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Hindawi Publishing Corporation ISRN Analytical Chemistry Volume 2013, Article ID 719483, 9 pages http://dx.doi.org/10.1155/2013/719483 Research Article An Approach of Laser-Induced Breakdown Spectroscopy to Detect Toxic Metals in Crushed Ice Ball Rahul Agrawal, 1 Ashok Kumar Pathak, 2 Awadhesh Kumar Rai, 3 and Gyanendra Kumar Rai 1 1 Centre of Food Technology, University of Allahabad, Allahabad 211002, India 2 Department of Physics, Ewing Christian College, University of Allahabad, Allahabad 211003, India 3 Department of Physics, University of Allahabad, Allahabad 211002, India Correspondence should be addressed to Rahul Agrawal; rahulcſt@gmail.com and Awadhesh Kumar Rai; awadheshkrai@rediffmail.com Received 23 July 2013; Accepted 1 September 2013 Academic Editors: S. Girousi, W. Miao, and T. Michalowski Copyright © 2013 Rahul Agrawal et al. is 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. is paper deals the application of laser-induced breakdown spectroscopy (LIBS) to toxic metals used as pigment in crushed ice-ball samples. e present work highlights the advantages of LIBS as in situ, real-time analytical tool for rapid detection of toxic or heavy metals like lead (Pb) and chromium (Cr) and non toxic elements like carbon (C), nitrogen (N), magnesium (Mg), calcium (Ca), sodium (Na), and potassium (K) in crushed ice-ball of different colors (red, green, yellow, pale yellow, and orange) collected from five different areas, with minimal sample preparation. For rapid surveillance of toxic metals we have used multivariate analysis, that is, principal component analysis (PCA) with the LIBS spectral data of ice-ball samples. is study suggests that LIBS coupled with PCA may be an instant diagnostic tool for identification and classification of adulterated and nonadulterated samples. 1. Introduction Many studies have shown that our acceptance of the food is difficult where the color of a food does not meet our expectations and aesthetics quality [14]. us, colors play very important role in our acceptance of food. Ice balls are prepared from crushed ice topped with sweetened colored syrup and served in the form of a ball in stick. Two types of food colors are frequently used in food and ice bar products: (i) natural or bio colors like carotenoids, flavnoids, antho- cyanidins, chlorophyll, betalain, curcumin, and so forth, which are extracted from plants, and (ii) synthetic colors like Sunset Yellow FCF, Tartrazine, Ponceau 4R, Carmoisine, Erythrosine, Brilliant Blue FCF, Fast Green FCF, and Indigo- carmine. e maximum permissible level of synthetic food colors that can be added either single or in mix proportion is 100 ppm [5]. Instead of the previous permitted colors, some street vendor’s and small-scale ice-ball makers use low-grade nonpermitted colors like clothes color, copper sulphate, vermilion (mercury sulphide), lead chromate, lead sulphate, and so forth, for gaining undue profits which leads to serious health problems and potential dangers, like cancer, lead poisoning, embryo toxicity, teratogenicity, dermatitis, and eczema from repeated exposures [58]. Adulteration is the mixing of inferior quality material or inferior substance to the superior product, which reduces the nature, quality and originality in taste, color, odor, and nutritional value causing ill effects on the health of the consumers. As a result of these malpractices, the ultimate victim is a consumer, who innocently takes adulterated foods, and, leads to serious health problems such as allergy, gastrointestinal diseases [5, 9]. us, we require to assess the current scenario of usage of toxic food colorants in colored food commodities like crushed or uncrushed ice ball and ice cream bars. erefore, there is a need for a technique, which has real-time, in- situ and quick detection capability, multielemental analysis of sample in any phase (solid, liquid, and gas) without or minimal sample preparation. LIBS is such an advanced tech- nique having the said features and that can do qualitative and

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Hindawi Publishing CorporationISRN Analytical ChemistryVolume 2013, Article ID 719483, 9 pageshttp://dx.doi.org/10.1155/2013/719483

Research ArticleAn Approach of Laser-Induced Breakdown Spectroscopy toDetect Toxic Metals in Crushed Ice Ball

Rahul Agrawal,1 Ashok Kumar Pathak,2

Awadhesh Kumar Rai,3 and Gyanendra Kumar Rai1

1 Centre of Food Technology, University of Allahabad, Allahabad 211002, India2Department of Physics, Ewing Christian College, University of Allahabad, Allahabad 211003, India3 Department of Physics, University of Allahabad, Allahabad 211002, India

Correspondence should be addressed to Rahul Agrawal; [email protected] Awadhesh Kumar Rai; [email protected]

Received 23 July 2013; Accepted 1 September 2013

Academic Editors: S. Girousi, W. Miao, and T. Michalowski

Copyright © 2013 Rahul Agrawal 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.

This paper deals the application of laser-induced breakdown spectroscopy (LIBS) to toxicmetals used as pigment in crushed ice-ballsamples.The present work highlights the advantages of LIBS as in situ, real-time analytical tool for rapid detection of toxic or heavymetals like lead (Pb) and chromium (Cr) and non toxic elements like carbon (C), nitrogen (N), magnesium (Mg), calcium (Ca),sodium (Na), and potassium (K) in crushed ice-ball of different colors (red, green, yellow, pale yellow, and orange) collected fromfive different areas, with minimal sample preparation. For rapid surveillance of toxic metals we have usedmultivariate analysis, thatis, principal component analysis (PCA) with the LIBS spectral data of ice-ball samples. This study suggests that LIBS coupled withPCA may be an instant diagnostic tool for identification and classification of adulterated and nonadulterated samples.

1. Introduction

Many studies have shown that our acceptance of the foodis difficult where the color of a food does not meet ourexpectations and aesthetics quality [1–4]. Thus, colors playvery important role in our acceptance of food. Ice balls areprepared from crushed ice topped with sweetened coloredsyrup and served in the form of a ball in stick. Two types offood colors are frequently used in food and ice bar products:(i) natural or bio colors like carotenoids, flavnoids, antho-cyanidins, chlorophyll, betalain, curcumin, and so forth,which are extracted from plants, and (ii) synthetic colorslike Sunset Yellow FCF, Tartrazine, Ponceau 4R, Carmoisine,Erythrosine, Brilliant Blue FCF, Fast Green FCF, and Indigo-carmine. The maximum permissible level of synthetic foodcolors that can be added either single or in mix proportionis 100 ppm [5]. Instead of the previous permitted colors,some street vendor’s and small-scale ice-ball makers uselow-grade nonpermitted colors like clothes color, coppersulphate, vermilion (mercury sulphide), lead chromate, lead

sulphate, and so forth, for gaining undue profits which leadsto serious health problems and potential dangers, like cancer,lead poisoning, embryo toxicity, teratogenicity, dermatitis,and eczema from repeated exposures [5–8].

Adulteration is the mixing of inferior quality material orinferior substance to the superior product, which reducesthe nature, quality and originality in taste, color, odor, andnutritional value causing ill effects on the health of theconsumers. As a result of these malpractices, the ultimatevictim is a consumer, who innocently takes adulteratedfoods, and, leads to serious health problems such as allergy,gastrointestinal diseases [5, 9].

Thus, we require to assess the current scenario of usageof toxic food colorants in colored food commodities likecrushed or uncrushed ice ball and ice cream bars. Therefore,there is a need for a technique, which has real-time, in-situ and quick detection capability, multielemental analysisof sample in any phase (solid, liquid, and gas) without orminimal sample preparation. LIBS is such an advanced tech-nique having the said features and that can do qualitative and

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2 ISRN Analytical Chemistry

Red Pale yellow Green Yellow Orange

Figure 1: Photograph of samples placed in glass beakers for freezing.

Power supply

Spectrometer with CCD

Nd:YAG laserLaser beam

Converging lens

Collecting lens translational stage

Computer

Sample

Fiber bundle Stand

2500

2000

1500

1000

500

0200 250 300 350 400 450 500

Wavelength (nm)

Inte

nsity

(a.u

)

LIBS spectra of food supplement brand A

Figure 2: Schematic diagram of LIBS experimental setup.

quantitative determination of toxic elements and differentiatefrom harmless elements by providing spectral signatures thatenable the unique identification of adulterated foods [10–19].

Considering the previously mentioned features in thepresent study, we have used LIBS technique to detect andcompare the toxic elements used in colored crushed ice ball.LIBS is an emission spectroscopy in which we compare theintensities of atomic lines of different species present in thesample under local thermodynamic equilibrium (LTE) [20].Therefore, before using the intensity of the spectral line foranalysis purposewe have determined the plasma temperatureand electron density in the laser-induced plasma to verify theexistence of LTE in laser-induced plasma plume.

Nowadays, multivariate analysis of LIBS data is used forinstant identification and classification of variety of samples[10, 11, 15]. Principal component analysis (PCA) is a lineartechnique used to map multidimensional data onto lowerdimension with minimal loss of variance. We have also usedPCA for rapid differentiation of adulterated and nonadulter-ated ice ball samples.

2. Material and Method

2.1. Sample Collection. Samples of crushed ice ball of differentcolors were collected from street vendors randomly from fivelocal areas of Allahabad city. Samples from the area are codedas A, B, C, D, and E, respectively. From each area we have

taken five different colored samples of crushed ice balls likedark yellow, pale yellow, orange, green, and red and are shownin Figure 1. The samples are kept in deep-freezer for 4 hoursat −20∘C in 100mL glass containers that provides solid andhardened matrix. These colored ice samples were kept outfrom glass container and placed in glass petridish as shownin Figure 2. LIBS spectra of the sample placed in petridishare directly recorded to do analysis by LIBS technique forcomplete profile of elements present in the samples.

2.2. Experimental Setup for LIBS. The schematic diagramof experimental setup of the LIBS is shown in Figure 2.The Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) la-ser (Continuum Surelite III-10) was used for the presentexperiment having repetition rate of 1Hz to 10Hz, pulsewidth, that is, full width at half maximum of 4 ns andmaximum energy of 425mJ at 532 nm. Laser beam of 9mmbeam waist was focused on the ice bar sample kept on amoving sample stage using a planoconvex quartz lens of30 cm focal length to get laser-induced plasma on the surfaceof the sample. The light emitted by the laser-induced plasmawas collected by a collecting lens fitted at one end of theoptical fiberwhich inclined at∼45∘with respect to laser beam.The other end of the optical fiber is connected to the entranceslit of a grating spectrometer (Ocean Optics, LIBS 2000+)equipped with a charge-coupled device (CCD). The signalswere analyzed using OOI LIBS 2000+ software. To avoid

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200 250 300 350 400 450 500

100

200

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150

250

350

450

50

500

550

0

Yellow ice A

Inte

nsity

(cou

nts)

K

NaPb

Pb

N

C

Cr

C

Ca

MgCa

Wavelength (nm)

Yellow ice BYellow ice D

Yellow ice CYellow ice E

350 355 360 365 3700

102030405060708090

100

Inte

nsity

(a.u

.) CrPb

PbCrCr

Wavelength (nm)

(a)

200 250 300 350 400 450 500

100

0

200

300

400

500

Pale yellow C

Wavelength (nm)

K

Na

Pb

Pb

N

C

Cr

Pale yellow E

C

Ca

MgCa

Pale yellow DPale yellow BPale yellow A

350 355 360 365 3700

102030405060708090

100

Wavelength (nm)

PbCrCrCr

Inte

nsity

(cou

nts)

Inte

nsity

(a.u

.)

(b)

200 250 300 350 400 450 5000

100

200

300

400

500

Orange AOrange BOrange C

Orange D

K

Na

Pb

Pb

N

C

CrC

Ca

Mg Ca

Orange E

350 355 360 365 3700

102030405060708090

100110120

Inte

nsity

(a.u

.)

Wavelength (nm)

CrCrCr

Cr CrCr

Wavelength (nm)

Inte

nsity

(cou

nts)

(c)

Figure 3: LIBS Spectra of yellow (a), pale yellow (b), and orange (c) ice-ball samples of five places (A, B, C, D, and E).

the formation of crater at the surface of the ice bar, thesamples were placed on moving sample stage so that everylaser pulse was targeted at a fresh location on the samplesurface. The averaged LIBS spectra for 10 laser shots ofdifferent color of ice bar samples were recorded to get bestsignal to background ratio at 80mJ energy, 10Hz repetitionrate, and 1.5 𝜇s gate delay with a spectral resolution of 0.1 nmfor 200–500 and a spectral resolution of 0.75 nm in thespectral range of 200–900 nm.

3. Results and Discussion

LIBS spectra of the different colored samples (ice balls)collected from different area were recorded in the spectralrange of 200 nm–900 nm and the elements in LIBS spectrawere identified using the NIST spectral database [21]. Atypical LIBS spectra of yellow, pale yellow and orange coloredice ball samples of all five region, that is, A, B, C, D, and E areshown in Figure 3. LIBS spectra of ice balls show the presence

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4 ISRN Analytical Chemistry

200 250 300 350 400 450 5000

200

300

400

500

100

50

150

250

350

450

550

Red ERed D

Red CRed B

K

Na

N

CC

Ca

MgCa

Red A

350 355 360 365 3700

102030405060708090

100

Wavelength (nm)

Inte

nsity

(a.u

.)

Wavelength (nm)

Inte

nsity

(cou

nts)

(a)

200 250 300 350 400 450 5000

100

200

300

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500

Green A Green DGreen E

Green C

K

Na

N

CC

Ca

MgCa

Green B

245 250 255 260 265 270 275 280 2850

100

102030405060

8090

70

Inte

nsity

(a.u

.)

Wavelength (nm)

MgC

Wavelength (nm)In

tens

ity (c

ount

s)

(b)

Figure 4: LIBS Spectra of red (a) and green (b) ice-ball samples of five places (A, B, C, D, and E).

of the persistent spectral lines of carbon (C), nitrogen (N),magnesium (Mg), sodium (Na), potassium (K) calcium (Ca),lead (Pb), and chromium (Cr). Yellow, pale yellow, and orangecolored ice ball samples basically made from yellow color andthe presence of lead and chromium reflect that some of thegreedy shopkeepers might have used lead chromate (toxicfood color) which is cheap yellow color for providing yellowappearance to different food products. The LIBS spectra ofred and green colored sample shown in Figure 4 clearly showthe presence of spectral lines of major elements like carbon(C), nitrogen (N), magnesium (Mg), calcium (Ca), sodium(Na), and potassium (K), but the spectral lines Pb and Cr areabsent.

We have also measured the intensities of spectral lines oflead and chromium in pale yellow, yellow, and orange coloredice ball samples and show them in terms of bar diagramin Figure 5. But before using the intensities of the spectrallines of the elements to correlate its concentration in thesamples, we have to verify the assumptions of stoichiometricablation, local thermal equilibrium, and optically thin plasmafor laser induced plasma of different samples [13, 14, 17,18]. Verification of these assumptions for the laser-inducedplasma in the present experiment is discussed in the followingsections.

3.1. Stoichiometric Ablation. To produce the laser-inducedplasma on the surface of the ice-ball we have focused thelaser beam on its surface using converging lens of 30 cm focal

length. At the focal point of the sample, the spot size “𝐷” iscalculated using the following formula:

𝐷 =

(4 × wavelength of laser light × focal length of lens)(𝜋 × diameter of laser beam)

= 2.26 × 10

−3 cm.(1)

Thus, the calculated power density at focal spot is ≈2 ×1012W⋅cm−2 which satisfies the stoichiometric ablation con-dition [22].

3.2. Optically Thin Plasma. The condition of optically thinplasma means that the radiation emitted from an excitedatom in the plasma should not be reabsorbed (self-absorptioneffect) by another atom in a lower energy state. Optically, thinplasma can be verified by comparing the intensity ratio oftwo interference free emission lines of a species, having closevalue of upper energy levels to the product of the ratio of theirtransition probabilities, their upper level degeneracies, andthe inverse ratio of their wavelengths [23].

The intensity ratios of Ca 315.8/317.9 nm, Cr 357.8/359.3nm, and Pb 363.9/368.3 nm are calculated from the LIBSspectra recorded for all five colors collected from all fiveregions and are tabulated in Table 1. The product of ratio oftheir transition probabilities, the ratio of their upper levelsdegeneracy, and the inverse ratio of their wavelengths are cal-culated using data from the literature and are also tabulated in

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ISRN Analytical Chemistry 5

0

5

10

15

20

25

30

35

40

45

Yello

wYe

llow

Yello

wYe

llow

Yello

wPa

le y

ello

wPa

le y

ello

wPa

le y

ello

wPa

le y

ello

wPa

le y

ello

wO

rang

eO

rang

eO

rang

eO

rang

eO

rang

eRe

dRe

dRe

dRe

dRe

dG

reen

Gre

enG

reen

Gre

enG

reen

A B C D E A B C D E A B C D E A B C D E A B C D E

Samples

Nor

mal

ised

inte

nsity

(a.u

.)

Ca-317.9 nmCr-359.3 nm/Ca-317.9 nmPb-368.3 nm/Ca-317.9 nm

Figure 5: Intensities of the spectral lines of Cr (359.9 nm), Pb (368.3 nm), and Ca (317.9 nm) present in the LIBS spectra of different samplescollected from different places—A, B, C, D, and E.

Table 1. It is clear from Table 1 that 𝐼/ 𝐼 is approximately equalto the corresponding 𝐴

𝑘𝑖𝑔

𝑘

𝜆/

𝐴

𝑘𝑖

𝑔

𝑘𝜆, which clearly satisfy

the condition of optically thin plasma.

3.3. Determination of Plasma Temperature and Electron Den-sity for the Fulfillment of Local Thermal Equilibrium Con-dition. The plasma temperatures for different samples weredetermined using Boltzmann plot obtained from Boltzmannequation:

ln𝐼

𝑘𝑖

𝜆

𝐴

𝑘𝑖𝑔

𝑘

= −

𝐸

𝑘

𝐾

𝐵

𝑇 + ln𝐶

𝑠𝐹

𝑈

𝑠(𝑇)

,

(2)

where “𝐾𝐵” is the Boltzmann constant, “𝑈

𝑠(𝑇)” is the parti-

tion function, “𝐴𝑘𝑖” is the transition probability, “𝑔

𝑘” is the

statistical weight for the upper level, “𝐸𝑘” is the excited level

energy, “𝑇” is the temperature, and “𝐹” is a constant depend-ing on experimental conditions. The Boltzmann plots weredrawn using spectral lines of Ca I, Ca II, Cr I, and Pb I presentin the LIBS spectra of all different colored samples collectedfrom one area “A” and are shown in Figure 6. It is clear fromFigure 6 that the slopes of all lines are approximately parallelwhich show that the plasma temperatures are in LTE for allsamples. Finally, the plasma temperatures for yellow ice ballcollected from all five areas are calculated and are shownin Table 2. Similarly the Boltzmann plots for other samplescollected from areas B, C, D, and E have been drawn and theslopes of these lines are also parallel. The condition of LTEwas verified.

The other criteria for establishment of LTE condition isrelated to the electron density (Ne) given by

Ne ≥ 1.6 × 1012[𝑇]1/2[Δ𝐸]3, (3)

where Ne (cm−3), 𝑇 (K), and Δ𝐸 (eV) are electron density,plasma temperature, and the largest observed transitionenergy, respectively [24, 25].

The electron density is calculated experimentally by stark-broadening of spectral line given by [19, 26]

FWHM of the Lorentzian plot (Δ𝜆1/2)

≈ 2

electron impact parameter (𝑤)10

16

Ne.(4)

The FWHM for Cr: 357.8 nm (yellow ice ball) and Ca:422.6 nm (green ice ball) line is shown in Figure 7.

The true value of Δ𝜆1/2= 𝜆observed − Δ𝜆instrumental, (5)

where Δ𝜆instrumental = 0.05 nm.In the present paper, the Cr line at 357.8 nm and Ca

lines at 422.6 nm are selected to measure the FWHM. ALorentzian fit to the observed experimental data for theselines for yellow and green samples is presented in Figure 7.The calculated lower limit of electron density using (3) andexperimentally estimated electron densities using (4) and (5)are tabulated inTable 2. It is clear fromTable 2 that the plasmatemperatures for yellow ice ball collected from all five areas

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6 ISRN Analytical Chemistry

25000 35000 45000 55000

Ca I yellow ice ballCa II yellow ice ball

CaII red ice ball

Ca II orange ice ballCr I orange ice ballCa I pale yellow ice ball

Cr I pale yellow ice ball

Ca I green ice ballCr I yellow ice ball

Ca I orange ice ball

Ca II pale yellow ice ball

Ca I red ice ball

Pb I yellow ice ball

Ca II green ice ball

−22

−21

−20

−19

−18

−17

−16

−15

−14

−13

Upper-energy level (cm−1)

ln(I/gA

ki)

Figure 6: Boltzmann plot using different spectral lines present in the LIBS spectra of each color ice balls collected from place—A.

357.6 357.7 357.8 357.9 358.0 358.1

46

48

50

52

54

56

Inte

nsity

(cou

nts)

Wavelength (nm)

Cr 357.8 nm for yellow ice ball

Equation0.97932

Value Standard errorData fileData fileData fileData fileData file

44.56626 0.51746357.87663 0.00297

0.15656 0.017462.66873 0.3529

55.41812A

y0xcw

H

Adj. R2

y = y0 + (2 ∗ A/PI) ∗ (w/(4 ∗ (x − xc)2 + w2))

(a)

422.3 422.4 422.5 422.6 422.7 422.8 422.9148

150

152

154

156

158

160

162

164

166

168

Wavelength (nm)

Inte

nsity

(cou

nts)

Ca 422.6 nm for green ice ball

Equation0.94018

Value Standard errorData fileData fileData fileData fileData file

148.11845 1.41636422.62947 0.00694

0.17842 0.032575.50212 1.15717

167.75057A

y0xcw

H

Adj. R2

y = y0 + (2 ∗ A/PI) ∗ (w/(4 ∗ (x − xc)2 + w2))

(b)

Figure 7: Lorentzian fit to the data points of Cr: 357.8 nm and Ca: 422.6 nm line in the laser-induced plasma of yellow and green ice ballcollected from one area—A.

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ISRN Analytical Chemistry 7

Table 1: The value of 𝐼/ 𝐼 for Ca, 315.8/317.9 nm, Cr, 357.8/359.3 nm, and Pb, 363.9/368.3 nm for different samples.

S.N. Area Sample Ca, 315.8/317.9 nm Cr, 357.8/359.3 nm Pb, 363.9/368.3 nm𝐼/

𝐼

𝐴

𝑘𝑖

𝑔

𝑘

𝜆/

𝐴

𝑘𝑖

𝑔

𝑘

𝜆

𝐼/

𝐼

𝐴

𝑘𝑖

𝑔

𝑘

𝜆/

𝐴

𝑘𝑖

𝑔

𝑘

𝜆

𝐼/

𝐼

𝐴

𝑘𝑖

𝑔

𝑘

𝜆/

𝐴

𝑘𝑖

𝑔

𝑘

𝜆

(1.24𝐸 + 09 ∗ 317.93)/(2.16𝐸 +09 ∗ 315.89)

(1.33𝐸 + 09 ∗ 359.35)/(1.05𝐸 +09 ∗ 357.87)

(1.02𝐸 + 08 ∗ 368.35)/(4.50𝐸 +08 ∗ 363.96)

(1) A Yellow 0.74 0.59 1.09 1.27 0.35 0.30(2) B Yellow 0.69 0.59 1.20 1.27 0.32 0.30(3) C Yellow 0.67 0.59 1.23 1.27 0.41 0.30(4) D Yellow 0.68 0.59 1.57 1.27 0.29 0.30(5) E Yellow 0.72 0.59 1.10 1.27 0.37 0.30(6) A Pale yellow 0.54 0.59 1.22 1.27 0.32 0.30(7) B Pale yellow 0.72 0.59 1.19 1.27 0.31 0.30(8) C Pale yellow 0.71 0.59 1.21 1.27 0.33 0.30(9) D Pale yellow 0.70 0.59 1.19 1.27 0.33 0.30(10) E Pale yellow 0.76 0.59 1.19 1.27 0.30 0.30(11) A Orange 0.60 0.59 1.22 1.27 0.29 0.30(12) B Orange 0.56 0.59 1.14 1.27 0.32 0.30(13) C Orange 0.70 0.59 1.38 1.27 0.37 0.30(14) D Orange 0.69 0.59 1.30 1.27 0.35 0.30(15) E Orange 0.63 0.59 1.52 1.27 0.33 0.30(16) A Red 0.65 0.59 NA 1.27 NA 0.30(17) B Red 0.64 0.59 NA 1.27 NA 0.30(18) C Red 0.63 0.59 NA 1.27 NA 0.30(19) D Red 0.66 0.59 NA 1.27 NA 0.30(20) E Red 0.72 0.59 NA 1.27 NA 0.30(21) A Green 0.60 0.59 NA 1.27 NA 0.30(22) B Green 0.56 0.59 NA 1.27 NA 0.30(23) C Green 0.70 0.59 NA 1.27 NA 0.30(24) D Green 0.69 0.59 NA 1.27 NA 0.30(25) E Green 0.63 0.59 NA 1.27 NA 0.30

Table 2: Plasma temperature and electron density of yellow ice ballcollected from all five areas.

S.No. Sample(Yellow Ice ball )

Plasma temp(Kelvin) Ne (exp) Ne (calc)

1 A 8630.3 1.44𝐸 + 17 3.75𝐸 + 15

2 B 8764.6 1.09𝐸 + 17 3.78𝐸 + 15

3 C 8737.1 1.09𝐸 + 17 3.48𝐸 + 15

4 D 8999.2 1.47𝐸 + 17 3.83𝐸 + 15

5 E 8578.4 1.09𝐸 + 17 3.74𝐸 + 15

are nearly the same and comes in the order of 104 Kelvin.Theelectron density (Ne) measured experimentally using (4) and(5) in plasma is greater to the lower limit of electron densitycalculated by (3) and this clearly reveals that plasma is in LTE.

After verifying the assumption of stoichiometric ablation,optically thin plasma, and LTE condition, one can use theintensities of spectral lines of the element to correlate itsconcentration in the samples. Figure 3 clearly shows thepresence of atomic lines of Cr at (357.8, 359.3, 360.5) nm

and Pb at (220.3, 363.8, 368.3) nm in the LIBS spectra ofyellow, pale yellow, and orange samples collected from all fivedifferent area.We expect that the presence of these lines in theLIBS spectra of the previous samples may be due to the use oflead chromate (PbCrO

4) for coloring of those food samples,

but PbCrO4is nonpermissible and banned toxic color and

causes serious health hazards and may also cause cancer inthe long run.

We have also measured the intensities of spectral lines oflead, chromium, and calcium in all samples and the resultsare shown in Figure 5. The intensity of the spectral line ofCa (317.9 nm) is almost the same in the LIBS spectra of allsamples (Figure 5), which reflect that the concentration ofCa is almost the same in all samples. Therefore, this lineis selected to get the spectral lines normalized intensity ofCr (359.9 nm) and Pb (368.3 nm) and the results are shownin Figure 5. It is clear from Figure 5 that the proportionof normalized intensity of lead and chromium and hencethe proportion of concentration of Pb and Cr in yellow iceball samples are equal which reflects that the same type ofchemical (PbCrO

4) might have been used in preparation of

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8 ISRN Analytical Chemistry

3025201510

50

−5

−10

−15

−20

−25

−200 −100 0 100

Adulterated

Scores

Yellow, pale yellow and orange ice ball

Red ice ballGreen ice ball

Non-adulterated

PC-2

(4%

)

PC-1 (95%)

(a)

0.5

0.4

0.3

0.2

0.1

0

−0.2

−0.1

0.09 0.1 0.11 0.12 0.13

Loadings

PC-2

(4%

)

PC-1 (95%)

(b)

0.5

0.4

0.3

0.2

0.1

0

0 0.1 0.2 0.3

Influence

Leverage (PC-2)

Resid

ualX

-var

ianc

e (PC

−2)

(c)

100

80

60

40

20

0

PC-0 PC-1 PC-2 PC-3 PC-4 PC-5 PC-6 PC-7PCs

Explained variance

X-v

aria

nce

(d)

Figure 8: PCA plot for different ice ball samples (A, B, C, D, and E).

yellow ice ball samples. But in case of pale yellow and orangesamples the proportion of Pb and Cr is not the same as theproportion of intensity of Pb and Cr and they are very muchdifferent in the LIBS spectra of these samples. Therefore, thisresult reveals that in addition to PbCrO

4some other salts of

chromiummay have been used for providing light yellow andorange color.

Recently, principal component analysis (PCA) of LIBSdata has been used for rapid classification of adulteratedand nonadulterated food materials [10, 11, 15]. Therefore,in the present paper, PCA has been also used for theidentification and classification of different colored samplescontaining toxic pigments or elements. For the fulfillment ofthis purpose, we have prepared a dataset using LIBS spectraof yellow, pale yellow, orange, red, and green ice ball samplescollected from five different places (A, B, C, D, and E) with100 features (25 × 100 matrix). The library of LIBS datasamples along with the Unscrambler PCA software (suppliedby CAMO Software India Pvt. Ltd.) has been used in thepresent analysis [9, 10, 14]. When these LIBS data are usedfor classification we get the principal components PC1 (95%)

andPC2 (4%) that explain the total variance (99%) among thedataset. Different plots are shown in Figure 8 that gives fourparameters (i) scores: represents sample patterns and showsample differences and similarities (ii) loading: representsvariable contribution and correlations, (iii) Influence plot:measures the distance from the projected sample, and (iv)variance plot: shows the percentage of total variance in thedata. PCA score plot (Figure 8) clearly differentiates thesamples containing lead and chromium in yellow, pale yellow,and orange ice ball samples of different regions from others.Thus, LIBS data with PCA enables us to rapidly classify andidentify adulterated samples from nonadulterated samples.

4. Conclusion

The experimental results clearly reveal that the ice ballhaving yellow, pale yellow, and orange colors are adulteratedby lead chromate, whereas red and green color ice ballsamples are not adulterated. The results of the presentstudy further demonstrate that LIBS coupled with PCA canbe used as online powerful diagnostic tool for detection

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ISRN Analytical Chemistry 9

and classification of adulterated and nonadulterated foodmaterials like ice balls, ice-cream, sweets, and so forth. InIndia, the consumption of ice balls by children and adult insummer season increases and thus calls for an appropriate fasttechnique to detect such adulteration which is met by LIBS.

Acknowledgments

Financial assistance from the BRNS, BARC, Mumbai (no.2009/37/30/BRNS/2063), is gratefully acknowledged. Mr.Rahul Agrawal is grateful to Centre of Food Technology,University ofAllahabad, for Financial Assistance.The authorsare also thankful to Ms. Manju Tiwari, Centre of FoodTechnology, University of Allahabad, for providing help insample collection.

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