Analysis of Five Different Soil and Wastewater Samples

This article examines the analysis of five different wastewater and soil samples, which are listed below. Note that samples 1 to 4 contained dilute HNO3.

  • Sample 1: Distilled water
  • Sample 2: Wastewater after treatment in wastewater plant (exit)
  • Sample 3: Wastewater before treatment in the waste plant
  • Sample 4: Industrial wastewater
  • Sample 5: Dried soil from agriculture waste, digested with HNO3 and HClO4

The abovementioned samples were initially analyzed using a semi-quantitative method in order to identify elements and their particular concentrations per sample. Profiles of each element were taken from all samples. They were then compared to show peaks and relative background levels. After this, a quantitative analysis was performed using calibration curves set at appropriate levels. Finally, the Standard Addition Method was utilized to obtain results from Sample 5. This sample is suspected to have a more significant matrix effect in comparison to the other four samples.

Principle

An elemental analysis of samples was made using an Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). After the samples have been nebulized, they were transferred to an argon plasma where it was decomposed, atomized, and ionized, fully exciting the atoms and ions. Light was emitted when atoms or ions returned to lower levels of energy. The intensity of this process was measured. Every element emits light at a particular wavelength. This enables users to quantitatively analyze the acquired data after calibration.

Instrument Specification

The primary device used in analysis was the ULTIMA 2. The specifications of such instrument are presented in the tables below.

Table 1. Specification of spectrometer

Parameters Specifications
Mounting Czerny Turner
Focal length 1 m
Nitrogen purge Yes
Variable resolution Yes
Grating number of grooves 2400 gr/mm
Order 2nd order

 

Table 2. Specification of RF Generator

Parameters Specifications
Type of generator Solid state
Observation Radial
Frequency 40.68 MHz
Control of gas flowrate by computer
Control of pump flow by computer
Cooling air

 

Semi-Quantitative Analysis

The method of analysis used in this article aimed to utilize a semi-quantitative approach to facilitate the detection of present elements and their concentration estimates, ultimately performing quantitative analysis to obtain accurate and precise results.

A semi-quantitative method is integrated into the Analyst software for the ICP. It allows for rapid identification of elements in the sample from a qualitative and quantitative point of view.

The current method focuses on 34 elements. Wavelengths have been selected to cover a large variety of samples, wherein the most sensitive lines were assigned to most elements (with the exception of Ca and Mg) as well as appropriate background correction positions. A background correction position is placed on both side of the Pb and Al peaks, incased of high AI or Ca concentrations, respectively. A calibration is performed with two points (0 and 5 mg/L in deionized water), however, both calibration and analyses are measured with one replicate. The acquisition time is 0.1 s per data point, with 7 data points measured to fit a gaussian curve.

With these conditions, a semi-quantitative analysis is undertaken in about 3-4 minutes for the 34 elements and allows the identification of different kinds of samples.

It should be noted, however, that the matrix for the calibration standards may be adjusted (NaCl 100 g/L, 20 % H2SO4 ...) according to the samples that need to be analyzed. This method provides more accurate results.

The following plasma conditions were applied. A key finding to note is the slight increase of power from 1200 W from the 1000 W. This would be typically used for clean water. The increase of power was undertaken in order to minimize matrix effects that may have an influence on signal quantity, since the standards are in deionized water and the samples are waste water and soil and acids.

Table 3. Operating conditions

Parameter Condition
RF Generator power 1200 W
Plasma gas flowrate 12 L/min
Auxiliary gas flowrate 0 L/min
Sheath gas flowrate 0.17 L/min
Nebulizer gas flowrate 0.76 L/min
Nebulizer flowrate 2.75 bars
Sample uptake 1 mL/min
Type of nebulizer Cross Flow
Type of spray chamber Scott
Argon humidifier No
Injector tube diameter 3.0 mm
Slits 20/15 µm

 

A K3- or C1-type Meinhard nebulizer and cyclonic spray chamber may be used to gain sensitivity, if required. The results can be printed or exported from the ICP software. To validate results, a certified sample was analyzed prior to sample measurement.

Table 4. Results for sample “Reference 1643-d”

Elements Concentration Unit Certified concentration
Ag 328.068 3.60 µg/L 1.27
Al 394.401 118.60 µg/L 127.6
Al 396.152 120.90 µg/L 127.6
As 189.042 56.10 µg/L 56.02
B 249.773 148.60 µg/L 144.8
Ba 455.403 485.90 µg/L 506.5
Be 313.042 8.60 µg/L 12.53
Ca 317.933 30.92 mg/L 31.04
Cd 228.802 5.20 µg/L 6.47
Co 228.616 22.00 µg/L 25.0
Cr 267.716 15.20 µg/L 18.53
Cu 324.754 20.10 µg/L 20.5
Fe 259.940 74.20 µg/L 91.2
Hg 194.164 < LD   n.c.
K 766.490 2.51 mg/L 2.36
Li 670.784 17.60 µg/L 16.5
Mg 279.806 7.44 mg/L 7.989
Mn 257.610 36.20 µg/L 37.66
Mo 202.030 111.30 µg/L 112.9
Na 589.592 21.06 mg/L 22.07
Ni 221.647 57.20 µg/L 58.1
P 178.229 < LD   n.c.
Pb 220.353 28.60 µg/L 18.15
S 181.978 144.80 µg/L n.c.
Sb 206.833 34.40 µg/L 54.1
Se 196.026 13.40   11.43
Si 251.611 2.68 mg/L 2.7
Sn 189.989 < LD   n.c.
Sr 407.771 282.60 µg/L 294.8
Ti 337.280 < LD   n.c.
Tl 190.864 9.30 µg/L 7.28
V 292.402 28.80 µg/L 35.1
V 311.071 36.80 µg/L 35.1
W 207.911 < LD   n.c.
Zn 213.856 68.70 µg/L 72.48
Zr 343.823 < LD   n.c.

n.c. means non-certified

Table 5. Results for various samples

Line Sample
1 2 3 4 5
Ag 328.068 < LD < LD < LD 0.010 0.179
Al 394.401 0.235 0.233 0.544 0.143 49.2
Al 396.152 0.271 0.256 0.592 0.120 48.5
As 189.042 < LD < LD < LD < LD 0.016
B 249.773 0.045 0.466 0.216 1.07 0.159
Ba 455.403 0.046 0.076 0.090 0.170 1.30
Be 313.042 < LD < LD < LD < LD < LD
Ca 317.933 0.969 49.4 38.4 157 645
Cd 228.802 < LD < LD < LD < LD 0.007
Co 228.616 < LD < LD < LD < LD < LD
Cr 267.716 < LD < LD 0.003 0.006 2.00
Cu 324.754 0.003 0.066 0.045 0.121 3.75
Fe 259.940 0.016 0.065 0.377 0.490 119
Hg 194.164 < LD < LD < LD 0.032 0.479
K 766.490 0.202 5.79 3.427 389 7.40
Li 670.784 < LD < LD < LD < LD 0.110
Mg 279.806 0.066 8.77 6.344 12.3 28.3
Mn 257.610 < LD 0.001 0.040 0.066 1.07
Mo 202.030 < LD < LD < LD < LD 0.013
Na 589.592 1.09 33.3492 25.4 797 3.66
Ni 221.647 < LD 0.0394 0.027 0.0102 1.01
P 178.229 0.024 0.7233 0.400 6.22 42.1
Pb 220.353 < LD < LD 0.031 < LD 0.632
S 181.978 0.384 10.0 7.19 56.8 26.2
Sb 206.833 < LD < LD < LD < LD < LD
Se 196.026 < LD < LD < LD < LD 0.020
Si 251.611 0.114 3.10 3.18 6.02 5.62
Sn 189.989 < LD < LD < LD < LD 0.248
Sr 407.771 0.005 0.162 0.117 0.382 1.87
Ti 337.280 < LD < LD 0.006 < LD 0.785
Tl 190.864 < LD < LD < LD < LD < LD
V 292.402 < LD < LD < LD < LD 0.181
V 311.071 < LD < LD < LD < LD 0.191
W 207.911 < LD < LD < LD < LD 0.087
Zn 213.856 0.098 0.181 0.184 0.184 6.38
Zr 343.823 < LD < LD < LD < LD < LD

 

Quantitative Analysis

The results obtained from the semi-quantitative method yielded several standards that were prepared in the appropriate concentration range for each element.

Table 6. Standard concentration

Element Standards (mg/L)
0 1 2 3 4 5 6 7
Al 0 0.02 0.05 0.1 1 10 37.3 150
As 0 0.02 0.05 0.1 1 10    
B 0 0.02 0.05 0.1 1 10    
Cd 0 0.02 0.05 0.1 1 10    
Cr 0 0.02 0.05 0.1 1 10    
Cu 0 0.02 0.05 0.1 1 10    
Fe 0 0.02 0.05 0.1 1 10 37.3 150
Mn 0 0.02 0.05 0.1 1 10    
Ni 0 0.02 0.05 0.1 1 10    
Pb 0 0.02 0.05 0.1 1 10    
Se 0 0.02 0.05 0.1 1 10    
Zn 0 0.02 0.05 0.1 1 10    

 

Meanwhile, plasma parameters are presented in the following table.

Table 7. Operating conditions

Parameter Condition
RF Generator power 1100 W
Plasma gas flowrate 12 L/min
Auxiliary gas flowrate 0 L/min
Sheath gas flowrate 0.17 L/min
Nebulizer gas flowrate 0.63 L/min
Nebulizer flowrate 2.84 bars
Sample uptake 1 mL/min
Type of nebulizer Meihnard C1
Type of spray chamber Cyclonic
Argon humidifier No
Injector tube diameter 3.0 mm
Slits 20/15 µm

 

The combination of a Meinhard C1 nebulizer and cyclonic Spray Chamber for sample introduction was used for optimum sensitivity and detection limits. It should be noted that sample 5 was analyzed using the Standard Addition Method. This is due to the hypothesis that a more significant matrix effect could be discovered in such sample due to the presence of major elements (650 mg/l of Ca and acids).

Profiles of several samples for Cd are presented in the below figure. This demonstrates that the matrix is different because the spectral background is raised in sample 5.

Cd spectrum in sample 5

Cd spectrum in sample 5

The methodology of the Standard Addition Method (S.A.M.) is as follows:

  1. Using a rapid semi-quantitative method, estimate the approximate concentration for each element of interest.
  2. Prepare a stock solution with all the elements of interest and with appropriate concentrations. Ensure that the solution is prepared 2 to 5 times for each element concentration.
  3. Prepare at least 3 standards. Spike the sample with increasing concentrations. There should be an unknown sample to be declared as a blank (standard 0) as well as 3 standards in the same matrix. In total, 4 standards are recommended.
  4. Prepare the method in the software using background correction for baseline correction. When creating the method, it can be set up as a Standard Addition Method.
  5. Run the calibration. The results will be presented under the Standard Addition Tab. Alternatively, if the method was not set up as a Standard Addition, the intercept (or BEC) of each curve corresponds to the concentration of the element in the sample.

From this calibration, other samples with similar matrices could be analyzed.

The global report of the quantitative analyses is shown below the following tables. Note the abbreviations that were used:

Conc.: from quantitative method;
Conc. (S.Q.): from semi-quantitative method;
Conc. SAM: from standard addition method.

Table 8. Results for Sample 1

Line Net Intensity Conc SD Unit RSD(%) Conc. (S.Q.)
Al 396.152 19 691.33 0.263 0.00459 mg/L 1.74 0.271
As 189.042 52.58 < LD   mg/L   < LD
B 249.773 20 185.33 0.0472 0.00071 mg/L 1.50 0.045
Cd 228.802 318.65 < LD   mg/L   < LD
Cr 267.716 327.00 < LD   mg/L   < LD
Cu 324.754 1 492.67 0.0046 0.00020 mg/L 4.39 0.0034
Fe 259.940 2 589.67 0.0373 0.00033 mg/L 0.89 0.0157
Mn 257.610 2 402.33 0.0018 0.00006 mg/L 3.01 < LD
Ni 221.647 651.67 < LD   mg/L   < LD
Pb 220.353 533.79 < LD   mg/L   < LD
Se 196.026 386.25 < LD   mg/L   < LD
Zn 213.856 108 289.33 0.1047 0.0010 mg/L 0.95 0.0981

 

Table 9. Results for Sample 2

Line Net Intensity Conc SD Unit RSD(%) Conc. (S.Q.)
Al 396.152 17 524.00 0.2343 0.0036 mg/L 1.53 0.256
As 189.042 155.17 < LD   mg/L   < LD
B 249.773 192 740.00 0.4689 0.0030 mg/L 0.63 0.466
Cd 228.802 386.80 < LD   mg/L   < LD
Cr 267.716 2 058.00 0.0077 0.0005 mg/L 6.50 < LD
Cu 324.754 12 826.00 0.0617 0.0014 mg/L 2.31 0.066
Fe 259.940 6 111.00 0.0852 0.0017 mg/L 1.98 0.065
Mn 257.610 8 728.00 0.0051 0.0001 mg/L 2.54 0.0012
Ni 221.647 9 888.33 0.0381 0.0006 mg/L 1.55 0.039
Pb 220.353 867.49 < LD   mg/L   < LD
Se 196.026 641.92 < LD   mg/L   < LD
Zn 213.856 195 355.00 0.1863 0.0010 mg/L 0.54 0.181

 

Table 10. Results for Sample 3

Line NetIntensity Conc SD Unit RSD(%) Conc. (S.Q.)
Al 396.152 39 239.67 0.5228 0.0040 mg/L 0.76 0.592
As 189.042 147.58 < LD   mg/L   < LD
B 249.773 92 747.33 0.2245 0.0028 mg/L 1.25 0.216
Cd 228.802 292.22 < LD   mg/L   < LD
Cr 267.716 2 158.33 0.0081 0.0003 mg/L 4.13 0.003
Cu 324.754 9 189.33 0.0434 0.0005 mg/L 1.09 0.045
Fe 259.940 25 223.67 0.3447 0.0047 mg/L 1.36 0.377
Mn 257.610 75 530.67 0.0401 0.0004 mg/L 0.94 0.0402
Ni 221.647 7 890.67 0.0301 0.0004 mg/L 1.21 0.027
Pb 220.353 1 759.30 0.0129 0.0002 mg/L 1.91 0.031
Se 196.026 572.92 < LD   mg/L   < LD
Zn 213.856 194 040.33 0.1851 0.0012 mg/L 0.63 0.184

 

Table 11. Results for Sample 4

Line Net Intensity Conc SD Unit RSD(%) Conc. (S.Q.)
Al 396.152 10 105.00 0.1358 0.0012 mg/L 0.91 0.12
As 189.042 387.25 0.0035 0.0007 mg/L 21.00 < LD
B 249.773 433 991.00 1.0585 0.0058 mg/L 0.55 1.07
Cd 228.802 361.35 0.00018
(2 * LD)
0.0001 mg/L 53.19 < LD
Cr 267.716 2 086.33 0.0078 0.0008 mg/L 10.40 0.006
Cu 324.754 24 860.33 0.1223 0.0011 mg/L 0.89 0.121
Fe 259.940 36 921.00 0.5036 0.0049 mg/L 0.98 0.49
Mn 257.610 118 608.33 0.0627 0.0004 mg/L 0.67 0.066
Ni 221.647 1 745.67 0.0052 0.0004 mg/L 6.80 0.01
Pb 220.353 618.03 0.0051 0.0021 mg/L 40.49 < LD
Se 196.026 516.25 < LD   mg/L   < LD
Zn 213.856 202 759.33 0.1933 0.0018 mg/L 0.93 0.184

 

Table 12. Results for Sample 5

Line Net Intensity Conc SD Unit RSD(%) Conc. (S.Q.) Conc S.A.M. RSD (%)
Al 396.152 3 794 058.00 50.3999 0.4916 mg/L 0.98 48.54    
As 189.042 2 939.67 0.0216 0.0013 mg/L 6.00 0.016 0.0204 3.4
B 249.773 61 938.00 0.1492 0.0006 mg/L 0.43 0.159 0.166 0.78
Cd 228.802 5 014.01 0.0078 0.0001 mg/L 1.10 0.007 0.0085 0.19
Cr 267.716 557 018.00 2.1941 0.0019 mg/L 0.09 2 2.52 0.66
Cu 324.754 714 754.00 3.6002 0.0154 mg/L 0.43 3.75 4.15 0.77
Fe 259.940 9 214 680.00 125.1386 1.8638 mg/L 1.49 119.4    
Mn 257.610 2 058 893.33 1.0787 0.0075 mg/L 0.70 1.07 1.2 0.45
Ni 221.647 251 921.67 1.0159 0.0147 mg/L 1.45 1.01 1.2 1.23
Pb 220.353 116 931.40 0.8052 0.0053 mg/L 0.66 0.632 1.04 0.95
Se 196.026 1 842.58 0.0107 0.0027 mg/L 25.52 0.02 0.0148 4.2
Zn 213.856 6 970 960.33 6.5373 0.0318 mg/L 0.49 6.38    

 

Table 13. Results for Standard 0.1

Line Net Intensity Conc SD Unit RSD(%)
Al 396.152 7 644.00 0.1031 0.0026 mg/L 2.49
As 189.042 13 906.330.0994 0.0005 mg/L 0.47  
B 249.773 41 796.670.1000 0.0006 mg/L 0.60  
Cd 228.802 61 493.200.0997 0.0008 mg/L 0.80  
Cr 267.716 25 540.000.1002 0.0006 mg/L 0.57  
Cu 324.754 20 453.000.1001 0.0002 mg/L 0.22  
Fe 259.940 6 399.67 0.0891 0.0009 mg/L 1.04
Mn 257.610 181 739.00 0.0957 0.0000 mg/L 0.02
Ni 221.647 25 957.330.1030 0.0009 mg/L 0.85  
Pb 220.353 15 678.110.1087 0.0013 mg/L 1.24  
Se 196.026 11 389.080.0977 0.0003 mg/L 0.29  
Zn 213.856 108 004.00 0.1045 0.0016 mg/L 1.54

 

The standard at 0.1 mg/l was analyzed to check and validate the calibration at the end of the analyses.

Table 14. Detection limits

Detection limits (µg/L) LOD
Quantitative Method (µg/L) Water
LOD
Semi-quantitative Method (µg/L) Environmental samples
Ag 328.068 0.60 2.50
Al 167.020 0.20 0.80
Al 394.401 1.50 6.0
Al 396.152 1.00 4.0
As 189.042 1.20 5.0
B 249.773 0.30 1.0
Ba 455.403 0.04 0.12
Be 313.042 0.04 0.12
Br 153.114 200 800
Ca 317.933 1.5 6.0
Ca 393.366 0.03 0.12
Cd 228.802 0.09 0.40
Cl 134.664 200 800
Co 228.616 0.21 0.80
Cr 267.716 0.15 0.70
Cu 324.754 0.18 0.80
Fe 259.940 0.20 0.80
Hg 194.164 1.30 6.0
I 178.218 5.0 20.0
I 179.847 20.0 80.0
K 766.490 1.50 6.0
Li 670.784 0.50 2.0
Mg 279.553 0.03 0.12
Mg 279.806 1.0 4.0
Mn 257.610 0.05 0.20
Mo 202.030 0.20 0.80
Na 589.592 0.60 2.50
Ni 221.647 0.30 1.60
P 178.229 1.50 6.0
Pb 220.353 1.50 6.0
S 181.978 3.0 10.0
Sb 206.833 1.50 6.0
Se 196.026 1.50 6.0
Si 251.611 1.50 6.0
Sn 189.989 1.30 6.0
Sr 407.771 0.03 0.12
Ti 337.280 0.15 0.60
Tl 190.864 1.0 4.0
V 292.402 0.20 1.0
V 311.071 0.20 1.0
W 207.911 2.0 8.0
Zn 213.856 0.10 0.50
Zr 343.823 0.30 1.20

 

Conclusion

The study presented the use of quantitative and semi-quantitative methods in yielding good results in a wide range of concentrations (µg/L levels to hundreds of mg/L), with radial viewing allowing the user to minimize matrix effects. The fast and precise semi-quantitative method could be used routinely.

This information has been sourced, reviewed and adapted from materials provided by HORIBA Scientific.

For more information on this source, please visit HORIBA Scientific.

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