Proksen (26) described a method for the deings indicated that there was some correlation between termination of the total nitrogen content in both organic relative humidity and absorption of water when a sample and inorganic materials after conversion’ to nitrogen gas. of granular triple superphosphate was ground in preparaThese investigators utilized a modified Dumas method of tion for analysis. It was suggested that care be exercised burning the sample with a mixture of CuO, Cu, and lime in the preparation of superphosphate samples for analysis in a closed tube under vacuum. By releasing the nitrogen and the relative humidity in the grinding room probably gas into an evacuated chamber of known volume, nitrogen should be 140%. pressure was measured to assay the nitrogen content of A collaborative study was made by Duncan ( 2 4 ) of the the sample. 1,4-dioxane extraction method for free water and the disGoh (33) has compared and evaluated a semimicro tillation method for total water in fertilizer. The extracmodification of the Olson method 1 o include nitrate-nitrotion method for free water compared favorably with the gen in the total nitrogen determinations of soil by the official vacuum desiccation method and was adopted as semimicro Kjeldahl method. The modified method was an official first action method by the AOAC. However, significantly superior to the salicylic acid method, and nitrate interfered with the proposed method for total comparable with the recently recI3mmended Raney catawater; therefore, study of the total water method was dislyst method. continued. Results using glucose as a nitrate reductant suggested that some nitrate nitrogen was “educed by soil organic NITROGEN matter in the normal total soil nitrcgen determinations. An automated spectrophotometric method, utilizing In a semi-automated method for the simultaneous deTechnicon AutoAnalyzer modules, to determine total nitermination of nitrogen and phosphorus in feeds and feedtrogen in fertilizers containing only ammoniacal, nitrate, stuffs, Law et a!. (55) used a single digest for both of these and urea nitrogen has been developed by Gehrke et al. elements. Digestion is accomplished on a semimicro scale (31). This colorimetric system employs the Berthelot amfollowed by the automated colorimetric analysis of the remonia-phenate-hypochlorite reaction. A homogeneous sulting ammonia and orthophosphate by the indophenol chromous/titanous reduction system for the automatic reblue and molybdenum blue metl- ods, respectively, N was duction of nitrates has been interfaced with the digestion determined in t h e range from 0-15% and P in the range of phase and color development manifold, resulting in a to0-4% a t a rate of 40 and 30 samples,/hr, respectively. tally automated system for determining nitrogen in fertilTwine e t al. (84) made a similar investigation in which izers with a n effective analysis rate of 20-25 samples p e ~ a common digest was used for N and P analysis. ANALYTICAL CHEMISTRY, VOL. 45, h 0 . 5, APRIL 1973
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Bremmer et al. (9) report the use of a n ammonis electrode for the determination of ammonium in Kjddahl analysis of soils. The distillation step in Kjeldakl soil analysis can be eliminated by use of an Orion NH3 electrode. When used with the digests obtained by the Kjeldah1 method, the electrode method for determining NH3 was precise, simple, rapid, and the NH3 recover3 was quantitative. The results by the Orion NH3 eleclrode method agreed closely with those obtained by the customary distillation-titration methods. Electrodes constructed of anion exchange resins coi~sisting of various reactive groups were investigated by Elclinskaya et al. (6) for their specific application to NO3-. Exchange capacity, application to ranges of concentrations, and effect of electrode swelling in water were studied. Cosgrove et al. (19) have developed a selective elecl rode for the NH4+ ion. The electrode is capable of measuring NH4+ in the presence of other cations. A N o s - selective electrode used in conjunction with a F- reference electrode which was placed in a soluticii of low concentration of F- ions was reported by Manpi < I ian (58). Nitrate ions in the range of 5 x 10-5 to 1 x 10 2M can be determined with *l% relative error. Kulyukin et al. (45) used a KU-2 cation exchange Itsin in the acid form for the analyses of nitrogen or potassium in simple fertilizer materials such as NH4NO3, KpiO3, KCl, etc. The fertilizer was dissolved and placed on the column. The eluate was titrated with 0.2N NaOH. .:’ormulas were given for calculating nitrogen or potassiuni in various fertilizers such as N in K N 0 3 , ammonia h in NH4N03, or K in KC1. Results are accurate to within f2.570. Ion-exchange resins were used in the detection m d quantitative determination of water-soluble nitrogen in mixed fertilizers. In their procedure, Rasmussen et al. ((23) extracted the total water-soluble nitrogen by shaking 10 grams of the fertilizer with 800 ml of water for 1 hcur. Ammonium-N and nitrate-N were separated by passing the solution through cation and anion exchange resins, 1 espectively. By subtracting the sum of the ammonium-N and nitrate-N from the total H20-soluble nitrogen, 1 he amide-nitrogen was determined. Cisnecos et al. (15) have reported a comparison betwccn the distillation and ion-exchange methods for the quan1.itative determination of nitrogen in ammonium sulfate f :rtilizers. Both methods were equally accurate, sensitive, and precise, with the ion-exchange method being fasior than the distillation method. A comparison of three methods to determine N W i l S made by Chromiak (13) which showed differences ‘10 greater than 2%. After passing the sample through a Dowex 50-W X 4 cation exchange column in the H+ forin, the amount of N in the NH4+ and N o s - forms was measured titrimetrically. The nitrogen concentration of NH4N03 was analyzed in a n aqueous acetone medium 1)y conductometric titration of NH4+ using 0.5N NaOH. The nitrogen content as the ammonium ion was also e v a l u a t d by the formaldehyde technique. Sajo et al. (71) have reported a rapid, direct readirig thermometric method for the analysis of N, P, and K 111 fertilizers. The temperature change of the test soluticii was measured in each of the following analytical steps. 111 the absence of Mg ions, phosphate was precipitated with i l magnesia mixture; in the presence of Mg ions, NH4 pho::phomolybdate was precipitated and the excess molybdate was then reacted with Hz02. Potassium was determine :I by precipitating with silicofluoride. For ammonium salt:, the NH4+ ions were condensed in a basic solution wit71 formalin to hexamethylenetetramine. Nitrogen as carbam70
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ide was decomposed with NaN02, and nitrogen as nitrate was reduced with Ti(II1). With this method, the time of analysis was reduced to, at most, about 15 minutes for any determination. According to Ashdrof et al. (4), nitrogen in organic compounds can be determined by a n iodometric method. The nitrogen which is present as (NH&S04 in the Kjeldahl digest was quantitated by the iodometric determination of the remaining KBr03 after the addition of a measured excess of KBr03 to the digestate. Ammonia N was calculated from the amount of KBr03 consumed. KBr03 can be replaced in the above method with KMn04 without a loss of accuracy. This method is applicable only following a regular Kjeldahl digestion. Ammonia nitrogen cannot be recovered from undigested samples. Halasz (35) reported a method for the determination of nitrogen by oxidation of NH4+ with hypobromite. The process, applicable to fertilizer samples, involved the determination of nitrogen as ammonia or urea by spectrophotometrically monitoring the change in BrO- concentration a t 333 nm after the oxidation reaction. Reducing compounds were found to interfere. Turek (83) has modified the hypobromite technique for the analysis of nonprotein nitrogen. He employed a photometric determination, in which sulfanilic acid was used to measure the excess hypobromite instead of potassium iodide. Turek found the yellow discoloration of the end product to be particularly advantageous for photocolorimetric measurement. Volatility resulting in color loss did not occur. Kruglova et al. (51) suggested a volumetric determination of the form of nitrogen in fertilizers. An accelerated formalin method for determining ammonium nitrogen with prevention of A1 phosphate separation had a mean square error of 0.10-0.15%; and a n accelerated volumetric method for determining the nitrate nitrogen based on the reaction of nitrate with Fe(I1) had a mean square error of 0.10-0.15%. Tsap et al. (82) presented a volumetric method for the determination of ammonium and protein nitrogen. The procedure involved an amperometric indication of the end point and elimination of the ammonia distillation step according to Kjeldahl. I n samples digested with HC1 and H2SO4, both NH4+ and protein nitrogen were determined by titration with hypobromite in the presence of sodium tetraborate and sodium,bromide. A conductometric diffusion rate method determining micro amounts of ammonical-nitrogen applicable to small samples (20% PzO5). The differential method differs from the direct method by the fact that measurements are performed in comparison with a reference solution. The time required for this determination was approximatidy 1 hour per sample with comparable accuracy to (0.2 to 0.5% relative) the standard gravimetric methods. Impurities such as CaO, FezO3, AI&., Si02, SiFGz-, and F- in large excess to P2O5 did not interfere. Another differential photometric method was reported by Sharopova (76) utilizing the phosphomolybdenum Iilue method. The absorbances of the samples containing 0 to 4.5 mg P205/100 ml of the colorimetric solution viere measured against a standard solution of 2.5 mg P205/100 ml. The results were evaluated from a calibration curve. Kerber et al. ( 4 7 ) compared the determination of pfosphorus by atomic absorption and flame emission specti oscopy. The atomic absorption analysis, using the li-ies 2136.20 and 2135.47 19, did not exhibit interferences due to Al, Ca, Cu, Fe, Na, and K, as did the flame emission of HPO molecules at 5262 F\. The detection limits were I30 pg P/ml for atomic absorption and 0.2 wg P/ml for flame emission. The Ar-H-entrained air flame was generally preferable to the air-H flame for flame emission, becaL::e of increased sensitivity and reduced background emission. A modification of the quinolinium molybdophosphal e method has been proposed by Melton e t al. (55) wherehy total P can be determined indirectly by atomic absorption of Mo. The official gravimetric procedure was followd until the quinolinium molybdophosphate precipitate wiis formed. The precipitate was then dissolved in "4011, and Mo was determined by atomic absorption. Phosphorus analyses of Magruder collaborative fertilizer samplc 3 by the AOAC and proposed methods agreed favorably. Corcoran e t al. (16, 17) determined Ca and P in phosphate rock by plasma emission spectrometry. The proce. dure involves fusion with LiB02, dissolution in 20% HN03, and subsequent dilution with H2O to 100 ml. Phosphorus and calcium were then determined by emis. sion spectrometry with a dc Ar plasma excitation sourct' a t 253.6 and 393.3 nm, respectively, and a high resonancc echelle grating, The precision of the plasma emission method was not so good as that of the flame emission method but was directly comparable to that of atomic absorption. The very high temperature of the excitation source reduced chemical interferences and permitted determination of P where it would not be excited under conventional methods; while the high dispersion monochrometer reduced the background interference which would normally accompany the high temperature source. 72 R
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An indirect neutron absorption method to determine fluorine and phosphorus apatites and fertilizers has been reported by Brafman et al. (8). Sample preparation includes precipitation of GdPOI and then redissolving the The absorption of neutrons precipitate in 1.OM "03. from a Pu-Be source in these solutions was measured with a Li-glass scintillator. The method is applicable in the range of 1to 30 mg of phosphorus per sample. Sedova (73) has described a titrimetric procedure for phosphorus in fertilizers based on its conversion with NHd molybdate in the presence of HzS04 to phosphomolybdic acid, which is then extracted with a BuOH-CHC13 (1:3) mixture. A potentiometric titration of the acid is then carried out with freshly prepared tetraethylammonium hydroxide in MeOH-BuOH. The relative error was 5%, and the time of analysis about 30-60 min. A volumetric method for determining total P205 in rock phosphate and phosphatic minerals has been reported by Sengupta et al. (75). The procedure involves dissolving and isolating the samthe sample with H3B03 and "03 ple by precipitating phosphorus as ammonium molybdophosphate. The precipitate was dissolved in NH40H and treated a t p H 10 with excess magnesium ammonium chloride. The excess Mg was then titrated with EDTA against Eriochrome Black T indicator. The absolute standard deviation for a 39.94%Pz05 sample was 0.15. However, the procedure allows for only about 6 analyses per day. An amperometric technique for the determination of PzO5 in fertilizers and phosphorites was developed by Rumyantseva (70). The best supporting electrolyte for the amperometric titration of Po43- with Bi salt solution was a buffer containing glycocoll NaN03 HN03. In the determination of 5 to 20 mg of P205, the mean square error was &1.33%. An ion-selective lead electrode was used by Selig (74) for the potentiometric microdetermination of phosphate. Phosphate (0.1 to 2.5 mg) was titrated potentiometrically with Pb(C104)z a t pH 8.25 to 8.75, without interference from NO3- or S042-. A Pb-selective electrode, a doublejunction reference electrode, and a n expanded scale p H meter were used. Chloride and F- can interfere slightly, and the silicate content must not exceed that of P. Anions forming insoluble P b salts (pK,, > 8) will interfere. The mean recovery for 0.1 to 2.5 mg of phosphate was 99 to 104%. An indirect polarographic method for the microdetermination of P in organophosphorous compounds has been described by Bishara (7). Alkaline hypobromite was used as oxidizing agent. Quinoline molybdophosphate was precipitated with a measured excess of standard molybdate solution and the unreacted Mo(V1) was determined polarographically. One determination takes about 40 minutes with no interference from N, C1, Br, and S. The results obtained fall generally within the acceptable limits of error. Rapid methods for the determination of the main components of fertilizer by direct-reading thermometry have been developed by Sajo et al. (71). In the absence of Mg ions, phosphate is precipitated with a magnesia mixture. In the presence of Mg ions, ammonium phosphomolybdate was prepitated and the excess of molybdate was reacted with H2Oz. In either case, the temperature change of the test solution was measured with time of analysis -15 minutes per determination.
+
+
POTASSIUM A collaborative study of the automated flame photometric method for potassium oxide in fertilizers was conducted with good results (37). Nine complete sets of anal-
A N A L Y T I C A L CHEMISTRY, VOL. 45, NO. 5, APRIL 1373
yses from the automated method were compared to those by the official AOAC STPB method, 2.090, (11th ed.) for ten typical fertilizer samples and a KNO3 primary standard. The data show no difference between different models of flame photometers and the means and standard deviations from the automated method were in good agreement with the official method. The automated method for KzO in fertilizers was adopted as an official first action method. Peuschel (65) has described a flame-photometric determination for high-percentage potassium fertilizer salts after precipitation of part of the potassium as perchlorate. The method is applicable for fertilizer with a 15 to 63.17% KzO range in which the potassium is present entirely as KC1. After dissolving the sample in H20, a known amount of NaC104 was added and the mixture filtered. The amount of potassium in the supernatant was then determined by flame photometry and added to the known amount precipitated by the NaC104. Within 95% confidence limits, the total random error was 4~0.24%KzO, compared with *0.30% by the gravimetric HC104 method. Hang1 (38) has reported a modification of the flame photometer for the determination of Na and K with Li as a n internal standard. The apparatus operates with light pulses of relatively high frequency without zero point control. A chopper and filter device are positioned just behind the burner; the chopper disk revolves rapidly while the filter changer successively introduces the filters in the light path a t a switching frequency which is relatively low with respect to the chopper frequency. The receiver signal is then supplied to a selecting amplifer and precision rectifier to give a dc signal which is switchable to an amplification control channel or a signal output synchronously with the filter change. Optimum parameters for flame emission spectrometry with the nitrous oxide-acetylene flame have been reported by Christian and Feldman (14). The wavelength, slitwidth, photomultiplier voltage, flame stoichiometry, and heights of measurement in the flame that give the maximum signal/noise ratio were optimized for K and various other elements. Improvements in thermometric methods of analysis for KzO in fertilizers have been reported. Peuschel and Hagedorn (66) described two methods based on the change of enthalpy during precipitation of KC104 and the negative heat of solution for KC1, respectively. The first method can be automated and is particularly valuable for K determination in multinutrient fertilizers (Mg and P can be determined simultaneously). Changing room temperature can significantly influence the results, although normally high data reproducibility was achieved. The second method is even less time-consuming, but is not applicable for K determination in Mg containing fertilizers. Sajo and Sipos (71) have reduced the time necessary for determining N, P, or K to a t most -15 minutes per determination. Potassium is precipitated with silicofluoride and the temperature change of the test solution measured with good results. A radiometric determination of potassium in fertilizers (85) has been reported which is 4 times faster than the gravimetric KC104 method, with an error of f l % . The determination is based on the radioactivity of the 40K constituent of natural K, decaying into isotopes of Ar and 66% y radiation a t maximum Ca and producing 34% p energies of 1.4 and 1.5 MeV, respectively. The p energy was measured because its dpm is unaffected by sample size and remains linear with K concentration. The accuracy is strongly affected by sample composition due to self
+
absorption, but humidity and particle irize 4 3 mm did not affect the dpm. Samples which have second emitterse.g., Ce-must have that value subtrzcted from the final result. Zhivopistsev et al. (89) have made a comparative evaluation of tetraphenylborate methods for potassium determination. They feel the argentometric method of precipitating K with NaBPh4, filtering, dissolving the precipitate in acetone, adding AgNO3 to form AgBPh4, and titrating excess AgN03 with NH4SCN involves the time-consuming disadvantage of precipitation and filtrs tion which give rise to inaccuracies. The potentiometric litration of K salts (fertilizers) with NaBPh4 with Pt/Cu or Pt/Ag electrodes is not a satisfactorily reproducible K determination when high levels of impurities are present. However, this situation was improved by introducing an acetate buffer (pH 5.2), NaC1, and so42- to the sample solution containing 5 to 25 mg of K. Bis(4-dimethylaminophenyl) antipyrinylcarbinol was used as the indicator since it forms slightly soluble compounds with BPh4-, with CHC13 added for sharpness of color change. A photoelectric titration method (901 for the determination of KC1 in mineral fertilizers by employing Na-tetraphenylborate has been described by Zagorovskaya et al. The titration of the slightly alkaline sztmple with NaBPh4 employed an electrophotometric titr stor, and the end point was determined when the microtimperometer needle stopped and would not respond to additional drops of the reagent. The described method produced reliable results showing a relative error in the range of 1,170. Thamm (79) has modified the official AOAC titrimetric NaBPhd method for K in fertilizers by using sterogenol (0.5% solution of cetylpyridinium bromide) and a mixture of bromophenol blue methyl orange ai3 indicator for back titration. A flame photometric deter mination was done from the same fertilizer with a 1% scllution prepared for titrimetric determination after a 100-fold dilution. The error for the titrimetric method was 0.5% and that for the photometric method 0.7%. Geyer (32) performed potentiometric titrations with NaBPh4 by using a graphite-indicating electrode which permitted the determination of 0.01M K + with a n 0.80% relative standard deviation, and without interferences from a 100-fold excess of Na or 10-fold excesses of Ca, Mg, or Al. At pH 2 to 8, 1 5 m M K + can oe determined. The graphite electrode was made of wax-,mpregnated C and was either anodically polarized or trcmated with a strong oxidant prior to use. Halasz and Pungor (36) described a 10- to 15-minute titrimetric determination of potassium with NaBPh4. The interfering metal ions were precipitated as hydroxides along with the KBPh4. A 0.7 wt% HCHO was added to eliminate NH4+ interference, and excess BPh4- was titrated with benzalkonium chloride against a bromophenol blue-Titan yellow mixed indicator. Khreish and Boltz (48) have described an indirect method for potassium analysis which involves precipitation of KBPh4 and the determination of the excess reagent in the supernate. The excess reagent was extracted into ethyl acetate as the tetrapheiiylborate-bis(2,9-dimethyl-1,lO phenanthroline)copper(l) complex and determined spectrophotometrically at 456 nm or by atomic absorption a t 324.7 nm. The relative !kandard deviations were 0.8 and 1.4% for determining 80 and 60 pg of K, respectively, by the spectrophotometric and A.A. methods. A considerable amount of work has been done with Kselective electrodes in the past two years. Although no published work specifically reports on fertilizers, a wide variety of applications in biological and soil mediums, etc. ANALYTICAL CHEMISTRY, VOL. 45, NO. 5, APRIL 1973
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was published. Response characteristics and differeni. parameters such as selectivity are known and different clectrode models are now on the market. A typical sensi;ivity appeared to be -lO-4M K+ as reported by Akimolo ( I ) with the selectivity varying, depending on the amounts and types of other cations present (52). Slight anicn effects occur with iodide, hydroxide, chromate, and ox:ilate, and large shifts with BPh4- with the Orion potassiu 71 selective electrode (54). Because of interferences, these effects may limit the usefulness of the electrodes as routine analytical tools, but they should still lend themr olves available to many special applications.
SECONDARY AND MICRONUTRIENTS Lerner (57) has produced a book which is a comprehensive collection of modern analytical methods for boron. The title of the book is “The Analysis of Elemmtal Boron.” Hofer (39) determined that boron could be det:cted spectrophotometrically by extraction with 2-ethyl 1,3hexanediol and color development with azomethiiie-H. Boron was separated from a 0.1N HC1 fertilizer extract by extraction with 20% 2-ethyl-1,3-hexanediol in isobutyl methyl ketone, re-extracted into 0.5N NaOH, and tictermined photometrically with azomethine-H a t pH 5 . 2 a t 415 nm. The sensitivity of the method was 0.001% in complex fertilizers. Pickett reported on a method (67) for B determin ii t’ion using 2-ethyl-1,3-hexanediol. This compound was recmtly applied to complex fertilizers for extraction of B and m a l ysis by atomic absorption. This extraction procedurc: can also be applied to flame emission spectroscopy usiIig a n air-H flame. This convenient method although us iig a relatively cool flame, excites the oxides of B to emission a t a high enough intensity to provide superior detection limits of about 0.1 ppm in the extract. The lack of int?rference provided by this extraction procedure permits very low background and very reliable measurement of B -jxide emission. Older flame photometers may be used, altk ough modern instruments with recorders are preferable. 1 riterferences and external factors were studied, and the Inethod was tested on several boronated fertilizers. A rapid method (87) for the determination of B WE'^ developed using azomethine-H in aqueous solutions. The method has been automated for rapid analysis. Plan1 material, soil extracts, composts, manures, water, and ~iutrient solutions have been tested for B extraction iii the presence of other elements. The preparation of reaE:ents and the analytical procedure are described in the Fjven reference. Holz has developed a method ( 4 0 ) for Cu detection using 2,2-bicinnamic acid. The Cu detection method used an AutoAnalyzer procedure on multinutrient fertiliz i x in the following manner. A ground sample of fertilize18 was extracted with 10% H2S04. Cu(I1) was reduced with NH20H.HC1, the color developed with 2,2-bicinr amic acid, and the absorbance of the violet complex measured a t 570 nm. A manual procedure was also described for the determination of Cu in which the absorbance was measured a t 578 nm. Nava (62) has made a comprehensive comparison c f five methods of analysis for Cu. The five methods are ilithizone carbamate, Zincon, neocuproin, versenate with chromazural S indicator, and versenate with murexide ir dicator. The first three methods gave values that were in close agreement. The neocuproin procedure was recommc iided for very small amounts of Cu. 74 R
A method for determining Fe (78) in solid phosphates has been developed capable of detecting 5 X 10-69’0 Fe. The sample was dissolved in 1:l H N 0 3 and the Fe extracted with an aqueous solution of n-dodecylamine nitrate in CHC13 and ethyl alcohol. Five milliliters of the extract were added to 2.5% sulfosalicylic acid (in 2.5% solution of “3) and shaken. After 20 minutes, the aqueous phase was filtered through a dry filter into a 10-nm cuvette and the absorbance read a t 420 nm with dodecylamine nitrate solution in the reference cuvette. The relative error of the determination was +7%. Ivanov (42) discovered that the effect of phosphate ions on Mg analysis by atomic absorption can be overcome by large amounts of Ca2+ ions. The presence of phosphate ions decreased the atomic absorption of Mg. The effect of the phosphates can be diminished or eliminated by addition of Ca which fixes the phosphate into a nonvolatile and very stable compound Ca3(P04)2. Spectrophotometry was based on the use of a ZMR-3 monochromator tube with hollow Cu cathode containing Mg in the form of an impurity, and a C~Hs-airflame of 15-mm diameter. A method (88) for Mn has been introduced by Yatrudakis using NaNO2 in an amperometric titration. The titration was conducted using a n amperometric titration unit equipped with a rotating Pt electrode (600 rpm) 30 mm long and 0.5 mm in diameter. A calomel electrode was used as a reference. The best equivalence point and reproducibility were obtained by acidifying the sample with 2.5 to 3.ON H2S04 or “ 0 3 . Both acids may be used when the amount of Mn(VI1) is more than 0.06 mg in the initial sample. Only H N 0 3 can be used when the M n content is below 0.06 mg. This method was used in the determination of total and mobile Mn in soil of the Tashkent region of the USSR and also in multinutrient fertilizers. The difference in results between photocalorimetric and amperometric methods never exceeded 8%. The method does not require the prior removal of H4Si04 and the plotting of a calibration curve. The Mn is determined immediately after decomposition of the sample and oxidation of Mn(I1) to Mn(VI1). Holz ( 4 1 ) determined Mn by use of potassium diorthoperiodatoargentate. The periodatoargentate(II1) reagent so: lution was made from 28 grams of KOH and 23 grams of KIOl in 100 ml of water to which 8.5 grams of AgNO3 were added. The mixture was heated to boiling and 20 grams of were added over a period of 30 minutes. The dark red solution was filtered and diluted 1:l with water. The orange reagent is stable but dark storage is advisable. Ag(II1) complex is a strong oxidant and instantly converts Mn(I1) to MnOd-. Analyses were run using a Technicon AutoAnalyzer a t a rate of 40 samples per hour from 0 to 25% Mn. The relative standard deviation was *0.1 to *0.4%. A collaborative study (80) was conducted to show that H2S04-HN03 digestion of fertilizer in the atomic absorption method for Mn more nearly reflects the available Mn than by the HC1 digestion. A method to detect water soluble Mn was also included in the study. Modifications of the HCl digestion for both total Mn including available Mn(I1) plus unavailable Mn(IV), and the H2S04-HN03 digestion for available Mn were adopted as official first action by the AOAC. The water extraction method ais0 was adopted as official first action for water soluble Mn. A new method for the analysis of Mo was reported by Koirtyohann (49). The fertilizer sample containing Mo was dissolved in HC1 to which 8-hydroxyquinoline was added to chelate the Mo. The Mo chelate was extracted with CHC13 a t a pH of 1.6. Fifty milliliters of the solution containing less than 200 pg of Mo were extracted with 10.0
A N A L Y T I C A L C H E M I S T R Y , VOL. 45, NO. 5, AF’RIL 1973
ml of CHC13 for 30 sec. The Mo was determined by atomic absorption using a nitrous oxide-CZHz flame. The sample mixture was aspirated directly into the flame. The molybdenum method of Koirtyohann (49) was studied collaboratively in 1972 (50). The results of this study indicated that additional work was needed to improve the precision a t low molybdenum levels and to evaluate a possible positive bias in the method. Graff (34) found that a t 1300 "C a n oxygen stream removes sulfur quantitatively from silicate rock but not from carbonate rock such as limestone or dolomite. For the latter, a turbidimetric method was proposed, based on the dissolution of the sample followed by the precipitation of B a s 0 4 by the addition of BaC12.2HzO. The extinction coefficient of the solution was measured a t 480 nm after the solution and precipitate has stood 2 4 hr but 420 hr. The method of Alimarin and Frid (1961) for determination of sulfur was modified by Trubetskova (81) for the determination of S in solutions containing phosphate. The phosphate was precipitated with CaClz after addition of NHdOH, and the sulfur was determined in the supernatant after centrifugation. A collaborative study (44) was made of a zincon ionexchange method for the quantitative determination of Zn to validate the method for the determination of Zn in fertilizers. Statistical evaluations were made to estimate the precision, accuracy, and dependability. Reference data for evaluation purposes were obtained by atomic absorption measurements. The method fell short of expectations as a n alternate approach to the dithizone method. It was recommended that the methods for determining Zn in fertilizer be further studied. The results of a collaborative study of the two official AOAC flame photometric methods for the determination of sodium in fertilizers were reported by Corominas (18). The methods compared, differed in the extraction used. One method used ammonium oxalate, and another ammonium carbonate. Also, both methods were evaluated with and withoug the use of an ion-exchange resin cleanup (Amberlite IR-4B) on the sample solutions. The results indicated that the sodium values obtained without the use of the ion-exchange resin were generally lower; however, i t was concluded that any of the four techniques studied gave adequate results. Contribution of the Missouri Agricultural Experiment Station. Journal Series No. 6641. Approved by the Director. LITERATURE CITED
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