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Anal. Chem. 1984, 56,106-109
Ion Chromatographic Determination of Morpholine and Cyclohexylamine in Aqueous Solutions Containing Ammonia and Hydrazine Roland Gilbert* and Reynald Rioux
Institut de recherche d'Hydro-Qugbec (IREQ), 1800 Montge Sainte- Julie, Varennes, QuCbec, Canada JOL 2P0 Souheil E. Saheb
Gentilly 2 Nuclear Power Plant, Gentilly, Qugbec, Canada GOX IGO
I n thls paper the analysis by Ion chromatography (IC) has been successfully applled for the quantlflcatlon of morphollne (C4H,NO) and cyclohexylamlne (C,H,,NH,) in aqueous solutions contalnlng parts-permllllon amounts of ammonla (NH,) and hydrazlne (N2H4)o The method Is proven to be sensltlve and selective at the concentration ranges normally found durlng water treatment of steam-generatlng systems. The column length, eluent flow rate, and eluent Ionic strength have been optlmlzed to obtaln satlsfactory resolutlon of the peaks of the four catlons C4H10NO+,CeHl1NH,+, NH,', and N,HS+ under three analytlcal modes. The analysis tlme for all those modes 1s approxlmately 50 mln. The detectlon llmlts are better than those obtalned wlth conventional methods, belng 0.1 ppm for both morphollne and cyclohexylamine. None of the water constltuents known to Interfere wlth the conventlonal technlque hampers the I C determlnatlon. Furthermore, under the amlne analytical condltlons, thls technique allows determlnatlon of concomltant species present as lmpurltles In steam-water cycles.
Volatile amines are widely used as corrosion inhibitors in the steam-water cycles of fossil and nuclear power stations. They are usually added to the feedwater to raise the pH of the condensate, feedwater, and drainwater to the level of 9.0-9.5 in order to counteract the corrosive action of any carbon dioxide present in the system. The amine distribution in the steam and condensate sections is obtained by volatilization or steam distillation from the steam generator or boiler. The two amines most widely used for this purpose are morpholine and cyclohexylamine, which in many cases are employed simultaneously. Along with these, hydrazine is injected to scavenge dissolved oxygen and passivate metal surfaces. All of these compounds are subject to thermal-hydraulic decomposition at the temperature and pressures of a medium-pressure steam generator, where the prevailing conditions are such that the major breakdown product is ammonia. Quantification of these additives and ammonia is an essential step in determining the appropriate amounts to use for maximum protection. Until recently, low levels of morpholine and cyclohexylamine in demineralized water were quantified by such conventional means as gas chromatography (1,Z), direct titration ( 3 , 4 ) ,and colorimetric tests (5) (commonly known as the carbon disulfide method for morpholine and the diazotization of p-nitroaniline method for cyclohexylamine). However, gas chromatography using flame ionization detection calls for a threshold of 1 ppm for both amines, a limit which unfortunately is a decade higher than the values expected in some critical parts of the steam-water 0003-2700/84/0356-01 O W 0 1.50/0
cycle. On the other hand, direct titration, based on determination of the total alkalinity of a sample, gives no information on specific contributors, e.g., ammonia, hydrazine, morpholine, and cyclohexylamine. Finally, when more than one of the amine species are present together, colorimetric procedures are of limited value and are applicable only a t higher limits of detection. There is clearly a need for a specific, interference-free, and more sensitive analytical method for the detection of morpholine and cyclohexylamine in aqueous solutions containing parts-per-million levels of ammonia and hydrazine. Those volatile amines are added to process waters contaminated by cation impurities such as Na+, K', Ca2+,and Mg2' which, since they can cause corrosion of system components, are governed by water quality specifications. In the search for a suitable analytical technique for evaluating the presence of morpholine, cyclohexylamine, ammonia, hydrazine, and the major impurities, the authors report herein upon the possibilities of ion chromatography (IC) as it applies to these amines in the lower concentration ranges found in various systems. The use of IC in power plants for the analysis of steam-condensate purity has already been reported in the literature (6-lo), while an on-line mode of analysis is currently under development to control high-pressure boilers by blowdown adjustment (11, 12).
EXPERIMENTAL SECTION Apparatus. A Dionex Model 16 ion chromatograph (Dionex Corp., Sunnyvale, CA) equipped with a HP 3390A reporting integrator (Hewlett-Packard Canada, Ltd.) was used for all analyses. The major components of this instrument are an eluent reservoir, a pumping system, a sample-introduction loop, a cation-exchange separator column, and an ion-exchange suppressor column for conversion of the eluent to a nonconductive form. A conductivity cell detector was used for all analyses except for N2H4 where the outlet of the separator column was fed through a Dionex electrochemical detector (potentiostat). Disposable plastic 3-mL syringes were used for sample loading in conjunction with an Acrodisc-CR 0.45-pm filter available from Gelman Sciences Inc. Reagents. Commercially available reagent-grade chemicals were used to prepare the eluents (HCl and HCl/L-lysine) and the cation stock solutions. Standard solutions of each cation of interest and of mixed cations were obtained by diluting aliquots of stock solutions. The sodium hydroxide regenerant (0.5 N) was prepared by using NaOH reagent-grade pellets. Extremely low conductivity water (e0.15 pmhos/cm) obtained by polishing demineralized water through an organic removal cartridge (Barnstead D8904) and an ultrapure mixed-bed ion exchange cartridge (Barnstead D8902) was used for all those preparations. Procedure. The separator and suppressor columns were first equilibrated with the eluent to be used by maintaining a pump flow rate of 0.7-1.9 mL/min for 45 min; the background conductivity due to the eluent was then electronically offset. The separator column was rinsed at the end of each day by recircu0 1983 American Chemical Soclaty
ANALYTICAL CHEMISTRY, VOL. 56, NO. 1, JANUARY 1984
107
Table I. Optimum Instrument Conditions for the Quantification of Ammonia, Hydrazine, Cyclohexylamine, and Morpholine by Ion Chromatography conditions
mode A
mode B
eluent
4 mm x 200 mm Dionex Normal Cation Separator 30831 9 mm x 100 mm Dionex Normal Cation Suppressor 30834 0.005 M HCl
flow rate, mL/min sample volume, gL detection ions quantified
1.92 100 conductivity C,H,,NO+, NH,+, Na+, K+
analytical column suppressor column
4 mm x 400 mm Dionex Normal Cation Separator 3083 1 9 mm x 100 mm Dionex Normal Cation Suppressor 30834 0.003M HC1 t 0.0025 M L-lysine 1.30 100 conductivity
4 mm X 200 mm Dionex Normal Cation Separator 30831 none 0.003 M HCl t 0.0025M L-lysine 0.11
100 electrochemical N,H,+
C6H11NH,+
-
-E5
mode C
s
Conditions:
Peak i d e n t i t y :
-
A
same as Table I
C K, 1 D CqHgNO, 10 ppm E CBH11m2, 10 ppm not d e t e c t e d : N2H4
- except for flow r a t e :
-
2.30 mL/min
tg
c, A
B
C
, ) 4,1,
jy, d
l!;c D
' ( 1
Na, 2 ppm
m3'
for NH3 and C & Y O
E
-
I#
A/
I
Figure 1. Typical ion chromatogram of a mixture of Na, NH, K, NpH4, C4H,N0, and CeH11NHp under optimum conditions for quantification of NH, and C4H,N0.
same as Table I for C$I1"2 Peak identity:
Table 11. Calibration Data for Morpholine, Cyclohexylamine, Hydrazine, and Ammonia-Concentration of Standard Solutions vs. HP 3390A Integrator Signal (Arbitrary Units)
A : Na,
2 p p ; NUS, 1 ppm: K. 0.5 ppm and C4H$JO, 10 ppm
B
I C6H11NHzr
5 io Time of iniection (min)
0
10 ppm
PPm injected 0.1 0.25 0.50
15
1
2 5 10 20 Conditions: name a8 Tabla
2.
I for N2H4
Paak identity: A : NzHq, 0.5
ppm
not detected: Na, "3, K , CI,H$O and C ~ H I I N H ~
.=g .%
I
PPm injected 0.001 0.005 0.01 0.02 0.025 0.05 0.1 0.2 0.25 0.5 1
morpholine cyclohexylamine integrator integrator counts x lo4 counts x lo4 0.456 1.038 1.940 3.164 7.813 20.190 36.184 63.840
0.400 1.063 2.065 4.013 8.709 23.519 45.183 99.015
hydrazine integrator counts x lo6
ammonia integrator counts x lo4
0.048 0.242 0.493 0.541 1.272 2.526 5.110 11.894 22.602 39.259
2.837 5.998 15.691 30.321
obtained under the final set of conditions: column length, eluent ionic strength, eluent flow rate, etc.
RESULTS AND DISCUSSION The separation of amines is illustrated in Figures 1,2,and 3. Figure 1 shows an ion chromatogram of a mixture of CdHSNO, CeHllNH2, NHB, N2H4, Na and K ions in which all the peaks are well resolved. This separation was obtained with
108
ANALYTICAL CHEMISTRY, VOL. 56, NO. 1, JANUARY 1984
species at the applied potential of +0.6 V by the potentiostat. The eluent at a flow rate of 0.77 mL/min was formulated with the L-lysine component, which here significantly reduces the elution time and allows under mode B the sensitive determination of C6H11NH3+. The HP 3390A integrator signals measured at various cation concentrations of standard solutions are given in Table 11. These standards were chromatographed in triplicate runs for each concentration in order to validate its reproducibility. A 10-pmhos/cm full-scale conductivity setting was found suitable for calibration down to sensitivities of 0.1 ppm for morpholine, 0.1 ppm for cyclohexylamine, and 0.02 ppm for ammonia. The hydrazine calibration data were obtained with an ECD setting at 1pA/V, full-scale,and the sensitivity is such that 0.001 ppm can be determined readily. The four calibration curves that can be obtained from the data of Table I1 pass through zero, indicating good linearity a t the low-concentration range studied, but deviate from linearity as the ionic strength increases. Typical concentrations of morpholine and cyclohexylamine required in feedwater, steam, and condensate to maintain the pH at an appropriate level are given in Table I11 along with specifications concerning hydrazine, ammonia, and some ionic impurities. As can be seen from the data, the detection limits achieved by IC are below the morpholine and cyclohexylamine prescriptions. For the four cations studied here, the upper limits of the permissible ranges are almost always before the point where the calibration curves deviate from linearity. As shown by Bouyoucos (13),the detector deviations from linearity for weak bases such as morpholine, cyclohexylamine, ammonia, and hydrazine could be eliminated if necessary by introducing a short column of chloride-form resin between the suppressor and the conductivity detector. It is even possible to improve the IC detection for more dilute concentrations of morpholine and cyclohexylamine by adding a cation concentrator column and/or a hollow fiber suppressor (14) to the analytical system. To investigate whether these amines interfere with each other when determined by IC, a series of solutions of different cation/interferent ratios in the parts-per-million range were examined. Sodium and potassium were also included as possible interferents because of their close elution with some amines. A sample of a standard cation was chromatographed, followed by a mixture made up from the same standard cation and an interferent. The percentage recoveries observed by comparing the peak area of the standard to that of the mixture are reported in Table IV. None of the constituents known to interfere with the conventional methods indicates a sig-
Table 111. Typical Water Chemistry Specifications in the Secondary Cycle of SteamGenerating Systems: Volatile Amines, Hydrazine, and Ionic Impurities parameter hydrazine, ppb
location CEPa SGB
",+, PPm Na+,PPb C1- and F-,ppb MgZ+,PPb morpholine, ppm
CEP CEP SGB SGB condenser feed water steam and condensate steam and condensate
first permissible action range limit 50-100 50-200
