V O L U M E 2 2 , NO. 4, A P R I L 1 9 5 0
567
cupric ions. Methods were also found ivhereby these nietals could bc determined in the presence of the other ions. A future publication will discuss thc industrial applications of ihis reagent.
( , 5 ) Sandell, E. B., "Colorimetrir Methods for the Determination of Traces of Metals," New York, Interscience Publishers, 1944. (6) Tomula, E. S., 2. anal. Cheni., 83,6 (1931). (7) VanderVoort, G , , Fletcher, B., Perry, bl., and Arsem, K., Ihid.,
LITERATURE CITED
Yoe, J. H.. "Photometric Chemical Analysis," p. 173, New York, John Wiley & Sons, 1928. ($2) Yoe, J. H., and Bartnn. C . .J.. TND. Esc;. CHEM.,ANAL.ED., 12,
128,518-22 (1948). (8)
Ihudisch, O., J . A m . Chem. Soc., 63,627 (1941). ( 2 ) Cronheim, G., IND.ENG.CHEY.,AS.LL.ED.,14,446--7 (1942). ( 3 ) AlcSaught, A r ~ a I ~ ( s64, t , 23 (1939). (1)Overholser, I,. G., and Yoe. J . H., 1 s ~E. x . CIimr., :\N,\I.. ED., 15,310--13 (1943). il)
405-9 (1940). ItECEIVED
October 12, 1949
Colorimetric Determination of Boron Using Carmine ,JOlIN.T. IIiTCHEK I
\\I)
I,. \ . WILCOX
. S. Regioricil Salinity a n d Rrihidorir Lnboruiories, Bureuu of Plan 1 Industry,
t 7 .S. Depurtment of ~griculLllrc~,
Riverside, Calif.
\ colorimetric method is described for the qiiantita-
determination of boron, based upon its reaction w i t h a solution of carmine in concentrated sulfuric acid. The method is applicable in concentrations of Imron from traces to several hundred parts per million and in such materials as waters, soil extracts, t i\e
T
flls:RE is nretl lor a rapid arid :wrur:tte niethod for the determination of boron in irrigation waters, soils, ant1 plants. 7'hc1 met hod should be suitahlo for small quantities of materid :tiit1 applicable to deficiency as \v(.11 as to tosicity studies. A number of colorimetric methods have appeared in th(x literature and scvcral of the most promising were tested. I n onc i ) f thrsc (Z), use of a carefully standarctizcd wagetit, containing fuming sulfui+c acid is somc\vh:%t inconvcnieni. I n another ( 1 ), fluoritics intcrfcre and 110 \yay IWS foulid to remove thcni without it loss of horon. Zorkin (6) has reported a qualitative test for ihransmittance.
~
~~
Boron Found in Water Samples Boron, Parts per Million
'
Sample SO.
1
PREPARATION OF STANDARD CURVE
.~~
2 3 4 5 6 7 8 9 10 11 12 13 14
--
Electrometric titration method
Proposed method
Difference
0.37 0.38 0.38 0.38 0.39 0.80 0.96 1.07 1.66 2.34 2.87 3.22 4.65 8.44
0.40 0.36 0.40 0.40 0.40 0.85 0.86 1.02 1.64 2.18 2.70 3.05 4.65 8.45
+0.03 -0.02 f0.02 f0.02 f0.01 +0.05 -0.10 -0.06 -0.02 -0.16 -0.17 -0.17 0 f0.01
drops of distilled water in place of the concentrated hydrochloric acid, since thkse samples are already strongly acid. Example. When 5 grams of sample 2 (Table 111),containing 37 p.p.m. of boron were ashed and the extract was diluted to 250 ml., 2 ml. taken for analysis gave a percentage transmittance of about 90.5. DISCUSSION
0
a
f
Procedure. Pipet 2 inl. of tlie sample into an Erlenmeyer flask and add 2 drops of concentrated hydrochloric acid. hdd 10 ml. of concentrated sulfuric acid, mix, and cool. 4 d d 10 ml. of carmine solution, mix, and allow to stand at least 45 minutes for color development. Determine the percentage transmittance a t a wave length of 585 millimicrons against a reference solution of 2 ml. of distilled water carried through the entire procedure. Read the boron concentration from the concentration-transmittance calibration graph (Figure 2 ) . Where the boron concentration is such that the measured transmittance value falls outside the recommended portion of the transmittance range (this method suggests 20 to 95%,),either dilute the sample or concentrate it to meet the above conditions. When boron concentration is too high, dilute the sample with distilled water to a known volume, mix, pipet 2 ml. into an Erlenmeyer flask, and proceed ac; directed above. When boron concentration is too low, pipet a suitable aliquot of the sample into a beaker, pIat,inum dish, or other suitable vessel. Xake alkaline with sodium hydroxide solution and add a slight excess. (-4dd the same amount to all samples, including a reference.) Evaporate to dryness on a steam bath or in an oven a t 95 O C., cool, add 5 nil. of dilute hydrochloric acid, and triturate with a rubber policeman. Pour the solution into a conical centrifuge tube and centrifuge a t 2000 r.p.m. Pipet 2 ml. of the clear solution into an Erlenmeyer flask and follow the procedure shown above, correcting the reading from the standard curve (Figure 2 ) to conform with the aliquot taken. Procedure for Plant Material. PREPARATION OF SAMPLE. Remove all foreign matter from the green plant material, but avoid excessive washing. Dry at 70" C., grind, dry again to constant weight, and store in tightly stoppered bottles. If it is desired to express the results on the green weight basis, weigh the material before and after drying. Weigh a portion of the dry sample and transfer to a glazed paper. The weight of material to be used will depend on the boron content of the sample. For each gram of the sample, add 0.1 gram of calcium oxide and mix well on paper. Transfer to a porcelain casserole or platinum dish, ignite as completely as possible in a muffle a t 500" to 550" C., cool, and moisten with water. Cover with a watch glass, introduce 6 N hydrochloric acid, 15 ml. for a 5-gram sample, which should make the solution strong1 acid, and heat on a steam bath for 30 minutes (4). Filter a n z w a s h the residue with distilled water. Dilute to a convenient volume. Pipet 2 ml. into an Erlenmeyer flask (boron-free glass) and follow the procedure given for water samples but add 2
Interference tests were made using a number of different cations and anions. When hydrochloric acid is added, nitrate and nitrite do not interfere, but in the absence of the acid the results are high. R t h germanium, molybdenum, cerium, silicates, ammonium, fluorides, mixed chlorides of calcium, magnesium, sodium, and potassium, phosphates, and the ions common to natural n-aters and extracts of ashed plant material, no interference could be detected. Results of analyses of several water samples are shown in Table I, along with the corresponding values determined by the electrometric titration method ( 5 ) . Table I1 shows results where the boron concentration was low and the sample had to be Concentrated before development of color. Fifty milliliters of sample were evaporated and taken up in
Table 11. .inal?;ses of Water Samples (Samples concentrated prior t o colorimetric determination of boron) Boron, Parts per Million Electrometric titration Proposed Sample No. method method Difference +0.01 Synthetic, 0.05 p.p.m. B 0.06 0.10 Synthetic, 0.10 p.p.m. B 0 0.07 1 0 : 05 +0.02 0.06 -0.03 2 0.09 0.09 0.09 0.11 0.15 0.17 0.19 0.19 0.20 0.40 0.56
3 4 5 6 7
8 9 10 11 12
0.10 0.10 0.07 0.14 0.15 0.15 0.20 0.18 0.40 0.57
+0.01 +0.01 -0.04 -0.01 -0.02 -0.04 +0.01 -0.02 0 +0.01
Table 111. Determination of Boron in Plant Samples Boron, Parts per Million Sample No. 1 2 9 4
5
6 7 8 9
Electrometric titration method 11 60 64
122 144 297 528
Proposed method 12 37 58 59 63 117 138 289 526
Difference +1 0 +3 -1
-1 -5 -6 -8 -2
V O L U M E 22, NO. 4, A P R I L 1 9 5 0
569
.7 nil. of hydrochloric solution and 2-ml. portions (equivalent to 20
nil. of the original sample) m r e used for the colorimetric determination. Electrometric results are shown for comparison, The results of analyses of several plant samples, shown in Table 111, indicate that the method is applicable to plant material. Temperature does not affect the results significantly over the range of 20’ to 35 C. Samples read after standing 45 minutes sho7ved no appreciable change at. the end of 4 hours. Samples of standard boric acid were included with each set of analyses made over a period of a year. During this time several different lots of sulfuric acid and carmine n-ere used but xithout effect on either the calibrat,ion curve or the recovery of boron from the stantlard solutions. This is interpreted to mean that the method is not sensitive to small changes in reagent, concentrations. The data obtained from standard boric acid solutions used in checking the precision of the method have been examined statisI
tically. A high order of reproducibility is indicated by the following values on 15 such sets of calibrations. Boron in standard boric acid solution, p.p.m. Percentage transmittance, mean Standard error of mean
1.0 86.2
*0.107
5.0 47.7 *0.097
10.0 23.3 +0.095
The accuracy of the method may be checked by the results in Tables I, 11, and 111. The standard error of the mean difference between the tvio methods shows that there is no significant difference a t the 5 % level. LITERATURE CITED
(1) Austin, C. RI., and LIcHargue, J. S., J . Assoc. Ofice. Agr. Chemists, 31, 427-31 (1948). (2) Berger, K. C., and Truog E., ISD. ENG.CHEM.,.%NAL. ED., 11, 540-5 (1939).
Kazarinora-Oknina, V. A., Z(icodskuya Lab., 14, 263-5 (1948). JI-ilc,ox,L. V.,Chronica Botan.. 6, 370-2 (1941). (5) Wilcox, L. V., ISD. ESG. CHEM.,AN.~L.,ED..4, 38-9 (1932). (6) Zorkin, F. P., J . A p p l i e d Chem. ( ~ . S . S . E . )9,, 1505 (1936). (3) (4)
RECEIVED J u n e 11. 1949.
Determination of Chloroform and Bromoform . J. GORDON HANNA AND SIDNEY SIGGIA General Aniline & Film Corporation, Easton, Pa. A procedure for determining chloroform and bromoform is described. The haloform reacts with aniline in the presence of alkali and the halide ion formed by the reaction is determined. ]
