Ion Chromatographic Analyses of Sea Waters, Brines and Related Samples

1. Natural Diversity of Waters

Figure 1. Concentration ranges of ions and other species which are of interest for ion chromatographic analyses and were observed in the Central European mineral and thermal waters [2].

Figure 2. Natural diversity in composition of the Central European mineral and thermal waters. Brines are presented in the right corner of the diamond.

2. Review Papers

3. Ion Chromatographic Analyses of Sea Waters, Brines and Related Samples

3.1. Total Anionic and/or Cationic Composition of Water

3.1.1. Anions and Cations

In ten natural mineral waters of different composition and different total mineralization F⁻, Cl⁻, Br⁻, SO₄²⁻, I⁻_, Na⁺, K⁺, Mg²⁺, Ca²⁺ were successfully determined within three runs on three different columns, one for iodide, another for the remaining anions and the third for the cations. More details are given in Table 1. Taking into account that NO₃⁻, NO₂⁻ and HPO₄²⁻ were not detected, 12 ions of the 20 usually included in an extended chemical analysis of natural waters were covered by ion chromatography alone representing at least 98.60% and up to 99.96% of total cation composition of water samples and between 98.90% and 99.96% of the remaining anion composition after hydrogen carbonate was determined titrimetricaly. Very good agreement of the anion-cation balance or a charge balance was obtained for all mineral waters confirming an excellent performance of ion chromatography for the basic and extended chemical analysis of highly mineralized water samples [15]. Typical chromatograms of a sample are in the original publication presented in Figure 3.

Table 1. Anionic and/or cationic composition of waters with high ionic strength determined as completely as possible with ion chromatography.

Table 1. Anionic and/or cationic composition of waters with high ionic strength determined as completely as possible with ion chromatography.

Analyte/Sample	Column	Eluent	Detection	Reference
F−, Cl−, Br−, SO42−, I−, Na+, K+, Mg2+, Ca2+ Mineral waters	AG4A, AS4A 1 (20 µeq, BD 15) AG5, AS5 1 (20 µeq, BD 15, LD 120) AG12, CS12 1 (2.8 meq, BD 8) (Dionex, IonPac)	NaHCO3 (15 mM) a NaHCO3, Na2CO3 (1.7 mM, 1.8 mM) a Methanesulphonic Acid (20 mM) b	UV + suppressed conductivity Suppressed conductivity	[15]
Cl−, NO3−, SO42−, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+ Oil field water	Anionic Column 2 Cationic Column 2 Cationic Column 2 (Laboratory prepared, BD 5)	Na benzoate (0.5 mM), Na citrate (0.1 mM) c HNO3 (0.1 mM) c Oxalic acid (1.5 mM), ethylene diamine (1.5 mM) c	Non-suppressed conductivity	[16]
F−, Cl−, Br−, NO3−, SO42−, Na+, K+, Mg2+, Ca2+, Sr2+ Sea, estuary water	AG9-HC, AS9-HC 1 (190 µeq, BD 9, LD 90) AG12A, CS12A 1 (2.8 meq, BD 8) (Dionex, IonPac)	Na2CO3 (9 mM) b Methanesulphonic Acid (20 mM) b	Suppressed conductivity	[17]
Na+, K+, Mg2+, Ca2+ Brine	AG12A, CS12A 1 (2.8 meq, BD 8) (Dionex, IonPac)	H2SO4 (8.25 mM) d	Suppressed conductivity	[18]
Li+, Na+, NH4+, K+, Mg2+, Ca2+, Sr2+ Eutrophic sea, fish otoliths (+Mn2+)	CS12A 1 (2.8 meq, BD 8) (Dionex, IonPac)	Methanesulphonic acid (18 mM) b	Suppressed conductivity	[19]

Notes: BD, Bead diameter/µm; LD, Latex diameter/nm; mM, mmol/L; ¹ Column size, I. D. × Length = (4 × 250) mm; ² Column size, I. D. × Length = (4.6 × 100) mm; ^a Flow rate = 2 mL/min; ^b Flow rate = 1 mL/min; ^c Flow rate = 1.5 mL/min; ^d Flow rate = 1.2 mL/min.

Determination of Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ in oilfield water was made possible by three runs under the conditions specified in Table 1. The anionic and the cationic column were prepared in the laboratory by chemically modifying 5 μm silica beads. The anionic exchange functionality was achieved by using γ-chloropropyl triethoxy silane, hexamethyl disilazane and N,N-dimethyl benzylamine, phenyl trichlorosilane, chlorosulfonic acid and hexamethyl disilazane were used to obtain the cationic exchange functionality. A good agreement with the results obtained with other conventional methods was confirmed [16]. Typical chromatograms of a sample are in the original publication presented in Figure 2.

Concentrations of F⁻, Cl⁻, Br, NO₃, SO₄²⁻, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Sr²⁺ in seawater and derived saline solutions were determined in two single IC runs, one for anions and another one for cations (Table 1) and the results so obtained were critically assessed in terms of anion-cation balance and further related to conductivity and salinity measurements aiming to evaluate the quality/completeness of ion chromatographic analyses and to search for other meaningful relations for efficient recognition/distinction between saline solutions of different types [17]. Typical chromatograms of the samples are in the original publication presented in Figure 3.

3.1.2. Cations

Even though lithium, sodium, ammonium, potassium, rubidium, caesium, calcium, magnesium and strontium were confirmed to be well separated with a gradient elution program the concentrations of Na⁺, K⁺, Mg²⁺ and Ca²⁺ were later successfully determined in brine samples under isocratic conditions (Table 1) in 1 µL injection volumes which required only minimal dilution and for which good recoveries were confirmed [18].

By successfully determining Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺ in coastal, off-shore and sediment waters and Mn²⁺ and other already mentioned cations in fish otoliths (Table 1) in the Adriatic Sea and the Canal of Sicily the authors enabled an insight into relation between fish growth and environmental conditions. By observing higher strontium concentrations in coastal waters than off-shore and recognizing a decrease in the Sr/Ca ratio with increasing weight of the otolith they confirmed the hypothesis that juveniles grow in proximity to eutrophic coastline waters [19]. Typical chromatograms of the samples are in the original publication presented in Figures 2 and 3.

3.2. Selected Anions

Among all ion chromatographic analyses of waters with a high ionic strength, the determinations of iodide concentration received the highest attention. An overview comprising the most essential experimental conditions is summarized in Table 2 and continues with the applications in which iodide was determined simultaneously with other anions, and further proceeds with the determinations of bromide as a single ion and ends with bromide and bromate. Another group of related applications, which are summarized in Table 3, is dedicated to nutrients: nitrate, nitrite and phospahate. Methods for ion chromatographic determinations of thiosulfate and polythionates; and perchlorate are described under separate headings at the end of this section and are not included in tables.

Table 2. Ion chromatographic determinations of iodide or bromide, alone or simultaneously with some other ions in waters with high ionic strength.

Table 2. Ion chromatographic determinations of iodide or bromide, alone or simultaneously with some other ions in waters with high ionic strength.

Analyte, Sample	Column	Eluent	Detection	Ref.
I− Saline (untreated)	AS11 1 (45 µeq, BD 13, LD 85) (Dionex, IonPac)	Methanesulphonic acid 0.4 mL/L), NaCl (5.84 g/L), 4,4'-bis(dimethylamino)-diphenylmethane (0.8 g/L), Methanol (200 mL/L), water a	Post-column derivatization: N-chlorosuccinimide, succinimide, succinate buffer VIS λ = 605 nm	[20]
I−, Sea water (untreated)	AG4A-SC, AS4A-SC 1(20 µeq, BD 13, LD 160) (Dionex, IonPac)	NaOH (100 mM) b	UV λ = 226 nm	[21]
I− Sea water (untreated, 2 mL)	Semi-microcolumn 2 Stationary phase: TSKgel SAX (Tosoh) (3.7 meq/g, BD 5)	NaClO4 (30 mM), NaCl (500 mM), sodium phosphate buffer pH 6.0 (5 mM) c	UV λ = 226 nm	[22]
I−, Sea water (untreated)	Zwittergent-3-14 modified ODS column 3 (BD 5)	NaClO4 (0.2 mM) Zwittergent-3-14 (0.3 mM) c	UV λ =210 nm	[23]
I− Sea water (untreated)	Microcolumn 4: PEG/C30 binary (BD 5) (Laboratory prepared)	Na2SO4 (500 mM), NaCl (50 mM) d	UV λ = 220 nm	[24]
I˗ Sea water (untreated)	Microcolumn 4: Polyoxyethylene oleyl ether modified C30 (BD 5) (Laboratory prepared)	NaCl (300 mM) d	UV λ = 220 nm	[25]
I−, IO3− Sea water (diluted)	G3154A/102, G3154A/101 5 (50 µeq/g, BD 10) (Agilent)	NH4NO3 (20 mM), pH 5.6 c	ICP-MS	[26]
I−, Br−, SO42− Oilfield waters (diluted)	AG9-SC, AS9-SC 1 ((30 to 35) µeq, BD 13, LD 110) (Dionex, IonPac)	Na2CO3 (3 mM) e	Suppressed conductivity	[27]
I−, Br−, NO3− Sea water	Zwittergent-3-14 modified ODS 3	Diluted artificial sea water c	UV λ = 210 nm	[28]
Br− Sea water (untreated)	Zwittergent-3-14 modified ODS 3	Pure water c	UV λ = 220 nm Non-suppressed conductivity	[29]
Br− Sea water (untreated)	Cetyltrimethylammonium ion modified monolithic silica capillary columns 6 (Laboratory prepared)	NaCl (500 mM), cetyltrimethylammonium chloride (0.1 mM) f	UV λ = 210 nm	[30]
Br−, BrO3− Sea water (diluted)	G3154A/101 (guard, separation column 5, 50 µeq/g, BD 10 (Agilent)	NH4NO3 (20 mM), pH 5.8 c	ICP-MS	[31]

Notes: BD, Bead diameter/µm; LD, Latex diameter/nm; mM, mmol/L; ¹ Column size, I. D. × Length = (4 × 250) mm; ² Column size, I. D. × Length = (1 × 35) mm; ³ Column size, I. D. × Length = (4.6 × 250) mm; ⁴ Column size, I. D. × Length = (0.32 × 100) mm; ⁵ Column size, I. D. × Length = (4.6 × 150) mm; ⁶ Column size, I. D. × Length = (0.1 × 200) mm; ^a Flow rate = 0.9 mL/min; ^b Flow rate = 1.5 mL/min; ^c Flow rate = 1 mL/min; ^d Flow rate = 2.1 µL/min; ^e Flow rate = 2 mL/min; ^f Flow rate = 5.6 µL/min.

Table 3. Ion chromatographic determinations of concentrations of nutrients in samples with high ionic strength.

Table 3. Ion chromatographic determinations of concentrations of nutrients in samples with high ionic strength.

Analyte, Sample	Column	Eluent	Detection	Ref.
NO3−, KCl soil extracts (diluted)	Hamilton PRP X-100 (Hamilton)	KCl (1000 mM) a	UV λ =210 nm	[32]
NO3−, NO2− Sea water (untreated)	Cetyltrimethylammonium chloride coated ODS monolithic columns Chromolith Speed ROD RP-18e 1, Chromolith RP-18e 2 (Merck)	NaCl (500 mM), sodium phosphate buffer (5 mM) pH 4.7 b	UV λ =225 nm	[33]
NO3−, NO2−, PO43− Estuary water (untreated)	AG9-HC, AG9-HC3, Valve AS9-HC 3 (190 µeq, BD 9, LD 90) (Dionex, IonPac)	NaHCO3, Na2CO3 (3 mM, 14 mM) c (elute-off) Na2CO3 (9 mM) c (elute)	Suppressed conductivity UV λ =225 nm	[34]
NO3−, NO2−, PO43− Saline Aquarium water	Metrosep ASUPP7-250 3 (108 µeq, BD 5) (Metrohm)	Na2CO3 (3.5 mM) d	Suppressed conductivity UV λ =215 nm	[35]
NO3−, PO43− Estuary water (untreated)	AG4A-SC, AS4A-SC3 (20 µeq, BD13, LD 160) (Dionex, IonPac)	NaHCO3, Na2CO3 (0.765 mM, 0.81 mM) a	Suppressed conductivity UV λ = 210 nm	[36]
NO3−, PO43− Marine sediment pore water	AG4A, AG4A, Valve AS4A-SC 3 (20 µeq, BD13, LD 160) (Dionex, IonPac)	NaHCO3, Na2CO3 (Two compositions, elute-off/elute) 1.4 mM, pH 9.16 and 20 mM, pH 9.5) b	Suppressed conductivity	[37]
PO43− Sea water (untreated)	ICE-AS1 4 (27 meq, BD 7.5) (Dionex, IonPac)	HCl (50 mM ) e	ICP-MS	[38]

Notes: BD, Bead diameter/μm; LD, Latex diameter/nm; mM, mmol/L; ¹ Column size, I. D. × Length = (4.6 × 50) mm; ² Column size, I. D. × Length = (4.6 × 100) mm; ³ Column size, I. D. × Length = (4 × 250) mm; ⁴ Column size, I. D. × Length = (9 × 250) mm; ^a Flow rate = 2.0 mL/min; ^b Flow rate = 3.0 mL/min; ^c Flow rate = 1.0 mL/min; ^d Flow rate = 0.7 mL/min; ^e Flow rate = 1.2 mL/min.

3.2.1. Iodide

The first six papers listed in Table 2 describe methods for determining iodide in untreated sea water samples [20,21,22,23,24,25]. Brandao et al. [20] used a post-column derivatization with N-chlorosuccinimide followed by a spectrometric detection at the wavelength 605 nm; in contrast to other authors who reported a direct spectrometric detection of iodide at the wavelengths between 210 and 226 nm. Typical chromatogram of a sample is in the original publication presented in Figure 2. Several methods share a similar approach for minimizing the interfering effect of chloride on the determination of iodide. This is most commonly resolved so that sodium chloride is one of the eluent components [20,22,24] or a sole eluent component [25]. In contrast to this approach Hu et al. prevented the interfering effect of chloride by reducing its affinity towards the stationary phase, by the technique termed electrostatic ion chromatography (EIC), in which zwitterionic surfactant layer is applied on the stationary phase and the zwitterionic surfactant was also present in the eluent [23]. Typical chromatograms of an unspiked and spiked sample are in the original publication presented in Figure 1. Ito used a large 2 mL sample injection volume and proved that by replacing a macrocolumn with a semi-microcolumn with an I.D. 1 mm the method sensitivity increased 2.8-fold [22]. Typical chromatogram of a sample is in the original publication presented in Figure 5. Rong et al. successfully used two different in house prepared microcolumns with an I. D. 0.32 mm for determining iodide in sea water [24,25]. Typical chromatograms of the samples are in the original publications presented in Figure 6 and 4, respectively. Limits of detection (S/N = 3) reported for iodide in different papers were 0.2 µg/L [22],0.8 ppb [20], 0.011 µmol/L [23], 13 µg/L [24] and 19 µg/L [25], respectively. Chandramouleeswaran et al. achieved the recoveries of iodide higher than 98% [21], Ito reported the recoveries 98.4% or 97.0% for a 2 mg/L or 5 mg/L iodide addition, respectively [22].

3.2.2. Iodide and Iodate

Linear plots were obtained in a concentration range (5.0 to 500) µg/L and the detection limits 1.5 µg/L and 2.0 µg/L were achieved for a simultaneous determination of iodate and iodide in seawater, respectively with a non-suppressed ion chromatographic method with inductively coupled plasma mass spectrometric detection (ICP-MS). An anion-exchange column (G3154A/101, Agilent) and an NH₄NO₃eluent at the pH 5.6 were used. The recoveries for iodate and iodide were 101.3% ± 1.8% and 97.2% ± 2.3%, respectively [26].

3.2.3. Iodide, Bromide and Sulfate

Bromide, iodide and sulfate are very important for the characterization of oilfield waters. An Dionex IonPac AS9-SC analytical column, sodium carbonate eluent and a suppressed conductometric detection were used and the limits of detection 0.1 mg/L for bromide and sulfate and 0.2 mg/L for iodide were achieved [27] Typical chromatograms of the samples are in the original publication presented in Figures 3 and 4.

3.2.4. Iodide, Bromide and Nitrate

An octadecylsilica column modified with a zwitterionic surfactant [3-(N,N-dimethylmyristylammonio) propanesulfonate] and a diluted artificial sea water as the eluent were used for simultaneous determination of iodide, bromide and nitrate in sea water with spectrometric detection at the wavelength 210 nm. Limits of detection were 0.75 µg/L for bromide, 0.52 µg/L for nitrate, and 0.8 µg/L for iodide [28]. Typical chromatogram of a sample is in the original publication presented in Figure 5.

3.2.5. Bromide

The concentration of bromide was directly determined in sea water with EIC with spectrometric and conductometric detection, the results obtained with this method were 0.059 mmol/L ± 1.0% and 0.057 mmol/L ± 0.94%, and were comparable with the results of IC. The zwitterionic surfactants immobilized on octadecylsilica surfaces acted as the stationary phase and water was used as the mobile phase [29]. Typical chromatograms of the samples are in the original publication presented in Figures 5 and 6.

Monolithic silica capillary columns, which were prepared with a sol–gel method, were dynamically modified with cetyltrimethylammonium ion and enabled a determination of 63 mg/L of bromide in 20 nL of untreated sea water sample. The eluent contained NaCl and cetyltrimethylammonium chloride (CTAC). Spectrometric detection was performed at the wavelength 210 nm [30]. Typical chromatogram of a sample is in the original publication presented in Figure 4.

3.2.6. Bromide and Bromate

An ion chromatographic method employing a G3154A/101 guard and separation column (Agilent), NH₄NO₃eluent at pH 5.8 and ICP-MS detection was developed, which enabled a direct determination of bromate and bromide in a diluted sea water sample with a limit of detection which ranged from (2.0 to 3.0) μg/L [31]. Typical chromatogram of a sample is in the original publication presented in Figure 2.

3.2.7. Nitrate

Nitrate was successfully determined in KCl soil extracts with ion chromatography employing KCl solution as an eluent and performing a spectrometric detection at the wavelength 210 nm. Bromide interference was avoided by spiking the diluted soil extracts with a constant amount of nitrate, which shifted a bromide nitrate ratio so that bromide did not interfere any more, and consequently nitrate was reliably determined in concentrations down to 25 µg/L [32].

3.2.8. Nitrite and Nitrate

Nitrite and nitrate were well resolved and eluted within three minutes from the CTAC modified monolithic ODS columns and successfully determined in untreated sea water in concentrations (10.8 ± 0.5) µg/L, and (21.3 ± 0.5) µg/L if the NaCl, sodium phosphate buffer eluent was used and spectrometric detection was performed at the wavelength 225 nm. The limits of detection (S/N = 3) for nitrite and nitrate were 0.8 μg/L and 1.6 µg/L, respectively [33]. Typical chromatogram of a sample is in the original publication presented in Figure 3.

3.2.9. Nitrate, Nitrite and Phosphate

For nitrate, nitrite and phosphate the limits of detection (0.1, 0.3 and 1) mg/L were achieved, respectively with the suppressed conductometric and spectrometric detection in series at the wavelength 225 nm. Chloride was eliminated with a column-switching method. Nitrate at the concentration level 5 mg/L was successfully determined in an estuary water, while nitrite and phosphate were undetectable [34]. Typical chromatogram of a sample is in the original publication presented in Figure 5.

Nitrate-N, nitrite-N and phosphate-P were successfully determined in saline aquarium water in concentrations as low as (0.026, 0.021 and 0.04) mg/L, respectively with the suppressed conductometric and spectrometric detection at the wavelength 215 nm. Concentrations of these anions in sea water were below the limits of detection [35].

3.2.10. Nitrate and Phosphate

An ion chromatographic method using spectrometric detection at the wavelength 210 nm for nitrate determination and suppressed conductometric detection for phosphate determination was reported. A limit of detection for phosphate in sea water was proved to be 0.1 mg/L and this ion was successfully determined in the estuary waters in concentrations between 0.3 and 1.6 mg/L during the winter months when salinity was lower due to dilution caused by the rainfall, and the nutrients were more intensively supplied by the in-coming streams. Concentration of nitrate between 0.3 and 11.1 mg/L were determined in the samples and the limit of detection was found out to be 0.04 mg/L [36]. Typical chromatogram of a sample is in the original publication presented in Figure 3.

The 0.5 µmol/L and 1 µmol/L limits of detections were achieved for nitrate and phosphate determination in the marine sediment pore water with an ion chromatographic method with suppressed conductometric detection. Experimental conditions defined by six factors were optimized using a fractional factorial experimental design. A column-switching method was used for reducing the chloride interference effect [37]. Typical chromatogram of a sample is in the original publication presented in Figure 6.

3.2.11. Phosphate

The 0.06 µmol/L limit of detection (3s) was achieved with ion-exclusion chromatography with ICP-MS detection for phosphate determination in untreated sea water. The concentration of dissolved phosphate determined in sea-water with this ion chromatographic method (1.69 ± 0.04) µmol/L is in good agreement with the result of the colorimetric procedure (1.71 ± 0.04) µmol/L [38]. Typical chromatogram of a sample is in the original publication presented in Figure 4.

3.2.12. Thiosulfate and Polythionates

A pre-concentration technique using an ion-exchange pre-column and a reversed phase analytical column in series and a water-acetonitrile eluent containing tetrabutylammonium ions and carbonate buffer was developed for determining thiosulfate and polythionates in natural saline waters. Limits of detection achieved with a pre-concentration of 6 mL of 50-times diluted seawater were: 1 nmol/L for trithionate, and 0.3 nmol/L for tetrathionate and pentathionate [39].

3.2.13. Perchlorate

The limit of detection 0.77 µg/L (S/N = 3) was reported for an ion chromatographic method intended for perchlorate determination in waters of different conductivities ranging up to 14.7 mS/cm. With a pre-concentration of a 2 mL sample volume and elimination of interfering ions by column-switching, higher recoveries of perchlorate ion were achieved than with the recommended EPA Method [40].

3.3. Selected Cations

The more comprehensive ion chromatographic determinations of cations closer matching the total cationic composition of water samples were presented in Section 1.1. Here we present methods that focus on determinations of selected cations or a single cation. The main experimental conditions defining these methods are summarized in Table 4.

Table 4. Ion chromatographic determinations of concentrations of selected cations in waters with high ionic strength.

Table 4. Ion chromatographic determinations of concentrations of selected cations in waters with high ionic strength.

Analyte, Sample	Column	Eluent	Detection	Ref.
Mg2+, Ca2+, Sr2+ Brine, Sea water (diluted)	CG-2, CS-2 (Dionex, IonPac)	Ethylenediamine (2.5 mM),HCl (5 mM), zinc acetate (1 mM)	Suppressed conductivity	[41]
Sr2+ Sea water (diluted)	high-speed cationic column (Cat.no.269-25, Wescan)	Ethylenediamine (0.5 mM), oxalic acid (0.5 mM), pH 6 a	Non-suppressed conductivity	[42]
NH4+ Sea water(diluted)	CG-12A Valve CS-12A1 (2800 µeq, BD 8) (Dionex, IonPac)	H2SO4 (25 mM) b	Suppressed conductivity	[43]
NH4+ Sea water (purge-and-trap)	CG-16A CS-16A2 (8400 µeq, BD 5) (Dionex, IonPac)	Methanesulphonic Acid (45 mM) b	Suppressed conductivity	[44]

Notes: BD, Bead diameter/μm; LD, Latex diameter/nm; mM, mmol/L; ¹ Column size, I. D. × Length = (4 × 250) mm; ² Column size, I. D. × Length = (5 × 250) mm; ^a Flow rate = 1.2 mL/min; ^b Flow rate = 1 mL/min.

3.3.1. Magnesium, Calcium and Strontium

Strontium, magnesium and calcium were successfully simultaneously determined in high salinity sub-surface waters with ion chromatography with suppresses conductometric detection using an eluent which comprised ethylenediamine, HCl and zinc acetate, and the results compared well with those obtained with atomic absorption spectrometry [41].

3.3.2. Strontium

A non-suppressed ion chromatographic method with conductometric detection was developed for determination of strontioum in coastal sea water and the results compared well with those obtained by ICP-OES. The eluent comprised ethylenediamine and oxalic acid. The limit of detection for strontium determination was found to be 1 mg/L [42]. Typical chromatogram of a sample is in the original publication presented in Figure 5.

3.3.3. Ammonium

Ion chromatographic method, with suppressed conductometric detection and an on-line sample pre-concentration with a column-switching, was developed for ammonium determination in sea water. The limit of detection for ammonium ion in the presence of 1000 mg/L sodium was 12.8 µg/L. It was proved that 90% of ammonium was introduced and concentrated if concentration was lower than 1 mg/L [43].Typical chromatogram of a sample is in the original publication presented in Figure 3.

The 1.35 µg/L (75 nmol/L) limit of detection was confirmed for ammonium determination in sea water samples with the approach that combined a purge-and-trap pre-concentration step with ion chromatography with suppressed conductometric detection. A linear range for ammonium extended from 50 nmol/L to 6.0 µmol/L [44]. Typical chromatogram of a sample is in the original publication presented in Figure 7.

3.4. Metals

The main experimental conditions for ion chromatographic determinations of metals in samples with high ionic strength are summarized in Table 5. Chelation ion chromatography as a pre-concentration step in combination with spectrometric detection in the visible range after post-column derivatization is most frequently reported. More details are given in continuation.

Table 5. Ion chromatographic determinations of concentrations of metals.

Table 5. Ion chromatographic determinations of concentrations of metals.

Analyte, Sample	Column	Eluent	Detection	Ref.
Zn, Pb, Ni, Cu Sea water, CASS-2 coastal sea-water certified reference material	Xylenol Orange-impregnated polystyrene-divinylbenzene neutral PLPRS resin (Polymer Laboratories) (BD 5)	KNO3 (500 mM), lactic acid (50 mM), pH adjustment NH3 or HNO3a	Post-column derivatization: Pyridyl-azo-resorcinol, NH3, NH4NO3 pH 10.2 VIS λ = (490 to 520) nm	[45]
Cu, Ni, Zn, Co Reference materials for trace metals estuarine water (SLEW-2) (diluted, pH 3)	MetPac-CC1 (iminodiacetate chelating concentrator column) CG5, CS5 1(BD 13, LD 110, 150 μeq sulfonic, 70 μeq alkanol quaternary ammonium) (Dionex, IonPac)	Pyridine-2, 6-dicarboxylic acid (6 mM), acetate buffer CH3COOH, (50 mM), CH3COONa (50 mM), pH 4.5 a	Post-column derivatization: Pyridyl-azo-resorcinolNH3, CH3COOH, pH 9.7 VIS λ = 520 nm	[46]
Selenium species Artificial sea water	AS10, AS10 1 (170 µeq, BD 8.5, LD 65) AG11, AS11 1 (45 µeq, BD 13, LD 85) (Dionex, IonPac)	Na2CO3 (10 mM) a NaOH (10 mM) a	ICP-AES	[47]
La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er Sea water	N-methyl-γ-amino-butyrohydroxamate resin guard and concentrator column 2, (1.5 to l.9) mM/g CS5 3(BD 13, LD 110, 150 μeq sulfonic, 70 μeq alkanol quaternary ammonium) (Dionex, IonPac)	Oxalic acid (30 mM, pH 4.5), diglycolic acid (5 mM)	Post-column derivatization: 4(2-pyridylazo)resorcinol ZnEDTA, NH3, NH4Cl, pH 10, VIS λ = 495 nm	[48]
Mn, Co, Ni, Cu, Zn, No, Cd, Sb, Pb, U Sea-Water Ref. Material NASS-4	Nitrilotriacetate (NTA)-type chelating poly (styrene-divinylbenzene) resin 4	KNO3 (500 mM) a	ICP-MS	[49]
Be Artificial sea water	Iminodiacetic acid functionalised silica gel (Bio-ChemMack) (BD 8)1	KNO3 (400 mM), adjusted to pH 2.5 using HNO3 a	Post-column deriv.: chrome azurol S, Triton X-100, 2-(N-morpholino) ethane-sulfonic acid, pH 6.0, VIS λ = 590 nm	[50]
V, Mo, W Artificial sea water	Chelated polystyrene-divinylbenzene resins: BAETM (bis (2-aminoethylthio) methylated) 5 Chelated acrylonitrile and divinylbenzene resin: γ-ABHX (γ-aminobutyrohydroxamate) 6	HNO3 pH 1.5 a	ICP-MS	[51]
Cd, Pb, Cu Mineral waters	Aurin tricarboxylic acid impregnated polystyrene divinylbenzene resin 3 (BD 7)	KNO3 (100 mM) pH gradient 1	Post-column derivatiz.: borate buffer, 4-(2-pyridylazo)resorcinol VIS λ = 520 nm	[52]

Notes: BD, Bead diameter/μm; LD, Latex diameter/nm; mM, mmol/L; ¹ Column size, I. D. × Length = (4 × 250) mm; ² Column size, I. D. × Length = (2 × 50) mm; ³ Column size, I. D. × Length = (4.6 × 250) mm; ⁴ Column size, I. D. × Length = (4.6 × 50) mm; ⁵ Column size, I. D. × Length = (4 × 50) mm; ⁶ Column size, I. D. × Length = (6 × 30) mm; ^a Flow rate = 1 mL/min.

Low µg/L levels of Zn-II, Pb-II, Ni-II and Cu-II were determined in CASS-2 coastal sea-water certified reference material with chelation ion chromatography with a pre-concentration and separation on a Xylenol Orange-impregnated resin, and spectrometric detection in the visible range after post-column derivatization [45]. Typical chromatograms of the samples are in the original publication presented in Figures 1 and 2.

The limits of detection 0.025 µg/L, 0.036 µg/L, 0.064 µg/L and 0.022 µg/L were achieved for copper, nickel, zinc and cobalt, respectively with a pre-concentration of a 25 mL-sample on an iminodiacetate chelating column. Desorption from the concentrator column and separation in an ion exchange column was achieved with an eluent containing pyridine-2,6-dicarboxylic acid in acetate buffer. Detection was spectrometric in the visible range after post-column derivatization, samples had to be diluted and pH set to 3. The reference material for trace metals in estuarine water (SLEW-2) was successfully analysed [46]. Typical chromatograms of the samples are in the original publication presented in Figure 8.

Inorganic and amino acid forms of selenium were determined by ion chromatography with inductively coupled plasma atomic emission spectroscopic (ICP-AES) detection. Three different columns were tested. The columns AS10 and AS11 (Dionex) both proved useful, but limits of detection were lower for the later and ranged between 0.32 mg/L (Se-methionine) and 0.62 mg/L (Se-cystine) and were close to 0.5 mg/L for HSeO₃⁻ and HSeO₄²⁻ [47]. Typical chromatograms of the samples are in the original publication presented in Figures 1 and 2.

The 2.5 μg/L detection limit was achieved for the determination of lanthanides in sea water by a pre-concentration of 25 mL of sea water on a chelation stationary phase followed by ion chromatographic separation and spectrometric detection in the visible range after a post-column derivatization [48]. Typical chromatogram of a sample is in the original publication presented in Figure 5.

The results of the determination of the concentrations of metals (Mn, Co, Ni, Cu, Zn, No, Cd, Sb, Pb and U) in the Open Ocean Sea-Water Reference Material NASS-4 obtained with a chelation ion chromatographic method with ICP-MS detection were in good agreement with the certified values. With the efficient preconcentration and simultaneous matrix elimination, the detection limits ranged from 4 ng/L for Cu to 0.7 µg/L for Mo [49].

Beryllium was successfully determined in artificial sea water using an iminodiacetic acid functionalized silica gel column and spectrometric detection in the visible range after a post-column derivatization. Detection limits for Be(II) in a standard solution and a typical tap water sample were 3 μg/L and 4 µg/L, respectively [50]. Typical chromatograms of the samples are in the original publication presented in Figures 5 and 6. Two kinds of chelating resin, bis (2-aminoethylthio) methylated resin (BAETM) and gamma-aminobutyrohydroxamate resin (gamma-ABHX) were synthesized and tested. The detection limit 0.01 µg/L was achieved for the determination of vanadium, molybdenum and tungsten with a BAETM resin column. The γ-ABHX resin column demonstrated efficient separation between target metals and sea water matrix cations [51]. Typical chromatogram of a sample is in the original publication presented in Figure 7.

Metal ions Cd (II), Pb (II) and Cu (II) were baseline separated from other transition metals and the alkaline earth metals within 30 min and their concentrations determined in highly mineralized water with a chromatographic system comprising aurin tricarboxylic acid impregnated polystyrene divinylbenzene resin, pH gradien elution and post-column derivatization with spectrometric detection in the visible range. The limits of detection were 1 µg/L for Cd (II) and 5 µg/L for both Pb (II) and Cu (II),respectively [52]. Typical chromatogram of a sample is in the original publication presented in Figure 7.

4. Conclusions

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