American Journal of Analytical Chemistry, 2013, 4, 661-667
Published Online November 2013 (http://www.scirp.org/journal/ajac)
http://dx.doi.org/10.4236/ajac.2013.411079
Open Access AJAC
Development of Optical Chemical Sensor Based on
Pararosaniline in Sol-Gel Matrix for Detection of
Formaldehyde in Food Samples
Agus Abdul Gani1, Mochammad Yuwono2, Bambang Kuswandi1
1Chemo and Biosensors Group, Faculty of Pharmacy, Jember University, Jember, Indonesia
2Faculty of Pharmacy, Airlangga University, Surabaya, Indonesia
Received September 29, 2013; revised November 1, 2013; accepted November 18, 2013
Copyright © 2013 Agus Abdul Gani et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Optical chemical sensor based on immobilesed pararosaniline into sol-gel matrix tetraethyl orthosilicate (TEOS) is a
simple tool that can be used to detect the presence of formalin (formaldehide) in food. Pararosaline in sol-gel matrix
was developed when contacted with food sample that contains formalin. The optical signal was produced by changing
color from purple to yellow, that can be used to detect quantitative formaldehide in sample. The results, chemo sensor
optic, have characteristic, maximum wave length 576.42 nm, with linier range 0 - 100 ppm, linearity coefficient R2 =
0.999, limit detection (LOD) 0.504 ppm, limit of quantification (LOQ) 1.680 ppm, sensitivity 0.087, disturbed matrix
selectivity 1.716 %. The optimum is operational at pH 4, and response time at 150 seconds of 2 ppm. This sensor can be
used to detect formalin in food sample in a simple mode and reusable for 4 times application. In addition, the sensor can
be regenerated using an acid 0.1 M HCl.
Keywords: Optical Chemical Sensor; Formaldehide; Pararosalin; Sol-Gel; Food Sample
1. Introduction
Some of food in public marketed discovered contains
formaldehyde or usually familiar formaldehyde [1]. For-
maldehyde is a very dangerous chemical in human health;
It gives negative effect to respiration channel, liver and
kidney function, and reproducing system [2,3]. Based on
the moment conditions, detecting process of formalde-
hyde in food, conducting by laboratory process, used GC,
HPLC and spectrometry instrument. The weakness me-
thods of the mentioned impracticably cannot be prepared
out of laboratory and need skilled persons who have
backgrounds in chemistry specialty. In addition, such
methods are not suitable to be employed in the fields [4].
Therefore, there is an acute need to develop new and
inexpensive methods of assessing the formaldehyde con-
tain in food, particularly those that can be employed in
the field. The alternative methods to detecting formalde-
hyde in food have simple process, low cost, and easy to
operate by general society [5,6].
In this respect, the chemical sensor represents tools
used for simple, quick and low-cost to detect of formal-
dehyde in food [7-11]. Developing simple specific opti-
cal sensor of formaldehyde is very urgent to give solu-
tions to problems in general public to detect formaldehy-
de contained in food. The detection of formal-dehyde in
food has been proposed using spectrometric [7,11]. Para-
rosaniline is one of the specific reagents to detect for-
maldehyde, and the reaction between pararosaniline and
formaldehyde is presented in Figure 1, next page [5,12].
The optical chemical sensor developing is based on re-
agent immobilizing to sol-gel system. Optical transducers
in particular have raised much interest currently [12-15].
Since, various novel materials can be used in optical sen-
sors such as zeolite, conducting polymers, sol-gel etc. [7-
9].
Sol-gel for instance, there are many advantages, such
as its optical clarity, the ability to entrap specific reagent,
thermal and chemical stability, simplicity of preparation
and flexibility in controlling its pore size and geometry
[11,13].
This research uses Tetra Ethyl Ortho Silicate (TEOS)
as sol-gel material and shaping as sol-gel granule. The
mechanism process, formaldehyde in solution system of

A. A. GANI ET AL. 662
+NH2Cl-
NH2 NH2
HSO 3-
NC
H2
SO3H
NH2NH2
+NH3
+NH3
Cl
+NH3
Cl
NCH2
H2CO
+NH3
+NH3
2,4 M HCl
+ H+
+ H2O
+ Cl-
Figure 1. Formaldehyde-pararosaniline reaction.
diluting food, diffuses sol-gel and reacts with para-
rosaniline reagent producing change color of sol-gel [12].
The specific colors changed sol-gel from yellow to violet
indicating that food solution contains formaldehyde, so
the food has been solute contains formaldehyde. The sol-
gel optical sensor can be used to detect formaldehyde
contains in food as qualitative and quantitative manner.
2. Experimental
2.1. Reagent
All reagents were used as purchased without further puri-
fication. Pararosaniline hydrochloride (SIGMA P3750)
was supplied from Sigma (UK). Tetra ethyl orthosilicate
(TEOS), hydrochloric acid (HCl 37% pa), Ethanol 96%,
Triton X-100, and sodium sulfite (Na2SO3) as precursor
of sol-gel, were obtained from BDH-Merck (UK). For
immobilization a phosphate buffer solution (PBS) with
pH 6,5 was prepared by adjusting amounts of NaCl, KCl,
Na2HPO4 and KH2PO4 buffer systems; in all cases, the
mixture were 0.1 M in each constituent. The standard
formaldehyde solutions of (2; 6; 10; 20; 100; 200; 300;
400; 500) ppm (grade of analytical, Merck) were
prepared by appropriate dilution with an appropriate
buffer solution in order to produce solutions of lower
concentration at a desired pH. Salt and sugar use as
interference material. All reagents and inorganic salts
were of analytical grade and made using double distillate
water.
2.2. Reagent Immobilizations
Pararosaniline reagent prepared by making solution, take
of 0.03 g pararosaniline hydrochloride, diluting by water
to total volume 10 mL used volumetric flask, this solu-
tion concentration is 3000 ppm. The solution on Na2SO3,
made of 0.1 g Na2SO3 diluting by water to total volume
10 mL used volumetric flask. Pararosaniline sol-gel
made by composing of 1.5 mL pararosaniline reagent,
0.5 mL HCl 37%, 250 μL Na2SO3 solution, 2 mL ethanol,
1.75 mL water, and 4.5 mL TEOS composing in beaker
glass, stirring a long 3 - 5 hours. After that adding 5
drops of triton X-100 and stirring again 30 minutes, after
that molding sol-gel as sol-gel.
2.3. Optical Fiber Biosensors Construction
The construction of the optical fiber sol-gel chemo sen-
sor has been carried out by carefully placed a single
sol-gel of pararosaniline into the specially designed flow-
cell (Figure 2). This flow-cell (15 × 10 mm and 15 mm
depth) has been designed as back pressure free flow cell,
so that the effect of pulse from the pump and air bubbles
could be removed. Since these problems often faced in
flow system, which in turn increasing noise in signal
response. This optical chemical sensor design also allows
reducing the effect of other incident light levels on the
flow-cell and optical system.
2.4. Results and Discussion
2.4.1. Sol-Gel Sensor Product.
The sol-gel sensor product fabrication and it color
change before to after interaction with formaldehyde
presenting as Figure 3.
Figure 2. Flow-cell for optical fiber chemical sensor.
(a) (b)
Figure 3. Shape and color change of chemical sensor.(a):
Chemical sensor before interaction with formalin; (b): Che-
mical sensor after interaction with formalin.
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A. A. GANI ET AL. 663
2.4.2. Optimization of Experimental Parameters
1) Optimum Wave Length Operational and Linearity
Range Concentration
The first step in parameter optimization is to finding
the optimal wave length, base on the scanning the spectra
of blank solution and some standard formaldehyde solu-
tion, 2 ppm, 10 ppm, 20 ppm, 100 ppm, 200 ppm, 800
ppm and 1000 ppm. Result of scanning as presenting by
Figure 4, from this spectra, have been result the opti-
mum wave length base on the correlation between stan-
dard formaldehyde concentrations with intensity of re-
flectance produced by sol-gel sensor after reacted with
formaldehyde in solution.
Based on Figure 4, it is able to resume the reflectance
intensity as Table 1 follows.
Base on Table 1, the optimum wave length operational
is 576.42 nm, and the linearity range concentration (0 -
100) ppm, has slope or sensitivity 0.087, intercept 10.310,
and linierity coefficient R2 = 0.999 [15,16].
2) Test the Confidence Level Linearity
Linearity test includes a margin of error sensitivity
(slope error) and the margin of error intercept (intercept
error). The results of calculations with a 95% of confi-
dence level obtained error bounds of sensitivity 0.087 ±
0.0003 and a margin error of intercept 10.31 ± 0.0109
[10,16].
3) Limit of Detection (LOD) and Limit of Quantifica-
tion (LOQ)
Referring to Figure 4 and Table 1 further tested the
linearity of the calibration curve in detail for the concen-
tration range of 0 ppm to 100 ppm, with measurements
repeated 7 times for each standard solution. The concen-
tration of the standard solution used is a concentration of
0 ppm, 2 ppm, 4 ppm, 6 ppm, 8 ppm, 10 ppm, 12 ppm,
14 ppm, 16 ppm, 18 ppm, 20 ppm, 40 ppm, 60 ppm, 80
ppm and 100 ppm. The next linearity test based on the
average concentration measurements every standard. The
test results give the following data as Table 2 and Figure
5.
Based on data from the linearity of the curve in Table
2 and Figure 5, it obtained the limit of detection (LOD)
worth 0.5041 ppm and limit of quantitation (LOQ) of
1.6804 ppm [16].
4) Sensor Reproducibility
The data resumes to detecting Sensor Repro-ducti-
vebility Measurement from 7 repeatbles as presenting
Table 3 followed. Table 3 data give reality, the variance
coefficient measurements base of reflectance signal,
minimum 0.025% and optimum 0.557%. The variance
coefficient measurements base of formalin contains,
minimum 0.8768% and optimum 4.7875%. This condi-
tion are lowest of 5%, so the chemical sensor is usable as
formalin detector [10,16].
5) Sensor Responses Time
Figure 4. Spectra profile of formaldehyde by pararosaline
TEOS optical chemical sensor.
Table 1. The optimum reflectance intensity some standard
formadehyde solution.
Left peaks Right peaks λ Tested
[H2CO]
(ppm) λ Int.Reflt λ Int.Reflt 447.30 448.26576.42
0 448.268.538576.42 10.377 8.456 8.53810.377
2 444.428.653576.42 10.547 8.429 8.51110.547
6 446.828.882576.42 10.888 8.871 8.83010.888
10 442.59.112576.42 11.228 8.907 8.99511.228
20 447.309.685576.42 11.867 9.685 9.62711.867
100 453.0614.551576.42 18.989 14.284 14.44318.989
200 448.2627.294576.42 35.354 27.245 27.29435.354
300 447.3031.518574.98 45.763 31.518 31.43845.634
400 447.3044.015574.94 64.237 44.015 43.97661.213
500 448.2651.101574.02 70.497 50.405 51.10170.249
Table 2. Reflectance intensity data of linierity curve 0 ppm -
100 ppm on 576.42 nm.
[Formalin]Measuring Intensity (Y) Kurve Intensity (Ŷ)(Y-Ŷ )2
0 10.328 10.310 0.00034
2 10.504 10.484 0.00040
4 10.669 10.658 0.00013
6 10.845 10.832 0.00017
8 11.026 11.006 0.00039
10 11.191 11.180 0.00013
12 11.348 11.354 0.00003
14 11.520 11.528 0.00007
16 11.693 11.702 0.00008
18 11.859 11.876 0.00028
20 12.037 12.050 0.00018
40 13.802 13.790 0.00014
60 15.539 15.530 0.00009
80 17.287 17.270 0.00028
100 19.019 19.010 0.00008
Deviasion Standard 0.01462
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A. A. GANI ET AL. 664
Figure 5. Test product of linearity on concentration range
of 0 ppm - 100 ppm, on wave length 576.42 nm, by 7 time
repetition for each standard solution.
Table 3. Data of reproducibility measurements.
Sensor Reflectance Measurement Concentration
[CH2O]
ppm Averg. STDev % KVAverg.
(ppm) STDev % KV
0 10.328 0.015 0.1420.948 0.01261.3240
2 10.504 0.003 0.0252.355 0.02971.2598
4 10.669 0.017 0,1604.361 0.19584.4902
6 10.845 0.022 0.2006.784 0.24983.6826
8 11.026 0.022 0.1978.617 0.24942.8939
10 11.191 0.039 0.34710.125 0.44574.4017
12 11.348 0.038 0.33111.358 0.43153.7992
14 11.520 0.041 0.35513.208 0.46773.5411
16 11.693 0.062 0.53014.865 0.71174.7875
18 11.859 0.030 0.24916.832 0.33872.0122
20 12.037 0.066 0.55119.847 0.76193.8390
40 13.802 0.077 0.55741.860 0.88292.1092
60 15.539 0.047 0,30261.426 0.53860.8768
80 17.287 0.086 0.49580.996 0.98281.2134
100 19.019 0.045 0.238100.564 0.51940.5164
The responses time of sensor has been affected by
concentration of formaldehyde in solution system. Type
of formaldehyde concentration affected to sensor re-
sponse time presenting like Figure 6, follow. Base on
Figure 6, the response time of sensor between 75.88
seconds for 500 ppm to 150 seconds for 2 ppm formal-
dehyde concentrations.
6) Operational Conditions of pH Sensor
The reaction between pararosaniline with formalin
affected by the pH, the influence of pH conditions the
sample system to the intensity of reflectance sensor inte-
raction with formalin results provide Figure 7, presented
above. Based on the Figure 7, obtained information that
the system for the detection of formaldehyde in the solu-
tion pH conditions are optimal system operating at pH 4.
7) Sensor Selectivity
Figure 6. Response time of sensor base formaldehyde con-
centration.
Figure 7. Effect of pH on the intensity of reflectance ope-
rational.
Figure 8. Sensor selectivity curve formalin to interference
ratio of sugar-salt at a concentration of 1:100.
The selectivity of the sensor for the identification of
formaldehyde in the system through the test solution with
sugar and salt. Selectivity trials conducted with formalin
concentration ratio, salt and sugar 1:10, 1:100 and 1:1000.
Sample spectra pattern measurements sugar disorders
and formalin shown as Figure 8 and the data as Table
4(a) the following.
According to the test result tampering sugar and salt at
Table 4(a), obtained information that the existence of
sugar and salt in aqueous system can provide a distrac-
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A. A. GANI ET AL.
Open Access AJAC
665
Table 4. (a): The intensity of reflectance on the condition of Interference Salt, Sugar, and Sugar-Salt Against Formalin; (b):
Recovery of optical chemichal sensor on determining formalin in sample solution using standard and standard addision
methode.
(a)
Composition of Test Sample Reflectance Intensity
0 ppm (Blank)
Formalin (F) 200 ppm
10.377
35.354 Interferences % Interferences
Salt (Sl) 2000 ppm
F:Sl = 1:10
10.194
35.273 0.081 0.229
Sugar (Sg) 2000 ppm
F:Sg = 1:10
10.425
35.292 0.062 0.175
Sugar-Salt 2000 ppm 10.306
F:Sg:Sl = 1:10:10 35.209 0.145 0.410
Formalin (F) 20 ppm 11.867
Salt (Sl) 2000 ppm 10.194
F: Sl = 1:100 11.839 0.028 0.236
Sugar (Sg) 2000 ppm 10,425
F: Sg = 1:100 11.767 0.100 0,843
Sugar-Salt 2000 ppm 10.306
F: Sg: Sl = 1:100:100 11.741 0.126 1.062
Formalin (F) 2 ppm 10.547
Salt (Sl) 2000 ppm 10.194
F:Sl = 1:1000 10.522 0.025 0.237
Sugar (Sg) 2000 ppm 10.425
F:Sg = 1:1000 10.388 0.159 1.507
Sugar-Salt 2000 ppm 10.306
F:Sg:Sl = 1:1000:1000 10.366 0.181 1.716
(b)
Standard Method Addition Method
Sample Obyek [Formalin] (ppm) [Formalin] RetrievalStd DevRecovery (%)t-Test[Formalin] Retrieval Std Dev Recovery (%)t-Test
10 9.524 0.29995.241 2.7559.847 0.171 98.470 1.552
20 19.286 0.35396.432 3.49819.487 0.303 97.434 2.932
60 58.153 0.84896.921 3.77258.865 0.512 98.108 3.837
Sea Fish Meat
100 98.636 0.77898.636 3.03698.379 0.755 98.379 3.716
10 9.879 0,07298.794 2.9119.964 0.050 99.640 1.246
20 19.548 0,26597.740 2.95919.826 0.153 99.132 1.969
60 59.533 0,26699.221 3.04559.704 0.157 99.507 3.257
Noodles Soggy
100 98.969 0,62598.969 2.85799.411 0.661 99.411 1.545
tion to the measurement of the levels of formaldehyde in
solution. The higher the concentration of sugar and salt,
or in solution, the greater the percentage of its disorders.
Selectivity of the sensor towards the sugar and salt as the
interference was 1.716% [10,16].
8)Sensors Acurration
The accuracy of the sensors are tested through sensor
application to a sample simulation known concentrations
of formaline content. Testing using two sample object i.e.
meat fish and noodles soggy, each with 4 kinds of
concentration, that is 10 ppm, 20 ppm, 60 ppm and 100
ppm. Testing is done through standard methods and
standard addisi. The test results are shown in Table 4(b)
up.
Based on the data of Table 4(b), indicating that the
retrieval of chemical sensor hoses both in standard
methods as well as standard addisi have trust between the
area range 95.241% - 99.640%. Test results of t-test
accurasion, have been obtained a quantity t-test is smaller
than the price of t-test table reference of 4.3. Such
conditions mean optical chemical sensors worth applies.
9) Reuse Sensor
Test reuse (regeneration) is done by using a solution of
formalin solution and blank with concentration of (10
ppm, 20 ppm, 40 ppm, 60 ppm, 80 ppm and 100 ppm).
The test results give a picture of a decrease in the
performance of the sensor as shown in Table 5.
Based on the data in Table 5, obtained the fact that

A. A. GANI ET AL. 666
optical chemical sensors can be used repeatedly for four
times, because its still 92.611% compared to the initial
state, means meets the minimum limit analysis method
rule capabilities sensor 90 % for reuse.
3. Applications Sensor for Real Samples
Application sensors for real samples performed using
standard additions methods tested Sea-Fish meat and
noodles soggy use of 5 sample objects. The results of
measurements of formaldehyde content in the real sam-
ple by using optical chemical sensors and UV-Vis as a
comparison method, as shown in the Table 6 below.
Based on the data in Table 6 brings about reality, that the
determination of formaldehyde in food samples between
using the chemical sensors and methods UV-Vis pro-
vides a different quantity. But quantitatively the diffe-
rence is relatively low and still meet the criteria analysis.
Table 5. Chemical sensors measure power capacity on the
use in the regeneration based on the intensity of reflektan.
Reflectance intensity and sensor % capacity
[Formalin] 1st 2nd 3th 4th 5th
11.191 11.013 10.962 10.804 10.663
10 100% 98.414 97.958 96.542 95.284
12.040 11.839 11.658 11.454 11.162
20 100% 98.331 96.822 95.126 92.705
13.856 13.607 13.266 12.869 12.260
40 100% 98.203 95.748 92.883 88.484
15.659 15.264 14.867 14.183 13.575
60 100% 97.479 94.945 90.578 86.692
17.361 16.931 16.474 15.699 14.789
80 100% 97.520 94.887 90.427 85.182
19.064 18.584 18.063 17.178 16.130
100 100% 97.480 94.751 90.108 84.611
Average % capacity 97.905 95.852 92.611 88.826
Table 6. Formaldehyde content determination results in
real sample solution by standard addition method.
Real sample [Formalin]
Real Sample Sample
object Chemical sensor UV-Vis
S1 413.199 412.875
S2 417.238 416.439
S3 410.818 410.783
S4 419.381 407.992
Sea Fish
Meat
S5 412.253 411.753
Average 414.578 411.968
S1 34.877 34.898
S2 34.753 33.786
S3 35.923 35.253
S4 36.943 36.856
Noodles
Soggy
S5 34.689 34.540
Average 35.437 35.066
Furthermore if the review of the results of the analysis of
the paired t-tests (Paired t-Test), found no difference
between the two methods of determination of the results
of the two system analysis [10,16].
4. Conclusion
Based on the test results of the operational characteristics
of the optic chemical sensor fabrication yield, it can be
concluded that the sensor has the feasibility to use in the
process of identifying and determinating the presence of
formalin in food. In addition, the sensor can be regene-
rated using an acid solution.
5. Acknowledgements
This research was funded by grants DIPA Airlangga
University in 2012 according to Rector Decree No.
2613/H3.1/KR/2012 and Jember University. The autor
convey thank’s for assistent forman and the staffs of
profusely, to the leadership and all staff LPPM UNAIR,
and members of Chemo and and Biosensor group Fac-
ulty of Pharmacy UNEJ. as well as all those who helped
conduct of this research.
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