Integration of Flow Injection Capillary Liquid Electrode Discharge

Subscriber access provided by United Arab Emirates University | Libraries Deanship

Article

Integration of Flow Injection Capillary Liquid Electrode Discharge OES and Microplasma-induced Vapor Generation: A System for Detection of Ultratrace Hg and Cd in Single Drop of Human Whole Blood Shu-an Xia, Anqin Leng, Yao Lin, Li Wu, Yunfei Tian, Xiandeng Hou, and Chengbin Zheng Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b04222 • Publication Date (Web): 07 Jan 2019 Downloaded from http://pubs.acs.org on January 11, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

Integration of Flow Injection Capillary Liquid Electrode Discharge OES and Microplasma-induced Vapor Generation: A System for Detection of Ultratrace Hg and Cd in Single Drop of Human Whole Blood Shu-an Xia†, Anqin Leng‡, Yao Lin †, Li Wu§, Yunfei Tian§, Xiandeng Hou†,§, Chengbin Zheng†* Key Laboratory of Green Chemistry & Technology of MOE, College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, China †

‡

Sichuan Center for Disease Control and Prevention, Chengdu, Sichuan 610041, China. Analytical & Testing Center, Sichuan University, Chengdu, Sichuan 610064, China

§

ABSTRACT: A simple and miniature analytical system was developed to determine Hg and Cd in small amounts of samples by integrating flow injection capillary liquid electrode discharge (CLED) optical emission spectrometry (OES) and microplasma-induced vapor generation (PIVG) atomic fluorescence spectrometry (AFS). With the assistance of the inherent capillary driving force and the force arising from the solution vaporization in the microplasma, the sample solution was automatically transported into the discharge chamber wherein analytes were simultaneously excited to generate their atomic emission lines and converted to their volatile species. Subsequently, the volatile species were further swept into AFS for their further determinations. Therefore, the same sample could be successively analyzed by OES and AFS. Owing to the unique independent linear-range and sensitivity of CLED-OES and PIVG-AFS, the developed system not only significantly extended its linear range to six orders of magnitude but also remarkably reduced the sample consumption to several microliters. Thus, wide linear-range and ultra-sensitive determination of Hg and Cd in limited amounts of samples were accomplished simply by sharing one single capillary liquid electrode discharge source. Under the optimized conditions, limits of detection (LODs) of 10 μg L-1 were obtained for both Hg and Cd when CLED-OES was used as detector, whereas the LODs for Hg and Cd were improved to 0.03 µg L-1 and 0.04 µg L-1 with AFS detector, respectively. In addition, the extremely wide linearrange of 0.001 – 100 mg L-1 and 0.001 – 40 mg L-1 were obtained for Hg and Cd, respectively. The potential application of this method was validated by successfully analyzing three Certified Reference Materials (ZK021-1, GBW(E)090033 and GBW(E)090034) and six human blood samples.

Trace elemental analysis of biological fluids is a key of signaling pathways to monitor exposure of toxic elements to human.1-7 In general, routine determination of elements in samples can be accomplished by using atomic spectrometry.814 However, it is still a continuing challenge to develop a suitable atomic spectrometric strategy for the accurate determination of toxic elements in complex matrices because the conventional atomic spectrometric techniques not only have their advantages but also remain insurmountable shortcomings. For examples, flame atomic absorption spectrometry (FAAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) have a simple structure and low running cost, whereas they provide relatively low sensitivities and/or narrow linear ranges. Although inductively coupled plasma mass spectrometry (ICP-MS) provides high sensitivity and wide linear range, it is quite expensive, and energy- and argon (Ar) gas-consuming. Moreover, the aforementioned atomic spectrometric

techniques using traditional pneumatic nebulizer usually consume large amounts of samples (several milligrams or milliliters) and then cannot be used for the determination of elements in limited amounts of samples, particularly those precious samples with unknown concentration range of analytes. However, the application of atomic spectrometry for the determination of elements in limited amounts of samples has attracted great interest over the past years because of the increasing requirements from the fields of single-cell analysis, forensic and biological analysis.15-19 Over the past decades, significant efforts have been devoted to developing novel sampling techniques for analytical atomic spectrometry to reduce their sample consumption.4,20-22 Micro-pneumatic nebulization, low-flow nebulization20 or some nonpneumatic nebulization techniques including electrothermal vaporization (ETV)23-25 and laser ablation (LA)26-28, monodisperse droplet sample introduction systems29-31 , and chip-based capillary electrophoresis32,33 etc.

1 ACS Paragon Plus Environment

Analytical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

have been adopted as an alternative to normal pneumatic nebulization method to significantly decrease sample consumption, thus making ICP-OES/ICP-MS suitable for analyzing limited amounts of samples. However, there are a number of impediments remaining to their further application to the determination of elements in small amounts of samples, such as serious memory effect, spectral and non-spectral interference associated with LA, the potential risk of clogging and difficulty in cleaning arising from reduction the size of the nebulizer nozzle. A mature and widely used approach to the potential alleviation of these impediments can be obtained through the use of chemical vapor generation (CVG) as a sampling technique.34-39 Although CVG signiﬁcantly improves the analytical performance of atomic spectrometry, its application to the analysis of micro-amounts of sample is rather limited because of the high blank and serious secondary contamination arising from concentrated mineral acids and reductants. Notably, the linear range of conventional atomic spectrometry is still not obviously improved no matter what sampling technique is used. Most recently, a pump- and valve-free flow injection capillary liquid electrode microdischarge (CLED) OES system has been developed for elemental analysis.40,34 Owing to the capillary action and sample vaporization in the microplasma, the sample solution could be automatically introduced into the plasma to generate atomic emission lines of analytes. In this system, sample consumption could be accurately controlled by sampling time and reduced to the nanoliter level. Unfortunately, this method was not sensitive enough to determine ultra-trace elements in small amounts of samples. In previous studies,41-44 various microdischarges have been used to accomplish CVG of some elements without using toxic and unstable reductant, thus realizing sensitive determination of trace Cd and Zn in limited amounts of samples and quantify mercury distribution in fish. However, application of flow injection CLED to microplasma-induced vapor generation (PIVG) has not yet been reported. Meanwhile, we believe that a flow injection CLED system can be not only used to excite atoms of analytes to produce their atomic emission lines but also convert analytes to their volatile species from limited amounts of samples. Therefore, the purpose of this work is to investigate the feasibility that integrates flow injection CLED-OES and PIVG atomic fluorescence spectrometry (AFS) into a miniature system. Mercury and cadmium were chosen as model elements to validate this system since they are listed as the 3rd and 7th most important hazardous substances by the Agency for Toxic Substances and Disease Registry, respectively. To the best of our knowledge, this is the first attempt to use one microplasma source to accomplish both flow injection microplasma OES and PIVG -AFS determination of elements in one sampling. Owing to low sample consumption of the flow injection CLED system and different linear-ranges and sensitivities to microplasma based OES and PIVG-AFS, respectively, the proposed system would be one of the most promising techniques for the determination of toxic elements in limited amounts of samples with high sensitivity and wide linearity.

Page 2 of 10

coupled device (CCD) (Maya 2000 Pro, Ocean Optics Inc., Dunedin, FL, USA) and an commercial double-channel hydride generation atomic fluorescence spectrometer (AFS-8220, Beijing Titan Instruments Co. Ltd., Beijing, China) equipped with a photomultiplier (PMT) and highly intensive hollow cathode lamps (HCLs) of mercury and cadmium, which can simultaneously determine Hg and Cd in sample. The CCD spectrometer has a 0.4 nm spectral resolution and a working spectral range of 180 to 600 nm. The CLED device includes a glass capillary (0.3 mm i.d. × 0.5 mm o.d. × 6 cm length) coated with a copper foil, a quartz T-tube (0.8 mm i.d. × 3.0 mm o.d. × 4.0 cm length), a polymethyl methacrylate (PMMA) chip (2.0 cm length × 2.0 cm width × 1.0 cm height) drilled five holes, and a tapered tungsten electrode (1.0 mm in diameter). As shown in Figure 1b, the Cu coated capillary is fastened to the center of the quartz T-tube and extends 1 cm beyond each end of the quartz T-tube. One end of the T-tube is sealed with 704 RTV silicone sealant (Guangdong Hengda New Materials Technology Co., China) and then subsequently inserted into the hole (3.0 mm in diameter × 1.0 cm length) drilled on the PMMA chip. The tungsten electrode is inserted through another hole (1.0 mm in diameter × 2.0 cm length) to face the capillary. A compact ac neon sign electric transformer power supply with a rated output of 8 kV, 30 kHz and a input of 24 W at 220 V, 60 Hz (NGB408BL, Electronic Equipment Factory of Jinshi, Guangzhou, China) is connected to the copper foil and the tungsten electrode, respectively. When the high voltage from the power supply is applied, the microplasma is generated and sustained in the largest hole (1 cm in diameter) of PMMA chip, which is sealed with two pieces of the quartz plate, and served as a discharge chamber. The atomic emission lines of Hg and Cd generated from the microplasma were transmitted through the quartz plates and focused onto an optical fiber attached to the CCD spectrometer. A transport tube is used to connect the CLED chamber with the atomic fluorescence spectrometer, which allows the generated volatile species of Hg and Cd to be swept to the atomizer of AFS with argon carrier gas flow. Meanwhile, another Ar flow is also introduced into the CLED chamber through the quartz T-tube and acted as a sheath gas to prevent sample solution from forming a liquid drop on the outer surface of the capillary. The PTFE droplet array platform is tightly attached to the electric displacement rail stage, which can automatically move to allow the capillary to reach sequential single drops. The photographs of the whole experimental setup are shown in Figures S1 (section 1 of the Supporting Information, SI).

EXPERIMENTAL SECTION Instrumentation. The main experimental setup is shown in Figure 1a. The analytical system consists of an electric displacement rail stage, a laboratory-made polytetrafluoroethylene (PTFE) droplet array platform (8.0 cm length× 7.0 cm width × 5.0 mm height), a CLED device, and a commercial hand-held spectrometer based on charge

2 Environment ACS Paragon Plus

Page 3 of 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) Schematic of the experimental setup and (b) a detailed drawing of the T tube.

Reagents and Materials. All chemicals are of at least analytical reagent grade. Argon (99.999%) is obtained from Qiaoyuan Gas Co. (Chengdu, China). High purity (18.2 MΩ-cm) deionized water (DIW) produced from a water purification system (Chengdu Ultrapure Technology Co., Ltd., China) is used throughout. 1000 mg L−1 stock solutions of Hg(II) and Cd(II) are obtained from the National Standard Material Centre of China (NSMCC, Beijing, China). Formic acid and nitric acid are purchased from Kelong Chemical Reagents Co. (Chengdu, China). L-cysteine is brought from Aladdin industrial Co. (Shanghai, China). Capillary tubes are purchased from Great Wall Science Instrument Store (Shanghai, China). Certified Reference Materials (CRMs) freeze-dried bovine blood (ZK021-1) and whole blood (GBW(E)090033 and GBW(E)090034) are obtained from Chinese Center for Disease Control and Prevention (CDC, Beijing, China). Real samples of human whole blood are collected from adult healthy volunteers into 3 mL of Monoject tubes containing heparin lithium purchased from Rich Science Co. (Chengdu, China). These blood samples are stored at 4 °C and analyzed within one week. Whatman 903 filter paper (GE Healthcare Europe GmbH, Germany) is used for sample preparation. Sample Preparation. The blood CRMs firstly used for the validation of the accuracy and practicability of the proposed system were digested by a modified microwave assisted digestion method. The detailed information about the digestion can be available from Section 2 of the SI. The feasibility of this analytical system on the analysis of limited amount of sample was evaluated by analyzing Hg and Cd in a single drop of blood. However, it is not easy to digest a single drop of blood ( 1 mg L-1) of Hg and Cd, their AFS responses exceed saturation of the detector and are no longer linear to the responses obtained at low concentration. On the contrary, the OES responses from high concentration of the analytes are obvious and become linear. These observations demonstrate the feasibility of this analytical system on the determination of Hg and Cd in limited amounts of samples with high sensitivity and wide linear range.

Page 4 of 10

Figure 2. 0.5 mg L-1 Hg(II) and Cd(II) were detected by CLED-PIVG-AFS (a) and CLED-OES (b).

Possible Process of CLED-OES and CLED-PIVG-AFS. In order to understand the process of CLED-OES and CLED-PIVGAFS, the identification of the volatile species of Hg and Cd were initially undertaken by comparing the signals from a standard solution containing 0.5 mg L−1 Cd(II) and 0.5 mg L−1 Hg(II) obtained by AFS with and without an Ar-H2 flame. According to previous work,42,43 20 mL min−1 of H2 was introduced to the CLED chamber together with 300 mL min−1 of Ar as both discharge gas and carrier gas in this investigation. At the same time, an auxiliary hydrogen gas flow (150 mL min-1) was introduced behind the CLED chamber and mixed with the carrier gas to steadily generate Ar-H2 flame for efficient atomization of the volatile species of Hg and Cd. As can be seen from Figure S3a in Section 4 of the SI, an obvious signal of Hg can be found, no matter what the Ar-H2 flame is ignited or not. Furthermore, the signal detected without Ar-H2 flame is obviously higher than that obtained with Ar-H2 flame. This result indicates that the volatile species generated from Hg(II) is mercury cold vapor (Hg0). The residue time of Hg0 in atomizer would be remarkably reduced as the ignition of the Ar-H2 flame, thus decreasing its signal, which agrees well with previous report46 using conventional mercury cold vapor generation system. For cadmium, the obvious signal was also observed even without igniting Ar-H2 flame, but much lower than that observed with Ar-H2 flame, implying that the generated volatile species of Cd may include free atomic vapor (Cd0) and molecular volatile species. To support this viewpoint, a comparison of the signals obtained by AFS with and without introducing 20 mL min-1 H2 to discharge gas was undertaken, as shown in Figures S3b of Section 4 of the SI. It is worthwhile to note that all of these signals obtained using Ar-H2 flame atomization. The results show that there is no obvious difference between the mercury signals obtained with or without introducing H2, whereas the signals of cadmium obtained with introducing H2 is improved 4-fold comparing that obtained without introducing H2. As no other chemical was involved in this reaction besides H2, the volatile species of Cd generated in CLED chamber were thus presumed to be Cd0 and hydride of Cd (CdH2)36. Therefore, the possible mechanism of this process can be described as Figure 3. Firstly, the microplasma constantly introduces the standard or sample solution in the form of a fine spray of droplets (Figure 3a). Meanwhile, the introduced hydrogen molecules are split into their free radicals by microplasma. Then, Hg(II) and Cd(II) contained in the droplets are reduced to their volatile species(Hg0, Cd0 and CdH2) by free electrons and the reductive radicals contained in the microplasma.


Page 5 of 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry tunately, there are no method can be available to distinguish the volatile species generated in microplasma. Therefore, it should be noted that the mechanism is just a rough speculation and a careful investigation is further required in future due to the complex nature of microplasma. Optimization of Experimental Parameters. As this is the first report to share one single CLED microplasma for the simultaneous OES and AFS analysis, it is necessary to undertake a detailed investigation of all physicochemical parameters influencing CLED-OES and PIVG-AFS, including solution medium, Ar and H2 gas flow rates, discharge voltage, discharge gap, etc. A standard solution containing 0.5 mg L−1 of Hg (II) and 0.5 mg L−1 of Cd(II) was used to optimize these parameters and the results are summarized in Section 5 of the SI. Finally, solution medium containing 1% HNO3 (v/v) and 6% (v/v) formic acid, discharge gas flow rate containing 300 mL min-1 of Ar and 20 mL min-1 of H2, 2.18kV of discharge voltage and 3 mm of discharge gap were used as the optimal operation parameters for the subsequent experiments. Analytical Figures of Merit. Analytical figures of merit using this CLED-OES/PIVG-AFS system were evaluated under optimized experimental conditions. The atomic emission and atomic fluorescence signal profiles of Hg and Cd are shown in Figure 4a and Figure 4b, respectively. The typical calibration curves obtained by comparing the concentrations of Hg(II) and Cd(II) to their intensities of atomic emission or atomic fluorescence are described in Figure 4a and Figure 4b. The linear correlation coefficients for these calibration curves are better than 0.998 regardless of the use of CLED-OES and PIVGAFS as a detector.

Figure 3. Mechanism of CLED-OES and PIVG-AFS. A portion of these volatile species is further excited by microplasma to generate the atomic emission lines of Hg and Cd, as shown in Figure 3b. Finally, all the excited and unexcited Hg0, Cd0 and CdH2 are transported into the Ar-H2 flame atomizer for their AFS analysis. On the other hand, the generated Cd0 may be also produced from the partial decomposition of CdH2 because this hydride is noticeably thermally unstable. Unfor-

Table 1. Comparison of Performance with other microplasma based atomic spectrometry method

linear upper limit (µg L-1)

limits of detection (µg L-1)

sample volume(μL)

detector

ref

Hg

Cd

Hg

Cd

CLED-OES

2.5 × 104

10 × 103

75

30

60

OES

40

FI-SD-SEGD-CVG-AFS

-

100

-

0.01

20

AFS

42

FI-SD-SEGD-CVG-AFS

200

-

0.01

-

20

AFS

44

PEVG-AFS

-

0.5

-

0.003

-

AFS

37

DBD-CVG-AFS using non-ionic surfactants

2

2

0.0045

0.0024

300

-

0.001

-

8750

OES

49

HS-SPME-PD-OES

AFS

48

DBD-CVG-DBD-OES

500

-

0.2

-

3000

OES

36

FLA-APGD

5 × 103

200

0.70

0.040

750 μL min-1

OES

50

-

50

-

0.05

2100 µL min-

OES

LE-DBD

2 × 105

9.5 × 105

1100

2300

20 µL min-1

OES

47

LFDBD

-

10 × 103

-

38

80

OES

52

LDA-APGD-OES

-

1000

-

0.20-0.40

50

OES

53

CLED-OES/PIVG-AFS

1 × 105

4 × 104

0.03

0.04

80

AFS

this work

CLED-OES/PIVG-AFS

1 × 105

4 × 104

10(OES)

10(OES)

80

OES

this work

SAGD

1

51

FI, flow injection; SD, single drop; PEVG, plasma electrochemical vapor generation; DBD, dielectric barrier discharge; HSSPME, headspace solid phase microextraction; PD, point discharge; SCGD, solution cathode glow discharge; FLA-APGD, flowing liquid anode atmospheric pressure glow discharge; SAGD, solution anode glow discharge; LE, liquid electrode; LF, liquid



Page 6 of 10

film; LDA-APGD, liquid drop anode atmospheric pressure glow discharge. Only 2-3 orders of magnitude of linear ranges can be achieved if only CLED-OES or PIVG-AFS is applied. It is obvious that their linearities should be limited by their sensitivities or signal saturation of the detectors. However, a wide concentration range of analytes is frequently encountered during routine analyses of unknown and real samples, thus it is impossible to accomplish accurate results through one-time measurement by a single atomic spectrometric method, without any sample dilution or analyte preconcentration procedure. Most interestingly, this system combing CLED-OES and CLED-AFS would take full advantages of the sensitivity difference between the OES and AFS. As a consequence, a linear dynamic range with six orders of magnitude (Figure 4c and Figure 4d) can be easily obtained. It should be noted that CLED-OES and PIVG-AFS are controlled by individual their operation software and then the combined calibration curves (Figure 4c and Figure 4d) are only used to show that the integrated analytical system can significantly be extended the analytical linear range, which is not mandatory. Most interestingly, just one sample introduction was required for this determination and the sample consumption could be reduced several microliters, which is beneficial to analyze elements in limited amounts of samples, particularly those samples with an unknown concentration range of analytes. The limits of detection (LODs) defined as the analyte concentration equivalent to three times the standard deviation of 11 measurements of a blank solution (DIW water)

divided by the slope of the calibration curve, were 10 μg L-1 for both Hg and Cd when CLED-OES was used as detector. Meanwhile, this analytical system also provided LODs of 0.03 μg L-1 and 0.04 μg L-1 for Hg and Cd, respectively, with the AFS detection. It is worth to note that the sample consumption was significantly reduced to about 850 nL with 10 s sampling time. According to previous work,35 the sample throughput and the analytical precision could be improved when a droplet array was used as a sampling platform to realize flow injection without using any valve and pump. Thus, the precision expressed as the relative standard deviation (RSDs) was investigated via 20 replicate measurements of standard solutions containing low concentration (50 µg L-1 of Hg and 30 µg L-1 of Cd) or high concentration (2 mg L-1 of Hg and 1 mg L1 Cd) of analytes. As shown in Figure 5, all of the RSDs obtained by either CLED-OES or CLED-PIVG-AFS are better than 2.6%. Table 1 and Figure S6 (Section 6 of the SI) summarize analytical figures of merit achieved by the proposed system and compare the performance of several similar and frequently used methods. Although the experimental setup of the CLED-OES/PIVG-AFS system is slightly complicated than those of other system, it not only retains lower LODs but also provides a wider linear dynamic range. These advantages make the developed system more suitable for determining toxic elements in limited amounts of samples with unknown concentration range of analytes compared to the reported system.

Figure 4. (a, b) Atomic emission and atomic fluorescence signal profiles of Hg(II) and Cd(II); (c, d) typical calibration curve using hyphenated CLED for detection of Hg(II) and Cd(II).


Page 7 of 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry unique advantages of much lower operation cost, sample and energy consumption compared to ICPMS. Quantification of Hg and Cd in Single Drop of Blood. Although the accuracy of the proposed system has been validated by analyzing the blood CRMs, another purpose of this work is to determine Hg and Cd in a single drop of human whole blood. Thus, the practicability of the proposed system on the determination of Hg and Cd in limited amounts of blood samples was investigated. A modified method of consisting DBS and MSPD was utilized to efficiently extract Hg and Cd from a single drop of blood. In order to improve the extraction efficiencies of Hg and Cd, the experimental conditions affecting the extraction efficiency were optimized and described in Section 7 of the SI. Since there are no suitable blood CRMs containing both Cd(II) and Hg(II) available for the evaluation of extraction efficiencies of Cd and Hg, two methods were thus utilized to investigate the efficiencies of the proposed MSPD on the extraction of Cd and Hg from a spiked whole blood sample. One is to compare the concentration of analytes in the eluent of each extraction to total concentration obtained from five times extraction, which was calculated through the following formula.

En % = Figure 5. (a) Signals obtained from repeat injections of solutions containing 50 μg L-1 and 2 mg L-1 Hg2+; and (b) signals obtained from repeat injections of solutions containing 30 μg L-1 and 1 mg L-1 Cd2+. The Accuracy of the Proposed System. The accuracy and practicability of the proposed system were firstly validated by analyzing three blood CRMs, including ZK021-1 (freeze-dried bovine blood), GBW(E)090033 (whole blood) and GBW(E)090034 (whole blood). A standard curve method was used to analyze these CRMs samples because the sample matrices had been completely digested by microwaveassisted digestion. In order to further demonstrate the advantages of the proposed system, the digested sample solutions were also analyzed by ICP-MS. Analytical results are summarized in Table 2. The results of the t-test show no significant differences among the certified values and the Table 2. Analytical Results of Hg and Cd in CRMs sample

element

certified value (mg

ZK021-1 GBW(E) 090033 GBW(E) 090034 a Mean

Hg

L-1)

this worka (mg L-1)

ICPMSa

12 ± 2

11 ± 3

12 ± 5

2.04 ± 0.44

2.29 ± 0.60

1.98 ± 0.45

4.02 ± 0.43

4.33 ± 0.56

3.99 ± 0.57

Cd

and standard deviation (n = 3).

values obtained using the proposed system and ICP-MS at the confidence level of 95%, demonstrating the accuracy and practicability of the proposed method. Although both the conventional ICP-MS and the proposed system can obtain satisfactory results, the proposed system provides several

Cn 100 C1 + C2 + C3 + C4 + C5

where En is the extraction efficiency of each extraction for analyte, Cn is the concentration (μg L-1) of Hg and Cd in eluent of the n-th extraction (n = 1, 2, 3, 4 or 5). As shown in Figure S6 (Section 8 in the SI), more than 90% of Hg and Cd can be extracted via three times extraction. In order to further validate these extraction efficiencies, the spiked blood sample was completely digested by microwave-assisted digestion method and subsequently analyzed by ICP-MS. Thus, the other method used for the evaluation of the extraction efficiencies of Cd and Hg is to compare the amounts of Cd and Hg obtained by the MSPD to those achieved using complete digestion coupling to ICP-MS analysis. The results indicate that the extraction efficiencies of 86% and 92% were obtained for Cd and Hg. The above results confirm that efficiently extraction of Cd and Hg from whole blood sample could be achieved by using this modified method of sample preparation, thus it was applied to couple to the flow injection CLED-OES/PIVG-AFS for the quantification of Cd and Hg in a single drop of blood. It should be noted that a standard addition method was applied to determine Hg and Cd in the real blood samples. The analytical results summarized in Table 3 show that Hg and Cd contained in most of the blood samples can be detected by PIVG-AFS, whereas none of them by CLED-OES. This is because that Hg and Cd levels in the tested samples are much lower than the LODs provided by the CLED-OES. In order to further evaluate the accuracy of the proposed method, standard solution containing various concentrations of Hg and Cd were spiked into the real blood samples before their MSPD procedure. The recoveries (91-114%) obtained by this analytical system for the spiked either low concentration or high concentration of Hg and Cd are summarized in Table 3, confirming the accuracy and the practicability of the analytical system on the determination of Hg and Cd in a single drop of blood with both high sensitivity and wide linearity. As can be seen from Table 2 and Table 3, the microwave assisted digestion leads much higher dilution factors and then provides worse imprecisions compared to the MSPD method.

Table 3. Analytical results of spiked elements



sample

element

Blood-1 Blood-2 Blood-3 Blood-4

Hg

PIVG-AFS detecteda (µg L-1) ND

Blood-6 a

founda (µg L-1) 1.08 ± 0.10

recovery (%) 108

CLED-OES detecteda (mg L-1) ND

added, (mg L-1) 1.00

founda (mg L-1) 0.97 ± 0.08

recovery (%) 97

Cd

1.02 ± 0.08

2.00

2.91 ± 0.23

95

ND

2.00

2.11 ± 0.14

105

Hg

5.75 ± 0.22

3.00

8.92 ± 0.41

106

ND

3.00

3.20 ± 0.11

106

Cd

1.56 ± 0.06

5.00

6.27 ± 0.36

94

ND

5.00

4.90 ± 0.23

98

Hg

1.64 ± 0.11

1.00

2.75 ± 0.25

111

ND

1.00

0.93 ± 0.05

93

Cd

4.02 ± 0.43

2.00

5.87 ± 0.41

93

ND

2.00

2.29 ± 0.27

114

Hg

6.15 ± 0.33

3.00

8.89 ± 0.45

91

ND

3.00

3.09 ± 0.32

103

94

ND

5.00

4.60 ± 0.24

92

Cd Blood-5

added, (µg L-1) 1.00

Page 8 of 10

2.40 ± 0.29

5.00

7.11 ± 0.39

Hg

ND

1.00

0.97 ± 0.05

97

ND

1.00

1.04 ± 0.08

104

Cd

3.56 ± 0.14

2.00

5.44 ± 0.28

94

ND

2.00

1.88 ± 0.19

94

3.00

2.97 ± 0.19

99

5.00

5.33 ± 0.31

106

Hg

2.67 ± 0.23

3.00

5.44 ± 0.17

92

ND

Cd

ND

5.00

4.79 ± 0.13

96

ND

Mean and standard deviation (n = 3)

Conclusion CLED-OES and PIVG-AFS can be integrated into a simple and novel analytical system simply by sharing one single capillary liquid electrode discharge, which has been successfully used for the simultaneous determination of Hg and Cd in a single drop of blood. Owing to the different linear-range and sensitivity of CLED-OES and PIVG-AFS, this analytical system can significantly improve the analytical figures of merit for microplasma atomic spectrometry, such as extending the linear range to six orders of magnitude and making the same sample simultaneously analyzed by OES and AFS. Meanwhile, the analytical system not only retains the reported advantages associated with flow injection CLED-OES, including the elimination of the use of a pump and a valve, high throughput and reduction of sample consumption to the nanoliter level, but also provides extremely low LODs for the detection of Hg and Cd. These are very beneficial to accurately analyze ultratrace toxic elements in microamounts of the sample, particularly those precious and rare samples with unknown concentration range of analyte. Additionally, the proposed system retains comparable linear ranges and LODs of ICPMS, but its sample-, energy- and Ar gas-consumption can be remarkably decreased. It is worth noting that the scope of elements amenable to this microplasma OES and PIVG-AFS determination has been readily broadening to Pb, Zn and other hydride-forming elements.54,55 Thus, the proposed system will retain the great potential for highly sensitive determination of other toxic elements in limited amounts of samples with high sensitivity and wide linear range.

Associated content Supporting Information. Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author

* E-mail: [email protected]. Fax and Phone: +86 28 8541 5810.

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors gratefully acknowledge the National Nature Science Foundation of China (Nos. 21529501, 21622508 and 21575092) and Ministry of Education of China through the 111 Project (B17030) for financial support.

REFERENCES (1) Thompson, K. H.; Orvig, C. Science 2003, 300, 936-939. (2) Gourdon, P.; Liu, X. Y.; Skjørringe, T.; Morth, J. P.; Møller, L. B.; Pedersen, B. P.; Nissen, P. Nature 2011, 475, 59-64. (3) Choi, J.; Ghaffari, R.; Baker, L. B.; Rogers, J. A. Sci. Adv. 2018, 4, eaar3921. (4) Huszank, R.; Csedreki, L.; Török, Z. Anal. Chem. 2017, 89, 1558-1564. (5) Arnaud, J.; Weber, J. P.; Weykamp, C. W.; Parsons, P. J.; Angerer, J.; Mairiaux, E.; Mazarrasa, O.; Valkonen, S.; Menditto, A.; Patriarca, M. Clin. Chem. 2008, 54, 1892-1899. (6) Parsons, P. J.; Barbosa, F. Spectrochim. Acta, Part B 2007, 62, 992-1003. (7) Angerer, J.; Ewers, U.; Wilhelm, M. Int. J. Hyg. Environ. Health 2007, 210, 201-228. (8) Runnels, J. H.; Merryfield, R.; Fisher, H. B. Anal. Chem. 1975, 47, 2438-2460. (9) Zheng, C. B.; Hu, L. G.; Hou, X. D.; He, B.; Jiang, G. B. Anal. Chem. 2018, 90, 3683-3691. (10) Luo, Y. J.; Yang, Y.; Lin, Y.; Tian, Y. F.; Wu, L.; Yang, L.; Hou, X. D.; Zheng, C. B. Anal. Chem. 2018, 90, 1547-1553. (11) Lin, Y.; Yang, Y.; Li, Y. X.; Yang, L.; Hou, X. D.; Feng, X. B.; Zheng, C. B. Environ. Sci. Technol. 2016, 50, 2468-2476.


Page 9 of 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12) Hu, L. G.; Cheng, T. F.; He, B.; Li, L.; Wang, Y. C.; Lai, Y. T.; Jiang, G. B.; Sun, H. Z. Angew. Chem. Int. Ed. 2013, 125, 50165020. (13) Tsang, C. N.; Ho, K. S.; Sun, H. Z.; Chan, W. T. J. Am. Chem. Soc. 2011, 133, 7355-7357. (14) Yan, X. W.; Yang, L. M.; Wang, Q. Q. Angew. Chem. 2011, 123, 5236-5239. (15) Zenobi, R. Science 2013, 342, 1243259. (16) Bendall, S. C.; Simonds, E. F.; Qiu, P.; Amir, E. D.; Krutzik, P. O.; Finck, R.; Bruggner, R. V.; Melamed, R.; Trejo, A.; Ornatsky, O. I. Science 2015, 332, 687-696. (17) Miyashita, S. I.; Groombridge, A. S.; Fujii, S. I.; Minoda, A.; Takatsu, A.; Hioki, A.; Chiba, K.; Inagaki, K. J. Anal. At. Spectrom. 2014, 29, 1598-1606. (18) Dettman, J. R.; Cassabaum, A. A.; Saunders, C. P.; Snyder, D. L.; Buscaglia, J. Anal. Chem. 2014, 86, 8176-8182. (19) Bian, Q. Z.; Jacob, P.; Berndt, H.; Niemax, K. Anal. Chim. Acta 2005, 538, 323-329. (20) Schaumlöffel, D.; Ruiz Encinar, J.; Łobiński, R. Anal. Chem. 2003, 75, 6837-6842. (21) Giusti, P.; Lobinski, R.; Szpunar, J.; Schaumlöffel, D. Anal. Chem. 2006, 78, 965-971. (22) Bings, N. H.; Niessen, J. O. O. V.; Schaper, J. N. Spectrochim. Acta, Part B 2014, 100, 14-37. (23) Venable, J. D.; Langer, D.; Holcombe, J. A. Anal. Chem. 2002, 74, 3744-3753. (24) Wallace, W. T.; Gazda, D. B.; Limero, T. F.; Minton, J. M.; Macatangay, A. V.; Dwivedi, P.; Fernández, F. M. Anal. Chem. 2015, 87, 5981-5988. (25) Jiang, X. M.; Chen, Y.; Zheng, C. B.; Hou, X. D. Anal. Chem. 2014, 86, 5220-5224. (26) Fernández, B.; Claverie, F.; Pécheyran, C.; Alexis, J.; Donard, O. F. X. Anal. Chem. 2008, 80, 6981-6994. (27) Liu, C.; Mao, X. L.; Mao, S. S.; Zeng, X.; Greif, R.; Russo, R. E. Anal. Chem. 2004, 76, 379-383. (28) Barst, B. D.; Gevertz, A. K.; Chumchal, M. M.; Smith, J. D.; Rainwater, T. R.; Drevnick, P. E.; Hudelson, K. E.; Hart, A.; Verbeck, G. F.; Roberts, A. P. Environ. Sci. Technol. 2011, 45, 8982-8988. (29) Olesik, J. W.; Hobbs, S. E. Anal. Chem. 1994, 66, 33713378. (30) Gschwind, S.; Hagendorfer, H.; Frick, D. A.; Günther, D. Anal. Chem. 2013, 85, 5875-5883. (31) Franze, B.; Strenge, I.; Engelhard, C. J. Anal. At. Spectrom. 2012, 27, 1074-1083. (32) Harrison, D. J.; Fluri, K.; Seiler, K.; Fan, Z.; Effenhauser, C. S.; Manz, A. Science 1993, 261, 895-897. (33) Lu, J. J.; Wang, S.; Li, G.; Wang, W.; Pu, Q.; Liu, S. Anal. Chem. 2012, 84, 7001-7007. (34) Zheng, C. B.; Li, Y.; He, Y. H.; Ma, Q.; Hou, X. D. J. Anal. At. Spectrom. 2005, 20, 746-750. (35) Luna, A. S.; Sturgeon, R. E.; de Campos, R. C. Anal. Chem. 2000, 72, 3523-3531. (36) Leng, A. Q.; Tian, Y. F.; Wang, M. X.; Wu, L.; Xu, K. L.; Hou, X. D.; Zheng, C. B. Chin. Chem. Lett. 2017, 28, 189-196. (37) Liu, X.; Liu, Z. F.; Zhu, Z. L.; He, D.; Yao, S. Q.; Zheng, H. T.; Hu, S. H. Anal. Chem. 2017, 89, 3739-3746. (38) Zhang, S.; Luo, H.; Peng, M. T.; Tian, Y. F.; Hou, X. D.; Jiang, X. M.; Zheng, C. B. Anal. Chem. 2015, 87, 10712-10718. (39) Zhang, S.; Tian, Y. F.; Yin, H. L.; Su, Y. B.; Wu, L.; Hou, X. D.; Zheng, C. B. Environ. Sci. Technol. 2017. (40) Leng, A. Q.; Lin, Y.; Tian, Y. F.; Wu, L.; Jiang, X. M.; Hou, X. D.; Zheng, C. B. Anal. Chem. 2017, 89, 703-710. (41) Zhu, Z. L.; Chan, G. C.-Y.; Ray, S. J.; Zhang, X. R.; Hieftje, G. M. Anal. Chem. 2008, 80, 7043-7050. (42) Li, Z. A.; Tan, Q.; Hou, X. D.; Xu, K. L.; Zheng, C. B. Anal. Chem. 2014, 86, 12093-12099.

(43) Liu, X.; Zhu, Z.; Li, H.; He, D.; Li, Y.; Zheng, H.; Gan, Y.; Li, Y.; Belshaw, N. S.; Hu, S. Anal. Chem. 2017, 89, 6827-6833. (44) Chen, Q.; Lin, Y.; Tian, Y. F.; Wu, L.; Yang, L.; Hou, X. D.; Zheng, C. B. Anal. Chem. 2017, 89, 2093-2100. (45) Oliveira, R. V.; Henion, J.; Wickremsinhe, E. Anal. Chem. 2014, 86, 1246-1253. (46) Huang, K.; Xu, K. L.; Hou, X. D.; Jia, Y.; Zheng, C. B.; Yang, L. J. Anal. At. Spectrom. 2013, 28, 510-515. (47) Krahling, T.; Michels, A.; Geisler, S.; Florek, S.; Franzke, J. Anal. Chem. 2014, 86, 5822-5828. (48) Li, Y.; Zhu, Z.; Zheng, H.; Jin, L.; Hu, S. J. Anal. At. Spectrom. 2016, 31, 383-389. (49) Zheng, C.; Hu, L.; Hou, X.; He, B.; Jiang, G. Anal. Chem. 2018, 90, 3683-3691. (50) Greda, K.; Swiderski, K.; Jamroz, P.; Pohl, P. Anal. Chem. 2016, 88, 8812-8820. (51) Liu, X.; Zhu, Z. L.; He, D.; Zheng, H. T.; Gan, Y. Q.; Belshaw, N. S.; Hu, S. H.; Wang, Y. X. J. Anal. At. Spectrom. 2016, 31, 1089-1096. (52) He, Q.; Zhu, Z. L.; Hu, S. H.; Zheng, H. T.; Jin, L. L. Anal. Chem. 2012, 84, 4179-4184. (53) Jamroz, P.; Greda, K.; Dzimitrowicz, A.; Swiderski, K.; Pohl, P. Anal. Chem. 2017, 89, 5729-5733. (54) Marcus, R. K.; Davis, W. C. Anal. Chem. 2001, 73, 29032910. (55) Cai, Y.; Zhang, Y. J.; Wu, D. F.; Yu, Y. L.; Wang, J. H. Anal. Chem. 2016, 88, 4192-4195.



For TOC only


Page 10 of 10

Integration of Flow Injection Capillary Liquid Electrode Discharge

Recommend Documents