1.3 1.2 1.1
11
magnesium, 200 ppm; manganese(II), 10 ppm; and iron(II), 10 ppm. The above concentrations of possible interferences neither suppressed nor enhanced the color formation prodbced by 10 ppb iodide a t 25 "C. Blanks also were not affected by their presence. The buffer and reagent solutions add at least 950 ppm phosphate and 390 ppm potassium to the final solution. Of the species found to interfere, nitrite and bromide enhanced color formation, and cyanide, sulfide, and phenol inhibited color formation. Nitrite interferes in concentration above 40 ppb but up to 2 ppm of nitrite can be destroyed by 30-minute reaction with the N - chlorosuccinimide-succinimide reagent. Less than 10 ppb cyanide, 100 ppb sulfide, or 50 ppb phenol can be tolerated; prior reaction with the N-chlorosuccinimide-succinimide reagent has no effect in reducing their interference. The sensitivity of this method would permit dilution of many types of samples either to bring the iodide or iodine concentrations down to within the measureable limits or to minimize possible interferences or turbidity. If the method were to be applied to samples with extremely high concentrations of one or more of the ions listed above, as for example sea water, a study should be made to see that they do not interfere under those conditions. As this method is responsive only to iodide, iodine, and hypoiodous acid, and does not distinguish between them, iodate cannot be determined directly nor can use be made of the chemical amplification reaction between iodide and iodate to produce iodine.
a'
/
/
I o d i d e Concentration (ppb)
Figure 1. Average of three absorbance measurements after 30-minUte reaction time: 0 25 O C ; A 35 OC (absorbance of blank is subtracted from the averages)
ther temperature. Because the apparent molar absorptivity of approximately 4.2 x IO6 for the crystal violet produced (calculated from the concentration of iodide ion present) exceeds the experimentally determined molar absorptivity of 1.00 X lo5 (13), the reaction mechanism must be presumed to be catalytic. However, because the absorbance does reach a maximum after 30 minutes, a self-quenching mechanism-probably iodination of the aromatic rings of the dye molecule-also presumably occurs. The probable reactions are
+ I' + H 2 0 RNCl + I, + H,O HOI + HCVH' RNCl
-
-
2HOI
+ +
RNH
+
I-
+
HOI
RNH
+ +
C1'
(1)
C1'
(2) (3)
RECEIVEDfor review March 5 , 1973. Resubmitted August 15,1974. Accepted October 17,1974.
(the I- produced in reaction 3 recycles via Reaction 1) where R = C4H402, HCVH+ is protonated leuco crystal violet, and CV+ is crystal violet. Although leuco crystal violet responds readily to hypochlorous acid (free chlorine in water), its reaction with fresh N - chlorosuccinimide solution is greatly inhibited. Excess succinimide stabilizes the N-chlorosuccinimide against hydrolysis to hypochlorous acid but permits the oxidation of iodide or iodine to hypoiodous acid, which oxidizes leuco crystal violet to crystal violet. The following ions were also tested for possible interference with the method: nitrate, 100 ppm; chloride, 200 ppm; fluoride, 10 ppm; sulfate, 200 ppm; bicarbonate, 200 ppm; sodium, 130 ppm; ammonium, 100 ppm; calcium, 200 ppm;
(1)T. S . Light, Anal. Chem., 44, 1038 (1972). (2) "Standard Methods for the Examination of Water and Wastewater," 13th ed., American Public Health Association, New York, N.Y., 1971,p 185. (3)F. Feigl and E. Jungreis, 2.Anal. Chem., 181, 87 (1958):Chem. Absb., 53, 118a(1959). (4) E. Jungreis and i. Gedalia, Mikrochim. Acta., 1960, 145 (in English). (5)E. Ramanauskas, Liet. TSR Aukst. Mokyklu Mokslo Darb.. Chem. Chem. Techno/., 5, 9 (1964);Chem. Abstr., 81, 10450b (1964). (6)A. P. Black and 0.P. Whittle, J. Amer. Water Works Ass., 59, 471 (1967). (7)J. L. Lambert, Anal. Chem., 23, 1247 (1951). (8)J. L. Lambert and S. C. Rhoads, Anal. Chem., 28, 1629 (1956). (9)J. L. Lambert and F. Zitomer, Anal. Chem., 35, 405 (1963). (10)M. M. Schnepfe, Anal. Chim. Acta, 58, 83 (1972). (1 1) C.A. Smith and H. H. Spieth, Anal. Chem., 45, 422 (1973). (12)Orion Research, Inc., Cambridge, Mass., Tech. Lit. Model 94-53. (13)H. A. Mottola, 8. E. Simpson, and G. Gorin, Anal. Chem., 42, 410 (1970).
CV'
H,O
+
H+
'Stable Reagents for the Colorimetric Determination of Cyanide by Modified Konig Reactions Jack L. Lambert, Jothi Ramasamy, and Joseph V. Paukstelis Department of Chemistry, Kansas State University, Manhattan, K S 66506
The reaction of cyanogen halides to cleave pyridine to produce glutaconic aldehyde was first described in dye synthesis by Konig ( I , 2 ) . This specific and quantitative reaction has been applied to the determination of cyanide by oxidation of CN- to a cyanogen halide, CNX, in which 916
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
CN+ is the reactive species. The CN' reacts with pyridine to produce an intermediate which hydrolyzes to a conjugated dialdehyde, glutaconic aldehyde. The glutaconic aldehyde is then coupled with a primary amine or a compound containing reactive methylene hydrogens ( R H d
CN-
+ OXIDANT +
CN'
Table I. Responses of Reagents to Cyanide Ion Reagent
cN-:N
+
2 H 2 0 -$ O-CHCH=CHCH$H=O
O=CHCH=CHCH2CH=O f 2RH2
f H2NCN -t H
Barbituric acid 2,4-@inolinediol 2 , 5-Piperazinedione Hydantoin
t
-+
R=CHCH=CHCH2CH=R j COLORED SPECIES
Schwarzenbach and Weber made a study of this reaction sequence as part of a general study of color-producing resonance systems ( 3 ) . The oxidant used in analytical methods for cyanide has been either chloroamine-T or bromine water. In a standard method originally reported by Epstein (4, 5 ) , chloramine-" is the oxidant and l-phenyl-3-methyl-5-pyrazoloneis the coupling component; each solution must be prepared daily. Aldridge described a method which employed bromine water with benzidine as the coupling compound (6, 7 ) , but the use of carcinogenic benzidine is hazardous. Asmus and Garschagen used chloramine-?' and barbituric acid (8). Bark and Higson studied three amine compounds as the coupling component, p-aminodiphenylamine, benzidine and p - phenylenediamine, with bromine water as the oxidant (9, IO), and concluded that p-phenylenediamine was the most desirable of the three from the standpoint of sensitivity and safety. The use of a solution of N-chlorosuccinimide stabilized with excess succinimide as the oxidizing solution, and a study of pyridine-stabilized barbituric acid, 2,4-quinolinediol, 2,5-piperazinedione, and hydantoin solutions as coupling components in the Konig reaction are reported in this study.
EXPERIMENTAL All solutions were prepared with deionized water. The reagent solutions described are stable for a t least six months. Absorbance measurements were made with a Bausch & Lomb Spectronic 20 spectrophotometer. Stock Solution of Cyanide. Dissolve 0.250 gram of potassium cyanide in 1 liter of water to obtain a 100-ppm solution. Prepare 10-ppm and 1-ppm working solutions by appropriate dilution as needed. N-Chlorosuccinimide-SuccinimideOxidizing Reagent. Recrystallize N-chlorosuccinimide (Aldrich Chemical Co.) from benzene and recrystallize succinimide (Eastman Kodak Co.) from water. Dissolve 10.0 grams of succinimide in several hundred ml of water. Add 1.0 gram of N-chlorosuccinimide and stir to dissolve. Dilute the solution to 1 liter. Barbituric Acid-Pyridine Reagent. Dissolve 3.00 grams of barbituric acid (Eastman Kodak Co.) in a small quantity of water and add 15 ml of pyridine. Dilute to 50 ml and store in the dark. The pH of the solution is between 7 and 8. 2,4-Quinolinediol-PyridineReagent. Dissolve 1.50 grams of 2,4-quinolinediol (Aldrich Chemical Co.) in a small quantity of water by adding a minimum amount of dilute sodium hydroxide solution. Adjust the pH to 7-8 by adding dilute hydrochloric acid. Add 15 ml of pyridine and dilute to 50 ml. 2,5-Piperazinedione-PyridineReagent. Dissolve 3.0 grams of 2,5-piperazinedione (Eastman Kodak Co.) in a small quantity of water. Add 30 ml of pyridine and dilute to 100 ml. Filter to remove suspended impurities. Hydantoin-Pyridine Reagent. Dissolve 3.0 grams of hydantoin (Eastman Kodak Co.) in a small quantity of water. Add 15 ml of pyridine and dilute to 50 ml. Filter to remove suspended impurities. Procedure. Add an appropriate volume of 1-ppm or 10-ppm working solution of cyanide. Add 1 ml of N-chlorosuccinimidesuccinimide reagent and 1 ml of coupling compound reagent. Di-
Absorbance maximum,nm
575 485 434
403
Color developmept, mm
Concentration range, ppb
12 13 1 1
0-100
0-600 0-5000
0-6000
Table 11. Data for Calibration Curve Using Barbituric Acid-Pyridine Reagent Concn, ppb
0 5
10 20 40 60 80 100
Av value'
0 .ooo
0.024 0.052 0.10
0.20 0.31 0.42 0.53
St dev
0 .ooo 0.001
0.003 0.003 0.001
0.006 0.004 0.004
Average of five determinations.
Table 111. Response of 2,4-Quinolinediol-Pyridine Reagent Concn, ppb
0 10 50 100 200 400 600 a
Av value'
0.005 0.017
0.035 0.13 0.26 0.51 0.76
S t dev
0.002 0.002 0.001
0.004 0.001 0.009
0.005
Average of five determinations.
lute to 25 ml and adjust the temperature to 25' i 0.5O. Measure the absorbance after the appropriate reaction time a t the wavelength specified for the reagent system.
RESULTS AND DISCUSSION The N- chlorosuccinimide-succinimide oxidizing solution was first developed for the determination of iodide and iodine ( 1 1 ) . N-Chlorosuccinimide alone in water rapidly hydrolyzes to hypochlorous acid, as shown by the color of crystal violet formed in a solution of leuco crystal violet a t pH < 5 . The hypohalites alone, of the oxyacids and anions of the halogens, oxidize leuco crystal violet rapidly. When excess succinimide is present, this hydrolysis is suppressed and leuco crystal violet is not oxidized. If iodide or iodine is present, hypoiodous acid is formed and crystal violet is produced. N-Bromosuccinimide and N-iodosuccinimide hydrolyze rapidly to produce the hypohalite whether succinimide is present or not, as demonstrated by the reaction with leuco crystal violet. The stabilizing effect of excess succinimide on N- chlorosuccinimide is not completely understood as yet, but the reagent has proved effective in the oxidation of CN- to CN+ and is stable. The reactions of the coupling reagents are summarized in Tables I, 11, and 111. This series of compounds was selected for study after consideration of the reactivity of barbituric acid, a proven reagent in the Konig reaction (8).All have potentially reactive methylene hydrogen atoms adjacent to one or two carbonyl groups in a cyclic structure. When all of the coupling compounds are considered-the four studied here plus l-phenyl-3-methyl-5-pyrazolone, benzidine, and p-phenylenediamine-it appears that those ANALYTICAL CHEMISTRY, VOL. 47, NO. 6 , MAY 1975
917
compounds which can upon reaction with glutaconic aldehyde yield structures which are stabilized by resonance produce the most sensitive methods. 2,4-Quinolinediol is less sensitive than barbituric acid, while 2,5-piperazinedione and hydantoin are much less sensitive. Compounds capable of acquiring a positive charge or charges as a result of resonance would have especially high molar absorptivities. Compounds of this type would be similar to the polymethine, or cyanine, dyes. The structures of the coupling compounds investigated and their tautomeric forms which lose methylene hydrogens by condensation with an aldehyde, RCHO, are:
OH NAN
0
H O V O H *
H
0
H~'NH N 5 O +' -)HO'$pOH CHR " u
compounds formed with glutaconic aldehyde. An effort is under way to synthesize 7-(N,N-dimethylamino)-2,4-quinolinediol and 7-hydroxy-2,4-quinolinediol to test this conclusion.
The stabilities of the barbituric acid-pyridine and 2,4quinolinediol-pyridine reagents should prove to be of value in analytical methods utilizing the Konig reaction, as most reagents previously used were not stable. The N-chlorosuccinimide-succinimide reagent should provide the analytical chemist with a new and stable oxidizing solution for this and other methods requiring a moderately strong oxidant. Interferences are virtually non-existent in reactions based on the Konig reaction, as it relies on the unique reaction between CN+ and pyridine to produce glutaconic aldehyde, followed by a selective coupling reaction.
( j H
OH
LITERATURE CITED Uc;
HH
HH
It would appear that derivatives of 2,4-quinolinediol having substituents in the 7-position capable of entering into resonance would greatly enhance the absorbance of the
(1)W. Konig, J. Prakt. Chem.. 6g, 105 (1904). (2)W. Konig, 2.Angew. Chem., 69, 115 (1905). (3)G.Schwarzenbach and R . Weber, Helv. Chim. Acta, 25, 1628 (1942). (4)J. Epstein, Anal. Chem., 19, 272 (1947). (5) "Standard Methods for the Examination of Water and Wastewater." 13th ed., Am. Public Health Assoc., Washington, DC, 1971,p 404. (6)W. N. Aldridge, Analyst, 6g, 262 (1944). (7)W. N. Aldridge, Analyst, 7 0 , 474 (1945). (8)E. Asmus and H. Garschagen, Fresenius' 2. Anal. Chem., 138, 414 (1953). (9)L. S.Bark and H. G. Higson, Taianta, 11, 471 (1964). (IO)L. S.Bark and H. G. Higson, Talanta, 11, 621 (1964). (11) J. L. Lambert, G. L. Hatch, and B. Mosier Anal. Chem., 47,915 (1975).
RECEIVED for review August 19, 1974. Accepted January
27, 1975.
Nuclear Magnetic Resonance Determination of Water in 66Nylon Fiber Charles E. Anderson E. I. Du Pont De Nemours & Company, Inc., Textile Fibers Department, Seaford, DE 19973
Accurate and precise measurement of water concentration in nylon fiber is required for proper control of some spinning processes and for correct billing of customers. The classic oven dry procedure in widespread use is time-consuming, involves several manual operations contributing to potential errors, and may give high results if the fiber sample contains a volatile finish. The NMR procedure developed as an alternate method is specific, not affected by finish, is faster and at least as precise as the oven dry procedure. When water is added to acetic acid, the COOH proton peak will shift up-field in the NMR spectrum; the shift is proportional to the amount of water added ( I ) . This phenomenon is used to measure the amount of water extracted from nylon fiber with a solvent containing acetic acid. The solvent used is a 1:l v/v acetic acid/acetone mixture. The acetone is added (a) to prevent dissolving some of the nylon which would cause a broad peak, and (b) to improve sensitivity by reducing the number of COOH protons present per unit volume of solvent. Figure 1 shows the extent of 918
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
the shift of the COOH proton when water is added to a 1:l vlv acetic acid/acetone solution. For lower concentrations of water, the shift can be amplified by changing sweep width (Hz).
EXPERIMENTAL Apparatus. A 4-02 screw cap bottle or equivalent is used to contain the sample and solvent. A mechanical shaker is required to shake the sample and solvent for 30 minutes. The NMR spectra were recorded on a Varian T-60 spectrometer equipped with a Permalock accessory. Reagents. The solvent used for extracting water from nylon fiber is a 1:l v/v glacial acetic acid/acetone mixture. Procedure for HzO Analysis. Five grams of sample is placed in a dry 4-02 screw cap bottle and capped to prevent a change in moisture content. The bottle cap is removed long enough to add 50.0 ml of 1:1 v/v acetic acid/acetone solution and recapped. A blank is prepared by adding.50.0 ml of 1:l v/v acetic acid/acetone solution to a dry bottle which is capped immediately. The blank and samples are placed on a mechanical shaker and shaken for 30 minutes, then removed to a fume hood. A dry 5-mm 0.d. NMR tube is filled V4-'h full with solution from the sample bottle and
