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DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A
PORTABLE HAND-HELD REFRACTOMETER
K. C. Ugwu1,*, C. C. Mbajiorgu2, W. I. Okonkwo2 and A. O. Ani3
1, DEPT. OF AGRIC. & BIORESOURCES ENGR., ENUGU STATE UNIV. OF SCI. AND TECH., ENUGU, ENUGU STATE, NIGERIA
2, 3,4, DEPT. OF AGRIC. AND BIORESOURCES ENGINEERING, UNIVERSITY OF NIGERIA, NSUKKA ENUGU STATE, NIGERIA
E-mail addresses:
1
chikwadok@yahoo.com,
2
constantine.mbajiorgu@unn.edu.ng,
3
wilfred.okonkwo@unn.edu.ng,
4
ozoemena.ani@unn.edu.ng
ABSTRACT
Refractometer is a simple optical instrument that measures the amount of light refracted in a liquid. It measures on a
"Brix" scale and the Brix level determines the flavor and quality of fruits and vegetables. The fabricated refractometer
has built-in temperature compensations for Brix measurements and it is only valid for fruit juices solutions The
refractometer is equipped with a thermometer and there is a means of circulating water through the refractometer to
maintain a given temperature The designed refractometer consists of a light source, filtered to a single wavelength,
which is directed towards the prism-sample interface by a converging lens. This creates a range of incidence angles,
some of which will be completely reflected. A Charge-coupled Device (CCD) sensor precisely measures the intensity of
the reflected light and determines the exact angle at which light begins to be completely reflected. The fabricated
refractomter consists of six main parts which include focus adjustment, calibration screw, daylight plate, eye piece,
rubber grip and main prism assembly. Actual tests were conducted using samples of orange, pineapple and cashew
juices at certain levels of pH values. The average percentage Brix values of orange, cashew and pineapple juices are
7.88%, 10.84% and 6.91% respectively. It was observed that cashew juice has highest percentage Brix followed by
orange and pineapple juices. This implies that cashew juice can deteriorate faster than the other two juices. The
analysis of variance (ANOVA) for the effect of temperature and pH used for the experiment show that F-calculated
(4.248) is greater than F-table (3.35) at 5% probability level; therefore, the pH of fruit juice has an effect on its brix
value. It appears that the rate of pH or temperature sensitivity of the fabricated refractometer used could not be the
actual or maximum rate for the experiment
Keywords: Design, Fabrication, Portable, Refractometer, pH, Temperature
1. INTRODUCTION
Refractive Index is the speed of light in vacuum relative
to the speed of light in the considered medium. The
refractive index is commonly determined as part of the
characterization of liquid samples, in much the same
way that melting points are routinely obtained to
characterize solid compounds. Whenever light changes
speed as it crosses a boundary from one medium into
another its direction of travel also changes, that is, it is
refracted. The refractive index depends not only on the
wavelength used to measure it, but also on the
temperature of the solution being measured [1].
The Brix degree represents the concentration in weight
percent of a mixture of pure sucrose and water. It is
used as the weight percentage concentration of sucrose
in general. This concentration is calculated from the
measured refractive index using the stored
concentration table (16th conference of the
International Commission of Uniform Methods for
Sugar Analysis, [2]. The result is given at the standard
reference temperature of 20 °C using the temperature
dependence for these solutions from the same source.
So the refractive index and the prism surface
temperature are measured and the Brix is calculated
from the tables. When substances other than sucrose
are present, Brix is calculated from the total refractive
index. In such a case the result in Brix will not indicate
the real sucrose concentration [3].
A refractometer is a laboratory or field device for the
measurement of an index of refraction (refractometry).
Refractometer is a simple optical instrument that
measures the amount of light refracted in a liquid.
Nigerian Journal of Technology (NIJOTECH)
Vol. 37, No. 2, April 2018, pp. 537 – 542
Copyright© Faculty of Engineering, University of Nigeria, Nsukka,
Print ISSN: 0331-8443, Electronic ISSN: 2467-8821
www.nijotech.com
http://dx.doi.org/10.4314/njt.v37i2.33
DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A PORTABLE HAND- HELD REFRACTOMETER, K.C. Ugwu et al
Nigerian Journal of Technology Vol. 37, No.2, April 2018 538
Refractometers measure on a "Brix" scale and
measuring the Brix level of fruits and vegetables is very
important because it is a great indicator of flavor and
quality [4].
The higher the brix level of your fruits juices, the higher
the dissolved solids in the fruits juices such as sucrose,
fructose, vitamins, minerals, amino acids, proteins,
hormones and all other nutrients that the plant puts
into the foods. It is estimated that in a healthy fruit or
vegetable, approximately 80% of the brix is
represented by the natural sugars which give the food
its great flavor and goodness. It is believed by many
people to be the best indicator of quality available in
one quick and simple test [5].
Different models of hand-held refractometers have
different internal scales on which to read fluid
concentrations. Some instruments have specialized
scales that indicate the exact mixture of the sample
being tested, while others have an arbitrary unit of
measure that works like shorthand for refractive index
measurements [6].
Hand held refractometers are one of the most popular
analytical devices. They are used in many places - like
in wine growing and wine making, both by
professionals and amateurs, in beer brewing, in garages
to check battery electrolyte and cooling liquid quality,
and so on. They are very simple to use and give almost
instant result, without tedious and costly laboratory
procedures to follow [7].
The refractometer is a relatively simple device for
measuring the angle of refraction at the liquid-solid
phase interface. The angle of refraction depends on the
composition of the solution, which allows the use of
refractometers for quick evaluation of concentration of
dissolved substances. They can also be used, although
to a lesser extent, to study the structure of chemical
compounds [8].
To take care of temperature differences, simple hand-
held refractometers have to be either calibrated before
taking measurements (using calibration screw and
distilled water), or the result have to be converted
using a temperature corrections table (which requires
separate temperature measurement). However, many
refractometers have in-built temperature
compensation - either scale or additional optical wedge
are mounted on the bimetallic strip [9].
The soluble solids and ascorbic acid are primarily
sugars; sucrose, fructose, and glucose. As the flesh of
fruit forms, it deposits nutrients such as starch, as the
fruit ripens, it transforms to sugar. The percentage
sugar, measured in degrees Brix indicates the
sweetness of the fruit by measuring the number of
soluble solids in the juice source. Citric acid and
minerals in the juice also contribute to the soluble
solids. The ratio of the Brix to total acid reading must
be above a certain tolerance level. Oranges need the
sugar level for sweetness and the acid for a tart taste
and preservation of the fruit [10].
The brix value or refractive index of fruits juice is
important for determination of storage duration of the
juice. The higher the brix value of fruit juice, the higher
the dissolved solid contents in the juice. The level of
dissolved solids in fruit juice determines the storage
duration of the particular juice. The objectives of this
research is to design and fabricate a portable hand held
refractometer, with available materials that will be
used in determining refractive index of a fruit juice
from orange, cashew and pineapple samples and its
performance evaluated
2. MATERIALS AND METHOD
The materials with significantly different physical
properties that, when combined, produced a material
with characteristics different from the individual
components are used for the construction. The
individual components remain separate and distinct
within the finished structure. The new material may be
preferred for many reasons: common examples include
materials which are stronger, lighter, or less expensive.
The materials used in the construction of the
refractometer include Prisms, Cylinder, Biometric
strips, Scale, Lens, Illuminating flap, Reflector, Lamp,
Mirror, Rubber Grip, Calibration Screw, Sensor, etc.
2.1 Location of the research
The Hand held Refractometer was designed and
fabricated using Mechanical and Agricultural and
Bioresource Engineering workshops of Enugu State
University of Science and Technology, Enugu, Nigeria.
2.2 Design considerations
Distilled water will be used to test the sample to learn
how to use the refractometer and its index of refraction
is 1.3329 at 200C of temperature. It is also designed
based on the reflection of light from the boundary
between the prism and the sample. The compensating
prisms are designed so that they can be adjusted to
correct (i.e., compensate for) the dispersion of the
sample in such a way that they reproduce the refractive
index that would be obtained with monochromatic
light of 589 nm, the sodium D line.
2.3 Design calculations and Selections
2.3.1 Triangular prism
A right triangular prism has a triangular base in which
the joining edges and faces are perpendicular to the
DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A PORTABLE HAND- HELD REFRACTOMETER, K.C. Ugwu et al
Nigerian Journal of Technology Vol. 37, No.2, April 2018 539
base edges. In a right triangular prism, all the lateral
faces are rectangles and are perpendicular to the bases.
Fig 1: Triangular prism
Total surface area of the triangular prism = Lateral
surface area of the prism + Area of two bases = ( (a +
b + c)h + ½ bh) square units
2.3.2 Surface area of cylinder
An open cylinder does not include either top or bottom
elements, and therefore has surface area (lateral area).
Fig 2: An Open cylinder
The total surface area of a closed cylinder is made up
the sum of all three components: top, bottom and side,
which is
Other parts were selected based on the functional use
on the refractometer.
2.4 Assembly/Description of the equipment
The fabricated refractomter consists of six main parts
which include focus adjustment which is used to adjust
the reading at centre, calibration screw is used to set
the reading at zero before any experiment, daylight
plate is where the water or the juice material to be
determined its brix values is placed, eye piece is the eye
is located to take the reading, rubber grip joins focus
adjustment, daylight plate and the calibration screw
and main prism assembly. These parts are joined
together using fasteners and electrodes.
2.5 Performance evaluation of the refractometer
The actual tests were conducted using samples of
orange, pineapple and cashew juices at certain levels of
pH values. The average percentage Brix values of
orange, cashew and pineapple juices were determined
and tabulated. The analysis of variance (ANOVA) for
the effect of temperature and pH used for the
experiment was determined at 5% probability level.
2.6 Selection of Optical Sensors
A sensor is any device that takes a physical quantity,
measures it, and converts it into information that can
be read and understood by an observer. There are a
wide variety of means by which a sensor collects and
converts data, many of them not involving any
electronics at all. All sensors share one general
characteristic: they are transducers. A transducer is a
device for transforming one type of energy into
another. For example, even a simple mercury
thermometer works by taking heat energy and
changing it to the volumetric expansion or contraction
of liquid for the purposes of measurement. Therefore,
all sensors can be categorized according to the kind of
energy they detect and convert. These categories are:
acoustic, chemical, electromagnetic, ionizing radiation,
mechanical, optical, and thermal. The sensor was
selected based on the kind of work it is going to
perform, which is optical.
2.7 Principle of Operation of a Refractomenter
The Figures 3 is labeled diagram of fabricated hand
held refractometer and Figure 4 is exploded Isometric
View of Fabricated Refractometer and The operation of
the refractometer is based on the physical principle of
s down as it
passes into more optically dense media, and speeds up
as it passes into less optically dense media. The change
in speed is accompanied by a change in direction, and
at a certain angle of incidence, the light does not refract
in the second medium at all, but is entirely reflected.
The angle at which this occurs is known as the critical
angle, and it is this angle that the refractometer
measures. A refractometer consists of a light source,
filtered to a single wavelength, which is directed
towards the prism-sample interface by a converging
lens. This creates a range of incidence angles, some of
which (those less than the critical angle) will be
completely reflected. A Charge-coupled Device (CCD)
sensor precisely measures the intensity of the reflected
light and determines the exact angle (
critical) at which
light begins to be completely reflected. Since this angle
is dependent on the ratio of the refractive index of the
prism to that of the sample, the refractive index of the
DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A PORTABLE HAND- HELD REFRACTOMETER, K.C. Ugwu et al
Nigerian Journal of Technology Vol. 37, No.2, April 2018 540
sample can be determined using the known refractive
index of the prism.
2.8 General Steps for Calibration
1. Inspect the refractometer prism for scratches, chips,
separations or other aberrations that will interfere
with proper readings. If dusty rinse with water and
wipe with a clean, soft, lint-free cloth.
2. Note the temperature at the time of readings. Most
ATC refractometers operate properly in the 20
300C (68 - 86ºF) range. A laboratory or office at
room temperature is used if out- side temperatures
exceed the manufacturer's recommended
temperature range.
3. Place a few drops of pure water on the prism
surface, close the cover. If bubbles form, gently
pressing the cover that removes the bubbles and
help disperse the water over the entire surface.
4. Hold the refractometer up to natural light or an
incandescent bulb to obtain the reading. Looking
into the eyepiece, a distinct separation between a
blue and white section is seen, and it is called a
ontrast line. If the contrast line is not directly at
zero, then adjust by turning the screw on the top of
the refractometer until it reads zero. The plastic cap
is replaced after adjusting the calibration screw to
prevent water from entering the refractometer.
Adjust the focus by turning the eyepiece until the
scale is seen clearly. Once the refractometer is
calibrated to zero with pure water, dry the surfaces
with a clean cloth.
5. Place some of the solution from the 5-packet bottle
on the prism and close the cover, making sure that
the entire surface is filled and void of bubbles. Note
the value and write it down. The value will remain
on the LED display until the next sample is read.
3. RESULTS AND DISCUSSION
The results obtained for the determination of refractive
index and percentage Brix of orange juice, cashew and
pine apple juice are presented in Tables 1-4.
The Table 1 shows the results obtained during the test
of orange juice with the fabricated refractometer, it also
shows that, the lowest pH of 3.03 has the refractive
index of 1.340 and the highest scale of pH of 3.85 has
the refractive index of 1.348. It means that the higher
the pH of orange juice the higher the refractive index at
200C of temperature. It was also shown that orange
juice can be consumed at maximum percentage brix
value of 11%.
The results obtained during the test of cashew juice
with the fabricated refractometer were presented in
Table 2. It also shows that the lowest pH of 3.20 has the
refractive index of 1.340 and the highest pH of 4.0 has
the refractive index of 1.357. The results also showed
that cashew juice has higher acid, total solid content
and sugar than orange and pineapple juices. This means
that it can deteriorate faster than orange and pineapple
juices.
The results obtained during the test of pineapple juice
with the fabricated refractometer are presented in
Table 3. It shows that the lowest pH of 3.05 has
refractive index of 1.337 and the highest pH scale of
3.86 has the refractive index of 1.354. It was observed
that pineapple and orange has almost the same pH, Brix
value and refractive index. Table 4 presents the results
on analysis of variance (ANOVA) for the effect of
temperature and pH used for the experiment. The
results show that F-calculated (4.248) is greater than F-
table (3.35) at 5% probability level; therefore, the pH of
fruit juice has an effect on its brix value. It appears that
the rate of pH for the fruit juice used on the fabricated
refractometer could not be the actual or maximum rate
for the experiment.
Figure 4: Exploded Isometric View of Fabricated
Refractometer
Table 1: The pH, Percentage Brix and Refractive Index
of Orange Juice
.
S/N
Orange
pH
%
Brix
Temperature
oC
Refractive
Index
1
3.03
4.8
20
1.340
2
3.14
5.5
20
1.341
3
3.12
6.2
20
1.342
4
3.15
7.5
20
1.344
5
3.22
8.1
20
1.345
6
3.34
8.8
20
1.346
7
3.51
8.8
20
1.346
8
3.54
9.5
20
1.347
9
3.62
9.5
20
1.347
10
3.85
10.1
20
1.348
DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A PORTABLE HAND- HELD REFRACTOMETER, K.C. Ugwu et al
Nigerian Journal of Technology Vol. 37, No.2, April 2018 541
Table 2: The pH, Percentage Brix and Refractive Index
of Cashew Juice.
S/N
Cashew
pH
%
Brix
Temperature
oC
Refractive
Index
1
3.20
4.8
20
1.340
2
3.21
6.8
20
1.343
3
3.22
7.5
20
1.344
4
3.40
8.8
20
1.346
5
3.50
11.4
20
1.350
6
3.51
12.7
20
1.352
7
3.60
12.7
20
1.352
8
3.70
13.3
20
1.353
9
3.90
14.6
20
1.355
10
4.0
15.8
20
1.357
Table 3: The pH, percentage Brix and Refractive Index
of Pineapple Juice.
S/N
Pineapple
pH
%
Brix
Temperature
oC
Refractive
Index
1
3.05
2.8
20
1.337
2
3.15
3.5
20
1.338
3
3.22
4.1
20
1.339
4
3.31
4.1
20
1.339
5
3.46
4.8
20
1.340
6
3.57
6.8
20
1.343
7
3.67
8.8
20
1.346
8
3.71
10.1
20
1.348
9
3.79
11.4
20
1.350
10
3.86
12.7
20
1.354
Table 4: Analysis of variance (ANOVA) of the Brix value of the three samples determined
Sources of variation
Degree of
Freedom
Sum of
square
Mean
Square
F-calculated
F-table
Among Treatment
2
83.821
41.911
4.248
3.350
Within Treatment (Experimental
Error)
27
266.389
9.866
Total
29
350.210
To take care of temperature differences, the fabricated
hand-held refractometer has to be calibrated before
taking measurements (using calibration screw and
distilled water), thermometer that take care of
temperature compensations is built inside the
refractometer but the result of other refractometers
have to be converted using a temperature corrections
table (which requires separate temperature
measurement).
An Abbé refractometer was used to determine the brix
values of these fruit juice and the results obtained were
7.3% brix at pH of 3.15 of orange, 11.3% brix at pH of
3.50 of cashew and 4.05% brix at pH of 3.22 of
pineapple as against the values obtained using
fabricated refractometer which include 7.5% brix at pH
of 3.15 of orange, 11.4% brix at pH of 3.50 of cashew
and 4.10% brix at pH of 3.22 of pineapple at 200C of
temperatures. The results obtained using the
fabricated refractometer were in line with the Abbe
refractometer measurements of the percentage Brix
but the little variation was due to the conversion done
on the Abbe refractometer.
4. CONCLUSION AND RECOMMENDATION
It is clear that the temperature correction is
concentration dependent and therefore it is necessary
to measure such a complex solution always at the
desired temperature. This Hand-held refractometer
has in-built temperature compensations for Brix
measurements. This temperature compensation is only
valid for fruit juices solutions and will give incorrect
temperature compensations for other samples, (eg
vegetables, wine, soft drinks and in the starch and
sugar manufacturing industry).
The results obtained using the fabricated
refractometer were in line with the standard
measurements of the percentage Brix and refractive
index of orange, pineapple and cashew juices. The
standard refractive index of all the samples (fruit
juices) ranged from 1.337 to 1.357 and the three
samples measured are in line with existing standard.
These values could be useful for quality control
assessment during preparation of juices in food
industry.
The percentage Brix measured of cashew, orange and
pineapple juices of fresh fruit at the same temperature
shows that cashew has highest pH and refractive index
than the other two juices investigated .
Hand-held refractometers are convenient because
they do not require an energy source. However, they
may not be accurate if used outside the specified
temperature range. Using an analog refractometer,
whenever possible, within a specific field or block
should be read by one person at a time, since readings
are somewhat subjective.
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DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A PORTABLE HAND- HELD REFRACTOMETER, K.C. Ugwu et al
Nigerian Journal of Technology Vol. 37, No.2, April 2018 542
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