**5. Experimental part**

114 Environmental Monitoring

The kinetic response of the electrode is almost instantaneous [32, 33], limited by the recorder response time of 0.5 sec., at least in the solutions containing fluoride concentrations greater than millimolar. In very dilute solutions, the response time is has been reported to be very long.

The chloride ion-selective electrode is a polycrystalline solid-state electrode that contains a membrane. The membrane consists of a solid salt of silver sulfide/silver chloride. The membrane must be insoluble in the analyte solution and contain the analyte ion of interest. The membrane is placed at the end of a solid plastic tube. This membrane is in contact with the analyte solution during the measurement. Inside of the tube is a reference solution, which contains a known and fixed concentration of analyte (Cl-) solution. The concentration difference between this inner solution and analyte solution causes the migration of charged species across the membrane. This ion exchange process at the surface of the membrane causes a potential to develop. Since the potential of both the reference electrode and the inner reference (immersed in the standard solution) are constant, any change in measured potential is caused only by a change in potential across the membrane and is a function of

The electrode is designed to detect chloride ions in aqueous and viscous solutions and is suitable for use in laboratory investigations. The method allows the determination of chloride in treated water, natural water, drinking water and most waste water with high accuracy and sensitivity. The method is applicable only to samples containing more than 10 000 mgL-1

All reagents used were of analytical reagent grade and were used without further

In the experimental work ISP as a choice method was used, and Mohr's method as a standard was the control method for the determination of chloride ions in drinking tap water. As a comparative method could be use the UV/vis spectrophotometric method with zirconium (IV) ion oxychloride and alizarin S for analysis of Fluoride contents. For the determination of chloride and fluoride ions in represented drinking water has not been required previously sample pre-treatment. Quantitative analyses were performed with calibration curves obtained with standard solutions. The calibration curve has been constructed by plotting obtained electrode potential vs. logarithm of concentrations of standard chloride and fluoride solutions. In our experiments, several standard solutions with different concentrations were prepared. Then, we measured the cell potential for each individual standard solution and plot Ecell vs. log CF-. This curve is our calibration curve and has been used to determine the concentration of the unknown. The F-ISE method for the fluoride determination can be applied either without pretreatment technique, namely conventional potentiometric method, or with pretreatment technique, such as coprecipitation and steam distillation. Frant and Ross [34] pointed out that there were changes

Since ion-selective electrode responds to activity of the analyte, it is extremely important ionic strength solution. From the literature it is known that the OH-ions are only interfering ions for fluoride electrode, at pH greater than eight. However, at pH lower than five, the hydrogen ions also interfere, but the pH can not be too low due to the formation of HF,

**3.1.2 Chloride electrode** 

dissolved substances.

purification.

**4. Results** 

the analyte chloride ion activity (or concentration).

in potential as the pH of fluoride solutions was changed.

#### **5.1 Potentiometric determination of fluoride**

A 1000 mg L-1 sodium fluoride stock solution was prepared by dissolving 2,21 g NaF in a 1000 mL polystyrene volumetric flask with deionised water. Sodium fluoride has been previously oven-dried at 105 °C for 1 hour and stored in a dessicator. The concentration of this stock solution is 1000 mgL-1. Standards at the required concentration were prepared by appropriate dilution of the stock solution.

Calibration diagrams were obtained by measuring of potential of six different sets of fluorid standard solutions ordered from low to high concentration. The concentration range is from 0.07 to 1.0 mgL-1. The meter reading was taken after a constant value has been attained that is drift < 0,1 mV/min. The results are given in Table 2.


Table 2. Potentiometric responses of the membrane towards different concentrations of fluoride ion.

On the basis of these results has been constructed diagram 1.

Log Conc. of Fluoride

Diagram 1. Calibration curve for Fluoride ISE obtained for fluoride standard solutions in range of concentration from 0,07 to 1 mol L-1. This calibration graph has been used for determination of the samples marked as SW1, SW2, SW3 and SW4.

Determination of Fluoride and Chloride Contents in Drinking Water by Ion Selective Electrode 117

y = -0,0874x + 159,79

KK1 Linear (KK1)

KK2

Linear (KK2)

0 50 100 150 200 250 300 Concentration of Chloride (mg/L)

In Table 6 are given the concentration of chloride solutions for KK2 calibration curve.

 (mgL-1) 1 3 5 10 15 20 Potential (mV) 183.3 179.6 177.8 171.5 166.8 161.3

y = -1,1263x + 183,52

0 5 10 15 20 25 Concentration of Chloride, mg/L

In Table 7 are shown the average concentrations of chloride ion determined in our tested

Sample FW TW GW Potential, mV 129.9 171,9 178,4 Concentration, mg/L 341.99 10,12 4,55 Table 7. Concentrations of chloride obtained for samples: FW, TW and GW determined

using appropriate calibration curve.

Potential, mV

Diagram 2. Shows the obtained calibration curve KK1.

Diagram 3. Shows the obtained calibration curve KK2.

Table 6. Electrode response on prepared chloride standard solutions.

Potential (mV)

Conc. Cl-

samples.

For determining the concentration of F-ions, the samples were placed in a clean, dry glass in quantities of 50 ml. [35] First of all, has been determined the pH of the sample. The measured pH value was in the range from 5 to 7, and then the sample has been stirred by using a magnetic stirrer for 5 minutes. After that, it has been measured the concentration of fluoride ions, by immersion of the reference and fluoride ion-selective electrode connected to the ionmeter. After a few minutes were read values of the potential. Each sample was measured three times in order to reduce experimental error. Based on the measured potential, was calculated the concentration of fluoride for each individual measurement, and then, calculated the average value of concentration.

In Table 3 are represented the obtained concentrations in samples marked as SW1, SW2, SW3 and SW4.


Table 3. Concentrations of fluoride obtained for samples: SW1, SW2, SW3 and SW4.

For these samples also have been determined the concentration of chloride by mercurimetric titration. The results are shown in table 4.


Table 4. Concentrations of chloride obtained by mercurimetric titration method.

#### **5.2 Potentiometric determination of chloride**

Specific ion electrodes measure activity and not concentration, a large amount of an inert strong electrolyte (e.g. nitrate ion) can be added to fix the ionic strength to a constant value. When the ionic strength is constant, the activity is constant and concentration can be accurately measured. To determine the concentration of chloride ions, samples were prepared as follows: in a glass flask of 100 ml was measured 2 ml of 5% NaNO3, and diluted to mark with water that is being analyzed (5% NaNO3 concentrations in all samples was 0.1 mol L-1). Then, 5 mL of prepared sample was transferred in clean, dry glass and stirred using a magnetic stirrer for 5 min with immersed electrodes. After 5 minutes of stirring, the magnetic stirrer has been stopped and then red the potential. Response time for all samples was in a range from 1 to 5 minutes. The samples marked by FW, TW and GW have been analyzed on chloride concentration using a chloride selective electrode. The sample designed as FW was analyzed using a calibration curve represented in diagram 2, while the samples marked as TW and GW by using a calibration curve shown in diagram 3. In Table 5 are given the concentration of chloride solutions for KK1 calibration curve.


Table 5. Electrode response on prepared chloride standard solutions.

Diagram 2. Shows the obtained calibration curve KK1.

116 Environmental Monitoring

For determining the concentration of F-ions, the samples were placed in a clean, dry glass in quantities of 50 ml. [35] First of all, has been determined the pH of the sample. The measured pH value was in the range from 5 to 7, and then the sample has been stirred by using a magnetic stirrer for 5 minutes. After that, it has been measured the concentration of fluoride ions, by immersion of the reference and fluoride ion-selective electrode connected to the ionmeter. After a few minutes were read values of the potential. Each sample was measured three times in order to reduce experimental error. Based on the measured potential, was calculated the concentration of fluoride for each individual measurement, and then,

In Table 3 are represented the obtained concentrations in samples marked as SW1, SW2,

Sample SW1 SW2 SW3 SW4 Potential (mV) 44,5 47,1 36,5 18,7 Conc. F- (mgL-1) 0,042 0.038 0.059 0.12 Table 3. Concentrations of fluoride obtained for samples: SW1, SW2, SW3 and SW4.

For these samples also have been determined the concentration of chloride by mercurimetric

Specific ion electrodes measure activity and not concentration, a large amount of an inert strong electrolyte (e.g. nitrate ion) can be added to fix the ionic strength to a constant value. When the ionic strength is constant, the activity is constant and concentration can be accurately measured. To determine the concentration of chloride ions, samples were prepared as follows: in a glass flask of 100 ml was measured 2 ml of 5% NaNO3, and diluted to mark with water that is being analyzed (5% NaNO3 concentrations in all samples was 0.1 mol L-1). Then, 5 mL of prepared sample was transferred in clean, dry glass and stirred using a magnetic stirrer for 5 min with immersed electrodes. After 5 minutes of stirring, the magnetic stirrer has been stopped and then red the potential. Response time for all samples was in a range from 1 to 5 minutes. The samples marked by FW, TW and GW have been analyzed on chloride concentration using a chloride selective electrode. The sample designed as FW was analyzed using a calibration curve represented in diagram 2, while the samples marked as TW and GW by using a calibration curve shown in diagram 3. In Table 5

> (mgL-1) 60 120 180 230 280 Potential (mV) 155.1 148.6 143.7 140.2 135.3

Sample Concentration of Chloride (mgL-1)

SW1 2,81 SW2 4,80 SW3 3,60 SW4 7,25

Table 4. Concentrations of chloride obtained by mercurimetric titration method.

are given the concentration of chloride solutions for KK1 calibration curve.

Table 5. Electrode response on prepared chloride standard solutions.

calculated the average value of concentration.

titration. The results are shown in table 4.

**5.2 Potentiometric determination of chloride** 

Conc. Cl-

SW3 and SW4.

In Table 6 are given the concentration of chloride solutions for KK2 calibration curve.


Table 6. Electrode response on prepared chloride standard solutions.

Diagram 3. Shows the obtained calibration curve KK2.

In Table 7 are shown the average concentrations of chloride ion determined in our tested samples.


Table 7. Concentrations of chloride obtained for samples: FW, TW and GW determined using appropriate calibration curve.

Determination of Fluoride and Chloride Contents in Drinking Water by Ion Selective Electrode 119

Directive 80/777/EEC provides that in case of bottled natural mineral waters, chloride concentrations exceed 200 mgL-1, and then the water is declared on the label as chlorinated.

Electroanalytical methods based on potentiometry with ion-selective electrodes seem to be the most popular and convenient methods of fluoride and chloride ion determination. Fluoride and chloride selective electrodes can be used to determine fluoride and chloride concentrations in drinking water due to its high selectivity, specificity and low detection limits. The advantages of this study include a short analysis time, elimination of sample pretreatment, simplicity of the measuring system and relatively low instrument cost. The concentration of fluoride ion was determined in 4 drinking water samples, while the concentrations of chloride have been determined in 3 samples (FW, TW and GW) by a chloride selective electrode as well as by Mohr's method. All these samples were analyzed with use direct reading method. By our experimental data we can conclude that the concentration of fluoride in samples marked as SW1, SW2, SW3 and SW4 is within allowed concentration according to World Health Organisation. On the basis of the results of analysis carried out on the water content chloride ions can be concluded that the applied electrochemical measurements and analytical shown that the content is the same within the limits of permissible concentration laid down by WHO. Method ISP when it proved more effective, fast and reliable enough to determine chloride ions in the water and the concentration in the range of 10-4 mol L-1 to 10-5mol L-1. Additionally, it has an advantage over any other analytical method because it is non-destructive and allows the use of samples for other types of analysis. Based on the results obtained it can be concluded that there are many advantages of using ion-selective potentiometry (ISP) in reference to standard spectrophotometric and Mohr's methods, because measurements with the ISP are faster, efficient and reliable. It does not require the use of many different chemicals, and does not require any preparation of samples before analysis, which directly affects the economic availability. Our experimental data give in evidence that the concentration in these samples are within the allowed concentration according to World Health Organisation except the concentration of chloride in tested bottled water. Therefore, determining of Fluoride and Chloride in drinking water is of great significance for human health because of daily

[2] Rowell, R. M.; Removal of metal ions from contaminated water using agricultural

[3] Hutchins, R. S.; Bachas, L. G.; In: Handbook of Instrumental Techniques for Analytical

[5] World Health Organisation (WHO) 2002, Fluorides, World Health Organization

residues, 2nd International Conference on Environmentally – Compatible Forest

Chemistry, (Ed.), Chapter 38, 727-748, Upper Saddle River, NJ: Prentice-Hall, 1997. [4] Institute of Medicine, (1997), Fluoride. In "Dietary reference intakes for calcium,

phosphorus, magnesium, vitamin D, and fluoride", 288-313. National Academy

**6. Conclusion** 

consumption of certain amounts.

[1] Fluoride in Drinking - water, WHO, 2004.

Products, Portugal (2006), 241-250.

Press. Washington, D.C., U.S.A.

(Environmental Health Criteria 227).

**7. References** 

#### **5.3 Mohr's method**

Cations and anions are systematized according to the analytical groups to make it easier to prove. When the sample contains a lot of cations and anions is difficult or even impossible to prove, because they interfere with each other. Ions belonging to a different groups defined by their relationship to reagent with which the ion is deposited in hard soluble salt. Chloride ion belongs to the fourth group of anions that precipitate reagent AgNO3. Mohr's method is used for volumetric determination of chloride by titration with AgNO3 solution in neutral or slightly alkaline solution and using of potassium or sodium chromate as indicator. It is based on the reactions of the formation of hardly soluble precipitates with the condition that the reaction of precipitation is fast and that there is a true indicator that shows the end of the titration. To determine the concentration of chloride by Mohr, samples were prepared as follows: the sample has been transferred by pipette of 25 mL into Erlenmayer flask and diluted by distilled water (about 100 mL) and added 2 mL of 5% K2CrO4. Thus, titration of the sample prepared in this way has been done with standard solution of 0,0984 mol/L AgNO3. The standardization of AgNO3 has been done previously. Titration was completed when appeared a reddish solution.

The amount of chloride was calculated using the equation:

$$m\_{\mathrm{CT}^-} = \mathbf{C}\_{A \& \mathrm{NO\_3}} \cdot V\_{A \& \mathrm{NO\_3}} \cdot M\_{\mathrm{CI}} \cdot \mathbb{R}$$

where:

mCl - the amount of chloride in water (g)

CAgNO3 - concentration of solution (mol L-1)

VAgNO3 – volume of AgNO3 used for titration (L)

R- dilution

Calculated values of chloride concentration by Mohr method is 14.8 mg L-1 for TW sample.

TW sample shows a significant discrepancy in values between the two methods used. The difference is caused by problems that can occur when working with a chloride electrode. Interference can cause:


(concentration ratio = interfering ion/measured ion):

In the table are given values of concentration relations for some interfering ions:


To determine accurately interfering ion present and its concentration in the sample, TW, require long and detailed chemical and bacteriological analysis of water. The results obtained for the GW and TW indicate that the chloride content is in the range of permissible limits prescribed by WHO.

Results for the FW sample show that the concentration of chloride ions is extremely high and exceeds the maximum limit. According to the Regulations of the Republic of Serbia, given that Bosnia and Herzegovina has no defined Rules on allowable concentrations of cations and anions in water, for the chloride limit is 200 mgL-1 (Official Gazette of SFRY 42/98). The limit in drinking water is 250 mgL-1. European Economic Community Directive 80/777/EEC provides that in case of bottled natural mineral waters, chloride concentrations exceed 200 mgL-1, and then the water is declared on the label as chlorinated.

### **6. Conclusion**

118 Environmental Monitoring

Cations and anions are systematized according to the analytical groups to make it easier to prove. When the sample contains a lot of cations and anions is difficult or even impossible to prove, because they interfere with each other. Ions belonging to a different groups defined by their relationship to reagent with which the ion is deposited in hard soluble salt. Chloride ion belongs to the fourth group of anions that precipitate reagent AgNO3. Mohr's method is used for volumetric determination of chloride by titration with AgNO3 solution in neutral or slightly alkaline solution and using of potassium or sodium chromate as indicator. It is based on the reactions of the formation of hardly soluble precipitates with the condition that the reaction of precipitation is fast and that there is a true indicator that shows the end of the titration. To determine the concentration of chloride by Mohr, samples were prepared as follows: the sample has been transferred by pipette of 25 mL into Erlenmayer flask and diluted by distilled water (about 100 mL) and added 2 mL of 5% K2CrO4. Thus, titration of the sample prepared in this way has been done with standard solution of 0,0984 mol/L AgNO3. The standardization of AgNO3 has been done previously. Titration was completed

*Cl AgNO AgNO Cl* 3 3 *m C V MR*

Calculated values of chloride concentration by Mohr method is 14.8 mg L-1 for TW sample. TW sample shows a significant discrepancy in values between the two methods used. The difference is caused by problems that can occur when working with a chloride electrode.

**5.3 Mohr's method** 

when appeared a reddish solution.

mCl - the amount of chloride in water (g) CAgNO3 - concentration of solution (mol L-1) VAgNO3 – volume of AgNO3 used for titration (L)

Complexes with Bi3+, Cd2+, Mn2+,Pb2+,Sn2+, Tl2+

(concentration ratio = interfering ion/measured ion):

OH- Br-

Interfering ions: 10 % error with the following concentration ratio.

In the table are given values of concentration relations for some interfering ions:

J- S2- CN-

80 3x10-3 5x10-3 1x10-6 2x10-7 0.12 0.01

To determine accurately interfering ion present and its concentration in the sample, TW, require long and detailed chemical and bacteriological analysis of water. The results obtained for the GW and TW indicate that the chloride content is in the range of permissible

Results for the FW sample show that the concentration of chloride ions is extremely high and exceeds the maximum limit. According to the Regulations of the Republic of Serbia, given that Bosnia and Herzegovina has no defined Rules on allowable concentrations of cations and anions in water, for the chloride limit is 200 mgL-1 (Official Gazette of SFRY 42/98). The limit in drinking water is 250 mgL-1. European Economic Community

NH3 S2O32-

where:

R- dilution

Interference can cause:

Reducing agents

limits prescribed by WHO.

The amount of chloride was calculated using the equation:

Electroanalytical methods based on potentiometry with ion-selective electrodes seem to be the most popular and convenient methods of fluoride and chloride ion determination. Fluoride and chloride selective electrodes can be used to determine fluoride and chloride concentrations in drinking water due to its high selectivity, specificity and low detection limits. The advantages of this study include a short analysis time, elimination of sample pretreatment, simplicity of the measuring system and relatively low instrument cost. The concentration of fluoride ion was determined in 4 drinking water samples, while the concentrations of chloride have been determined in 3 samples (FW, TW and GW) by a chloride selective electrode as well as by Mohr's method. All these samples were analyzed with use direct reading method. By our experimental data we can conclude that the concentration of fluoride in samples marked as SW1, SW2, SW3 and SW4 is within allowed concentration according to World Health Organisation. On the basis of the results of analysis carried out on the water content chloride ions can be concluded that the applied electrochemical measurements and analytical shown that the content is the same within the limits of permissible concentration laid down by WHO. Method ISP when it proved more effective, fast and reliable enough to determine chloride ions in the water and the concentration in the range of 10-4 mol L-1 to 10-5mol L-1. Additionally, it has an advantage over any other analytical method because it is non-destructive and allows the use of samples for other types of analysis. Based on the results obtained it can be concluded that there are many advantages of using ion-selective potentiometry (ISP) in reference to standard spectrophotometric and Mohr's methods, because measurements with the ISP are faster, efficient and reliable. It does not require the use of many different chemicals, and does not require any preparation of samples before analysis, which directly affects the economic availability. Our experimental data give in evidence that the concentration in these samples are within the allowed concentration according to World Health Organisation except the concentration of chloride in tested bottled water. Therefore, determining of Fluoride and Chloride in drinking water is of great significance for human health because of daily consumption of certain amounts.

#### **7. References**


**8** 

*Japan* 

**Environmental Background** 

*1Advanced Materials Science R&D Center,* 

**Radiation Monitoring Utilizing Passive Solid Sate Dosimeters** 

*2Research Laboratory for Integrated Technological Systems, Kanazawa Institute of Technology, Hakusan, Ishikawa,* 

Hidehito Nanto1,2, Yoshinori Takei1,2 and Yuka Miyamoto2,3

*3Oarai Research Center, Chiyoda Technol Corporation, Oarai-machi, Higashi Ibaragi,* 

Natural environmental background radiation is radiation that is constantly present in the environment and is emitted from a variety of natural and artificial sources. Primary contribution comes from sources in the earth, from space and in the atmosphere. Naturally occurring sources are responsible for the vast majority of radiation exposure. However, not including direct exposure from radiological imaging or therapy, about 3% of background radiation comes from man-made sources such as self-luminous dials and signs, global radioactive contamination due to historical nuclear weapons testing, nuclear power station or nuclear fuel reprocessing accidents, normal operation of facilities used for nuclear power and scientific research, emission from burning fossil fuels and emission from nuclear

We are all exposed to ionizing radiation every day. In fact, the environmental background radiation contributes about two-thirds of our radiation exposure. Therefore, it is important to determine the exact environmental background radiation dose. Active dosimeters have been formally appropriate for monitoring dose equivalent rates of environmental background radiation. On 2001 in Japan, not only dose equivalent rate but also dose equivalent can be applied to environmental background radiation monitoring, which is based on the Japanese law modification concerned with radiation protection. Thus, there is the possibility that passive solid state dosimeters are also appropriate for environmental

So far, some types of solid state dosimeter have been developed not only for personal monitoring but also for environmental background radiation monitoring. For instance, a thermoluminescence (TL) dosimeter has been studied to monitor the environmental background radiation (Nanto, 2011). Recently newly passive solid state dosimeters utilizing optically stimulated luminescence (OSL), direct ion storage (DIS) and radiophotoluminescence (RPL) phenomena have been developed to monitor the personal and environmental radiation

In the following, the basic principle of the passive solid state dosimeters utilizing TL, OSL, DIS and RPL phenomenon are reviewed and the results on environmental background

**1. Introduction** 

medicine facilities and patients.

background radiation monitoring.

(Ranogajec-Komor, 2008; Koyama, 2010).

