Review of
APPLIED ANA LYSIS
FERTILIZERS J . A . Brabson Tennessee Valley Authority, Wilson Dam, Ala.
T
review covers articles in the biennium ending August 15, 1958, which the author considers particularly pertinent to the analysis of fertilizers. The last review in this series appeared in April 1957 (11). HIS
OFFICIAL METHODS
The biennium saw the Association of Official Agricultural Chemists (AOAC) incorporate rather extensive changes into its methods. It adopted as “first action” a reduced iron method for nitrogen, a differential spectrophotometric method for total phosphorus, and volumetric and flame photometric methods for potassium. The AOAC gave “official” status to methods for the determination of acidinsoluble ash and carbonate carbon, a technique for the mechanical analysis of phosphate rock, and a nitric-perchloric acid method for the preparation of solutions for determination of phosphorus. SAMPLING AND SAMPLE PREPARATION
Statistical approaches proved valuable in studies of the sampling of highanalysis mixtures, including no-phosphate grades that contained nitrogen compounds in pellet form (39, 34). Several coring tools were compared. Tests of various methods for reduction of samples to laboratory size led to the conclusion that grinding of the gross sample to -20 mesh mas desirable ( 3 ); equipment was described for sampling and sample preparation. Construction details of a multiple riffle for reduction of gross sample to laboratory size were reported, and its performance u-as evaluated by means of screen analyscs ( 7 2 ) . Segregation in laboratory samples of a 10-10-16 fertilizer n a s traced to a particular crystal form of ammonium sulfate n hose growth was promoted b y granulation (50). Only when the crystals vere fractured by grinding the sample to pass 30 mesh (British standard 410: 1943) could satisfactory checks be obtained in duplicate analysts. AMMONIACAL SOLUTIONS AND LIQUID FERTl LlZERS
Problems in the sampling and analysis 688
ANALYTICAL CHEMISTRY
of liquid fertilizer matc4als continued to receive attention. A hydrometer method for field evaluation of aqua ammonia compared favorably with chemical analyses (69). A later report (70) on a collaborative study of the method included procedures deemed suitable for sampling of various liquid fertilizers. I n a technique proposed (44) for the sampling of pressure fertilizer solutions, the solution was released through a n appropriate valve into a partially collapsed polyethylcne bottle containing water for dissolution of thr sample and reduction of the ammonia pressure. Apparatus for field sampling and laboratory assay of anhydrous ammonia a as described (52).
WATER
Moisture in ammonium nitrate was determined rapidly through direct use of Karl Fischer reagent, with substitution of a volumetric measurement for analytical n-eighing of the sample (28). Alternatively (27), water was extracted with a stream of dry nitrogen and determined by the thermistor bridgc-calcium hydride method (48). Because extraction of water by nitrogen n a s incomplete, the method was calibrated against analyses made n ith Karl Fischrr reagent
(28 9
K a t e r in ammoilium nitrate was titrated n ith an iodine-pyridine solution containing no methanol, in a simplified procedure (67) found directly applicable to samples containing over 1% nioisturc. -4 knonn amount of water was added n hen the content was under 1%. Free and hydrate n ater contents of ordinary superphosphate (fresh and aged) were estimated (46) by an azeotropic distillation in n hich benzene removed free n ater- xylene picked up free and hydrate nater. Free acid caused some removal of hydrate jvater by benzene, an effect largely overcome b y adding calcium carbonate.
for nitrate-containing samples ($3)and a reduced-iron method (22, 23) proposed earlier (37). The first study led to recomniendations that 15 grams of potassium sulfate be used to raise the temperature, that the burners be adjusted to a standard rate of heating, and that samples containing organic matter be digested for 2 hours after clarification. A study of the acid requirements of the Kjeldahl digestion (17) shon ed that nitrogen is lost n hen the amount of acid is so small that solidification occurs. Sodium sulfate proved less satisfactory than potassium sulfate for increasing the temperature, because sodium arid sulfate is less soluble than potawum acid sulfate. Collaborative studies (22, 23) shon ed that results by the reduced-iron method uwally n rre higher than results by the Kjeldalil method on samples having high ratios of chloride to nitrate. The reduced-iron method proved especially useful in the analysis of liquid fertilizers and n as adopted as first action (76). For dirwt determination of nitrate nitrogen. an earlier oxidimetric method (60) proved n ell suited to conventional fertilizers, a slight modification making it applicable to urea-containing samples (2.9). Iiitrate n as determined directly also by potentiometric titration with ferrow sulfate (58). Its reaction n i t h sulfamic acid n a s used for determination of nitrate ion, the excess sulfamic acid being titrated with sodium nitrite solution (49). The method n-as applied to fertilizrrs, although chloride ion had to be reinowd by addition of sih er sulfate. Urea in mixed fertilizers, containing phosphate, n as determined dirertly through an adaptation (69)of a volumetric urease method (39). h i o t h e r urease method (76) proved applicable to the rapid determination of urea in nitrogen solutions. Crea in u-atcr extracts of fertilizers and feeds \\as determined by the p dimethylaniinobenzaldehyde color rcwtion (55).
NITROGEN
PHOSPHORUS
Collaborative studies of nitrogen methods concerned the Kjeldahl method
I n a collaborative study (63) of methods for preparing solutions of
organic materials for deterniiiiation of total phosphorus, solute phosphorus was determined by t'he official volumetric method. Xitric-perchloric acid digestion compared favorably nit11 the magnesium nitrat'e-hydrochloric acid treatment and was made a n official procedure (76). Kitric-sulfuric acid digestions usually led to higher results. Precautions in the handling and use of perchloric acid n-cre formalized by a n ,401C committee into a statement (14) that will tie incorporated into the "Official Methods of Analysis." Ken- emphasis was given errors cntailed in the persistent bad prartice of using volumetric flasks where beakers sliould be used in the analysis of fluorinecont'aining materials (16). The molybdovanadophosphate color rcJaction provided a basis for tn-o collnhorative studies (la,S I ) of the diffrrcntial spectrophotometric deterniination of phosphorus. Spcctrophotoriic.tric results gencrally n-ere l o w r than the volunietric results in both s t d i e s . One study (12) included Sational Bureau of Standards phosphate rocks, arid the results strongly indicate that the sl)cctrophotomctric method approaches tlic true phosphorus content closer than the volumetric nic.thoc1. The sl,ectr~)l)liotomctrict method was adopted a s first action by the AOAC (76). R(moiis for discrepancics in anal,Y-S:T of concentrated suprrphosphate 1voi-c sought through quc'stionnaircs and cd1abor:itive studic>s hy the C'hcniical C'ontrol Committee of the Satioiial P h i i t Food Inst'itute (62). The coniniittw found rvide differences in cheniists' intcrprcltations of official proccdurclr. E\-cn col!aborators using the w i i e lmsic nicchanics obtaincd diffiwiit rc8wlts. Rcsults for citrateinsolublr~ phosphorus reflected in partirular the failure of chemists to adhere strivtly to details. l k t h o d s dcscribcd for the dctcriiiination of t,otal phosphorus iiicliided (15) application of the Sargmt-3Ialnistadt aut'oniatic titrator (61) to the titration of ammonium niolybdophosphat,e n.itli alkali. Addition of forniald(,hyd~ sharpened the cqui\-alence point. Th: automat'ic titration cliniinatc,s the, pcrson:aI crror of ciid point perception inhcrcnt in tlic official rnc~tllod. Pliospliorus n-as prcc4pitatcd :is l m r l pliosphate and determined gravinietric:iIly (79) or volumetrically (78) n-ith a cliloroform solution of dithizonc as the indicator. Swcral long-standing unccJrtaiiities wcrc removed (13) from a nietliocl in \vhich phosphorus is wighc,d as osine iiiol!-l,dopliosphate (757, and the revised iiicthod was applied t o pliospliate rocks. Several recent methods were judged siibstantially cheaper and att least as
accurate in a comparison (26) with official methods for phosphorus. The newer methods included a differential spectrophotometric method, a n alkalimetric met,hod involving an initial precipitation of quinoline niolybdophosphate, an alkalimetric method based on separation of ammonium molybdophosphate in t,he presence of citrate, and an improved nicthod for separation of phosphorus as magnesium ammonium phosphate.. I n a rapid method ( 4 7 ) for the determination of n-ater-soluble phosphorus in superphosphate, precipitation of calciuni from the n-atcr extract by nddition of potassium oxalate made> possible tit'ration of the phosphoric acid with sodium hydroxide. A niethod ( 1 ) for available phosphorus was adapted ( 2 ) to fc)rtilizc,rs containing calciuni metaphosphate. For convenience. the filtering apparatus was modified to eliniinatc transfer of solution from filter flasks to volumetric flasks. Further collaborative tcsting (54) of methods for the niechanical analysis of phosphate rock confirmed the supc'riority of a combination \vet-dry sieving method ovcr dry sieving alonc and led to official adoption of the comliinat'ion method (76). ii dispersant aided in the n-et sieving of Florida soft phospliat'e containing mlloidal clay hut was of little help n-it'h ground phosphate
rock. POTASSIUM
TIT-ohibliograpliics 0 1 1 the dctcrniinatioii of potassium (8, 47 rc.fercnces; 9, 64 rcfcrences) reflwted a continuing livrly interest in tlic reagent sodium t,etraplienylborate. Tet,raphenyiboratc procedures developed primarily for tlic analysis of fcrtilizers includcd (71) a precipitation of the potassium from a solution in n hich ammonia was complexed n-ith fornialdehyde. Excess tetraphenylhorate in the filtrate n-as tit'rated n-ith a standard solution of a quaternary ammonium salt. Bromophenol blue nas thr, indicator. The Association of Official Agricultural Chemists adopted t,he method as first action (76) after collaborative study (38). Anirnonia was also complexed n-ith formaldehyde in a gravimetric method (SO) for precipitation of potassium n-ith tetraphenylborate. Ammonia was removed by distillation after addition of sodium carbonate in another procedure (36). The tetraphenylborate was redissolved and titrated wit,h silver nitrate. Other proposals for determining potassium, once precipitated as the tetraphenylborate, inclucled a spcctrophoto-
metric method (65), an amperometric method (32), and a volumetric method (35) ending as an EDTA titration. Anion interferences proved troublesome in several collaborative studies of flame photometric methods for potassium, especially in direct intensity methods. Tests of various ion exchange resins as media for eliminating the interferences (42) led to a method that AOAC studied collaboratively (38) and adopted as first action (76). Potassium in potash concentrates and tailings n as determined by nieans of the x-ray spectrograph; t h e requirement vias G minutes for tailing and 3 for concentrate (46). The niethod can probably be standardized for fertilizer mixtures, including liquids.
CALCIUM A N D MAGNESIUM
The speed potential of (ethylenedinitrilo) tetraacetic acid (EDTA) as a reagent for the determination of calcium and magnesium led to the del elopnient of many procedures. A revieir (4-7) on the nature of the EDTA titration and methods for the detection of thc end point included many references to methods for calcium and magnesium. In the E D T A titration of calcium in blast-furnace and open-henrth slags, triethanolamine was added to eliminate interference from aluniinum. iron, and inaiiganese (49). Magnesium in basic slags n as determined by EDTA titration, n i t h Eriochronic Black T as indicator (26). Calciuni n as rcinoved as thc oxalate. Aluminum, iron, and manganese in the filtrate I\ cre masked by sodium sulfite, tartaric acid, and potas5iuiii cyanide in basic medium. An EDTA titration procedure (IS) n as adapted (77) to the determination of magnesium in mixed fertilizers after a separation of phosphoruc a' the iron(111) salt a t a pH low enough t o prevent copreciprtation of magnesium. A flame photometric procedure was described (51) for the determination of calcium and magnesium in basic slag. The depressive effects of aluniinum and phosphorus on the intensity of the caIciurn emission were offset by addition of wfficient aluniinum to act as a radiation huffcr. Additions of aluminum also prevented iiiterfercnces by aluniiiium and calciuni in the magnesium drtcrniination.
SULFUR
Among errors affecting the determination of sulfur by precipitation and ignition of barium sulfate, interference by phosphate is especially troublesome. Optimum conditions for separation of barium sulfate in the presence of phosVOL. 31, NO. 4, APRIL 1959
e
689
pliatcl n.iw eiiunieratetl (56): io\r pH, dropn-ise addition of barium chloride precipitant with both solutions a t 90" C.: niid restriction of (witact tinit. hetween precipit,ate and solution to 24 hours or less. DPterniinations of sulfate in technical phosphoric n i d and phosphates to ivithin =3% in the range 0.01 to 2% sulfur trioxide w r e rcported for a turbidiniet,ric nirthod ( . $ I ) . C'ondensed phosphates n w e first converted to orthophosphate. FLUORINE
The bleaching action of flnorinc on thc red zircoaiuni-aliznriIi lakc providcd a basis for the detc.rminution of fluorine in phosphatr minerals without R prcliminary distillation (80). Conditions n-ere descrilied for avoiding the prccipitation of zirconium pho~phatc. An indirect method for the dcterniiiiation of fluorine in inorganic compounds \vas based oii the drterniination oi silicon, distilled as silicon trtrafluoride (21). The distillate was hydrolyzed in a boric acid-sodium borate buffer solution, and silicon was detcrniined as the het'eropoly blue complex. Organic fluorine compounds n-ere decomposed by combustion in a quartz tube packed with quartz chips and platinum gauze, the effluent gas passing into the buffrr solution. S p e c t'r o p h o t'om e t r i c and visual methods for tit'ration of fluorine \\-it11 thorium nit'rate showed about the same accuracy in a coinparison (ad),but, the visual nict'hod was much fast,er.
from macro elenients proved advantageous in the spectrographic analysis oi soils. frrtilizers, and biological niaterials for silver, cobalt, copper, mangancw, molybtie$um, nickel, lead, vanatiiimi, aut1 zinc (7'4). The trace metal 11)-rollidinc dithiocarbamates 11-erc estractctl in chloroform from a sulfosalicylic acid solution a t pH 4.8. The extracts n w e aslied, and an internal standart1 n'as added.
I n the flanie photometric dcterniination of boron in fertilizers ( I O ) , a dilute acid extract n as passed through ion exchange resins (H and HCOO forms, respectively) to remove interfering ions. The boron emission a t 548 mp in an osyhydrogen flame n a s measured n i t h a Beckman DL- spectrophotometer. Boron was also determined titrimetrically or colorimetrically in solutions freed of interfering ions by treatment with the resins IR-120, H form, and IRA-400, C1 form (61). Once separated from interferences, as by a methyl borate distillation, boron can be determined by various spectrophotometric methods. Recent studies of color reactions included chromotropic acid (59); diaminochrysazin, dianiinoanthrarufin. and tribronioanthrarufin (BO); carminic acid ( 6 7 ) ; 1,l'-dianthriniidc ( 6 8 ) ; and curcumin (66). MINOR ELEMENTS-GENERAL
An initial separation of trace elements
690
a
ANALYTICAL CHEMISTRY
1.
(1957). COBALT, COPPER, A N D ZINC
The r ~ coniplcs d b c t w c n cobalt and 2-iiitroso-1-naphthol provided a basis for a aensitivc colorimetric method (19) that n as applicd t o phosphate rock and prohabl>- is suitable for the analysis of fertilizers. Paper chromatography 7 1 - m used to separate cobalt, coppcr, nickel, and zinc for detrrniination by spwtrophotometric proccdurcs ($0). The method proved applicable to any combination of the four elements.
LITERATURE CITED
i.76.
18) Barnard, X. J., Jr., Burchl, H., Ibid.,
46, 16 (1957). 9) Ibid., 47,46 (1958). 10; Bovav. E.. Coesv. .%.. M i l t . Gebiete L e b e n s k . u. Hyg 48; 59 (1957). 11 1 Brabson. J. A , , AWAL.CHEJI.29, 643
(1957).
(43) Gottlieh, 0. K., AIagnlh8ea, 11. T., - 1 S h L . C H E U . 30,995 (1958 i . (44) Greene, P. A , , J . ;Issoc. 0.8~..1 y r . C h e m f s t s 40, 305 (1957;l. (45) Gulbransen, L. B., - 1 s . t ~CHEM. . 28, 1632 (1956). (46) Harel, S.,Talnii, .I..Ibifl., 29, I694 (195i). (47) Harel, S., Tamari, 31.. Tdmi, h., J . d u r . Food Cheui. 6, 589 (1958). (48) Harris, F. E., S a s h , L. I\,,ASAJ.. CHEX 23, 736 (1951). (49) Hirano. S..Kurohe,, AI.< Bunseki , Kagakrt. 5 ,' 680 ( I 956). (50) Howes, H. S., =Inalyst 83,379 (1958). (51) Ikeda, S.,Sci. Repts. Re.vnrch I n s f s . T G ~ o ~C'niv., I L S e i . -4: 8, 134 11956). (52) Ineram, K.J.. J . Assoc. Ofic. ART. Cheni?sts 41,626 (19581. (53) Jacob, K. I),,Hoffman, K. >I., Ibid., 40,690 (1957). (54) Zbzd., p. ill. 155) Jongen. G H , BeiLhout, H. IT., ' &em. i ~ e k ~ a52,909 d . (19~). (56) liar, K. R., Sath, S . , J . Sci. I n d . Research (India)16B,563 (1957). (,57) Kontorovich, L. 31., Solov'eva, I. G., T r u d y ,\-nuch.-Issledoratei. i Proekt. Tnst. B z o t . Prom. 1954,S o . 4, 234. (58) Krejci, F., Kacetl, L.. Cheiii. & I d . ( L o n d o n ) 1957, 598. (59) Kiiemmel, D. F.. Mellon, AI. G., - 1 s ~CHEJI. ~ . 29, 378 (19.57'1. (60) Leithe, \I7.,J b i d . , 20, 1082 (1948). (61) Nalmstadt, H. Y.!Fett. E. R., Jbid., 26, 1348 (1954). (62) Marshall, H. L.> Reploglr, 11. H., - 4 g ~ Ciienz. . 12, S o . 4, 48, 120 ( l % i J . (63) Morgan, IT. A, Harford, E. F., J . \
,
~
12) Brabson, J. A,, Dunn, R. L., Epps, E. A., ,Jr.) Hoffman, TT'. )I., Jacob, K. D., J . dssoc. O f i c . &4gr.Chemists 41, 51 7
11958). 13) Brabson, J. A,, Edwards, 0 . X Y ~ LCHEX . 28, 1485 (1956).
( 3 2 ) Findeis: *I,F., De I-rieq, T., A h . 4 ~ . CHEJI.28, 1899 (1956). (33j Fiskell, J. G. .I,,Chev. I-,,J . Assoc. O&. Agr. Cheni2'si.s 40,0:3G (1!!57). (34) Fiskell, J . G. Ai.,& l I > ~ , IT. H., Myers) J. AI,, Crooks. R . C., l h o n , R., T:i>.lor, J. J., Ibid., 41, 640 [l058). (35) Flaachka, H., Sadel.;. F.,Chemist dncrlyst 47,30 (19% I. (36) Fontana, P., Zanetti! B., P i i b h l . wziu. caltolicn S. Cuore. An,?. t i i i . . r i g m i . . 60, 201 (1956). (37) Ford, 0. IT,,J . .4saoc~. 0,fic. .tu/'. Chel,i.is/s 39. 763 (1956 I . (38)Ibid., 41,'533 (1958). (39) Fox, E. J., Geldard. IT-.J . , I>id. Eny. Chenz. 15, 743 (1923). (40) Frierson, IT. J., R ~ x ~ r kL),. -1, Toe. J. H., .1\%L. CHEJI 30, 468 (lO58). (41) Gassner, K., Fiiedel. H., Z. a n d . Chem. 152,420(1956). ($21 Gehrke. C. I\-.. TVootl. E. L., Nissouri Univ., *Igr, kxpt. gt;i,>Rrsenrch Bull. 635 (1957). ~
(1) .Illen, H. li., J . Issoc. Ofic. d g r . Chemists 36,872 (1953). 12) Ibid.. 40.992 11957). (3) Archer, 'JY. .I.,Agr. Chem. 12, 10. 2 , 45, 09 (1957). ( 4 ) Barnard, ;i.J., Jr., Broad, W. C., Flaschka. €I., Chemist dnalust 45, 86 (1956). (5) Ibid., 46, 18 (1957). 16) Ibid.. a. 46. ( 7 ) Ibid.;
BORON
(25) Ilonalil, It., Ychn-ehr: E. \V,> Kilsoii, H. S . ,J . Sci.Food A g r , 7,ti77 (1956). ( 2 6 ) Entlo, I-., Hattori, I\., Bunseki k-ogaI:ic 6,243 (1957). ( 2 7 ) Engrlbrecht, R. AI.. DrcJxler, S., . i S . I L . C H E l I . 29, 1100 fl957,'. 128) Engelhrecht, R . 31., Lhesler, S., ~ I c C OF.~ ,A,, J . -4g t ~ ,Fooil L'hc,,~. 4, 786 (19?~6). 129) Engelbrecht, R. 11,; SIcCoj., F. -I., -1x.i~.CHEX.28, 1619 [ I 9 5 6 (30) J b i d . , p. 177%. 131) Epps, E. -I.,Jr., Jucoh. I\. D , , J . dssoc. Ofic. d g r . C'he
W.,
14) Brabson, J. .I.,Stein, C., Jacob, K. D., J . dssoc. Ofic. A g r . Chemists 41, 76 119j8). (15) Brabsbn, J. .I.,Kilhide, \Ti. D., I b i d . , 40, 594 (1957). (16) I b i d . , 41,629 (1958). (17) Bradstreet, R . B., ANAL. CHEII. 29 944 (1957). (18) Cheng, K. L., Kurtz, T., Bray, R. €I., I b i d . , 24, 1640 (1952). 119) Clark, L. J., I b i d . 30, 1153 (1958). (20) Cogbill, E. C., Toe, J. H., I b i d . , 29, 1251 (1957). (21) Curry, R. P., hlellon, 31. G., Ibid., 29, 1632 (1957). (22) Davis, €I, A,, J . dssoc. Ofic. A y i . C'hrmists 41,525 (1958). (23) Davis, H. h.,Miles S. R., Zbid.,40, 675 (1957). (24) Dean, J. Buehler, 11,H., Hardin, L. J., Ibid., 40, 949 (1957).
O f i c . A g r . Chemists 41, 637 (1958). (64) Muto, s., Bull. Chei/f. S O C . J n p a n 30, 881 (1957). (65) Pflaum, R. T., Hon-ick, L.C., -IS.II>. CHEII.28, 1542 (1956). Jssoc.
.I ., J .
Poirell, IT. -I.,PoiiitlestPr, I:. IT., Zhic/.> CCC-1024-TR-226 ( F e l ~20! . 1957~1, I 68, Ibid,, CCC-1024-TR-229 (Ilirrch 8 , [,ti:)
Clitl.
"ill
Rerie~cof
FOOD
APPLIED
Kenneth _Iforgaiaeidge Food and Drug Reseaidi Laboratories, Inc., .llaspeth 78, -1..Y .
T
covers adv:tnces in represented by pulilications available to the author prior to Dcccwiher 1, 1958, and n-hich 1i:tx-e :Ippearccl since the date of the last rcviiv ( 1 79). This period has lieen iiiarketl liy steady progress in tlic allplicatioii of newer t'ecliniques t'o the problems tlealt with by the food analyst paralleling similar advances in other :inalyticaal fic~lds. However, excepting tlie niorc' sycctacular achievements resulting from the application of the more advanccd chromatographic niethods. particihrly in the vapor pliasc, progress in food analysis has h e m largely a niat'ter of refinenic.nt of prrvious nicthods or their application tfJ i m v situations. Limitations in both space and time hnvr made necessary tlie selection of rrpresentative papers for review in ai1 cffort to prewnt a cross section of curwrit litt7rature. Many northwliilo contributions have doubtless bern oaerlooked or have bccn omitted for lack of space. Such omissions :ire not to be construed as constituting a judgment as t o their place in tho pcrniaiient literature on the subjcct. HI>
review
of tlie extraction process is eseiiiplifiecl b>-a method for water in dairy products including cheese, butter, and pondered milk, wherein xylene or carbon tetrachloride are employed in mixed solterns with alcohol (149). M-ater can he i~:tcrniined in cereal grains by grinding in a mc .Med Stein mill prior to extraction of n-atrr n-ith methanol (67). An ingcmious approach t o tlic knotty problem of determining moisture in sugar products was suggested, IT-hereby the sugar \yas ground n-ith cobaltous bromide in dry chloroform ( 5 5 ) . Conihination of the salt with \ v a t u caust~sit to precipitate from solution; it is styarated subsequently by filtration and the remaining cobaltous bromidc is n-cighed aftrr evaporation of the solvcnt. Iiiiprovenient in the vacuum o w n mttliod for nioisturi, in glJ-ccrol, fats, and oils was b a e d on tlic use of a special apparatus n.1iich greatly inc r e a s d the surface area ~x110s(d( I 70). Caution lias betn sounded against the uncritical use of rcfracatomctric riietliods in heavy paste-e.g., toiliato (86).
AMINO ACIDS, PROTEINS, AND MEAT FOODS MOISTURE
Problems csoni-crned lvith the cstension of the Karl Fischer method to iionhoiiiogencous materials have continued to rwrirc. nttention. The principal clifficulty arises from the lack of roniplete water extraction. 3Ioclificaation
Rcports Iiavc continued to deal with efforts to increase the accuracy and reliability of amino acid determinations by paper chromatography. One method reconiniendcd a combination of ninhydrin and 8-quinolinol as forniing niore intense and stablr colors on
i,
pa pi^ n-liicli could hi. vliit[d aiitl r e d photometrically (130). The reproducibility of amino acid a - h a ! ~ by clircct photoinc.tric cstiniation on paper h:is also hrcn studicd ( 1 ~ 4 3 ) . Greatly increased spcctl of sopxxt ion on paper has licc~n clainiid for :I c,onibination of horizontal solvent f l o aiicl ~ ail incrwsc. (to 60" C.) in tlic tltvlopiiig toniporaturcx (144). Tlie time wyuircd for t~~o-climi~nsionnl tl(>r-c.lolini(intand s('ji:tration of a mixturc. of 20 amino acids n-as rrduwd froni tlir c,oiir-c~iitioiial24 Iiours to 2 Iioiirs. T l i ~~ r w i > x f urel placcnic~ntof phenol in t lic fir-t d c ing solwrit for amino cicitl clironiatography was reported (19.;). 1 niisture of butanol, nirtliyl etliJ.1 krtonc. aninionia, and n-ater in the fir.*t tlirrction, follonc~l by butanol arrtic wid, ant! n-ater in the sccoiid clircction was URCCI. Iniprovtd procPdiirt+ for the chroniatograpliy of amino ncitl mixtures 011 c.olullins of sulfonatecl poly.tyrcne rt>sins have b w n rc~porteil (110). This rlcgant method rquires a Iiigli tlcgree of autoination for cunr-ciiient appliciition h i t it has tlic ndvantagc of exwllcnt resolving power :md high prccision. -4.n interesting application of gas clironi:~tograph>to the uiiiiio acid probleni (aisisted in tlieir rccluction t o volatile altleh\-des in which form tliq- are separated on a silicoiie-Celite column (1-98). I s the aldehydps emerge from the column, they are hydrocracked to methane (nickel catalyst), dried, and detected by a thermal contluctivitj- ccll. The
VOL. 31, NO. 4, APRIL 1959
691
