Author’s Accepted Manuscript Paper-based analytical device for sampling, on-site precon preconcen centra tratio tion n and and detect detection ion of ppb ppb lead lead in water water Thiphol Satarpai, Juwadee Shiowatana, Atitaya Siripinyanond Siripinyanond
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To appear in: Talanta Receiv Received ed date: date: 24 Februa February ry 2016 2016 Rev Revised ised date date:: 4 April pril 2016 2016 Accep Accepted ted date: date: 5 April April 2016 2016 Cite this article as: Thiphol Satarpai, Juwadee Shiowatana and Atitay Siripinyanond, Paper-based analytical device for sampling, on-sit precon preconcen centra tratio tion n and and detect detection ion of ppb lead lead in water water,, Talant http://dx.doi.org/10.1016/j.talanta.2016.04.017 This is a PDF file of an unedited manuscript that has been accepted f public publicati ation on.. As a service service to our custom customers ers we are prov providi iding ng this this early early versio version no the manuscript. The manuscript will undergo copyediting, typesetting, an review of the resulting galley proof before it is published in its final citable for Please note that during the production process errors may be discovered whic could affect the content, and all legal disclaimers that apply to the journal pertain
Paper-based
analytical
device
for
sampling,
on-site
preconcentration preconcentration and detection of ppb lead in water 1
1
Thiphol Satarpai , Juwadee Shiowatana , and Atitaya Siripinyanond
*
Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand *
Fax: +662-354-7151; Tel: +662-201-5195; E-mail:
[email protected]
Abstract A simple and cost effectiveness procedure based on a paper based analytical device (PAD) for sampling, on-site preconcentration and determination of Pb(II) in water samples was developed. developed. The inkjet printing method was was used for patterning of PAD. PAD. Colorimetric assay was developed on a PAD for Pb(II) detection in µg L -1 level.
This µg L-1 level
detection limit was achieved by b y in situ- and on-site preconcentration of Pb(II) onto adsorption filter paper disc with a home-made home-made holder before color development. development. Water sample was loaded onto a circular filter paper coated with zirconium silicate in 3% sodium carboxymethylcellulose for Pb(II) Pb(II) preconcentration. Subsequently, sodium rhodizonate rhodizonate in tartrate buffer solution (pH 2.8) was used as colorimetric reagent for direct Pb(II) detection on a PAD. PAD. Detection was achieved by measuring the pink color color and recorded by scanner or digital camera. ImageJ software software was used for for measuring grey scale values. The calibration curve was linear in the range of 10 µg L -1 and 100 µg L -1, with a detection limit of 10 µg L -1. The developed method was successfully applied to the determination of Pb(II) in drinking
1
Fax: +662-354-7151; Tel: +662-201-5195 -1-
Paper-based
analytical
device
for
sampling,
on-site
preconcentration preconcentration and detection of ppb lead in water 1
1
Thiphol Satarpai , Juwadee Shiowatana , and Atitaya Siripinyanond
*
Department of Chemistry and Center for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand *
Fax: +662-354-7151; Tel: +662-201-5195; E-mail:
[email protected]
Abstract A simple and cost effectiveness procedure based on a paper based analytical device (PAD) for sampling, on-site preconcentration and determination of Pb(II) in water samples was developed. developed. The inkjet printing method was was used for patterning of PAD. PAD. Colorimetric assay was developed on a PAD for Pb(II) detection in µg L -1 level.
This µg L-1 level
detection limit was achieved by b y in situ- and on-site preconcentration of Pb(II) onto adsorption filter paper disc with a home-made home-made holder before color development. development. Water sample was loaded onto a circular filter paper coated with zirconium silicate in 3% sodium carboxymethylcellulose for Pb(II) Pb(II) preconcentration. Subsequently, sodium rhodizonate rhodizonate in tartrate buffer solution (pH 2.8) was used as colorimetric reagent for direct Pb(II) detection on a PAD. PAD. Detection was achieved by measuring the pink color color and recorded by scanner or digital camera. ImageJ software software was used for for measuring grey scale values. The calibration curve was linear in the range of 10 µg L -1 and 100 µg L -1, with a detection limit of 10 µg L -1. The developed method was successfully applied to the determination of Pb(II) in drinking
1
Fax: +662-354-7151; Tel: +662-201-5195 -1-
water, tap water and surface water near electronic waste storage and the results were compared with those by graphite furnace atomic absorption spectroscopy (GF-AAS) with good agreement. Keywords : PAD, GF-AAS, Colorimetric assay, Lead, Water sample analysis
1. Introduction Lead, Pb(II), is a toxic element and often contaminated in food and water due to its wide application [1]. Lead contamination commonly occurs occurs from metal corrosion corrosion of lead-bearing materials distributed through lead pipes in the water supply supply or the premise premise plumbing. Human intakes lead through various routes, including respiratory and digestive systems. Current guidelines on lead in drinking water are mostly in the range of 10-15 µg L -1. The United States Environmental Protection Agency (EPA) has established a maximum allowable limit of lead in drinking water to be 10 µg L -1 [2]. Exposure to lead is a public health health concern, particularly as it can affect affe ct the neuro-development of young children [3]. [ 3]. Drinking water in household water represents a potential source of lead exposure for children [3]. The study of health effect of lead, the release and removal of lead has been reported continuously since the last 20 years [4]. Thus research on lead has become an important topic for environmental monitoring. Several methods for lead detection in water sample are based on instrumentation techniques such as atomic absorption spectrometry with preconcentration techniques [5-7], gamma spectrometry [8], atomic fluorescence spectrometry [9], stripping voltammetry [1014],
differential
pulse
voltammetry
[15],
potentiometric
stripping
analysis
[16],
chronopotentiometric analysis [17], immunochromatographic assay [18], high-performance
-2-
liquid chromatography (HPLC) [19], light scattering [20], laser-induced breakdown spectroscopy [21], inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively
coupled
plasma
mass
spectrometry
(ICP-MS)
desorption/ionization mass spectrometry (LDI-MS) [25].
[22-24]
and
laser
Furthermore, various types of
sensors including chemical, biological, and optical sensors have been developed for lead detection with the use of UV-vis spectrophotometer, fluorescence or attenuated total reflectance for measuring the intensity of the color change [26-29]. Nonetheless, in order to detect lead ions in the community water or in the field, a simple and low cost technique without the need for expensive and sophisticated instruments should be developed. It is therefore essential to develop a simple and reliable method for lead determination in water samples. Paper-based analytical device (PAD) is a low-cost analytical platform. The main component of paper is cellulose fiber which allows hydrophilic liquid as water to penetrate or transport within its hydrophilic part using capillary forces [30]. Fabrication of the channels on paper can be performed by modifying some hydrophilic parts to become hydrophobic as a barrier in order to confine liquid flow within the hydrophilic channels. Therefore, liquid flow can be designed in a controlled manner. Many fabrication techniques were used to pattern hydrophilic-hydrophobic contrast on a paper [30]. The principles of paper fabrication can be divided into three categories: physical blocking of the pores in paper; physical deposition of a hydrophobizing reagent on the paper; and chemical modification of cellulose fiber surfaces using paper sizing/hydrophobizing agents such as alkyl ketene dimer (AKD), which is an amphiphilic compound normally used in the papermaking industry [31]. In this work, inkjet printing technique was used to introduce AKD onto the paper, as reported by Li et al. [32], because it is simple and requires only a computer and desktop inkjet printer, apart from the AKD reagent.
The chemical modification of cellulose on the paper occurs through the -3-
replacement of hydroxyl group of cellulose by beta-keto ester group. Various applications of these PADs include health diagnostics such as the analyses of nitrite ion and uric acid [33], biochemical analysis by studying enzyme activity of alkaline phosphatase [32], biomedical analysis by detection of nicotinamide adenine dinucleotide (NADH) [34], and environment monitoring by detection of nitrite and nitrate [35]. Previously the detection of Pb(II) in PAD was based on electrochemical detection [36-38] or electrochemi-luminescence detection [39] or colorimetric detection with nanogold-based membrane after acid leaching of AuNPs by microwave irradiation [40]. In order to monitor metal concentration in natural waters, sample collection and preservation are often additional to the quality control aspects [41]. The collected water sample from an environmental source must maintain concentrations of heavy metals as its original source and the volume of water sample must be enough for handling the required analysis. Sample preservation methods include chemical addition, pH control, refrigeration, and freezing [42], for example. Thus, collecting a large number of water samples requires appropriate store capacity and the sample preservation during transport to laboratory. A good solution to this problem is to use adsorption filter paper disc for simultaneous collection and preconcentration, without the necessity to store or preserve a large volume of sample, by which the trace heavy metals from water sources can be kept in adsorption filter paper discs. Use of adsorption filter paper disc for sampling and preconcentration can decrease contamination from sample container and also avoid losing of trace heavy metals from adsorption to the wall of the sample container during water sample collection.
After
sampling and preconcentration on adsorption filter paper disc, colorimetric detection method was carried out for detection of Pb(II) ions on the adsorption filter paper disc. In this work, paper-based analytical device (PAD) was developed to allow sampling, on-site preconcentration and preservation on adsorption filter paper disc for field monitoring. -4-
Specific colorimetric assay for Pb(II) detection as sodium rhodizonate (NaR), a well-known colorimetric test for Pb(II) [45, 46], was employed for direct Pb(II) detection on PAD. The rhodizonate changes from orange-brown to pink upon Pb(II) binding. The adsorption filter paper disc was made from a circular filter paper as a substrate which was coated with zirconium silicate in 3% sodium carboxymethylcellulose as adsorbent to preconcentrate lead ions on site on the disc, with subsequent colorimetric detection on the disc after placing it onto PAD. The preconcentration was carried out using a home-made filter holder. Thus, the combination between a simple preconcentration and selective colorimetric method effectively creates a low cost paper-based device for Pb(II) detection in water samples with low detection limit.
2. Experimental 2.1. Chemicals and reagents
All chemicals used were of analytical reagent grade.
Lead (II) nitrate, sodium
carboxymethylcellulose, sodium bitartrate monohydrate and tartaric acid were purchased from Sigma-Aldrich (MO, USA). Zirconium silicate was obtained from Yong Thai Chemical (BKK, Thailand). Rhodizonic acid disodium salt was purchased from Acros Organics (NJ, USA). Hydrochloric acid, nitric acid and n-heptane were purchased from RCI Labscan Co., Ltd. (BKK, Thailand). Deionized water with a resistivity of 18 MΩ.cm (Easypure®II model D7031, Barnstead, Iowa, USA) was used for solution preparation. All glasswares and plastic bottles were first soaked in diluted nitric acid and then rinsed with deionized water before use.
Polypropylene microcentrifuge tube was purchased from Plastibrand® (Wertheim,
Germany). Whatman® filter paper no. 4 was purchased from GE (Buckinghamshire, UK).
-5-
2.2. Instrumentation
Atomic absorption measurement of Pb(II) was performed with a Perkin Elmer Model AAnalyst 100 (Norwalk, CT, USA) equipped with an HGA-800 graphite-furnace system, an AS-72 autosampler and a deuterium background corrector. L ′vov graphite tube (Perkin Elmer, CT, USA) was used. A Pb hollow-cathode lamp (PHOTRON, Victoria, Australia) was used as the radiation source and operated at 8 mA. The selected wavelength was 283.3 nm and slit width was set at 0.70 nm. Atomization was set at 1900 °C for 5 s. The paper-based analytical device was created by AKD sizing [34] using inkjet printer (PIXMA iP3680, Canon ®) and scanned using Scanner (CanoScan LiDE100, Canon ®). A peristaltic pump (ISMATEC®, Switzerland) was used to systematically control the flow rate of lead solution passing through adsorption filter paper disc. The pH measurement was made by Thermo Orion pH-meter model 420 equipped with glass electrode.
2.3.
Preparation
of
adsorption
filter
paper
disc
for
sampling
and
preconcentration of water sample
Adsorption filter paper disc was prepared from Whatman® filter paper no.4 as a substrate and zirconium silicate as a sorbent material. The paper was cut to a diameter of 5.5 mm. The sorbent material was prepared from 0.1 g of zirconium silicate suspended in 1 mL of 3% sodium carboxymethylcellulose. To prepare the adsorption filter paper disc, 10 µL of sorbent material was pipetted onto the paper substrate, and allowed to dry in an oven at 100 ºC for 1 hour. An in-house simple filter holder was made using a cap of microcentrifuge tube (size 1.5 mL) and a plastic volumetric flask stopper (mouth size #10/19). A hole (ca. size
-6-
about 1 mm) was drilled onto the volumetric flask stopper at the center, and also another hole was punched onto the microcentrifuge tube cap at the center. A fluoropolymer (FEP) tubing (OD. 1/16″, ID. 0.030″) was inserted through the holes of the volumetric flask stopper and the microcentrifuge tube cap for sample introduction.
To perform preconcentration, a
circular filter paper loaded with zirconium silicate (adsorption filter paper disc) was placed on top of the inside of the microcentrifuge tube cap and the volumetric flask stopper. Sample solution was introduced through the fluoropolymer (FEP) tubing inlet by means of peristaltic pump (Fig. 1). 2.4. PAD fabrication for colorimetric detection
Ink-jet printing technique with alkyl ketene dimer (AKD) sizing agent (3% in heptane) was applied onto Whatman® filter paper no. 4 to fabricate PAD. The pattern used for printing is illustrated in Fig. 2a. The pattern consisted of two sample reservoirs (left and right) and one detection zone (center), all with the circular shape of 5 x 5 mm. After AKD printing, the paper was heat-treated in an oven at 50 °C for 45 min. Then, the patterned paper was punched to create a hole at the center reservoir and the paper was cut in the dash lines area: one between the left and the center ports; and another one between the center and the right ports, to allow the paper to flap, creating valves (A and B). With the paper flaps lifted up, it was not possible for the solution to flow from one port to another, acting as valve closing. With the paper flaps placed down, however, it was possible for the solution to flow from one port to another, acting as valve opening. The PAD was folded at half and doublesided tape was used to stick the paper together as shown in Fig. 2a. 2.5. Preconcentration and colorimetric detection procedure
To perform preconcentration, a 25 mL of water sample was introduced through the adsorption filter paper disc in a simple filter holder at a flow rate of 2 mL min -1 by peristaltic -7-
pump. After adsorption of lead ions, the adsorption filter paper disc was removed, allowed to dry, and placed at the center of detection zone of the PAD (Fig. 2b) (For field sampling, the adsorption filter paper disc can be kept in a well-prepared cabinet for transportation to the laboratory for later detection). The adsorbed lead ion on the adsorbent was detected by placing the filter paper disc in the center port of the PAD, then adding 15 µL of 0.5% sodium rhodizonate reagent in aqueous tartrate buffer (pH 2.8) at the right reservoir. With the valve opening, the chemical reaction of sodium rhodizonate reagent and Pb(II) ions took place, yielding the pink color product (Reaction as shown in Fig. 3). The color was recorded by taking a photograph with a smart phone or a scanner. The color intensity in the detection zone was quantified by measuring as the grey intensity using image processing by ImageJ (NIH, USA). The higher concentration of Pb(II) gave the more intense pink color, resulting in the lower grey intensity values (values ranging from 0 to 255). To determine % remaining Pb(II) in solution, Pb(II) in the filtrate was measured by using GF-AAS to check the mass balances.
2.6. Interference studies
Different amounts of Co 2+, Ni2+, Zn2+, Cd2+, Cr 3+, Cu2+, Mn2+, Fe2+, and Ba2+ ions, which may be present in water samples, were added to the test solution containing 60 µg L -1 Pb(II), with the Pb(II)/interferent ions ratio of 1/25, 1/50, and 1/100.
2.7. Sampling procedure
To prove the concept of lead ions preconcentration on adsorption filter paper disc before colorimetric measurement using PAD, the analysis of lead in water samples from
-8-
various sources was performed. These samples included drinking water sample collected from a local market in Bangkok, domestic tap water sample from Thonburi and our laboratory (Phayathai campus, Mahidol University, Bangkok, Thailand).
Surface water
samples were collected from the area near the local electronic waste storage at Khong Chai, Kalasin, Thailand. These water samples were also spiked with 40 µg L-1 and 100 µg L -1 of Pb(II).
3. Results and discussion 3.1. The adsorption study of lead ion onto the adsorbent
To test the potential of zirconium silicate as the adsorbent, the batch adsorption experiments of Pb(II) on this adsorbent were conducted in a 100 mL conical flask at room temperature (25 ºC). 100 mg adsorbent was weighed and added in the flask containing 25 mL of Pb(II) solution (ranging from 10 to 500 µg L -1) at pH about 6.7 with a stirring time at 10 min using a magnetic stirrer. After each run, the suspension was filtered and the filtrate was measured for the concentration of Pb(II) by using GF-AAS. The adsorption percentage ( was calculated from
: where is the initial conce
ntration of
Pb(II); is the residual concentration of Pb(II) in the solution. The results in Fig. 4 show that the adsorption percentage were > 97% (n =3) for all Pb(II) concentrations studied herein. Therefore, zirconium silicate can be used as an adsorbent on sorption of lead ions. Furthermore the effect of lead concentration on its adsorption on the adsorbent was studied (data not shown). The initial lead concentration ranging from 10 to 10,000 µg L -1 were prepared and were examined under optimum conditions for their sorption on the adsorbent filter paper disc (see preparation in 2.3). The filtrate was collected for further -9-
determination of residual concentration of lead ions in the solution by using GF-AAS and
were calculated. The results show that the percentage lead ions adsorbed decreased with increasing initial lead concentration, which is due to less favorable sites of zirconium silicate.
3.2. Effect of pH on adsorption of lead ions
The effect of pH in the aqueous solution on the adsorption of lead ions on the adsorbent was investigated. A wide range of pH from 1 to 8 was examined by adjusting the pH with hydrochloric acid and sodium hydroxide. The % remaining Pb(II) in solution was determined by using GF-AAS, with the results shown in Fig. 5. The % remaining Pb(II) in solution were found to be the lowest when the pH was adjusted to be between 6.0 and 7.0. At pH lower than 6.0, lead ions cannot be adsorbed or retained on the surface of adsorbent resulting in the high % remaining Pb(II) in solution. At pH values higher than 7.0, precipitation of lead hydroxide occurred. Thus, lead ions were effectively adsorbed with unmodified adsorbent in pH range 6.0-7.0, in agreement with the report by Hussain et al. [43] and Mahmoud et al. [44].
3.3. Effect of sample flow rate on adsorbent
The effect of sample flow rate on lead adsorption was studied. After the adsorption process was completed, the adsorption filter paper disc was removed, allowed to dry, and placed at the center of the PAD detection zone as shown in Fig. 2b to start the colorimetric detection by dropping NaR reagent on the right port and placing down the paper flap to allow the reagent to flow to the detection port.
In the presence of Pb(II), the red color was - 10 -
developed. The filtrate was also collected to determine % remaining Pb(II) in solution. The flow rates were examined in the range of 0.5-3.0 mL min -1, with the results shown in Fig. 6. With the very slow flow rate, lead adsorption on the adsorbent increased but the color spot upon interaction with rhodizonate became quite dispersed resulting in the higher relative standard deviation of the grey intensity color values. With higher flow rates, the efficiency of adsorption was reduced, resulting in higher % remaining Pb(II). The lowest % remaining Pb(II) in solution was found in the flow rates ranging from 0.5-1.5 mL min -1. However, to obtain the shortest preconcentration time the flow rate at 2.0-2.5 mL min-1 were considered as they offered the well-defined spot to determine the grey intensity values with the shorter time than using flow rate at 0.5-1.5 mL min -1. Thus, the flow rate of 2.0 mL min -1 was selected for further experiments. With this selected flow rate, it would take approximately 13 min to preconcentrate 25 mL of water sample, leading to the total analysis time of approximately 15 min for each sample.
3.4. Interferences
Various ions were tested for their interference effects on the preconcentration and the colorimetric detection of Pb(II). Different amounts of these ions normally present in water samples were added to the test solution containing 60 µg L -1 of Pb(II) and the developed method was applied. Fig. 7 is the plot of the grey intensity values of Pb(II)-rhodizonate in the presence of various foreign ions. Uneven background occurred for Fe2+ interference ions which is caused by the brown color of iron hydroxide precipitate as the pH of the solution was approximately 6.0 (see Fig. 7). To fix this problem, background subtraction before measuring the grey intensity values was performed. The results indicated that these foreign ions have no effect on the determination of Pb(II) on the PAD. Nonetheless, the Pb2+/Ba2+
- 11 -
ratio of 1/50 showed positive effect with sodium rhodizonate reagent, similar to the report by Bartsch et al. [45]. Upon reacting with sodium rhodizonate, barium ion gave similar color to Pb(II).
In order to indicate if the pink color was attributed from Pb2+ or Ba2+, the left
reservoir on the PAD was loaded with 5% HCl. With the valve opening, acid could flow to the detection port. In the presence of 5% HCl, Ba(II)-rhodizonate was decolorized, whereas the red-pink color of Pb(II)-rhodizonate would turn into the blue color. This blue color was proposed to come from the formation of Pb(II) complex with the alternating tetrahydroxyquinone (THQ) ligand rather than the rhodizonate [45]. Therefore, addition of 5% HCl to the left port was performed as a confirmation test. The dark pink color should be immediately changed to the blue color when the pink color occurred from Pb(II)-rhodizonate complex [46]. However, the blue color may fade with time. The tolerable levels of foreign ions are summarized in Table 1. Under the conditions used herein, the concentration levels of these foreign ions found in natural water do not cause any interference effect on colorimetric detection of Pb(II).
3.5. Analytical performance and determination of Pb(II) ions in real samples
The analytical features of the developed method including the linear range of the calibration curve, limit of detection, precision, and accuracy were investigated. The linearity of the calibration curve (grey intensity value) was found to be 10-100 µg L -1 with a correlation coefficient of 0.969 (Fig. 8). The detection limit of Pb(II) ions was 10 µg L-1. The precision of the developed method was less than 20 %RSD for Pb(II) in the solutions. The accuracy was checked by using the spiked standard and validated by GF-AAS. The developed method was applied for the determination of Pb(II) in household tap waters, drinking waters and surface water near electronic waste storage in Thailand. The results are
- 12 -
summarized in Table 2.
Pb(II) ions were not detectable in these samples by using the
developed PAD and GF-AAS. These samples were then spiked with 40 µg L-1 and 100 µg L 1
of Pb(II) and good recoveries were obtained, suggesting that the developed PAD can be
applied to determine lead ions in these matrices. The results given in Table 2 showed good agreement between the proposed method with those from the GF-AAS technique.
4. Conclusions The developed method is composed of two steps: preconcentration and colorimetric detection of lead ions. Preconcentration was performed by using an adsorption filter paper disc placed in a home-made filter holder following sensitive colorimetric detection of Pb(II) ions directly in situ on the PAD without elution step. An unmodified zirconium silicate in 3% sodium carboxymethylcellulose was used as adsorbent. The proposed method can detect Pb(II) in the µg L -1 level by the naked eye after approximately 13 min preconcentration step (for 25 mL water samples). The total analysis time of the proposed method was less than 15 min. Accuracy was tested and validated by GF-AAS with good agreement. The PAD was successfully applied for the determination of Pb(II) in drinking water, tap water and waste water matrices.
The proposed method ensures many merits such as simplicity, cost
effectiveness, and ease in preparation and operation. The method can be further modified for on-site and real time monitoring of Pb(II) by using plastic syringe instead of peristaltic pump to control the flow of solution.
- 13 -
Acknowledgements We are grateful for the scholarship given to TS and the funding for equipment from Mahidol University under the National Research Universities Initiative. Thanks are also due to Miss Rattaporn Saenmuangchin for collecting surface water sample near an electronic waste storage in Thailand.
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Figure Captions
Fig. 1. Photograph of a home-made adsorption filter paper disc holder, consisting of a modified plastic volumetric flask stopper and a cap of microcentrifuge tube used as adsorption filter paper disc supporter. Fig. 2. Images showing (a) the pattern and fabrication of the PAD (Magenta color represents hydrophobic area and white color represents hydrophilic area) and (b) the colorimetric detection procedure after lead preconcentration with the adsorption filter paper disc. Fig. 3. The chemical reaction of sodium rhodizonate reagent with Pb(II) ion. Fig. 4. The adsorption efficiency of adsorbent. Fig. 5. Effect of solution pH on Pb(II) sorption on adsorption filter paper disc. Fig. 6. Effect of sample flow rate on Pb(II) sorption and colorimetric detection of Pb(II). Fig. 7. Effect of interfering ions on the determination of 60 µg L -1 Pb(II) using PAD. The concentrations of interfering ions were 1500 µg L -1 for Cd2+, Cr 3+, Cu2+, Mn2+, Fe2+ and 3000 µg L-1 for Ba2+, Co2+, Ni2+, Zn2+. Fig. 8. Calibration curve of standard Pb(II). The linear equation was y = -0.4626x + 152.05 and correlation coefficient was 0.9695.
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Table 1. Tolerance limits of interference ions Tolerance limits (µg L-1) 3000
Interference ions Ni2+, Co2+, Zn2+ Cr 3+, Cu2+, Cd2+, Mn2+, Fe2+
1500
Table 2. Determination of Pb(II) in water samples and the analytical recovery by PAD and GF-AAS PAD
GF-
AAS Samples
Pb(II) (µg L-1)
Recovery
Pb(II) (µg L-1)
Recovery
Added
Found a
(%)
Added
Found a
0.0 41.2 103.0
ND b 41.2±3.8 99.1±10.4
100.0 96.2
0.0 41.2 103.0
ND c 38.2±7.8 103.2±1.1
92.6 100.2
0.0 41.2 103.0 Tap water (T1) 0.0 41.2 103.0 Tap water (T2) 0.0 41.2 103.0 Waste water (A) 0.0 41.2 103.0 Waste water (B) 0.0 41.2 103.0 a Mean ± SD (n=3)
ND 48.3±4.9 89.5±11.0 ND 45.1±8.1 89.2±4.4 ND 43.6±5.4 84.3±2.6 ND 39.7±5.5 97.9±12.4 ND 43.8±12.0 101.0±15.2
117.2 86.9 109.5 80.5 105.9 81.8 96.3 95.1 106.4 98.1
0.0 41.2 103.0 0.0 41.2 103.0 0.0 41.2 103.0 0.0 41.2 103.0 0.0 41.2 103.0
ND 39.2±0.5 106.7±6.0 ND 39.2±6.9 117.2±7.1 ND 42.2±6.0 89.5±20.3 ND 38.7±3.4 111.2±7.9 ND 42.8±1.2 117.1±2.0
95.3 103.6 95.3 113.8 102.3 86.9 93.9 107.9 104.0 113.7
Drinking water (D1)
Drinking water (D2)
b
Not detectable (<10 µg L -1)
c
Not detectable (<4.7 µg L -1)
Highlights - 22 -
(%)
Paper device was developed for on-site preconcentration and determination of Pb.
Zirconium silicate adsorbent coated on the filter paper was used for Pb sorption.
Rhodizonate color reaction with Pb(II) was performed directly on the paper device.
The detection limit of 10 µg L was obtained.
-1
- 23 -
Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
- 27 -
Fig. 5
- 28 -
Fig. 6
- 29 -
Fig. 7
- 30 -
Fig. 8
- 31 -
