separations Review Ion Chromatography Applications in Wastewater Analysis Rajmund Michalski Institute of Environmental Engineering, Polish Academy of Sciences, 41-819 Zabrze, Poland; [email protected] Received: 13 November 2017; Accepted: 11 February 2018; Published: 26 February 2018 Abstract: Wastewater analysis is an important area in analytical and environmental chemistry. It can be performed with both the classic wet methods and instrumental techniques. The development of new methods, and modification of the existing ones, constitute a major task for researchers. Ion chromatography plays a predominant role in ion determinations with the instrumental methods. It offers several advantages over the conventional methods, such as simultaneous determinations of alkali and alkaline earth cations and ammonia. Ammonium ions cannot be determined by spectroscopic methods. Ion chromatography has been accepted world-wide as a reference method for analyzing anions and cations in water and wastewater due to the fact that it enables the replacement of several individual wet chemistry methods for common ions with one instrumental technique. The following article describes the principles of ion chromatography, such as stationary phases, eluents, detectors, and sample preparation methods. Moreover, the applications of ion chromatography in wastewater analyses and international standards are presented. Keywords: ion chromatography; wastewater; anions; cations; reference method 1. Introduction The monitoring of the wastewater quality parameters is currently a subject of growing research interest due to the requirements of the environmental protection and introduction of new technologies. Many directives and recommendations put pressure on the wastewater treatment industry to fulfill specific requirements. Substances present in various types of wastewater may be classified as chemical, physical, biological, or radiological ones. Anions and cations were routinely analyzed with the traditional wet chemical methods, including titration, photometry, or colorimetry methods. Unfortunately, many of these techniques suffered from interferences and limited accuracy. They could also be labor-intensive and difficult to automate. Thus, it was necessary to develop more effective, repeatable, and cheaper methods that could be available in ordinary laboratories. In this respect, ion chromatography has become an alternative to the classic wet methods, especially for laboratories that need to analyze inorganic and organic ions in a large number of samples (i.e., wastewater). Chromatography was discovered in 1903 by Mikhail Semyonovich Tswett, a Russian botanist who worked at the University of Warsaw in Poland [1]. Recently, chromatographic methods have been used at both the preparative and analytical stages. At first, gas chromatography (GC), thin layer chromatography (TLC) and liquid chromatography (LC) were applied mostly to the separation and determination of organic substances. The challenge was to apply the chromatographic methods for inorganic analyses (mainly for ionic substances). In 1975, Small et al. [2] described a new ion-exchange chromatographic method for the separation and conductometric detection of anions and cations. In September 1975, Dionex Corporation presented the first commercially available ion chromatograph (Dionex DX 10) [3]. The key problem in the ion chromatography evolution was developing a suppression method for the eluent conductivity. It was a significant challenge to determine separated analytes against the Separations 2018, 5, 16; doi:10.3390/separations5010016 www.mdpi.com/journal/separations Separations 2018, 5, x FOR PEER REVIEW 2 of 12 detection of anions and cations. In September 1975, Dionex Corporation presented the first commercially available ion chromatograph (Dionex DX 10) [3]. SeparationsThe 2018key, 5problem, 16 in the ion chromatography evolution was developing a suppression method2 of 12 for the eluent conductivity. It was a significant challenge to determine separated analytes against the background of the eluent ions because the eluent is also an electrolyte. In 1980s, Gjerde et al. [4] used background of the eluent ions because the eluent is also an electrolyte. In 1980s, Gjerde et al. [4] used the the ion chromatography system without the suppression device for the first time. They also used ion chromatography system without the suppression device for the first time. They also used eluents eluents with very low conductivity. They created a new type of ion chromatography, i.e., the with very low conductivity. They created a new type of ion chromatography, i.e., the non-suppressed non-suppressed ion chromatography. Both the suppressed and non-suppressed ion chromatography ion chromatography. Both the suppressed and non-suppressed ion chromatography modes can be modes can be applied to examine various sample matrices. However, when it comes to anion applied to examine various sample matrices. However, when it comes to anion analyses, the application analyses, the application of the suppressed ion chromatography is much more popular. of the suppressed ion chromatography is much more popular. Although the ion exchange remains a prevailing separation mode in ion chromatography [5,6], Although the ion exchange remains a prevailing separation mode in ion chromatography [5,6], other related methods, such as ion-exclusion (IEC) [7], ion-pairing chromatography (IPC) [8], and other related methods, such as ion-exclusion (IEC) [7], ion-pairing chromatography (IPC) [8], reversed phase liquid chromatography (RPLC) [9], can also be employed. A short overview of ion and reversed phase liquid chromatography (RPLC) [9], can also be employed. A short overview chromatography and related methods (with consideration for separation mechanism, eluents, and of ion chromatography and related methods (with consideration for separation mechanism, eluents, detectors) is given in Table 1. and detectors) is given in Table1. The obtaining of reliable results in ion chromatography depend on many factors, such as types The obtaining of reliable results in ion chromatography depend on many factors, such as types of of eluents and stationary phases, detection modes, and sample preparation methods. The eluents and stationary phases, detection modes, and sample preparation methods. The applications of applications of ion-exchangers in the chemical analysis were described by Qureshi and Varshney ion-exchangers in the chemical analysis were described by Qureshi and Varshney [10]. The stationary [10]. The stationary phases used in the ion-exchange chromatography columns can be classified phases used in the ion-exchange chromatography columns can be classified according to their applications according to their applications and ion-exchange capacities. An overview of stationary phases used and ion-exchange capacities. An overview of stationary phases used for ion chromatography is given by for ion chromatography is given by Weiss and Jensen [11]. Figure 1 shows a list of selected Weiss and Jensen [11]. Figure1 shows a list of selected stationary phases used in ion chromatography. stationary phases used in ion chromatography. Figure 1. Stationary phases used in ion chromatography. Figure 1. Stationary phases used in ion chromatography. 2 Separations 2018, 5, 16 3 of 12 Table 1. Separation methods and their applications in ion chromatography. Separation Functional Method Typical Eluents Selected Analytes Detection Modes Mechanism Group F−, Cl−, Br−,I−, ClO −, ClO −, ClO −, BrO −, Suppressed ion chromatography: 2 3 4 3 Anion-exchange HPO 2−, SCN−, CN−,P O 4−, NO −, NO −,S2−, Na CO + NaHCO , NaOH, KOH 4 2 7 2 3 Conductivity, UV-VIS, chromatography 2 3 3 SO 2−, SO 2−,S O 2−, AsO 2−, WO 2−, MnO 2−, Ion-exchange –NR + Non-suppressed ion chromatography: 3 4 2 3 3 4 4 amperometric, MS, (suppressed and 3 CrO 2−, SiO 2−, SeO 2−, SeO 2−, SiF −, Cr O 2−, benzioc acid, phtalic acid, aromatic and 4 3 3 4 6 4 7 ICP-MS non-suppressed) BF −, aliphatic carboxylic acids, sulfonic acid 4 carboxylic acids, Suppressed ion chromatography: + + + + + + 2+ 2+ 2+ 2+ − H2SO4, HCl, HNO3, methylosulfonic acid (MSA) Rb , Cs , Li , Na ,K , NH4 , Mg , Ca , Ba , Sr , Conductivity, UV-VIS, –SO3 Cation-exchange Non-suppressed ion chromatography: aliphatic amines MS, ICP-MS chromatography HNO3, tartaric acid, dipicolinic acid (DPA) Ion-exchange (suppressed and Cu2+, Ni2+, Cd2+, Pb2+, Mn2+, Fe2+, Fe3+, Sn2+, Zn2+, non-suppressed) 2,4-pyridinedicarboxylic acid Co2+, Sn4+, Cr3+, As3+, As5+, UO 2+, La3+, Ce3+,P3+, UV-VIS, MS, –SO −/NR + 2 3 3 (PDCA), oxalic acid Nd3+, Sm3+, Eu3+,V4+,V5+, Gd3+, Tb3+, Dy3+, Tm3+, ICP-MS Yb3+, Ho3+, Er3+, Lu3+, Am3+, Pu3+ Ion-exclusion ClO −,I−, BrO −, Cl−, NO −, NO −, carboxylic acids, Conductivity, UV-VIS, Ion-exclusion –SO −/NR + Water, diluted mineral acids, 4 4 2 3 chromatography 3 3 aldehydes, silicates, amines, carbohydrates amperometric − − − − − − NH4OH, tetramethylammonium hydroxide F , Cl , Br ,I , SCN , CN , − − − − − 2− 2− Anion-pair (TMAOH), tetrapropylammonium hydroxide ClO3 , ClO4 , BrO3 , NO2 , NO3 , SO3 , SO4 , Neutral 2− 2− Conductivity, UV-VIS chromatography (TPAOH), tetrabutylammonium SeO3 , SeO4 , anionic surfactants, Ion-pairs hydroxide (TBAOH) metal complexes, aromatic carboxylic acids aliphatic sulfonated hydrocarbons, (C –C ), Li+, Na+,K+, NH +, Rb+, Cs+, Mg2+, Ca2+, Ba2+, Sr2+, Cation-pair 2 10 4 Neutral selected inorganic anions (e.g., PF −, alkylamines, alkanolamines, cationic surfactants, Conductivity, UV-VIS chromatography