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
~
Table I. Data Obtained from Three Types of Nylon Fiber for NMR vs. Oven Dry Method
x, Fiber type
6-T-833 3-T-200 2.3-T-420
Oven dry
0.09 0.11 0.10
4.40 4.67 2.73
4.52 4.66 2.59
0.26 0.53 0.26
0.0
6 IPPYI
Figure 1. Carboxyl proton shift for 50% H20 in 1:l v/v acetic acid/ acetone
llc
HZO*
NMR
a = standard deviation. * determinations.
ID.
'/e
N M R Oven dry
NMR Oven dry
21 20 20
21 20 20
= average 90HzO. n = number of
RESULTS The results for three types of nylon fiber are listed in Table I. Precision, of course, is affected by sample exposure to ambient air, particularly if the nylon is significantly wetter or dryer than the equilibrium moisture level for the particular ambient RH.
0%
lo so
10 28
9
I O I1
eo
6 (PPMI
Figure 2. Moisture-on-yarn standards, carboxyl proton shift optimized for 0.0 to 12% moisture
capped. At least one tube is prepared for each sample and blank. The tubes are conditioned in the NMR sample storage compartment for 10 minutes. With a "blank" sample tube in the NMR sample chamber, the following instrument settings are verified: Filter ( 2 ) , R F Power Level (0.031, Spectrum Amplitude (3.2), Sweep Time (50 sec), Sweep Width (500 Hz),Sweep Offset (0 Hz), Power (on), RPS (45). The spectrum is scanned from 250 Hz (4.2 ppm) through the two peaks a t -105 Hz (1.8 ppm). With the Permalock accessory locked on the larger (CH3, acetic acid) of the two peaks, the 25-Hz sweep width is used for samples containing < 5% Hz0; 50 Hz is used for samples containing 5-10% HzO. With the pen carriage a t the extreme left, adjust the sweep offset until the COOH proton appears on the left side of the chart. Scan through the peak after adjusting for maximum resolution. Insert the sample tube and scan through the COOH proton peak. Measure the distance in mm between the peak for the blank and the peak for the sample. This distance is converted to % H20 by reference to a calibration equation or table. The calibration curve is parabolic: % H20 (dry fiber basis) = -0.0153 + 0.03933 mm 0.000087 mm2.
.
+
DISCUSSION The various solvents that were investigated for this application included formic acid, acetic acid, acetone, acetic anhydride, 1:l v/v acetic acidlmethanol and 25-15% v/v acetic acid in acetone. The 1:l vlv acetic acidlacetone solution gave the best results. Nylon fiber samples were extracted for 30 minutes, 1 hour, 2 hours, 4 hours, and 24 hours; no significant difference in extraction efficiency was observed. Known amounts of H2O were added to dried nylon and extracted with complete recovery. The calibration was made by adding known amounts of water, based on a 5.0-g sample and 50.0 ml of solvent per sample, and determining the COOH proton shift for each concentration, Figure 2. An analysis can be performed in
