Structural, Spectroscopic and Thermal Studies of Potassium Di-Hydrogen Citrate Crystal

Mechanics, Materials Science & Engineering, May 2017

ISSN 2412-5954

Structural, Spectroscopic and Thermal Studies of Potassium Di-Hydrogen Citrate Crystal20 N.D. Pandya1, J.H. Joshi1, H.O. Jethva1, M.J. Joshi1 1

Crystal Growth Laboratory, Department of Physics, Saurashtra University, Rajkot

360 005, India

DOI 10.2412/mmse.6.81.837provided by Seo4U.link

Keywords: potassium dihydrogen citrate, powder XRD, FT-IR, TGA.

ABSTRACT. Potassium dihydrogen citrate (KDC) finds wide applications in food products. Pure potassium dihydrogen citrate crystal was grown by slow solvent evaporation technique at room temperature. Grown crystal exhibited needle like morphology. The powder XRD shows triclinic structure symmetry with lattice parameters a b c confirmed by using FT-IR spectroscopy. The thermogram indicates the thermal stability of the sample up to 100 oC and then decomposes slowly into oxide stage through two stages. The results are discussed here.

Introduction. Potassium Dihydrogen Citrate (KDC) is a salt of tri-potassium citrate and citric acid.

It is widely found in citrus fruits, kiwi, strawberries and many other fruits [1]. KDC is known by its various functions in food as an acidifying agent, as an emulsifier, as a flavor enhancer, to increase an effect of preservatives, to inhibit bacterial action, as a buffer, as a sequestrant to protect food from reaction with metals e.g. soft drinks, biscuit filings, jams, desert mixes and processed cheese [2]. It regulates the blood balance and acid-base balance in the blood and tissues [3]. Along with food application, KDC exhibits some applications in medical and pharmaceutical field also. The reduction of urinary pH below recommended value forms uric acid which can further develop a uric acid stone causing urolithiasis often known as neprolithiasis.The presence of potassium in KDC controls the reduction of pH and maintains from 6.5 to 7 to dissolve existing uric acid kidney stone [4].

Carefully looking at the litrature, very scenty of work is reported in this material. The crystal structure of citrate salt is studied by Love et al. [5] and of double citrate salt by Zacharias et al. [6] and solubility study is explained by Van Auken [7]. Previously, Aygun performed structural study by AFM & SEM of VO+2 doped KDC with different magnifications[8] and EPR study of Cu+2 and VO+2 doped KDC [9]. Yarbasi et.al. done EPR and Optical study of vanadium doped KDC [10]. In the present context, the authors investigated structral, spectroscopic and thermal properties of pure KDC crystals.

Experimental. The growth of Potassium dihydrogen citrate crystal was carried out by using slow solvent evaporation technique at room temperature. The saturated solution was prepared in double distilled water. The solution was stirred for about 5-6 hours to make it homogeneous. This solution was kept at room temperature to evaporate solvent. The solution was sealed with porous lid and placed in dust free atmosphere for solvent evapouration. Evaporation of solvent gives rise to crystallization of needle shaped, transparent and colorless KDC crystal which was generally harvested in 20-25 days.

The photograph of grown KDC crystal is shown in the fig. 1.

The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Fig. 1. Grown KDC Crystal.

Powder XRD. radiation within the range of 2 -X software.

FTIR was carried out on the THERMO NIKOLET 6700 within the frequency range 4000 cm-1 to 400 cm-1 in KBr media. TGA was carried out on the Linseis STA-PT-1600 from room temperature to 7000C at a heating rate 100C/min in an inert atmosphere.

Fig. 2. Powder XRD pattern of KDC crystals.

Fig. 2 shows powder XRD pattern of pure KDC crystals. The crystal structure of KDC showed triclinic symmetry with lattice parameters a b c = triclinic symmetry with lattice parameters: a

b c ation of above crystal structure.

3

. The crystallite size was determined by using

Debye-

D=

where

is FWHM; MMSE Journal. Open Access www.mmse.xyz

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is the wavelength of incident radiation; is the FTIR Spectroscopy.

Fig. 3. FTIR spectrum of KDC crystals.

The FTIR spectrum of the KDC crystal is shown in the figure 3. The spectrum confirms the presence of different functional groups. The CH2 out of phase and in-phase stretching vibrations are confirmed by peaks at 2941.7 cm-1 and 2831 cm-1. This stretching leads to the vibrations (symmetric and antisymmetric) of O=C-OH carboxylate ion which is followed by oscillations of C-OH group for wave numbers 1307.2 cm-1, 1249.9 cm-1, 1184.5 cm-1, 1127.5 cm-1, 1041.5 cm-1. These vibrations generate stretching vibrations in C-C chains shown by a very small absorption endothermic peak for wave number 963.9 cm-1. The observed vibrational frequencies and their assignments are listed in table 1.

Table 1. Assignments for different absorptions in FTIR spectra of KDC. Wave Number (cm-1)

Bond Assignment

5731, 3423.1

O-H Stretching

2941.7, 2831.3

CH2 out of phase & in phase stretching vibrations

1695

C=O stretching vibrations

1638.1, 1454.3

Symmetric & Antisymmetric oscillations O=C-OH (carboxylate) ion

1307.2,1249.9,1184.6, 1127.4,1041.5

Oscillations of C-OH group

963.9

C-C Stretching Vibrations

849.5, 825.0, 772.8

K-O (metal-oxygen ) Vibration

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Fig. 4 shows the thermo-gram of KDC crystals, which shows that the crystal is stable up to nearly 95oC. Then dehydration takes place through two stages at 100oC and 150oC, respectively, and becomes dehydrated at 150oC after the loss of approximately 15% of its original weight. Then, the anhydrous sample is converted into carbonate form at nearly 213oC followed by the loss of approximately 49% of its original weight. During the final stage of decomposition at 500oC, the sample is converted into oxide form after the loss of nearly 66% of its original weight. From the analysis, it was found that two water molecules are associated with the crystals.

Thermal analysis.

Fig. 4. TGA curve of KDC crystal.

Table 2 gives details of the thermal decomposition of pure KDC with theoretically calculated and experimentally obtained values of weight % of the sample at different stages.

Table 2. Theoretical and experimental weight % of KDC. T(OC)

Substance

Theoretical mass loss (%)

Experimental mass loss (%)

34.81 Summary. KDC crystals were grown by slow-solvent evaporation technique by giving rise to needle shaped, transparent and colorless crystals. The triclinic symmetry of pure KDC was verified by powder XRD. The existence of various functional groups was verified by FT-IR spectroscopy.

Thermal decomposition of KDC followed by various meta-stable stages was monitored by TGA analysis. Two water molecules are found to be associated with the crystal.

References MMSE Journal. Open Access www.mmse.xyz

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[1] Potassium dihydrogen citrate:IN 332(i), available at: www.foodnetindia.in/potassiumdihydrogen-citratein-332i-3/ [2] Charles Sinclair, Dictionary of food, A & C Black Publishers Ltd, 1998.

[3] Elson M. Haas, Role of Potassium www.hkpp.org/patients/potassium-health

in

[4] Treament with potassium citrate, emedicine.medscape.com/article/444968-overview#a15

Maintaining

Health,

Hypocitraturia,

available available

at: at:

[5] Love W.E., A.L.Patterson. Acta cryst. Vol. 13 (1993), p. 426.

[6] Za lithium potassium hydrogen citrate monohydrate, Acta cryst. C49, (1993), pp. 1727-1730, DOI 10.1107/S0108270193002112 [7] Thomas V. Van Auken, Solubility and heat of solution of potassium dihydrogen citrate, J.Chem.

Eng. Data 36, (1991), pp. 255-257, DOI 10.1021/je00002a028 [8] Aygun Z., AFM and SEM Studies of VO2+ Doped Potassium Dihydrogen Citrate Single Crystal Obtained by Slow Evaporation Method, J.Chem cryst. Vol. 43 (2013), pp. 103-107, DOI 10.1007/s10870-013-0391-4 [9] Aygun Z., Variable temperature EPR studies of Cu2+ and VO2+ doped potassium dihydrogen citrate (C6H7KO7), Spectrochimica Acta. Vol. 104 (2013), pp. 130-133, DOI 10.1016/j.saa.2012.10.079 [10] vanadium doped potassium dihydrogen citrate (C6H7KO7) single crystal, Spectrochimica Acta. Vol. 79 (2011), pp. 1304-1307, DOI 10.1016/j.saa.2011.04.059

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