determination of copper content in drinking water by using aas[1] rev 1

7/28/2019 Determination of Copper Content in Drinking Water by Using AAS[1] Rev 1

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Group Name Group 1

Date November 25, 2011

Module Name Environmental Trace Analysis

Module Code SCGS 6113

Assignment Determination of Copper content in JBA water using AAS

Page 1

Determination of copper content in drinking water using Atomic Absorption Spectrometer

(AAS)

1. IntroductionCopper is essential to human metabolism, but too much copper can cause stomach and intestinal

distress and a form of Wilsons diseases. Copper metal fumes or salts cause salivation, nausea,

vomiting, gastric pain etc. Contact with skin causes itching eczema. In chronic exposure, liver,

kidney and spleen may be injured and may develop anemia (Davison, C.R.; Malette 1945).

Toxicity of dissolved copper (II) is considered less than mercury but greater than cadmium,

silver, lead and zinc (Florence, T.M.; Batley, 1977). A limit of 0.1 mg m-3

for copper fume has

been tentatively suggested. The Public Health Service for drinking water standard is 1 mg dm-3

or 1 ppm (Davison, C.R.; Malette 1945). As a pollutant, copper is of particular concern, because

of its high degree of toxicity to aquatic organism. In view of this, simple and sensitive methods

are required for the trace determination of copper.

The United States' Safe Drinking Water Act recommends an acceptable Cu2+

level of 1.3 ppm in

drinking water. Unfortunately, when copper pipes in older homes corrode, the Cu2+ content in

the water can rise above the recommended level. Therefore, there is a need for a simple,

inexpensive home screening method to determine Cu2+

content in tap water.

The fate of elemental copper in water is complex and influenced by pH, dissolved oxygen and

the presence of oxidizing agents and chelating compounds or ions (US EPA, 1995). Surface

oxidation of copper produces copper (I) oxide or hydroxide. In most instances, copper (I) ion is

subsequently oxidized to copper (II) ion. However, copper (I) ammonium and copper (I) chloride

complexes, when they form, are stable in aqueous solution.

In pure water, the copper (II) ion is the more common oxidation state (US EPA, 1995) and will

form complexes with hydroxide and carbonate ions. The formation of insoluble malachite

[Cu2(OH)2CO3] is a major factor in controlling the level of free copper (II) ion in aqueous

solution. Copper(II) ion is the major species in water up to pH 6; at pH 69.3, aqueous CuCO3 is


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prevalent; and at pH 9.310.7, the aqueous [Cu(CO3)2]2-

ion predominates (Stumm& Morgan,

1996). Dissolved copper ions are removed from solution by sorption to clays, minerals andorganic solids or by precipitation.

Copper strongly adsorbs to clay materials in a pH dependent fashion, and adsorption is increased

by the presence of particulate organic materials (Barceloux, 1999; Landner&Lindestrom, 1999).

Copper discharged to wastewater is concentrated in sludge during treatment. Various studies of

leaching from sludge indicate that the copper is not mobile (ATSDR, 2002). Free copper ions are

chelated by humic acids and polyvalent organic anions (Landner&Lindestrom, 1999).

Copper is found in surface water, groundwater, seawater and drinking-water, but it is primarily

present in complexes or as particulate matter (ATSDR, 2002). Copper concentrations in surface

waters ranged from 0.0005 to 1 mg/liter; the median value was 0.01 mg/liter (ATSDR, 2002).

Copper concentrations in drinking-water vary widely as a result of variations in water

characteristics, such as pH, hardness and copper availability in the distribution system. Levels of

copper in running or fully flushed water tend to be low, whereas those of standing or partially

flushed water samples are more variable and can be substantially higher.

Copper concentrations in drinking-water often increase during distribution, especially in systems

with an acid pH or high-carbonate waters with an alkaline pH (US EPA, 1995).

In this study, copper content in water sample supplied by JBA (Water Supply Department) was

determined using Atomic Absorption Spectrometer (AAS), a validated method APHA 3111B

:1995 was employed for these analyses.


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2. Material and methods

2.1 Instrumentation

Atomic absorption spectrometer brand Zeenit 700 Analytic Jena with deuterium and

Zeeman background correction equipped with acetylene/air flame as atomizers, with

AS52 S auto-samplers for flame. The atomization cell was purged with argon. Hollow

cathode lamp was used. The condition of the instrument was as follow:

Wavelength (nm) 324.8

Slit width (nm) 1.2

Lamp current (mA) 3

Background correction Deuterium

Mode Double beam

Technique Flame

Flame condition

i. Fuel flowii. Burner typeiii. Burner heightiv. Nebulizer rate

C2H2/air

401/h

50mm

7mm

5.0 ml/min

Table 1: Condition of Flame AAS for operation


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2.2Reagents and solution2.2.1 Air, cleaned and dried through a suitable filter to remove oil, water, and other

unwanted substances. The source could a compressor or commercially bottled

gas

2.2.2 Acetylene, standard commercial grade. Acetone which is often found inacetylene cylinders can be avoided form entering and damaging the burner

head by replacing a cylinder when its pressure has fallen to 689 kPa acetylene.

2.2.3 Metal-free water: it is used to prepare all reagents and calibration standardsand as dilution water. It is prepared by deionizing tap water

2.2.4 Concentrated nitric acid was of analytical grade

2.3Sample PreparationIncoming JBA (Water Supply Department) water (use directly)

2.4Standard Preparation2.4.1 Standard Stock Solution 100 ppmDissolve 0.100g copper metal in 2ml conc. HNO3, add 10.0ml conc. HNO3 and

dilute to 1000ml with water

2.4.2 Working standard solution5 working standard solution with the concentration 0.05 ppm, 0.1 ppm, 0.5 ppm, 1

ppm, 2 ppm were prepared.

0.05 ppmpipette 1ml standard stock solution and dilute to 100ml water, again

pipette 5ml and dilute to 100ml water

0.1 ppmpipette 1ml standard stock solution and dilute to 100ml water, again pipette

10ml and dilute to 100ml water


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0.5 ppmpipette 1ml standard stock solution and dilute to 200ml water

1.0 ppmpipette 1ml standard stock solution and dilute to 100ml water

2.0 ppm - pipette 2ml standard stock solution and dilute to 100ml water

2.5Analytical procedures2.5.1 Turn on instrument, apply to Cu hollow cathode lamp the current suggested2.5.2 Let instrument warm up until energy source stabilizes2.5.3 Readjust current as necessary after warm up2.5.4 Optimize energy gain is obtained2.5.5 Align lamp in accordance with manufacturers instructions2.5.6 Adjust burner head position2.5.7 Turn on air and adjust flow rate to that specify by manufacturer to give

maximum sensitivity for metal being measured

2.5.8 Turn on acetylene, adjust flow rate to value specified and ignite flame2.5.9 Stabilize flame for a few minutes2.5.10 Aspirate blank consisting of deionized water containing the same

concentration of acid in standards and samples

2.5.11 Zero the instrument2.5.12 Aspirate a standard solution and adjust aspiration rate of the nebulizer to

obtain maximum sensitivity

2.5.13 Adjust burner both vertically and horizontally to obtain maximum response2.5.14 Aspirate blank again and rezero the instrument2.5.15

Aspirate standard working solution of 0.05 ppm, 0.1 ppm, 0.5 ppm, 1.0 ppmand 2.0 ppm, record absorbance of these standards

2.5.16 Aspirate blank and zero the instrument each time when each standard isaspirated

2.5.17 Prepare a Cu calibration curve by plotting on linear graph absorbance ofstandards versus their concentrations


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2.5.18 Rinse nebulizer by aspirating water containing 1.5ml conc. HNO3/L2.5.19 Aspirate blank and zero instrument2.5.20 Aspirate sample and determine its absorbance

3.0 Results and Discussion

Calibration curve was plotted as of the absorbance signal versus the concentration. A

series of 5 standard solutions were prepared and a calibration curve was plotted with

relative responses on the Y-axis and the corresponding concentrations on the X-axis are

shown below.

Copper concentration of

working

standard solution (ppm)

Absorbance

0.05 0.007

0.10 0.014

0.50 0.063

1.00 0.115

2.00 0.215

Table 2 : The absorbance and corresponding concentration


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The correlation coefficient (R2) of Copper standard working solution calibration curve obtained

was 0.998 which indicates linearity (R2>0.99) was acceptable and can be used to determine the

copper concentration of the samples.

Quantification can be performed by using variables such as peak height, peak area, and also the

ratio of peak areas of analyte to internal standard peak. Based on Beers law, quantification of

the analyte should be linear over a concentration range. Hence, the working sample

concentration and samples have to be in the linear range.

Copper concentration of

JBA water

Absorbance

Unknown 1 -0.003

Unknown 2 -0.001

Unknown 3 -0.002

y = 0.1062x + 0.0052

R = 0.998

0

0.05

0.1

0.15

0.2

0.25

0 0.5 1 1.5 2 2.5

Absorbance

Concentration (ppm)

Calibration Curve of Copper Standard Working

Solution


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Accuracy

Accuracy is a measure of the closeness of test results obtained by a method to the true value

Accuracy indicates the deviation between the mean value found and the true value. It is

determined by applying the method to samples to which known amounts of analyte have been

added. These should be analysed against standard and blank solutions to ensure that no

interference exists. The accuracy is then calculated from the test results as a percentage of theanalyte recovered by the assay.

No % Recovery of 1 ppm

of Copper

% Recovery of 1.5

ppm of Copper

1 101.09 101.102 100.80 98.36

3 97.43 103.20

4 102.34 101.40

5 102.41 102.56

6 98.20 98.87

7 101.80 103.20

Mean 100.58 101.24

SD 1.99 1.97

%RSD 1.98% 1.95%

Table 3 : Accuracy data of 1 ppm and 1.5 ppm of copper

From table 3, the accuracy is good with % recovery within 95-105% recovery from the true

value


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Precision

The precision of an analytical method is the degree of agreement among individual test resultsobtained when the method is applied to multiple sampling of a homogenous sample

Precision is a measure of the reproducibility of the whole analytical method (including sampling,sample preparation and analysis) under normal operating circumstances.

Precision is determined by using the method to assay a sample for a sufficient number of times to

obtain statistically valid results (i.e. between 6 - 10). The precision is then expressed as therelative standard deviation

std dev x 100%

%RSD = __________

mean

Concentration of copper

Analysis

0.5 ppm 1 ppm 2 ppm

1 0.502 1.005 2.088

2 0.505 1.024 2.056

3 0.497 1.014 2.033

4 0.498 1.013 2.021

5 0.501 0.986 1.9826 0.504 0.994 1.991

7 0.501 0.991 1.987

Mean 0.5011 1.0039 2.0226

SD 0.0029 0.0140 0.0396

%RSD 0.58% 1.39% 1.96%

Table 4: The precision data of 1 ppm, 1.5 ppm and 2 ppm of copper concentration

From table 4, the precision is good with %RSD


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10

Linearity

This is the method's ability to obtain results which are either directly, or after mathematicaltransformation proportional to the concentration of the analyte within a given range.

Linearity is determined by calculating the regression line using a mathematical treatment of theresults (i.e. least mean squares) vs. analyte concentration.

Based on the calibration curve in page 7, the correlation coefficient (R2) of Copper standard

working solution calibration curve obtained was 0.998 which indicates linearity (R2>0.99) was

achieved

RepeatabilityRepeatability is the closeness of agreement between measurements obtained by using the same

method or instrument on the same sample and under the same condition. The condition includes

procedure, same operator, location and also time interval. Repeatability is achieved if thevariation between the measurements is fall within the agreed limit.

Copper Concentration

Sample #

1 ppm 2 ppm

Concentration

Reading

%

recovery

Concentration

Reading

%

recovery

1 0.987 98.70 2.040 102.00

2 1.024 102.40 1.956 98.80

3 0.975 99.50 1.963 98.15

4 0.993 99.30 2.102 103.10

5 1.017 101.70 1.891 98.55

6 1.008 100.80 1.912 98.60

7 0.924 98.40 2.094 101.70

8 1.096 104.60 2.123 102.15

9 0.932 99.20 1.956 98.80

10 0.945 98.90 1.932 98.60Mean 100.35 Mean 100.05

SD 2.0018 SD 1.9272

%RSD 1.99% RSD 1.93%

Table 5 : The repeatability for 1ppm and 2 ppm of copper in water


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11

Ten measurements of 1 ppm and 2 ppm of copper standard solution were performed. %RSD

obtained for these measurements were 1.99% and 1.93% respectively for 1 and 2 ppm. It showshigh repeatability of this method.

Control Chart

Control chart is also known as Shewhart chart which is used to determine if a process is in the

statistical control. It can be used to monitor the quality characteristic too. Variation and its source

can be eliminated with plotting a control chart. The component of a control chart consisting of

a) X-axis : represent sample order, sequence, run time, site and etcb) Y-axis : a scale according to the corresponding summary statistic, such as standard

deviation and mean.

c) Point present in the chart representing measurement of a quality characteristic in samplestaken from the process at different time

d) The centre line represents the mean of the data. The upper and lower control limit lines(UCL and LCL) indicate the range of the expected variations in the summary statistic.

Any point appear above the UCL or below the LCL lines are out of control while points

that are appear in between the UCL and LCL are in control.

Eight measurements for 1.5 ppm copper standard were made on daily basis throughout

the laboratory period. A control chart was constructed by plotting determined

concentration versus time. Upper warning limit (UWL) and lower warning limit (LWL)

were displayed in the chart as well.

UCL = mean + 3SD

LCL = mean3SD

UWL = mean + 2SD

LWL = mean2SD


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Time(day)

Concentration reading of1.5 ppm copper

1 1.5080

2 1.4900

3 1.5020

4 1.4970

5 1.5090

6 1.5050

7 1.4910

8 1.5080

Mean 1.5013

SD 0.0077

2SD 0.0154

3SD 0.0231

UCL 1.5244

LCL 1.4781

UWL 1.5167

LWL 1.4858

Table 6: Control chart data


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Based on control chart in page 12 above, all results obtained over the 8 days were well withinWarning Limit (+ 2SD) and Control Limit (+ 3SD) of the Copper concentration reading. No

outlier data was observed which indicate no instrumentation failure

Ruggedness

Ruggedness is the degree of reproducibility of results obtained by the analysis of the same

sample under a variety of normal test conditions i.e. different analysts, laboratories, instruments,reagents, assay temperatures, small variations in mobile phase, different days

etc. (i.e. from laboratory to laboratory, from analyst to analyst.)

Based on the control chart data in page 12, the reproducibility of 1.5 ppm Copper obtained by theanalysis of the same sample at different days (8 days) shown that the test method is rugged

enough for Copper determination

Sensitivity

Selectivity is the ability to measure accurately and specifically the analyte in the presenceof components that may be expected to be present in the sample matrix.

Concentration of Copper in sample matrix

containing Calcium

Analysis 0.8 ppm 1 ppm

1 0.801 1.003

2 0.798 1.01

3 0.816 0.994

Mean 0.805 1.002

SD 0.01 0.008

2SD 0.019 0.016

3SD 0.029 0.024

Table 7 : The sensitivity data of Copper at 0.8 ppm and 1 ppm

From table 7, there is no significant variation was found for Copper recoveries at 0.8 ppm and 1ppm in sample matrix containing Calcium. Thus, selectivity of Atomic Absorption Spectrometeris unique only to those selected analyte determination as presence of other impurities in the same

sample matrix will not interfere on the recovery.


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Limit of Detection (LOD)

LOD is defined as the lowest concentration of an analyte in a sample that can be detected but it isnot necessary to perform the quantification. It is a limit test that specifies whether an analyte is

above or below a certain value. Ten blanks reading were taken and the SD is calculated.

The detection limit is estimated from the mean of the blank, the standard deviation of blank and

some confidence factors. For example, cleanliness of the glassware, instruments used andhandling methods.

In this study, all the samples were in liquid form. The dilution was using deionised water. The

analysis found that the lowest acceptable concentration for copper is 0.01 ppm with 10 replicates.

Sample Copper, ppm

1 0.012

2 0.010

3 0.011

4 0.012

5 0.010

6 0.009

7 0.010

8 0.012

9 0.015

10 0.011

Mean 0.011

SD 0.002

Table 8 : The copper detection limit

LOD of copper = 3 x SD

= 3 x 0.002

= 0.006 ppm


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Limit of Quantitation (LOQ)Limit of Quantitation is the lowest concentration at which the analyte can not only be reliably

detected but at which some predefined goals for bias and imprecision are met.

LOQ of copper = 10 x SD= 10 x 0.002

= 0.02 ppm

Conclusions

No. Parameter Acceptance Criteria Results Conclusions

1 Accuracy 95-105% recovery

from the true value

97-104% recovery

from the true value

Within

specifications

2 Precision %RSD


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Based on the sample analysis results of JBA water, negative readings were obtained which

indicate absence of copper in the JBA water. However, as the LOD of the AAS found to be

0.006 ppm, thus Copper content in JBA water determined using AAS found to be

determination of copper content in drinking water by using aas[1] rev 1

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