MODELING OF DEGRADATION OF CREATININE
USING UV PHOTO-OXIDATION
Sri Suryani
Jurusan Fisika – FMIPA – Universitas Hasanuddin – Kampus UNHAS Tamalanrea – Jln.
Perintis Kemerdekaan – Tamalanrea – Makassar 90245
E-mail : sri_sumah@yahoo.com
Abstract
Nowadays, in the study of degradation of organic matters (anthropic and natural
wastewater), initial and final states are usually object of researches. Intermediate state is
rarely studied, because it involves the compounds which are usually unstable. In order to
know the intermediate state and also the reaction steps of transformation of organic
matters, creatinine was chosen as a model. By using, a method based on the direct UV
photo-oxidation, the evolution of UV spectra of model compound can be followed during
degradation. In the same time, analyze of photo-oxidation samples with HPLC might
identify the intermediate compounds. Then, the spectra were analyzed using UV spectral
semi-deterministic deconvolution method. By observing the evolution of coefficient
values of the reference spectra, the evolution of the model compounds could be followed.
Introduction
Creatinine is a chemical compound which can be found in the blood and in the
urine. Actually creatinine is a chemical waste compound, produced from creatine which
is an important molecule for muscles to produce energy. As a waste, creatinine is
transported through the bloodstream to the kidneys. Then, kidneys filter out most of the
creatinine and dispose of it in the urine. Although, creatinine is an organic acid of urine,
its concentration level is relatively constant, because body does not use it.
Obviously, kidneys play an important task in order to keep the creatinine level
relatively constant. As the kidneys have a problem for any reason, the creatinine level in
the blood will rise due to poor clearance by the kidneys. Therefore, abnormally high
levels of creatinine thus warn of possible malfunction or failure of the kidneys.
Sometimes, abnormally high creatinine clearance in the urine is detected, and for some
condition, the creatinine clearance level reaches for overestimated. This condition is
happened, because the active secretion of creatinine of renal, in cases of severe renal
dysfunction. So, renal function can also be detected using creatinine level test in the
urine, as well as electrolytes and urea (Dugdale 2009).
Creatinine is also a nitrogen organic compound. Nitrogen organic is a chemical
compound which can be found in the domestic wastewater, either in raw wastewater or
treated wastewater (Metcalf 1991 and Manahan 1992). It exists in different forms.
Evolution one to other takes place through physicochemical and biological mechanisms
which exist in wastewater treatment plant (Figure 1).
Nitrogen organic
Region of treatment
Nitrogen ammoniac
Nitrite
Receptor media
Nitrate
Figure 1 : Evolution of chemical form of nitrogen
Nitrogen organic compound is very attractive, because its degradation conducts to
formation of nitrite and nitrate which are absorbed in ultraviolet region (Lourenço et al.
2006, Thomas et al. 1990). Specially for creatinine which is a simple nitrogen organic
compound. Generally, creatinine is biodegraded by creatinine -deaminase and creatinase
enzymes to form ammonium ion and creatine. Then, creatinase enzyme decomposes
creatine molecule to sarcosine, urea, and nitrate, and these compounds are absorbed in
UV region. That is why, this research is conducted. Furthermore, this compound is a
heterocyclic molecule which can be found in wastewater and also in natural water, and
absorbed in UV region (Manahan 1992).
H
N
HN
O
N
CH3
Figure 2: Chemical structure of creatinine compound.
Methodology
Creatinine is chosen as a sample, because it is simple organic compound, has
unsaturated bonds, and absorbed in UV region. The concentration of creatinine is 20
mg/L, in order to have good spectrum. The 5 reference spectra are pure compounds, one
spectrum represents for initial product (creatinine), 3 spectra of intermediate state, they
are methylhydantoine, creatine, and sarcosine, and one spectrum of the final product
(nitrate)
The UV spectra of samples were obtained using UV-Visible Spectrophotometer
S1000PC SECOMAM. The wavelength of the spectrum was in the range of 200 – 350
nm. For the system of photo-oxidation was set up as showed in Figure 3. This system
used UV lamp covered by quartz transparent formed cylinder where samples passed
inside with the aid of a peristaltic pump, and UV detector. System with closed circuit was
chosen, in order to have continuous photo-degradation process, shown in Figure 3. So
each step of evolution of degradation can be observed by the evolution of UV spectra.
UV lamp
Quartz
UV detector
Pump
Figure 3: Photo-oxidation system.
For determining the type of chemical compounds which are produced during
photo-degradation process, a semi-deterministic deconvolution method is used (Thomas
et al.1990, Thomas et al.1993, Thomas et al.1996). This method uses mathematical
calculation, which each spectrum of sample considered as a linear combination of some
specifics spectra called reference spectra. These reference spectra are chosen
automatically from a group of specific spectra of pure products in the data bases. In the
mathematical form, the relation between reference spectra and sample’s spectrum is
presented below
n
A s ( )   c i .A ref i ( )  r
i 1
where As(λ) is the absorbance values of sample’s spectrum, c is the coefficient of the
reference spectra, Aref(λ) is the absorbance values of reference spectrum, and r is the error
of restitution or the difference value of absorbance obtained by the calculation and
experiment.
Figure 4 shows the general form of UV spectra of photo-degradation of
creatinine. It shows that there is a little decrease of absorbance in all spectra for first 5
minutes. Then, after 2 hours of experiment, the absorbance increase in region of
wavelength between 200 nm and 240 nm. This phenomenon is associated to oxidation of
ammonium, which produces nitrite and then nitrate. This result is supported by analyzed
from High Performance Liquid Chromatography (HPLC) of photo-degradation samples
which shows the existence of ammonium.
Absorbance
Wavelength (nm)
Time (minutes)
Figure 4: General form of UV spectra of photo-degradation of creatinine (20 mg/L)
In order to follow the evolution of the spectra during process of the photodegradation, and the step of the degradation, 5 spectra of pure compounds as products of
degradation of creatinine were chosen. These spectra will become reference spectra for
the deconvolution method. These 5 spectra are one spectrum for initial product
(creatinine), 3 spectra of intermediate state, they are methylhydantoine, creatine, and
sarcosine, and one spectrum of the final product (nitrate), see Figure 5.
Figure 5: Reference spectra associated to photo-degradation of creatinine.
In first 5 minutes, process of hydroxylation of creatinine by hydrogen is observed.
This process is observed from the change of UV spectrum. Two minutes after irradiation,
a shift of the peak from 240 nm to 230 nm occurred, and the increase of absorbance value
at 205 nm were observed. This condition showed the opening of double bonds, and
starting formation of methylhydantoine. Then, it is followed by opening nitrogen chain to
get ion of ammonium, it is showed by the increase of absorbance value at 205 nm. After
3 minutes of irradiation, the peak absorbance at 230 nm rapidly decreased. This process is
given in Figure 6.
Absorbance
Wavelength (nm)
Figure 6: Evolution of UV spectra of creatinine for 5 minutes photo-degradation process.
To get better understanding and also to examine the correct step of chemical
photo-degradation of creatinine, the samples then were analyzed by High Performance
Liquid Chromatography (HPLC). Later, the information gave by HPLC in form of
chemical compounds were arranged systematically. Result of this arrangement for 5
minutes photo-degradation is presented in Figure 7. Obviously in Figure 7, there are
some chemical compounds which are not detected by HPLC, but theoretically they exist.
This is because these chemical compounds are not produced by this photo-degradation
process, but maybe in other degradation process, or in other chemical environment, they
can be produced.
or
Figure 7: Chemical compounds products associated to photo-degradation of creatinine
during 5 minutes experiment.
After 20 minutes of photo-degradation process, the contribution of spectra of
creatine and sarcosine slowly increase. This condition can be translated as the broken of
methylhydantoine into 2 chemical compounds (sarcosine and creatine). On the other
hand, the coefficient of the reference spectrum nitrate starts to increase. It means that
during breaking process of methylhydantoine, the nitrate ion which is released in the first
step of degradation transforms into nitrate.
Table 2 : Evolution of the coefficients of the reference spectra (Aref).
Reference spectra
Creatinine
Methylhydantoine
Creatine
Sarcosine
Nitrate
Time of photo-degradation
Coefficients of the reference spectra (Aref)
5 min.
10 min
30 min
120 min
0.6945
0.2929
0.02
0
0.4262
0.1198
0
0
0
0.3196
0.021
0
0
0
0.017
0.017
0
0
0
0.17
After 30 minutes later, all the coefficients of the reference spectra continuously
decrease, except the coefficient of the reference spectrum of nitrate. This condition
occurs for about 2 hours. This thing means that the photo-degradation of creatinine is
complete (see Figure 8 and 9).
Figure 8: Evolution of UV spectra of creatinine for 2 hours of photo-degradation process
Figure 9: Chemical compounds products at the last step of photo-degradation process of
creatinine
Finally, all steps of photo-degradation process of creatinine (initial, intermediate, and
final states) are presented in Figure 10.
Figure 10: The complete chemical steps of photo-degradation process of creatinine
include its chemical compounds.
Conclusion.
Creatinine is a simple nitrogen organic compound, which has unsaturated bonds,
and exists in the human urine or in other words, in wastewaters. Therefore, this
compound is chosen as a sample. By using closed circuit of photo-degradation process,
each state (initial, intermediate, and final) of degradation process of creatinine can be
observed. Then UV spectra as a result of this degradation process is analyzed by a semideterministic deconvolution method, which using 5 reference spectra (creatinine,
methylhydantoine, creatine, sarcosine, and nitrate), and as a result, it gives the
information of sequences of chemical compounds production. After the arrangement, the
complete and detail evolution of photo-degradation process of creatinine is obtained.
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