Journal of Analytical Methods in Chemistry
Volume 2015 (2015), Article ID 372459, 18 pages
http://dx.doi.org/10.1155/2015/372459

Review Article

Recent Developments in the Speciation and Determination of Mercury Using Various Analytical Techniques

Lakshmi Narayana Suvarapu and Sung-Ok Baek

Department of Environmental Engineering, Yeungnam University, Gyeongsan-si 712 749, Republic of Korea

Received 8 May 2015; Accepted 15 June 2015

Academic Editor: Antony C. Calokerinos

Copyright © 2015 Lakshmi Narayana Suvarapu and Sung-Ok Baek. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

This paper reviews the speciation and determination of mercury by various analytical techniques such as atomic absorption spectrometry, voltammetry, inductively coupled plasma techniques, spectrophotometry, spectrofluorometry, high performance liquid chromatography, and gas chromatography. Approximately 126 research papers on the speciation and determination of mercury by various analytical techniques published in international journals since 2013 are reviewed.

1. Introduction

Mercury, which is also known as quick silver, is only the metal (Figure 1) in the modern periodic table that exists in liquid form at room temperature. The sources of mercury in the environment include the natural processes, such as breakdown of minerals in rocks and volcanic activities. The anthropogenic sources are not limited to mining and the burning of fossil fuels. Regarding the toxicity of mercury and its different species, methylmercury poisoning affects the nervous system of humans and damages the brain and kidneys [1]. Most of the mercury emitted into the environment is converted to methylmercury, which spreads to the food chain due to the bioaccumulation nature of methylmercury [2]. Owing to the toxicity nature and bioaccumulation nature of mercury, most studies in this area have focused on the determination of mercury and its species in various environmental and biological samples.

Figure 1: Elemental mercury.

Marumoto and Imai [3] reported the determination of dissolved gaseous mercury in the seawater of Minamata Bay of Japan. This study also estimated the exchange of mercury across the air-sea interface. Panichev and Panicheva [4] reported the determination of the total mercury content in fish and sea products by thermal decomposition atomic absorption spectrometry. Fernández-Martínez et al. [5] evaluated different digestion systems for the determination of mercury with CV-AFS (cold-vapor atomic fluorescence spectrometer) in seaweeds. Pinedo-Hernández et al. [6] examined the speciation and bioavailability of mercury in sediments that had been impacted by gold mining in Colombia.

This paper presented the recent developments in this topic after a previous review published in 2013 [2]. The present study reviews the recent developments in the speciation and determination studies of mercury reported and published since 2013. For this purpose, approximately 136 research papers published were reviewed. All the analytical parameters such as limit of detection, linearity range, and interference study reported by the reviewed papers are presented in Tables 1–4 [7–133]. This extensive collection of literature and the analytical parameters of the reviewed papers established the recent developments in the determination and speciation studies of mercury using a range of analytical techniques.

2. Discussion

The toxicity and bioaccumulation nature of mercury has prompted extensive studies to determine the concentrations of mercury species in different environmental and biological samples. This paper reviewed a large number of studies on the determination and speciation of toxic metals including mercury. The reviews regarding the determination of mercury published since 2013 are discussed hereunder.

Suvarapu et al. [2] reviewed research papers published between 2010 and 2011 regarding the speciation and determination of mercury using a variety of analytical techniques. They concluded that most researchers prefer cold-vapor atomic absorption spectrometry (CV-AAS) and atomic absorption spectrofluorometry (CV-AFS) for the speciation and determination studies of mercury in various environmental samples. Suvarapu et al. [134] also reviewed research papers published in 2012 regarding the determination of mercury in various environmental samples. El-Shahawi and Al-Saidi [135] reviewed the dispersive liquid-liquid microextraction (DLLME) method for the speciation and determination of metal ions including mercury. This review concluded that the method of DLLME has the advantages of simplicity, speed, and low cost for the determination of metal ions using various analytical techniques. Ferreira et al. [136] reviewed the use of reflux systems for the sample preparation in the determination of elements, such as arsenic, antimony, cadmium, lead, and mercury. This study concluded that the use of the reflux systems is very rare in the determination of elements, such as Hg. Gao et al. [137] reviewed the application of chemical vapor generation method for the determination of metal ions, such as mercury and cadmium with ICP-MS. Sańchez et al. [138] reviewed the determination of trace elements including mercury present in petroleum products using ICP techniques. This study concluded that the electrothermal vaporization and laser ablation methods were promising for the analysis of petroleum for trace elements. Martín-Yerga et al. [139] reviewed the determination of mercury using electrochemical methods. This study discussed the advantages and disadvantages of the use of different electrodes in the determination of mercury. Chang et al. [140] reviewed the detection of heavy metals, such as cadmium, lead, and mercury in water samples using graphene based sensors. This study concluded that it is a very challenging task to detect heavy metals in water in real time due to the interference of large chemical and biological species in water. Yu and Wang [141] reviewed the determination of metal ions including mercury by atomic spectrometry by applying flow-based sample pretreatment methods. They concluded that the ICP-AES, AAS, AFS, and ICP-MS are the major detection techniques for trace metal analysis. Yin et al. [142] reviewed the speciation analysis of mercury, arsenic, and selenium using a range of analytical techniques. Gao and Huang [143] reviewed the determination of mercury(II) ions by voltammetry and concluded that stripping voltammetry is still an active field of research regarding the determination of mercury. Duarte et al. [144] reviewed disposable sensors and electrochemical sensors for the environmental monitoring of Pb, Cd, and Hg. They recommended the recycling of materials used in sensors for future studies. Recently, Ferreira et al. [145] reviewed the analytical strategies of sample preparation for the determination of mercury in food matrices.

In recent days, few research papers were published about the determination and analysis of mercury species in various environmental and biological samples and some of them are discussed hereunder. Lima et al. [146] reported an efficient method for the determination of mercury in inorganic fertilizers by using CV-AAS combined with microwave-induced plasma spectrometry. Pelcová et al. [147] reported the simultaneous determination of mercury species by LC-AFS with a low detection limit of 13–38 ng L⁻¹. Chen et al. [148] reported a colorimetric method for the determination of mercury ions based on gold nanoparticles and thiocyanuric acid. Fernández et al. [149] reported gold nanostructured screen-printed carbon electrodes for the determination of mercury using dispersive liquid-liquid microextraction. Fernández-Martínez et al. [5] evaluated the different digestion systems for determination of mercury in seaweeds using CV-AFS. Silva et al. [150] determined the trace amounts of mercury in alcohol vinegar samples collected from Salvador, Bahia of Brazil. Jarujamrus et al. [151] reported a colorimetric method using unmodified silver nanoparticles for the determination of mercury in water samples. A highly selective method for the determination of mercury using a glassy carbon electrode modified with nano-TiO₂ and multiwalled carbon nanotubes in river and industrial wastewater was reported by Mao et al. [152].

As mentioned in our previous review [2], spectrometric techniques are used widely by many researchers for the determination of mercury over the world. Regarding the determination of mercury with various analytical instruments in the papers reviewed, more than 55% of the researchers used spectrometric instruments, such as atomic absorption spectrometry (AAS), inductively coupled plasma techniques (ICP-OES, AES, and MS), and atomic fluorescence spectrometer (AFS) (Table 1). ICP-MS technique has an advantage of low detection limits and wide range of linearity in the determination of mercury [153]. Around 20% of the researchers chose the spectrophotometer and spectrofluorometer (Table 2) for the determination and speciation of mercury. Approximately 10% of researchers in the papers reviewed used electrochemical instruments for the determination and speciation studies of mercury (Table 3). Only a few authors chose the HPLC, GC, and other techniques (Table 4) but they coupled these instruments with AAS or other instruments. Regarding the analysis of the environmental biological samples for mercury and its species, most researchers analyzed various water samples (drinking, seawater, wastewater, river, and lake waters) followed by food samples (mostly fish), human hair, and ambient air. Only a few authors determined the concentration of mercury in ambient air and atmospheric particulate matter [26, 48, 52, 66, 119, 126]. Various measurement techniques that can be available for the determination of mercury species in ambient air were reviewed by Pandey et al. [154]. This study also concluded that most of the researchers preferred CV-AAS and CV-AFS technique for the measurement of different mercury species in ambient air. In comparison of methods, acid digestion and thermal method, for the analysis of mercury in ambient air acid digestion, is better than thermal method. By the thermal methods the values can be obtained 30% lower than the acid digestion method [155].

Table 1: Analytical parameters of reviewed research papers about the speciation and determination of mercury by spectrometric instruments (AAS, ICP-OES, AES, MS, and AFS).

S. number
Analyte
Analytical instrument used for the detection
Method
Limit of detection (LOD)#
Linearity range
Analyzed samples
Interference study
Supporting media
Reference

1
Total Hg
CV-AAS and ICP-AES
Microwave acid digestion
4.83 × 10⁻¹⁰ M
—
Fish samples
Cadmium and lead also analyzed along with mercury
—
[7]

2
Hg(II)
CV-AAS
Preconcentration
1.79 × 10⁻¹⁰ M
—
Water and human hair
Recovery of Hg²⁺ is in the range of 95.6–104.9% in presence of Cu²⁺, Co²⁺, Zn²⁺, Ni²⁺, Cd²⁺, Mn²⁺, Ba²⁺, Pb²⁺, Fe³⁺, Cr³⁺, Al³⁺, Ag⁺, K⁺, Na⁺, , Mg²⁺, and Ca²⁺ ions, from 750 to 2500-fold
Dithizone
[8]

3
Total Hg
CV-AAS
Ultrasound extraction
6.98 × 10⁻¹¹ M
—
Alcohol vinegar
—
—
[9]

4
Total Hg
CV-AAS
SPE¹
4.98 × 10⁻¹¹ M

Rice, canned fish, and tea leaves
The tolerance limit for Na⁺, K⁺, Mg²⁺, and Ca²⁺ is 4000-fold, for Ba²⁺ and Zn²⁺ is 40-fold, for Fe³⁺, Cr³⁺, Co²⁺, and Ni²⁺ is 10-fold, and for Al³⁺ is 200-fold compared to Hg²⁺
Fe₃O₄ nanoparticles
[10]

5
Hg(II)
CV-AAS
SPE
9.97 × 10⁻¹² M
Up to 500 μg L⁻¹
Water samples
As, Al, Fe, Mo, and Sb are depressed the Hg signal
Carbon nanotubes
[11]

6
Total Hg
CV-AAS
Acid digestion
3.6 × 10⁻⁹ M
—
Marine fish
—
—
[12]

7
Total Hg
CV-AAS
Wet digestion
3.0 × 10⁻⁹ M
—
Green tiger shrimp
Arsenic also determined along with mercury
—
[13]

8
Total Hg
CV-AAS
Alkaline fusion digestion
0.06 ng g⁻¹
0.006–4000 ng g⁻¹
Phosphate rock
—
—
[14]

9
THg
AAS
Acid digestion
4.98 × 10⁻¹² M
—
Fish muscle tissues
Cadmium and lead also detected along with mercury
—
[15]

10
Hg(II)
CV-AAS
SPE
1.19 × 10⁻¹¹ M
0.01–2.30 μg L⁻¹
Water samples
Fe³⁺, Cu²⁺, Zn²⁺, Cd²⁺, Co²⁺, and Mn²⁺ are not interfered up to 5 mg L⁻¹ and and Tl³⁺ are not interfered up to 1 mg L⁻¹
Polymer supported ionic liquid
[16]

11
Hg(II)
CV-AAS
SPE
9.97 × 10⁻¹¹ M
0.07–2.00 μg L⁻¹
Water samples
Tolerable amount of major metals is limited up to 50 μg L⁻¹
Polytetrafluoroethylene
[17]

12
Total Hg
CV-AAS
Digestion
3.98 × 10⁻¹⁰ M
2.5–10.0 μg L⁻¹
Biological samples
—
Cold finger
[18]

13
Total Hg
CV-AAS
Combustion
2.99 × 10⁻¹³ M
—
Water and fish
Arsenic and selenium also determined along with mercury
—
[19]

14
Total Hg
AAS
Amalgamation
0.2 ng/g for hair and 0.02 ng/g for blood
—
Hair and blood samples
Arsenic and selenium also determined along with mercury
—
[20]

15
Total Hg
CV-AAS (total Hg) and GC-ICPMS (MeHg)
Cold-vapor reduction with NaBH₄
5.98 × 10⁻¹¹ M (total Hg) and 2.3 × 10⁻⁹ M (MeHg)
—
Blood of birds
Selenium also determined along with mercury and methylmercury
—
[21]

16
Total Hg and MeHg
CV-AAS (total Hg) and CV-AFS (MeHg)
Digestion
0.03–0.1 ng/g
—
Fish, vegetables, and mushrooms
Selenium and cadmium also determined with mercury species
—
[22]

17
Hg speciation
CV-AAS (total Hg) and CV-AFS (MeHg)
Acid digestion
—

Water samples
—
—
[23]

18
Hg speciation
CV-AAS
LLME²
1.49 × 10⁻¹⁰ M (Hg²⁺) and
1.8 × 10⁻⁹ M (MeHg)
0.5–100 ng mL⁻¹
Water samples and CRMs
The recovery of Hg²⁺ in presence of foreign ions is 95–105 and for MeHg is 96–106%
—
[24]

19
Total Hg
GF-AAS
Acid mineralization
6.97 × 10⁻¹¹ M
—
Fish muscle samples
—
Copper nitrate
[25]

20
GEM
AAS

Ambient air
—
—
[26]

21
Total Hg
CV-AAS
Acid digestion
0.0006 μg g⁻¹
—
Freshwater fish samples
—
Stannous chloride
[27]

22
Total Hg
AAS
Combustion
0.01 ng
—
Soil samples
Interference of various heavy metals was overcome by using sample pretreatment
—
[28]

23
Hg speciation
AAS (THg) and ICP-MS-HPLC (MeHg)
Hydride generation
5.33 × 10⁻¹⁴ M
20 μg L⁻¹
Fish samples
Cd, Pb, As, and Sn also measured along with Hg
—
[29]

24
THg
HG-AAS
Hydride generation
98.4% (accuracy)
—
Irrigation water wells
Along with mercury Pb, Cd, and Al Cr also measured
—
[30]

25
THg
CV-AAS and AAS
Thermal decomposition and amalgamation
1.34 × 10⁻⁹ M (TD-amalgamation AAS) and 3.14 × 10⁻⁹ M (CV-AAS),
—
Soil samples
—
—
[31]

26
Total Hg speciation
HV-AAS and
HPLC-CV-AFS
Extraction
—
—
Aqueous solutions and fish tissue
—
Multiwalled carbon nanotubes
[32]

27
Total Hg
CV-AAS (DMA)
Microwave oven digestion
—
—
Canned fish
Selenium and tin also measured along with mercury
—
[33]

28
THg
AMA (AAS)
AAS principles and without digestion process
—
—
Fish red muscle and
white muscle
—
—
[34]

29
THg
AES
LIBS and SIBS
2 × 10⁻³ M (LIBS) and 9.97 × 10⁻⁵ M (SIBS)

Soil samples
At 534.074 nm has less spectral interference
—
[35]

30
Hg speciation
CV-AFS
Extraction
1.0 (total Hg) and 0.01 MeHg ng g⁻¹
—
Sea water and sediments
—
—
[36]

31
Hg speciation
CV-AFS
Extraction
0.01 × 10⁻¹² M (Hg⁰) and 0.002 × 10⁻¹² M (DM Hg)
—
Sea waters
—
—
[37]

32
Total Hg
CV-AFS
Microwave assisted digestion
3.98 × 10⁻¹³ M
—
Nuts
Interference of fat in nuts is removed by treatment with chloroform and methanol
—
[38]

33
Hg(II)
AFS
Fluorescence optical sensor
9.57 × 10⁻¹² M
2.27 × 10⁻¹¹–1.13 × 10⁻³ M
Human hair, urine, and
well water samples
Most of the alkali, alkaline, and transition metal ions did not interfere in the determination of Hg²⁺
N-(2-Hydroxy phenyl)-N-(2-mercapto phenyl)-o-phthalylidene
[39]

34
GEM
CV-AFS
Gold amalgamation
0.0002 ng
—
Total suspended particulates
—
QFF (quartz fiber filters)
[40]

35
MeHg
AAS and CV-AFS
Acid digestion
0.005 μg/g
—
Water, soil, sediments, and foodstuffs
—
—
[41]

36
Total Hg
CV-AFS
Microwave assisted digestion
0.5 ng g⁻¹
—
Sediments
—
Sequential injection system
[42]

37
Total Hg
CV-AFS
Acid digestion
0.48 ng g⁻¹
—
Rice
Interference of other metal ions is eliminated by acid wash and kept storage of samples for 24 h
Multisyringe flow injection analysis
[43]

38
Hg speciation
HPLC-AFS
UV-induced atomization
1.9 × 10⁻⁹ (Hg²⁺), 1.9 × 10⁻⁹ (MeHg), and 2.0 × 10⁻⁹ (EtHg) M

CRMs
—
—
[44]

39
Hg(II)
UV-AFS
SPE
1.49 × 10⁻¹³–3.98 × 10⁻¹³ M
1–5000 ng L⁻¹
Natural waters
10 mg L⁻¹ of Fe²⁺, Fe³⁺, Cu²⁺, Pb²⁺, and As³⁺ and 10 g L⁻¹ of Na⁺, K⁺, and Ca²⁺ did not interfere in the determination of 100 ng L⁻¹ of Hg²⁺
Sodium diethyldithiocarbamate
[45]

40
Hg(II)
AFS
Micro-SPE
5.98 × 10⁻¹¹ M
Up to 5 μg L⁻¹
Water samples
—
Mesofluidic platform
[46]

41
Hg speciation
EX-AFS

0.5 ng g⁻¹ (total Hg)
—
Waste calcines
—
—
[47]

42
Hg speciation
CV-AFS
Extraction
~0.5 pg
—
Atmospheric air
—
PTFE filter papers
[48]

43
MeHg
GC-AFS
SPE
12 ng g⁻¹
Up to 1.5 ng mL⁻¹
Biological samples
—
—
[49]

44
Hg speciation
HPLC-AFS
Liquid-liquid microextraction
1.54 × 10⁻¹⁰ (Hg²⁺), 7.42 × 10⁻¹¹ (MeHg), 1.045 × 10⁻¹⁰ (EtHg), and 3.31 × 10⁻¹⁰ M (PhHg)
0.0–20 μg L⁻¹
Environmental waters
No interference from other metal ions
1-Octyl-3-meth-l imidazolium hexafluorophosphate
[50]

45
MeHg
CV-AFS
Extraction
0.515 ng g⁻¹
—
Petroleum
—
TMAH³, KOH/CH₃OH, HCl, and acidic CuSO₄/KBr
[51]

46
GEM
CV-AFS
—
—
—
Ambient air
—
—
[52]

47
Hg(II)
AFS
Fluorescence
0.07  10⁻⁶ M
0.1–4.5 μM
Aqueous solutions
Longer excitation and emission wavelength could shield the interference
Fe₃O₄ magnetic nanoparticles
[53]

48
Hg speciation
CV-AFS
Thermal decomposition
—
—
Fish liver
Method validity is tested with CRM
—
[54]

49
THg
AFS
—
<4.98 × 10⁻¹² M
—
Snow
—
K₂Cr₂O₇/SnCl₂
[55]

50
Atmospheric Hg
CV-AFS
Extraction
—
—
Particulate matter
—
—
[56]

51
THg
CV-AFS
Flow injection mercury system
—
—
Herbal products
—
Protease papain
[57]

52
Hg speciation
LC-UV-CV-AFS
Microwave digestion
4.98 × 10⁻¹² (total Hg), 1.39 × 10⁻¹² (MeHg), and 1.99 × 10⁻¹² (Hg²⁺) M
—
Sea food
Simultaneously determined both Hg(II) and MeHg
—
[58]

53
MeHg and total Hg
CV-AAS
Digestion
0.088 (MeHg) and 0.005 (total Hg) μg g⁻¹
—
Hair and milk of mothers
—
—
[59]

54
Hg(II)
ICP-MS
Microfluidic
3.49 × 10⁻¹⁰ M
0.2–4.0 μg L⁻¹
Aqueous samples
The recovery of Hg²⁺ in the presence of 100 μg L⁻¹ of Ca²⁺, Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, K⁺, Mg²⁺, Na⁺, Ni²⁺, Pb²⁺, and Zn²⁺ is in the range of 97.5–101.7%
Gold nanoparticles
[60]

55
Total Hg
ICP-MS
Acid digestion
0.053–0.01 μg g⁻¹
—
Pharmaceutical ingredients
Low residual carbon content in digests is desirable to minimize some interference
—
[61]

56
Hg(II)
ICP-MS
Adsorption
—
—
Wastewaters
—
Multiwalled carbon nanotubes
[62]

57
Hg(II)
ICP-OES
Extraction
1.49 × 10⁻¹¹ M
—
Fish samples
Selective in presence of Na⁺, K⁺, Cs⁺, Ca²⁺, Mg²⁺, Zn²⁺, Fe²⁺, Cu²⁺, Co²⁺, Ni²⁺, Mn²⁺, Cd²⁺, and Pb²⁺ into 1 mg L⁻¹ solutions of Hg(II) in pH 8
Ion imprinted polymer
[63]

58
Total Hg
CV-ICP-MS
Microwave digestion
3 ng g⁻¹
—
Plants and soil
—
—
[64]

59
Total Hg
ICP-MS
Microwave assisted digestion
—
—
Rice
—
—
[65]

60
GEM
CV-ICP-MS
Thermal analysis
20 × 10⁻¹⁵ g
—
Atmospheric particulates
—
—
[66]

61
Hg(II) and MeHg
HPLC-ICPMS
HF-LPME⁴
5.48 × 10⁻¹⁰  (Hg²⁺) and 1 × 10⁻⁹  (MeHg) M
Up to 50 μg L⁻¹
Tap, river, and estuarine waters
Simultaneously selenium also determined along with mercury
—
[67]

62
Hg speciation
ICP-MS
Ion exchange chromatography
9.47 × 10⁻¹¹  (Hg²⁺), 1.25 × 10−10  (MeHg), 1.35 × 10⁻¹⁰  (EtHg), and 7.92 × 10⁻¹⁰  (PhHg) M
0.1–100 μg L⁻¹ (all Hg species)
Sea water and marine fish
—
L-Cysteine or thiourea
[68]

63
Hg speciation
GC-ICP-MS
Preconcentration
27 (Hg²⁺) and 12 ng g⁻¹ (MeHg)
—
Human hair
—
—
[69]

64
Total Hg
MC-ICPMS
Isotope ratio analysis
0.1–0.2 disintegrations per minute
—
Sediment core
Mercury and mercury isotope compositions are determined
—
[70]

65
Hg(II) and MeHg
CVG-ICP-MS
Extraction
1.7 (Hg(II)) and 2.3 ng g⁻¹ (MeHg)
—
Fish samples
—
—
[71]

66
MeHg, Hg(II), and
EtHg
HPLC-CV-ICPMS
Extraction and separation
5.98 × 10⁻¹¹ (Hg(II)), 2.17 × 10⁻¹¹ (EtHg), and 1.8 × 10⁻⁸ (MeHg) M
—
Plasma/serum samples
—
—
[72]

67
Total Hg
ICP-MS
Microwave assisted digestion
—
—
Freshwater fish samples
—
—
[73]

68
Total Hg
ICP-MS
Isotope dilution and UV-photochemical vapor generation
0.5 pg g⁻¹
—
Biological tissues
Polyatomic interference is not detectable
Formic acid
[74]

69
Total Hg
ICP-MS
Calcination-isotope dilution
2 × 10⁻¹⁵ M
—
Diploria specimens
No isobaric interference was found
—
[75]

70
Hg speciation
ICP-MS
Anion exchange chromatographic separation
3.98 × 10⁻¹¹ (Hg²⁺), 1.11 × 10⁻¹⁰ (MeHg), 1.26 × 10⁻¹⁰ (EtHg), and 1.22 × 10⁻¹⁰ (PhHg) M
—
Fish samples
—
3-Mercapto-1-propanesulfonate
[76]

71
Total Hg
ICP-MS
Ultrasonic slurry sampling electrothermal vaporization
0.2 ng g⁻¹
—
Herbal samples
As, Cd, and Pb also determined along with Hg
8-Hydroxyquinoline
[77]

72
Total Hg
ICP-MS
Electrothermal vaporization
5.98 × 10⁻¹¹ M
—
Water associated with crude oil production
By preconcentration of analyte interference is avoided
—
[78]

73
THg
ICP-MS
Isotope dilution equation
4.98 10⁻¹¹ M for THg
0.0005–1.321 mg/kg for MeHg
Arctic cod
—
—
[79]

For the conversion of limit of detection values into moles per liter (M) the atomic weight of Hg is taken as 200.59 g, MeHg as 215.59 g, EtHg as 229.59 g, and PhHg as 277.59 g.

¹Solid-phase extraction; ²LLME: liquid-liquid microextraction; ³TMAH: tetramethylammonium hydroxide; ⁴HF-LPME: hallow fiber liquid phase microextraction.

Analytical instruments: CV-AAS: cloud vapor atomic absorption spectrometer; HG-AAS: hydride generation AAS; GF-AAS: graphite furnace AAS; ICP-OES: inductively coupled plasma optical emission spectrometer; ICP-MS: ICP-mass spectrometer; ICP-AES: ICP-atomic emission spectrometer; HPLC: high performance liquid chromatography; AFS: atomic fluorescence spectrometer; AMA: automatic mercury analyzer; DMA: direct mercury analyzer.

Table 2: Analytical parameters of reviewed research papers about the speciation and determination of mercury by spectrophotometer and spectrofluorometer.

S. number
Analyte
Analytical instrument used for the detection
Method
Limit of detection (LOD)#
Linearity range
Analyzed samples
Interference study
Supporting media
Reference

1
Hg(II)
Fluorescence spectrophotometer
Fluorescence
4.0 × 10⁻⁹ M
6.0–450 nM
Water samples
10-fold of Pb²⁺, Cu²⁺, and Ag⁺ shows <7% influence on the determination of Hg²⁺ compared to reported ones
CdTe quantum dots
[80]

2
Hg(II)
Spectrophotometer
Colorimetric
23 × 10⁻⁹ M
0.00–0.31 μM
River water
Selective in presence of Ag⁺, Cd²⁺, Cu²⁺, Co²⁺, Ni²⁺, and Pb²⁺
Carbon nanodots
[81]

3
Hg(II)
Spectrophotometer
Colorimetric
2.6 × 10⁻⁹ M
0.001–1 μM
Water samples
Selective in presence of 20 μM of Al³⁺, Ca²⁺, Co²⁺, Cu²⁺, Cd²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺
Gold nanoparticles
[82]

4
Hg(II)
Spectrophotometer
Colorimetric
—
0.83–8.6 μg mL⁻¹
Water samples
The tolerance limit of Cu²⁺, V⁵⁺, Ag⁺, Pd²⁺, Pt⁴⁺, Au³⁺, Fe²⁺, Ni²⁺, Cd²⁺, Pb²⁺, and Cr⁶⁺ is in the range of 0.11–041 μg mL−1 in the determination of 1.91 μg mL⁻¹ of Hg²⁺
5-Methylthiophene-2-carboxaldehyde ethylenediamine
[83]

5
Hg(II)
Spectrofluorometer
Fluorescence
1.73 × 10⁻⁹ M
2.0 nM–60 μM
—
Interference of major cations studied
ONPCRs¹
[84]

6
Hg(II)
Spectrophotometer
Colorimetric
50 × 10⁻⁹ M²
0–1000 nM
Water samplers
Selective in presence of Ni²⁺, Co²⁺, Ca²⁺, Cu²⁺, Na⁺, K⁺, As³⁺, Mg²⁺, Cd²⁺, and Fe²⁺
Silver nanoparticles
[85]

7
Hg(II)
UV-Vis spectrophotometer
Colorimetric
1.35 × 10⁻⁶ M
—
Drinking water
Cd²⁺, Pb²⁺, Fe³⁺, and Ba²⁺ do not interfere in the determination of Hg²⁺ but Mg²⁺, Ca²⁺, and Mn²⁺ interfere slightly
Gold nanoparticles
[86]

8
Hg(II)
Spectrofluorometer and UV-spectrometer
Colorimetric and fluorescent sensor
2.7 × 10⁻⁸ M
0–1.0 × 10⁻⁶ M
Water samples and living cells
The fluorescent signal for Hg(II) is not influenced by the major metal ions including Fe(III), Cu(II), and Al(III)
2,4-Dichloroquinazoline
[87]

9
Hg(II)
Spectrophotometer
Colorimetric
5.3 × 10⁻¹³ M
1.0 × 10⁻¹²–8.6 × 10⁻⁴ M
Water samples and SRM
Selective in presence of Mn²⁺, Fe²⁺, Fe³⁺, Ni²⁺, Co²⁺, Cd²⁺, and Pb²⁺
Chromoionophore V
[88]

10
Hg(II)
Spectrofluorometer
Fluorescent and colorimetric
1.0 × 10⁻⁹ M
—
Spiked water samples
Na⁺, Mg²⁺, K⁺, Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, and Pb²⁺ did not interfere
Rhodamine B
[89]

11
Hg(II)
Spectrofluorometer
Fluorescence
14.2 × 10⁻⁹ M
0–5 × 10⁻⁷ M
Aqueous solutions
Cd²⁺, Cu²⁺, and Ag⁺ do not interfere
Thioether-appended dipeptide
[90]

12
Hg(II)
Spectrofluorometer
Fluorescence
0.5 × 10⁻⁹ M
0.0005–0.01 μM
Lake water samples
Zn²⁺, Pb²⁺, Ni²⁺, Ca²⁺, Mg²⁺, Cu²⁺, Co²⁺, Cd²⁺, Fe³⁺, and Mn²⁺ did not interfere
Carbon nanotubes
[91]

13
Hg(II)
Spectrofluorometer
Fluorescent
1.74–3.83 × 10⁻⁶ M
—
Living cells
Minor interference from Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, Rb⁺, and Zn²⁺
Pyrene
[92]

14
Hg(II)
Spectrophotometer
Colorimetric
0.4 × 10⁻⁶ M
0.1–4.2 μg mL⁻¹
Water, biological, plant leaves, and soil samples
Tolerance limit of the Cd²⁺, Zn²⁺, Ce³⁺, Ce⁴⁺, In³⁺, Cr³⁺, La³⁺, Yb³⁺, and Eu³⁺ is 300 μg mL⁻¹ and the tolerance limit of the Co²⁺, Cu²⁺, Fe³⁺, Ti⁴⁺, Pb²⁺, Ni²⁺, and Ag⁺ is 100 μg mL⁻¹ and at Hg(II) is 2.0 μg mL⁻¹
2,4,7-Triamino-6-phenylpteridine
[93]

15
Hg(II)
Spectrofluorophotometer
Fluorescent
1.0 × 10⁻⁷ M
2.0 × 10⁻⁷–3.0 × 10⁻⁵ M
Water samples
Selective in presence of Na⁺, K⁺, , Ba²⁺, Zn²⁺, Cd²⁺, Mg²⁺, Ca²⁺, and Ni²⁺
Conjugated polymer multilayer films
[94]

16
Hg(II)
Spectrophotometer
TGFRET³
0.49–0.87 × 10⁻⁹ M
1.0 × 10⁻⁹–1.0 × 10⁻⁸ M
Water samples
Selective in presence of Mn²⁺, Ba²⁺, Ni²⁺, Cu²⁺, Ca²⁺, Cr²⁺, Co²⁺, Cd²⁺, Mg²⁺, Zn²⁺, Al³⁺, Fe³⁺, and Pb²⁺
Gold nanoparticles
[95]

17
Hg(II)
Spectrofluorometer
Fluorescent
1 × 10⁻⁹ M
0.01–0.12 μM
Water samples
Selective in presence of Zn²⁺, Pb²⁺, Ni²⁺, Co²⁺, Ca²⁺, Cu²⁺, Mg²⁺, Cd²⁺, Fe³⁺, and Mn²⁺
Carbon nanodots
[96]

18
Hg(II)
Spectrofluorometer
Fluorescent
0.012 × 10⁻⁶ M
0-1 μM
Tap and river water samples
Selective in presence of Ag⁺, Pb²⁺, Na⁺, K⁺, Cr³⁺, Cd²⁺, Ba²⁺, Zn²⁺, Mg²⁺, Cu²⁺, Ni²⁺, Ca²⁺, Al³⁺, and Fe³⁺
Rhodamine
[97]

19
Hg(II)
Spectrofluorometer
Fluorescence
2.24 × 10⁻⁹ M
5.0–100 nM
Drinking water
20-fold of Ca²⁺, Mg²⁺, Zn²⁺, Cr³⁺, Pb²⁺, Cr⁶⁺, Mn²⁺, Cd²⁺, Fe³⁺, Al³⁺, and Ni²⁺, 10-fold of Fe²⁺, and Co²⁺, 5-fold of Cu²⁺, and the same concentration of Ag⁺ caused almost no interference
Gold nanoparticles
[98]

20
Hg(II)
Spectrophotometer
Optical chemical sensor
0.18 × 10⁻¹² M
7.2 × 10⁻¹³–4.7 × 10⁻⁴ M
Tap water, river water, and canned tuna fish
Interference of Cu(II) eliminated with the addition of L-histidine as a masking agent
Synthesized ionophore
[99]

21
Hg(II)
UV-Vis spectrophotometer
Colorimetric sensor
5.0 × 10⁻⁶ M (visual), 1.0 × 10⁻⁷ M (UV-Vis)
—
Aqueous solutions
Mg²⁺, Ca²⁺, Zn²⁺, Cu²⁺, Cr³⁺, Fe³⁺, Pb²⁺, Ni²⁺, Co²⁺, and Ag⁺ did not interfere
Dimethyl sulphoxide
[100]

22
Hg(II)
Fluorescence spectrophotometer
Fluorescence probe
16 × 10⁻⁹ M
0.02–1.0 μM
Aqueous solutions
Selective in the determination of Hg²⁺ over other metal ions such as Fe³⁺, Ca²⁺, Mg²⁺, Mn²⁺, Cr³⁺, Ni²⁺, Cu²⁺, Co²⁺, and Pb²⁺
Gold nanoparticles
[101]

23
Hg(II)
—
Colorimetric
1.2 × 10⁻⁹ M
2–30 nM
Water samples
Na⁺ (2 mM), K⁺ (2 mM), Fe³⁺, Zn²⁺ and Mg²⁺ (0.1 mM), Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺ and Cu²⁺ (50 μM), and Ag⁺ (3.5 μM) did not interfere with the detection of Hg²⁺ (25 nM) in the mentioned amounts
Rhodamine B thiolactone
[102]

For the conversion of limit of detection values into moles per liter (M) the atomic weight of Hg is taken as 200.59 g, MeHg as 215.59 g, EtHg as 229.59 g, and PhHg as 277.59 g.

¹ONPCRs: oxygen-doped nitrogen-rich photoluminescent polymer carbon nanoribbons; ²Limit of quantification; ³TGFRET: time-gated fluorescence resonance energy transfer.

Table 3: Analytical parameters of reviewed research papers about the speciation and determination of mercury by electrochemical instruments.

S. number
Analyte
Analytical instrument used for the detection
Method
Limit of detection (LOD)#
Linearity range
Analyzed samples
Interference study
Supporting media
Reference

1
Hg(II)
DP-ASV
Electrochemical
4.99 × 10⁻⁸ M
—
Ambient water, tap, and wastewaters
Palladium-natural phosphate-carbon paste electrode enhances the selectivity for Hg²⁺
Natural phosphate electrodes
[103]

2
Hg(II)
SW-ASV
Electrochemical
0.04 × 10⁻⁶ M
0.2–10.0 μM
Foodstuffs
Simultaneously both Cd²⁺ and Hg²⁺ are determined and 1,000-fold for K⁺, Na⁺, Li⁺, , Ca²⁺, Mg²⁺, Pb²⁺, Zn²⁺, Cr³⁺, Fe²⁺, Co²⁺, and Al³⁺ did not interfere
Carbon paste electrode
[104]

3
Hg(II)
Differential pulse voltammeter
Electrochemical
4.48 × 10⁻¹⁰ M
0.2–10 μg L⁻¹
Spiked fish and plant samples
Cu(II), Mg(II), As(III), and Cr(II) were possible interferers
4,4′-Bipyridine-silver polymer
[105]

4
Hg(II)
Cyclic voltammeter
Electrochemical
0.8 × 10⁻¹⁴ M
10⁻¹⁴–10⁻⁷ M
—
Cu²⁺, Pb²⁺, Ni²⁺, Zn²⁺, Cr3⁺, Co³⁺, As⁵⁺, Fe²⁺, and Fe³⁺ did not interfere
Gold atomic cluster-chitosan
[106]

5
Hg(II)
Voltammeter
(cyclic and differential pulse)
Biosensor
3.93 × 10⁻¹² M
0.005–0.034 mM
Water samples
The working potential controlled to minimize the interference of other metal ions in test medium
PANI and PANI-co-PDTDA polymer films
[107]

6
Hg(II)
ASV
Electrochemical
4.98 × 10⁻⁹ M
4–160 ppb
Aquatic solutions
—
Glassy carbon electrode
[108]

7
Hg(II)
SW-ASV
Electrochemical
9.2 × 10⁻⁵ M
0.1–150.0 nM
Soil, gasoline, fish, tap, and wastewaters
400-fold mass ratio of Cu²⁺, Mn²⁺, Zn²⁺, Cr³⁺, Cr⁶⁺, Fe³⁺, Fe²⁺, Ni²⁺, and Co²⁺ did not interfere in the simultaneous determination of Cd²⁺, Pb²⁺, and Hg²⁺
Triphenyl phosphine
[109]

8
Hg(II)
Potentiometer
Electrochemical
9.77 × 10⁻⁶ M (PME)¹
7.76 × 10⁻⁷ M (CGE)¹
1.0 × 10⁻¹–5.0 × 10⁻⁶ M (PME) 
1.0 × 10⁻¹–5.0 × 10⁻⁷ M (CGE)
Water samples
Ag⁺ has small interference in the determination of Hg²⁺
1,3-Alternate thiacalixcrown
[110]

9
Hg(II)
Potentiometer
Electrochemical
1.0 × 10⁻⁸ M
5.0 × 10⁻⁸–1.0 × 10⁻² M
—
The selectivity coefficient of the other ions is ranging from 2.9 to 4.9
PVC membrane
[111]

10
Hg(II)
DPSV
Electrochemical
0.05 × 10⁻¹² M
1–500 nM
Water samples
Pb²⁺, Th³⁺, Cu²⁺, Cd²⁺, Ni²⁺, and Al³⁺ did not interfere
Gold nanoparticles
[112]

11
Hg(II)
SW-ASV
Ultrasonic extraction
—
—
Indoor dust samples
—
Gold nanoparticles
[113]

12
Hg(II)
Cyclic voltammeter
Electrochemical
1.9 × 10⁻⁹ M
40–170 μg L⁻¹
Wastewaters
—
Biotinyl Somatostatin-14 peptide
[114]

13
Hg(II)
Potentiometer
Electrochemical
3 × 10⁻⁶ M
5 × 10⁻⁶–1 × 10⁻² M
Contaminated water
Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Cu²⁺, Cr³⁺, Fe³⁺, and Pb²⁺ did not interfere in the determination of Hg²⁺
Dithizone and di-n-butyl phthalate
[115]

14
Hg(II)
DP-ASV
Electrochemical
0.483 × 10⁻⁶ M
300–700 ng mL⁻¹
—
No interference of Cd, Ni, Zn, and Cu in 50-, 25-, 100-, and 5-fold in excess, respectively
Nanocellulosic fibers
[116]

15
Hg(II)
—
Electrochemical
0.5 × 10⁻⁹ M
1.0 nM–1.0 μM

Zn²⁺, Mg²⁺, Ca²⁺, Pb²⁺, Cd²⁺, Mn²⁺, Cu²⁺, Ni²⁺, and Fe³⁺ did not interfere
G-quadruplex–hemin (G4–hemin)
[117]

For the conversion of limit of detection values into moles per liter (M) the atomic weight of Hg is taken as 200.59 g, MeHg as 215.59 g, EtHg as 229.59 g, and PhHg as 277.59 g.

¹PME: polymeric membrane electrode and CGE: coated graphite electrode.

Analytical instruments: DP-ASV: differential pulse anodic stripping voltammeter; SW-ASV: square wave anodic stripping voltammeter.

Table 4: Analytical parameters of reviewed research papers about the speciation and determination of mercury by miscellaneous techniques.

S. number
Analyte
Analytical instrument used for the detection
Method
Limit of detection (LOD)#
Linearity range
Analyzed samples
Interference study
Supporting media
Reference

1
Speciation
Continuous mercury analyzer
Thermal desorption
—
—
Solid samples (fly ash)
—
—
[118]

2
GEM
Portable mercury analyzer
—
—
—
Atmosphere
—
—
[119]

3
Hg(II)
SERS¹
—
2.24 × 10⁻¹² M
0.001–0.5 ng mL⁻¹
Drinking water samples
Selective in presence of Zn²⁺, Mg²⁺, Fe³⁺, Cu²⁺, Pb²⁺, and Mn²⁺
Gold nanoparticles
[120]

4
Hg(II)
HPLC
SPE
1.99 × 10⁻¹⁰–4.48 × 10⁻⁹ M
2.7–300 μg L⁻¹
Water samples
Simultaneously Ni²⁺, Co²⁺, and Hg²⁺ are determined
Carbon nanotubes
[121]

5
Hg(II)
SERS
—
0.1 × 10⁻⁹ M
0.1–1000 nM
Groundwater
Ag⁺ was also determined along with Hg²⁺ and K⁺, Cu²⁺, Ag⁺, Cr³⁺, Fe³⁺, , Ca²⁺, Co²⁺, Cd²⁺, and Zn²⁺ did not interfere
Oligonucleotide-functionalized magnetic silica sphere
[122]

6
Total Hg
AMA
Acid digestion
—
—
Eggs and blood of Eretmochelys imbricata
Along with mercury Cd, Cu, Zn, and Pb are also determined
—
[123]

7
Hg(II)
Luminescence spectrometer
Fluorescence
3.0–9.0 × 10⁻⁹ M
0.05–1.0 μM
Water samples
Fairly selective in presence of Ag⁺, Fe³⁺, Zn²⁺, Ca²⁺, Mn²⁺, Mg²⁺, Co²⁺, Pb²⁺, Ni²⁺, Cd²⁺, and Cu²⁺
Silver nanoclusters
[124]

8
Hg(II)
X-ray fluorescence spectrometer
Preconcentration
4.98 × 10⁻¹² M
Upto 20 mg L⁻¹
Drinking water
—
Activated carbon
[125]

9
Total Hg
DMA

0.14 ng
—
Particulate matter
—
GF/C filters
[126]

10
MeHg and EtHg
HPLC
Chemiluminescence
0.16 ng g⁻¹
0.5–20 ng Hg
Soil and sediment samples
Back extraction and another chemical process make the method selective for MeHg and EtHg
Emetine dithiocarbamate
[127]

11
Total Hg
CV-CCPM-OES²
Microwave digestion
2.39 × 10⁻¹¹ M
0.27–55 mg kg⁻¹
Soil samples
—
—
[128]

12
Hg(II)
Chemodosimeter
Fluorescence
1.71 × 10⁻⁹ M
1.0 × 10⁻⁷–1.0 × 10⁻⁶ M
Blood serum of mice
—
Rhodamine
[129]

13
Hg(0)
XRF
Acid digestion
9.97 × 10⁻⁸ M
—
Soils from industrial complex
—
—
[130]

14
Total Hg
DMA
Combustion
0.12 ng
0.5–5 ng
Soil and leaf samples
—
—
[131]

15
MeHg and Hg(II)
GC-MS
Matrix solid-phase dispersion
0.06 (MeHg) and 0.12 (Hg(II)) μg/g
—
Tuna fish, angel shark, and guitarfish
—
—
[132]

16
GEM
—
Concentration-weighted trajectory model
—
—
Particulate matter
—
QFF
[133]

For the conversion of limit of detection values into moles per liter (M) the atomic weight of Hg is taken as 200.59 g, MeHg as 215.59 g, EtHg as 229.59 g, and PhHg as 277.59 g.

¹SERS: surface enhanced Raman scattering; ²CV-CCPM-OES: cold-vapor capacitively coupled plasma microtorch fluorescence spectrometry.

Analytical instruments: HPLC: high performance liquid chromatography; AMA: automatic mercury analyzer; DMA: direct mercury analyzer; XRF: X-ray fluorescence.

In the analysis of mercury species in various environmental samples, selectivity and range of linearity of the method also play a major role due to the presence of multielements in the real samples. Based on the present study, most of the spectrophotometric, spectrofluorometric, and electroanalytical methods were discussed regarding the interfering ion studies and linearity range of the method. These studies will give a clear picture about the determination of mercury species in presence of other ions which validates the methods.

Regarding the merits of the different methods for speciation and analysis of mercury, the usage of nonchromatographic methods has an advantage in terms of speed of analysis, inexpensiveness, and convenience to find the mercury in various environmental samples. But for the complete speciation studies of mercury in biological and environmental samples chromatographic methods are useful [156]. The validity of analytical methods can be enhanced with the analysis of the certified reference materials along with the real samples. In recent years, the researchers mostly preferred GC coupled with AFS or ICP-MS for the determination and speciation of mercury in natural waters [157]. In electroanalytical methods, the validity of the methods depends on various factors such as type of electrode, preconcentration, and supporting materials [139] and these methods are cost-effective, selective, and sensitive [143].

3. Conclusions

The present study revealed the recent developments in the determination and speciation studies of mercury by a range of analytical techniques. Our previous study [2] also described the challenges in the methodology for mercury determination. This review showed that most researchers focused on the determination of Hg(II) rather than speciation studies. On the other hand, the speciation studies [23, 24, 29, 36, 37, 44, 47, 50, 54, 58, 68, 69, 76, 118] accurately revealed the toxicity of mercury rather than the total mercury or single species determinations. In the papers reviewed, most researchers were aware of the interfering ions in the determination of mercury and its different forms. In the analytical method, a study of interfering ions is very important because it can predict the selectivity of the method. In future studies, it will be important to focus on speciation studies of mercury rather than a determination of the total mercury.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

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