Quantitative colorimetric determination of Ni2+ metal ions using
conventional and smart phone digital-imaging methods
1. Importance of the experiment:
Nickel is a transition element and commonly exists in +2 oxidation state, though +1, +3 and
+4 states are also observed in nickel complexes. Nickel plays an important role in biological
systems as a constituent of several enzymes. Nickel is also present in soils and plants, and its
concentration varies widely from trace quantities to being a major constituent. Therefore,
determination of nickel at different concentration levels in variety of samples becomes very
important.
2. Nickel Toxicity: Compared with other transition metals, Nickel is a moderately toxic
element. However, it is known that inhalation of nickel and its compounds can lead to serious
problems, including cancer in the respiratory system. Moreover, Nickel can cause a skin
disorder known as nickel-eczema (10.1016/j.kijoms.2016.08.003).
3. Nickel in Industries: A thin layer of nickel onto a metal object can be decorative, provide
corrosion resistance, wear resistance, or used to build up worn or undersized parts for salvage
purposes. Nickel alloys are used extensively because of their corrosion resistance, high
temperature strength and special magnetic and thermal expansion properties.
The major alloy types that are used are:
Iron-Nickel-Chromium alloys
Stainless Steels
Copper-Nickel alloys and Nickel-Copper alloys
Nickel-Chromium Alloys
Nickel-Chromium-Iron alloys
Low Expansion Alloys
Magnetic Alloys (http://www.nickel-alloys.net/nickelalloys.html)
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NAME: AKASH K
REG NO.: 20BCL0081
Expt. No.: 04 DATE: 03-11-2020
Quantitative colorimetric determination of Ni2+ metal ions using
Experiment
conventional and smart phone digital-imaging methods
Corrosion protection in steel depends on the amount of Ni (acts as
Problem definition passivating metal) in its composition. Hence, it is important to analyze the
amount of Ni in steel for its use in industry.
Ni-DMG forms a stable colored complex. With increasing concentration
of Ni in solution, its color intensity also increases. In turn, the color
Methodology
intensity is a function of color coordinates (Red, Blue and Green, RGB) in
the image taken using mobile phone camera.
Estimation of Ni concentration in the unknown sample from the
Solution
calibration graph plotted based on different known Ni concentrations.
Student learning Students will learn to perform colorimetric method, perform RGB
outcomes response analysis and analyze Ni composition in different grades of steel
(i). Principle:
(a). Colorimetric method:
Photo-sensitive measurements are expressed in terms of
absorbance, (A)as given in Eq. (1). Further, the linear relationship between absorbance (A)
and concentration of the analyte
ɛcl=A = log(I0/I) … (1)
Where, I0 is the incident light power, I the transmitted light power, ɛ = molar absorptivity, c =
concentration of analyte and l= thickness of the solution.
(b). Digital-imaging method:
The color and intensity of digital image are usually 24 bit data (8 bit R + 8 bit G + 8 bit B)
forming an additive color space, in which R, G and B lights are added together in various
combinations to reproduce a broad range of colors. By using combination of R, G and B
intensities, many colors can be displayed. The intensity of each color has 256 levels (from 0
to 255). The value of R = 0, G = 0, B = 0 refers to pure black while R = 255, G = 255, B =
255 is pure white. With this system, unique combinations of R, G and B values are allowed,
providing for millions of differenthue, saturation and lightness shades. These extensive
dynamic colors of images provide the database for quantitative analysis. The goal of this
study is to employ digital images-based colorimetry for the determination of
Ni2+concentration in aqueous samples.
The concentration of analyte is a function of color coordinates: 𝑐 = 𝑅𝐺𝐵 … (2)
(ii). Reagents, solutions and Instrumentation: NiSO4 (100 ppm), NaOH (1 N) solution,
DMG, K3[Fe(CN)6], Colorimetry and smartphone.
(iii). Reaction Scheme: Dimethylglyoxime (DMG) reacts with Ni2+to form a pink-colored
Ni(dmg)2 complex in alkaline medium, and gets oxidized by potassium ferricyanide
(K3[Fe(CN)6])to form a brown-red, water soluble oxidized Ni (dmg)2 complex (Scheme 1).
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Absorption spectrum of the oxidized complex shows absorption maxima at a wavelength of
440 nm (Fig. 1). Concentration of Ni2+in the given unknown sample is determined from the
calibration graph (Fig. 2).
Scheme - 1
(iv). Procedure:
(a). Colorimetry method:Take 5 standard 50 mL volumetric flasks (to prepare 4 known and
1 unknown solution). Fill the burette with Ni stock solution (100 ppm). Add 1, 2, 3 and 4 mL
of the Ni solution in burette to the std. flasks to get 2, 4, 6 and 8 ppm of steel containing
nickel(II) solutions. The unknown sample will be furnished in another 50 ml volumetric
flask. Further, add 0.5 mL of DMG solution followed by 0.5 mL of K3[Fe(CN)6] solution
using a burette to all the 5 std. flasks. All the flasks are shaken well once and waited for 5
minutes. After that, make up the 50 mL mark in std. flask with 1N NaOH solution. Allow the
flasks at least 10 minutes for the complete complex formation. Absorbance of the formed
brown-red solution is measured at 440 nm against NaOH solution (blank). Record these
absorbance readings in Table 1.
Draw a calibration graph taking concentration of Ni2+ (in ppm) as X-axis and absorbance
readings as Y-axis. A straight line that passes through the origin (see Fig. 2) is an indication
that the measured data obeys Beer’s Law. From the calibration plot, measure the
concentration of nickel in the given unknown sample.
(b). Digital imaging method:The prepared standard solutions are lined up along with
unknown concentration sample and blank. Using a white paper as background, take a
photograph of the samples by holding the camera around 50 cm away. Calibration curve will
be constructed through the RGB values of analytical response with different conc. of Ni2+
ions using “RGB Tool” APP. In the plotted graph, RGB response varies linearly vs the
analyte concentration. In order to get precise analysis, follow the steps given below:
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RGB Method Method
Flow
RGB Chart Flow Chart
Transfer prepared standard
Transfer solution
prepared and unknown
standard solution
solution and unknown solution
into different into
colorimetric
differenttest tubes
colorimetric test tubes
Take image ofTake
all test tubeofsolution
image all test tube solution
using smart phone
usingcamera
smart phone camera
Open the image processing
Open app
the image (RGB colour
processing detector)
app (RGB colour detector)
Go to gallery,Go
opento the image
gallery, stored
open the in app stored
image and in app and
extract RGB values
extractfor each
RGB image/conc.
values for each image/conc.
Process the RGB values
Process the(R/G)
RGB or (R/B)
values or (G/B)
(R/G) or (R/B) or (G/B)
etc., till to getetc.,
linear
tillresponse
to get linear response
Plot the calibration curve
Plot the using RGB
calibration linear
curve using RGB linear
response vs concentration
response vs concentration
Find the unknown conc
Find the using the
unknown conc using the
calibration curve
calibration curve
Table 1: Experimental Data
S. No. Data collected from
Data collected from smartphone device*
Colorimetric device
Conc. Abs R G B R/G G/B R/B
(ppm, X-axis) (Y- axis)
1. 2 0.09 159 190 183 0.83 1.03 0.86
2. 4 0.11 130 135 80 0.96 1.68 1.62
3. 6 0.16 139 119 109 1.16 1.09 1.27
4. 8 0.22 164 88 61 1.86 1.44 2.68
5. Unknown 0.12 136 77 35 1.76 2.20 3.88
*Corresponding ratio that is linearly increasing with analyte concentration is used for plotting Fig. 2.
Find the unknown conc.
Find the Using the
unknown conc. Using the
calibration curve
calibration curve
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Result:
(i). Concentration of Ni in steel sample (using colorimetry) = ___4.4__ppm (mg/L)
(ii). Concentration of Ni in steel sample (using digital imaging) = __7.2__ ppm (mg/L)
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