A Low-Cost Method for Quantifying Sodium in ...

1 1 2 3 4 5

A Low-Cost Method for Quantifying Sodium in Coconut Water and Seawater for the Undergraduate Analytical Chemistry Laboratory: Flame Test, a Mobile Phone Camera and Image Processing Supporting information

6 7 8 9 10

Detailed experimental procedures Overview

11 12

This practice lecture was developed to evidence the relationship between the intensity of

13

a spontaneous emission of radiation and the atom concentration. Consequently, the

14

experiment is intended for a second-year undergraduate classes. The intensity of sodium

15

atomic emission is given by Equation 1:

16 17

(1)

18 19

Where

20

transition,

21

sample of making a radiative transition between the discrete states 3s-3p and

22

average number of sodium atoms on the level 3p.

23

In this context, the intensity of sodium atomic emission is proportional to sodium

24

concentration in the sample. The intensities of RGB channels will increase in the digital

25

images according increase the sodium concentration. As a result, RGB responses could

26

be directly related to sodium concentration in our experiments. It is possible to explore

27

image processing aspects, and additionally, to introduce R statistics, a powerful statistic

28

platform of freely accessible that has a huge range of functionalities in different areas.

29 30 31 32 33

is Planck´s constant,

is the frequency of photon emission from 3p-3s

is the average probability per unit time for one sodium atom in our is the

2 1 2 3

Flame Test

4

diluting 163 mg of sodium chloride in a 100 mL volumetric flask;

5

Prepare working solutions from the stock solution by dilutions, namely: 20, 40, 80, 120,

6

and 160 mg dm-3 of sodium;

7

Complete the perfume bottles with the working solutions;

8

Discover which student has the mobile phone equipped with the highest resolution

9

camera;

Prepare a sodium chloride stock solution in distilled water at 640 mg dm-3 of sodium,

10

Arrange the experiment as shown in Figure 1. The distance between the flame and the

11

mobile phone must be fixed (~ 40 cm)For this, the test needs two people to perform: one

12

to spray the sample and one to acquire the image;

13

Start spraying distilled water into the flame. Record a video (Blank) of the experiment

14

using a mobile phone. Apply this procedure in duplicate;

15

Repeat the previous step using the working solutions;

16

For seawater, transfer 1 mL of the sample to a 100 mL volumetric flask. Complete with

17

distilled water and homogenize;

18

For coconut water, complete the perfume bottle with pure coconut water;

19

Spray the sample into the Bunsen burner. Record a video (Sample) of the experiment

20

using a mobile phone. Apply this procedure in triplicate.

21 22 23 24

Data Treatment

25

intense light. Reproduce each video using the program of your preference;

26

Advance the video frame-by-frame to find which frame exhibited the most intense light.

27

To accomplish this task, each student could use a program of his or her preference. Our

28

group used Windows Live Move Maker (Microsoft Corporation). Once the specific frame

29

was identified, stop the video and use the print screen to copy and paste the frame into

30

freely accessible GIMP 2.8.6 (GNU) software;

31

Download of GIMP 2 software (www.gimp.org). Install the software;

32

Go to GIMP 2, create a new image and paste the captured image in the print screen;

The resulting video files must be studied to determine which frame exhibited the most

3 1

Cut a square spot (10 x 10 pixels) of the region of the flame that exhibited the most

2

intense light and saved in JPEG format.

3

Repeat the previous step for all videos and name as follow: Dark1.jpg and Dark1.jpg

4

(only the flame), Blank1.jpg and Blank2.jpg (water), Na20mg1.jpg, Na20mg2.jpg,

5

Na40mg1.jpg,

6

Na160mg1.jpg, Na160mg2.jpg, Sample1.jpg, Sample2.jpg and Sample3.jpg;

7

Choose the folder location and save the files to your local system.

8

Download R (www.r-project.org). Install and open;

9

Change the directory for the folder location where the images were recorded;

Na40mg2.jpg,

Na80mg1.jpg,

Na80mg2.jpg,

Na120mg1.jpg,

10

Open Flame Image Processing Script attached on the Support Information;

11

Press Ctrl+R.

12

Next, a script based on the EBImage package (bioconductor.org) was formulated to treat

13

the images. EBImage1 is an R package (R Foundation for Statistical Computing) that is

14

normally used for bioinformatics. First, the background was subtracted using the dark

15

filter, resulting in only the flame image. Second, the RGB channels of the digital image

16

were extracted, and the average values of each channel were calculated. Next, a vector

17

norm ||v||2,3 was determined based on RGB:

18 19

(2)

20 21

where

22

differences between the RGB channels from the sample digital images and the RGB

23

channels from the blank (distilled water). The script generates the calibration curve, a

24

statistics analysis and the sodium concentration. The limit of quantification (LOQ) and

25

limit of detection (LOD) were calculated according to Da Silva and co-workers2,3.

26 27 28 29 30

,

and

are the normalized average values obtained from the

4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Figure 1. Flame test experimental arrangement.

5 1

#################### Flame Image Processing Script ####################

2 3 4

# To install the EBImage package:

5 6

source("http://bioconductor.org/biocLite.R")

7

biocLite("EBImage")

8 9 10

# To cite this package in a publication (http://www.bioconductor.org/packages/2.12/bioc/html/EBImage.html)

11 12

citation("EBImage")

13 14

# Loading the EBImage package

15 16

library("EBImage")

17 18

# Reading dark and mean

19 20

dark1 = readImage('Dark1.jpg')

21

dark2 = readImage('Dark2.jpg')

22

dark = (dark1 + dark2)/2

23

if (interactive()) display(dark)

24 25

# Reading blank and mean

26 27

blank1 = readImage('Blank1.jpg')

28

blank2 = readImage('Blank2.jpg')

29

blankm = (blank1 + blank2)/2

30

blank = blankm - dark

31

if (interactive()) display(blank)

6 1 2

# Reading 20 mg and mean

3 4

Na20mg1 = readImage('Na20mg1.jpg')

5


6

Na20mgm = (Na20mg1 + Na20mg2)/2

7

Na20mgn = Na20mgm - dark

8

if (interactive()) display(Na20mgn)

9 10


11 12


13


14


15


16


17 18


19 20


21


22


23


24


25 26


27 28


29


30

Na120mgm = (Na120mg1 + Na120mg2)/2

31


7 1


2 3


4 5


6


7

Na160mgm = (Na160mg1 + Na160mg2)/2

8


9


10 11

# RGB Image

12 13

Na20red = channel(Na20mgn, 'red')

14

Na20redm = mean (Na20red)*255

15

Na20redm

16

Na20green = channel(Na20mgn, 'green')

17

Na20greenm = mean (Na20green)*255

18

Na20greenm

19

Na20blue = channel(Na20mgn, 'blue')

20

Na20bluem = mean (Na20blue)*255

21

Na20bluem

22 23 24


25


26

Na40redm

27


28


29

Na40greenm

30


31


8 1

Na40bluem

2 3


4


5

Na80redm

6


7


8

Na80greenm

9


10


11

Na80bluem

12 13


14


15

Na120redm

16


17


18

Na120greenm

19


20


21

Na120bluem

22 23


24


25

Na160redm

26


27


28

Na160greenm

29


30


31

Na160bluem

9 1 2

# RGB blank

3 4 5

RGBblank1 = blank1 - dark

6

blankred1 = channel(RGBblank1, 'red')

7

blankred1m = mean (blankred1)*255

8

blankred1m

9

blankgreen1 = channel(RGBblank1, 'green')

10

blankgreen1m = mean (blankgreen1)*255

11

blankgreen1m

12

blankblue1 = channel(RGBblank1, 'blue')

13

blankblue1m = mean (blankblue1)*255

14

blankblue1m

15 16

RGBblank2 = blank2 - dark

17

blankred2 = channel(RGBblank2, 'red')

18

blankred2m = mean (blankred2)*255

19

blankred2m

20

blankgreen2 = channel(RGBblank2, 'green')

21

blankgreen2m = mean (blankgreen2)*255

22

blankgreen2m

23

blankblue2 = channel(RGBblank2, 'blue')

24

blankblue2m = mean (blankblue2)*255

25

blankblue2m

26 27

blankredm = (blankred1m + blankred2m)/2

28

blankredm

29

blankgreenm = (blankgreen1m + blankgreen2m)/2

30

blankgreenm

31

blankbluem = (blankblue1m + blankblue2m)/2

10 1

blankbluem

2 3 4

# ||v|| = Sqrt(R^2+G^2+B^2)

5 6

Na20mg = sqrt((Na20redm-blankredm)^2+(Na20greenm-blankgreenm)^2+(Na20bluem-

7

blankbluem)^2)

8

Na20mg

9 10


11

blankbluem)^2)

12

Na40mg

13 14


15

blankbluem)^2)

16

Na80mg

17 18

Na120mg = sqrt((Na120redm-blankredm)^2+(Na120greenm-

19

blankgreenm)^2+(Na120bluem-blankbluem)^2)

20

Na120mg

21 22

Na160mg = sqrt((Na160redm-blankredm)^2+(Na160greenm-

23

blankgreenm)^2+(Na160bluem-blankbluem)^2)

24

Na160mg

25 26

# ||v|| Blank

27 28

Vblank = sqrt(blankredm^2+blankgreenm^2+blankbluem^2)

29

Vblank

30 31

# Analytical curve and residuals

11 1 2

# Concentration of sodium (mmol L-1)

3

a=c(20,40,80,120,160)

4 5

# Intensities

6

b=c(Na20mg,Na40mg,Na80mg,Na120mg,Na160mg)

7 8

# Graph

9 10

y