Xrf X Ray Fluorescence Spectroscopy Biology Essay

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Soil samples were collected across the sheaf river catchment particularly in the area, which has more chances to occur floods. Sheaf River is located in Sheffield, south Yorkshire, England. The river flows northwards towards Dore through the valley called abbey dale. The river has been polluted centuries ago because of the past industrial activity. There were iron and steel working sites across the river. River was used to provide the power as water powered working sites. The soil samples were analysed to get the concentrations of the heavy metals most importantly lead levels and also get the concentrations of other heavy metals like iron, aluminium, cupper, chromium, manganese magnesium, zinc, and cadmium. The samples were analysed by two methods one is XRF which is X-ray florescence method and ICPOES which is inductively coupled plasma optical emission spectrum. These two methods were carried to get the concentrations of the heavy metals in soils and they were compared to understand the actual lead levels on the sites. Samples were analysed according to standard reference material (SRM), which is buffalo river sediment. Previous studies have been investigated the sub urban area of Sheffield near the river floodplains at different time periods particularly in summer and winter the soil samples were analysed to metal analysis. Metal levels in the upper river sheaf were relatively very high compared to normal value.

There were really considerable levels of lead has been identified on the sites and they pose the threat of public health issue most importantly children health issue because the residential areas and public parks might appear in the future.

Introduction:

Potentially undesirable concentration of metals in the soils has the threat of environmental hazard. Toxic metals that were produced by the mining industries during the decades have the potential to affect the fluvial system when they were mixed with the water and they pose a serious threat to the water quality. These heavy metals can be lethal to humans and their habitats. In this study lead has more importance than any other heavy metals because the study area has past lead working sites.

Lead is a heavy, soft and grey coloured material is found generally in soil, plants, and animals. Human activities made the lead levels high in the environment, which is very toxic. Lead levels were become higher because of emission of lead from gasoline, lead paints usage and lead waste from mining industries. The toxic effects of these metals on human health are damaging the organs, disorders in the respiratory tract, lung diseases and dysfunction of heart and etc. most effectively children pose a serious threat of lead concentrations in soils where they usually play.

The study site:

The study site is located approximately 2 miles from the city centre of Sheffield, England. Sheffield belongs to south Yorkshire. The study site is located on southwest of Sheffield. The area has a very low housings and it is a suburban area and also has the wide-open areas and parks. Samples were collected along the catchment of river sheaf, which flows towards north. The area where the samples were collected has the soil of sedimentary from the Upper Carboniferous sand stones and shells. River sheaf has sources of union of Tetley brook and old hey brook and now it is a suburb of Sheffield. Sheaf River flows towards north passes by Dore and north of Heeley. It passes through Calvert and enters in to the centre of Sheffield and then flows until it mixes with the river Don near Blonk Street Bridge.

In Sheffield there are five rivers flowing in to the river Don. Sheffield historic development has surveyed that there was number water powered industries across the river sheaf and also stated that lead industries were having importance along this river. The fast flowing water of these rivers provided the energy to rotate the water wheels. In 17th to the 19th century there were number of steel industries along theses rivers and they were making all types of cutlery ware like razors, blades, axes and tools and the industry was much more increased and there were more than 30,000 people employed. Abbey dale industrial hamlet was located along the river sheaf and it had eighteen water powered steel working sites. There was a lot of waste material discharged into the environment due to the industrial activity. During the floods the lead, which is already on the soil, is mixing with the floodwater and then spreads in to the long open areas.

XRF: X-ray fluorescence spectroscopy:

Environment is effecting with lot of pollutants everyday and it is important to measure and analyse the levels of toxic elements in the soil in order to reduce and remediate the areas, which are effected. Researchers have been using one traditional method to analyse the sample contamination, which is a typically microwave or acid digestion of soil sample and then finally analysing the solution by flame or furnace AAS (atomic absorption spectroscopy) or ICP-OES. Several new techniques have been arrived in to the field, which are used for the analysis of soil and sediments for example ETV-ICP-MS, GDMS, de Arc-AES and XRF. Among all these techniques XRF is commonly used technique for all type of soil samples.

XRF technique can be used for qualitative and quantitative analysis of elements. Samples have wide range they can be geological, industrial, environmental and biological also other samples. XRF is a direct method of analysis, which is we can analyse

The samples directly from the sample bag and it can be done very rapidly and it makes the whole process very simple and cost effective, and in very less time about 90-120 sec per sample. It eliminates the sample contamination problem from chemical reagents and also it saves the sample for further analysis. By providing the accurate results in short span of time that can challenge the standard laboratory techniques for example ICPOES. Soil sample is prepared by removing the debris, fragments and other foreign objects and grinded and sieved thoroughly so that the effects of fundamental errors and XRF related bias can be reduced. And it is a non-destructive method, requires a little or no sample preparation that means samples can be reused for the verification.

HOW THE XRF WORKS:

The main principle involved in XRF elemental analysis is detecting the elements on the spectra corresponds to their emitted energy and wavelength. In Xrf the sample is irradiated by the X-rays the inner shell electrons absorbs energy and they lack their stability and jumps in to the outer shells and they leave the unoccupied place and this place is occupied by the another electron form the inner most orbit. The difference in the energy will be delivered to the detector and it produces a spectrum of different peaks and the corresponding elements can be detected on the spectrum. The intensity of the peaks on the spectrum will give the quantitative analysis of the sample. The radioisotopes or x-ray tubes can provide the irradiation of the sample by the X-rays.

Sample preparation has an importance because the raw sample may contain foreign materials and soil debris. Sample must be screened and the unwanted objects are separated by sieving the sample through the 2-mm mesh and also moisture must be removed from the soil samples by drying the sample, the sample must be carefully packed in to the plastic transparent bags. Soil samples stirred for homogeneity before packing them to make at-least they are loosened for the depth of 1.5-2 cm.

Even though the method is very simple and easy to do but the method need constant reassurance for the sample cup and the results will vary on the sample analysis time. And also it is important that we cannot know the actual concentrations of the contaminants in the soil sample this makes it hard to find the real values of the analysis. So it is important to use the confirmatory method, which is ICPOES (inductively coupled plasma optical emission spectroscopy) to make sure the values are correct and it is also be a total elemental method like xrf.

ICPOES (inductively coupled optical emission spectroscopy):

Finding the elemental concentrations is the most important process in the analytical chemistry. In recent years, it has been very important in finding the spatial concentrations of the heavy metals on the fields because their high toxicity to humans and animals. Inductively coupled optical emission spectroscopy is a potential and major technique to find the heavy metal concentrations in the soil samples. Inductively coupled plasma optical emission spectroscopy is a multi element analytical technique. It can analyze a sample to give the concentrations of the large number of metals according to the spectral resolution of the instrument obtained on the detector. This method is commonly used to determine the concentration of the metals form the soil samples, the advantage of this method is a single sample run off less than one minute and the samples can be analyzed in a different aqueous or organic concentrations. Solid samples must be digested or dissolved in an acid before they are prepared for analysis and at least 4 ml to 5 ml is needed for good run. The acid digestion is produced at certain PH value and it reproducible at the same PH hence the ICPOES does not yields absolute concentrations that can be used directly for analysis without careful interpretations. The detection limit for the ICP is less than one ppm. In ICP the collector can be separated easily from the matrix by carrying the filtering, centrifuging and washing the precipitate. And it is also characterized that high temperatures leading to some chemical interference and wide linear response. Another limitation for the ICP is acid digestion can destroy the soil sample material and fraction of metal that the process extracts is dependent on the geological matrix of the sample. And also ICPOES require along sample preparation and analysis time.

Procedure of ICPOES:

During the ICPOES the first step is if the sample is solid it must be dissolved or digested with the organic liquids for instance nitric acid and then mixed with distilled water before it being sent in to the plasma. During the process the sample molecules are converted in to atoms and ions by using the high temperature radio frequency argon plasma. Once the molecules are converted to free atoms they can be detected and determined quantitatively by atomic absorption or emission spectrum.

Plasma is a hot gas, which is partially ionized and is produced by the interaction of the very intense magnetic field which is produced by radiofrequency generator (RF) and passing through the coil on a tangential flow of gas, which is normally argon. Argon gas flows through the quartz tube about 15 L/min. when the source of electrons from the spark of high voltage the gas ionizes and a high temperature is occurred at the end of the tube. The plasma is oriented vertically in icpoes and is used to generate the photons of light by the excitation of ground state electron atoms to jump in to high-energy orbital. When these electrons coming back to their normal state they emit wavelength specific photons that are characteristic to the element of interest. The most commonly used device for the sample injection in to the plasma is nebulizer. In nebulizer the sample is sprayed as small droplets in to the flame of plasma. And another important part of ICPOES is detector. In the detector the grating monochromatar separates the emission of light detected by the every elements present in the sample and disperses the wavelength of each individual wavelength to the appropriate photo detector and the elements can be measured simultaneously.

ICPOES performance can be affected by the parameters like nebulizer gas flow rate, RF power, torch gas flow rate and viewing height and sample induction rate. These parameters should select appropriately to get the best performance from the ICPOES.

Materials and methods:

Soil samples were collected from three different sites across the river sheaf catchment from the top 0-5 cm to bottom of 50-60 cm.

Reagents:

Soil samples collected from river sheaf catchment (Sheffield)

Nitric acid (S. G . 1.42, (70%) Batch No 0936045, Fischer scientific.)

Deionized water from the ICP lab

Soil Reference material â€"(Buffalo river sediments, 8704)

Equipments

XRF (innovXsystem)

Micro pipette

Digital dispenser

25 ml volumetric flasks

30 ml universal containers

Microwave vessels

Filters (labXpress filtration assembly consisting of turntable (574165), funnel 20 (166480) and diaphragm pump assembly 50 Hz (542570). (CEM)

Microwave (MARS press, CEM.)

ICPOES (Varian 720-ES)

Dish washer in the soil lab

Safety glasses, Lab coat and rubber gloves.

Experiment

ICPOES

Weighing

The soil samples were transferred to the beakers and they kept in the oven for overnight drying at 1050C for 24 hours. After 24 hours of drying samples were cooled and then weighed to approximately 0.2g. The precise weights are shown in below table.

Sample sites(LSW)

(ladies spring wood)

Sample numbers

Samples (Depth in cm)

Weight (g)

3A

1

0-5 cm

0.2112

3A

2

5-10 cm

0.2187

3A

3

10-15 cm

0.2109

3A

4

45-50 cm

0.2008

3A

5

50-55 cm

0.2046

3A

6

55-60 cm

0.2012

3A

7

70-75 cm

0.2008

3A

8

75-80 cm

0.2148

3A

9

80-90 cm

0.2074

2B*

10

5-10 cm

0.2055

2B*

11

10-15 cm

0.2108

2B*

12

45- 50 cm

0.2050

2B*

13

50- 60 cm

0.2155

3d

14

5-10 cm

0.2173

3d

15

10-15 cm

0.2010

3d

16

15- 20 cm

0.2073

3d

17

40- 45 cm

0.2023

3d

18

45-50 cm

0.2143

BLANK

19

CRM

20

0.2132

The samples were labeled according to their names and added to microwave vessel and to each microwave vessel 10 ml of nitric acid was added. White rubber bungs were inserted to each vessel and the cap was tightened to finger tight and by another half turn. This was done to ensure that there was no water on the brown Kevlar outer tubes. The tubes were stacked in the carousel. The carousel were balanced in an even pattern, starting with the inner locations first.

Microwave digestor:

Power (max)

1600 w (60%)

Control (0 C)

60

Hold

15 minutes

The microwave digestor was programmed as shown in table 2. The whole digestion of samples took about 1 hour including the cooling time for samples. After the digestion and cooling down of microwave vessels (tubes), tubes were taken to the fume cupboard and opened pointing away from face.

Filtration:

LabXpress filtration assembly was used for the filtration. It is designed to filter acid digestion solution from MARS system.

Assembly of filter and filtration:

For the filtration the turn table assembly was used. First the table height was adjusted to accommodate the height of 25 ml flasks and then each flask was inserted by the funnels and each flask needs a different funnel. The adjusting was done by loosening the thumb screw on the center post of the turntable and the height was adjusted as desired, and the thumb screw was tightened. The filter cups were placed into each funnel. The tubing was connected extending from the diaphragm pump to the fitting of the pressure cap. The power cord of the pump was plugged into an electrical outlet. As for adjusting the air flow of the pump, the control knob located on the front of the pump was rotated clockwise to decrease the pressure and anticlockwise to increase the air flow. The solutions were poured into the filter cups. The pressure cap was placed on a filter cup, held with pressure until all of the liquid was drained through the filter. The turntable accommodated 20 filter cups

The volumetric flasks were precisely made up to (25 ml) mark with deionized water. The solution was transferred into (30 ml) universal containers for storage.

Preparation of water samples for ICPOES analysis:

From the universal containers, the (5 ml) filtrate was pipette into a 25 ml volumetric flask and was made up to the mark with deionised water. The filtrate was transferred to a falcon centrifuge tube and was made up to the 14 ml mark. The tubes were capped and stored in a rack. Each tube was labeled according to the samples. All water samples were acidified with nitric acid to a 7% concentration before any storage in the fridge. No sediments were present in any of the samples.

Elemental analysis using ICPOES:

Making up the standards

To make up the standard solution Alfa Aesar. Multi element plasma solution was used.

Table 3.

standard

Standard solution

Made up to

10ppm

1ml of 1000µg/ml

100ml

5 ppm

0.5ml of 1000µg/ml

100ml

1 ppm

0.1ml of 1000µg/ml

100ml

0.5 ppm

5ml of 10ppm

100ml

100ppb

1ml of 10ppm

100ml

50 ppb

0.5ml of 10ppm

100ml

10 ppb standard

0.1ml of 10ppm

100ml

Blank

2% nitric acid

Machine set up

The ICP machine was turned on at switch at the right hand side.

Argon regulator screwed

Pressure 7 bar on gauge

Nitrogen regulator screwed

Pressure 3 bar on gauge

Hood

Venting. Extract fan light turned green

Tubing

Good condition

Computer

Switched on

Plasma

Switched on and ignited within a minute

The machine was left to run for 15 minutes to stabilize.

Analyzing samples

To create a method on the computer, file was clicked on and then method editor to choose the method. The calibration tab was clicked on along bottom of method editor window. On the side of method editor window was define standards tab which was clicked on. In Id column, the details of blank, calib 1, calib 2, calib 3 and the rest were labeled 1-20. The machine was switched on and was left to run for all samples.

XRF

(http://www.equipcoservices.com/rentals/xrf-rental/xrf-analyzer.html)Fig 1 hand held XRF and fig 2 is attached to the stand to analyze the samples in the polyethylene bags. The soil samples were homogenized with a pestle by grinding them. The soils were kept in a polyethylene bag and leveled flat to ensure surface homogeneity. The soil samples were placed on an x-ray detector for immediate analysis. The readings were taken by digital assistance attached to it and can be used directly for analysis.

Results and discussion:

Soil samples were collected from the river catchment sheaf where they had been a past industrial activity in 17th to 19th century. Samples were collected from different sites across the river flood plains and they are named and labeled according to their specific grid reference and the depth from the ground they had been taken. They were 13 different sites about 90 samples had been taken for analysis. Some of the samples were core samples about 0-80 cm from the ground and some of the samples were peat samples, they are about 0-15 cm form the ground.

The map below shown taken from the dig map collections and it shows all the sample sites according to their grid references.

All the samples were subjected to XRF analysis and the Pb concentration of each and every site is analyzed and observed that the pb concentration of these sites are very much higher than the soil guideline value(300 ppm) and the rest of the heavy metals like Fe, Mn, Cr, Al, Ba, Ca and Mg are also have high concentrations.

The concentration of Lb has been shown below according to XRF analysis.

sheaf river samples

site 1 A

DEPTH

pb(ppm)

BD

top

bot

mid

mass

SD

0

5

2.5

1459.000

20

5

10

7.5

1491.000

16

10

15

12.5

1582.000

21

15

20

17.5

1303.000

18

20

25

22.5

1702.000

22

25

30

27.5

1473.000

20

30

35

32.5

1786.000

23

35

40

37.5

2080.000

26

40

45

42.5

1950.000

25

mean

1647.333

site 2A

Depth

pb(ppm)

top

bot

mid

mass

SD

0

5

2.5

2811.000

33.00

5

10

7.5

2925.000

35.00

10

15

12.5

3137.000

37.00

15

20

17.5

3110.000

36.00

20

25

22.5

3308.000

38.00

25

30

27.5

3168.000

37.00

30

35

32.5

3818.000

43.00

35

40

37.5

3327.000

39.00

40

45

42.5

3394.000

39.00

45

50

47.5

3633.000

42.00

50

55

52.5

3778.000

45.00

55

60

57.5

3840.000

44.00

60

65

62.5

4354.000

50.00

mean

3431.000

site3A

Depth

pb(ppm)

top

bot

mid

mass

sd

0

5

2.5

1612.000

21.00

5

10

7.5

1735.000

22.00

10

15

12.5

1433.000

20.00

15

20

17.5

1452.000

20.00

20

25

22.5

1765.000

25.00

25

30

27.5

2055.000

26.00

30

35

32.5

2875.000

36.00

35

40

37.5

2934.000

34.00

40

45

42.5

3673.000

42.00

45

50

47.5

3552.000

41.00

50

55

52.5

3997.000

45.00

55

60

57.5

4461.000

50.00

60

65

62.5

5080.000

56.00

65

70

67.5

5366.000

61.00

70

75

72.5

5894.000

67.00

75

80

77.5

6625.000

73.00

80

85

82.5

7496.000

82

mean

3647.353

SITE 1C

Depth

pb(ppm)

top

bot

mid

mass

SD

0

5

2.5

1612.000

21.00

5

10

7.5

1735.000

22.00

10

15

12.5

1712.000

22.00

15

20

17.5

1746.000

23

20

25

22.5

1940.000

24

25

30

27.5

1715.000

22.00

30

35

32.5

1704.000

22

35

40

37.5

1940.000

25

40

45

42.5

2236.000

28

45

50

47.5

2138.000

26

50

55

52.5

2119.000

27.00

55

60

57.5

2229.000

28.00

60

65

62.5

1947.000

25.00

65

70

67.5

2474.000

30.00

70

75

72.5

1942.000

21.00

75

80

77.5

1480.000

21.00

80

85

82.5

1493.000

21.00

mean

1891.882

site 2C

pb(ppm)

top

bot

mid

mass

sd

0

5

2.5

5

10

7.5

10

15

12.5

1902.000

30.00

15

20

17.5

1607.000

26.00

20

25

22.5

1757.000

29.00

25

30

27.5

1780.000

28.00

30

35

32.5

2105.000

33.00

35

40

37.5

2644.000

39.00

40

45

42.5

3245.000

47.00

mean

2148.571

site 2B*

Depth

pb(ppm)

top

bot

mid

mass

sd

0

5

2.5

2492.000

36.00

5

10

7.5

2729.000

39.00

10

15

12.5

2655.000

38.00

15

20

17.5

2914.000

42.00

20

25

22.5

2663.000

39.00

25

30

27.5

2653.000

38.00

30

35

32.5

2847.000

40.00

35

40

37.5

3486.000

49.00

40

45

42.5

3635.000

50.00

45

50

47.5

3725.000

52.00

50

55

52.5

3785.000

52.00

60

70

65

2404.000

36.00

mean

2999.000

site 2C*

pb(ppm)

top

bot

mid

mass

sd

0

5

2.5

1672.000

27.00

5

10

7.5

1730.000

28.00

10

15

12.5

1922.000

30

15

20

17.5

1899.000

30.00

20

25

22.5

2046.000

31.00

25

30

27.5

2081.000

32

mean

1891.667

site 3d

pb(pm)

top

bot

mid

mass

sd

0

5

2.5

3212.000

45

5

10

7.5

3687.000

52

10

15

12.5

3697.000

52

15

20

17.5

3646.000

51

20

25

22.5

3808.000

52

25

30

27.5

3847.000

54

30

35

32.5

3984.000

56

35

40

37.5

3662.000

51.00

40

45

42.5

4969.000

69.00

45

50

47.5

5728.000

80.00

mean

4024.000

site2B

pb(ppm)

top

bot

mid

mass

sd

0

5

2.5

1774.000

28

5

10

7.5

1959.000

30

mean

1866.500

site 3B

top

bot

mid

mass

sd

0

5

2.5

2065.000

31

5

10

7.5

2474.000

36

10

15

12.5

2726.000

39

mean

2421.667

site 3C

top

bot

mid

mass

sd

0

5

2.5

2765.000

40

5

10

7.5

3589.000

52

mean

3177.000

site 3D

top

bot

mid

mass

sd

0

5

2.5

2051.000

32

5

10

7.5

1773.000

28

10

15

12.5

1919.000

30

mean

1914.333

site 4

top

bot

mid

mass

sd

0

5

2.5

1653.000

27

5

10

7.5

2722.000

40

10

15

12.5

3290.000

47

mean

2555.000

The average mean concentration of lead in each site calculated and shown in the table and the total average mean value of lead concentration calculated as 2585 ppm. The total graphs plotted according to depth verse concentration are shown below.

XRF is very simple method and it can be done directly without any sample preparation and also it can be done in short time span .It has chosen the time for the xrf as 90 sec for each sample and observed that when u take the time as 120 sec the standard deviation was slightly decreased so that the the time taken for the sample to analyze can change

For the icpoes analysis the soil sample digestion is most important and also labeling. One sample wrong label might give the wrong results and whole analysis might be wrong so each and every sample were thoroughly rechecked before doing any thing. Some of the samples were formed a yellowish color at the bottom of the microwave vessel and some of them have dark brown. Solid residues were observed at the bottom of the microwave vessels after digestion and centrifugation and the filtration has been done effectively. The major elemental results were shown in the tables below according to their sites as calculated in ppm. According to the soil guideline values (SGV) of United Kingdom lead levels should be less than 450 mg/kg on residential land and less than 750 mg/kg on lead levels and other heavy metals. The readings have been collected from the icpoes analysis are calculated to analyze the actual concentrations of the heavy metals in mg/kg as shown below.

Concentration = actual value from icp X 25 X 5/original weight of the sample

The lead concentrations are shown in the table below according to the sites.

Site label

sample num

pb (220.353)ppm

actual weight

cal value in mg/kg

3A

1

3.29455

0.2112

1949.899384

3A

2

0.894252

0.2187

511.1179698

3A

3

2.56476

0.2109

1520.128023

3A

4

5.38397

0.2008

3351.57495

3A

5

6.61732

0.2046

4042.839687

3A

6

6.13438

0.2012

3811.120775

3A

7

9.55385

0.2008

5947.366783

3A

8

6.84497

0.2148

3983.339153

3A

9

15.1093

0.2074

9106.376567

2B*

10

4.93962

0.2055

3004.635036

2B*

11

3.3409

0.2108

1981.083966

2B*

12

6.61817

0.2051

4033.50195

2B*

13

5.49815

0.2155

3189.182135

3d

14

4.0039

0.2173

2303.209848

3d

15

4.11598

0.201

2559.689055

3d

16

6.75034

0.2073

4070.39315

3d

17

8.24482

0.2023

5094.426594

3d

18

13.2178

0.2143

7709.869342

Blank

blank 19

-0.024385

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