## 3 Wastewater Analysis with Ion Chromatography  
Wastewater is a dynamic system containing organic and inorganic compounds, dissolved compounds, and insoluble substances. Moreover, the composition of samples can change dramatically during or after the sampling [41]. Therefore, analyses require available, reliable, and fully-automatic methods for simultaneous determinations of several analytes. Ion chromatography offers several advantages over the classic wet methods for determinations of inorganic and organic ions in wastewater, such as: short time of analysis (\(\approx\)10-15 min); high sensitivity and selectivity in samples with complex matrices (e.g., if the ratio of Na+:NH4+ or Cl-:NO2+ is 10,000:1); simple sample pre-treatment (usually filtration with a filter with a 0.45-\(\upmu\)m pore of is enough); possibilities of simultaneous separation and determination of anions and cations; species analysis (e.g., NO2-/NO3-/NH4+ or Cr3+/Cr6+); use of different detection modes (e.g., conductivity, UV-VIS, amperometry); and safe, cheap, and environmentally friendly chemicals (e.g., diluted water solution of Na2 CO3/NaHCO3 or HCl, HNO3). Moreover, ion chromatography is a direct method for the simultaneous determinations of alkali and alkaline earth cations and ammonia. The majority of applications of ion chromatography in wastewater analysis concern determinations of inorganic anions and cations [42; 43]. Examples of anion chromatograms for a standard sample and industrial wastewater (emulsion sample) are given in Figure 3.  
The simultaneous analysis of alkali and alkaline-earth metals and ammonium ions is another important ion chromatographic application in the field of wastewater analysis. An example chromatogram is given in Figure 4.  
Figure 4: Chromatogram of cations in a municipal waste water sample. Separation conditions: analytical column: Metrohm Metrosep C2 (250 \(\times\) 4.6 mm); eluent: 4 mM tartaric acid + 0.75 mM DPA; detection: non-suppressed conductivity. Figure 3: Chromatograms of anions standard + sample of water-based emulsion (not diluted and diluted 1:10 \(\
icefrac{{v}}{{v}}\)). Separation condtions: column: Metrohm Metrosep A Supp 3 (250 \(\times\) 4.6 mm); eluent: 1.7 mM Na2 CO3 + 1.6 mM NaHCO3; eluent flow rate: 0.85 mL/min injection volume: 20 \(\upmu\)L; detection: suppressed conductivity detection. The samples with low levels of ammonium/nitrite in matrices and high concentrations of sodium/chloride are a typical case. Unfortunately, these pairs of ions (NH4\({}^{+}\)/Na\({}^{+}\) and Cl\({}^{-}\)/NO\({}_{2}\)\({}^{-}\)) have similar selectivities for common stationary phases. The application of ion chromatography for the analysis of waste water with high ion concentrations is given by [PERSON] et al. [44]. Another important example is determination of toxic cyanide in various wastewater samples. Thanks to ion chromatography, ions such as cyanides and sulfides can be separated and determined simultaneously [45]. Moreover, the chelating agents, such as nitriltriacetate acid (NTA) and ethylenediaminetetraacetic acid (EDTA), and polyphosphates can be analyzed in wastewater [46]. In addition to common inorganic ions, some metals and metalloids can be determined in wastewater with ion chromatography. For instance, toxic hexavalent chromium must be monitored in industrial wastewater [47]. From the toxicological data, the chemical form of a specific element or its oxidation state is usually more important for living organisms than its total quantity. Ion chromatography as a separation method plays an important role in hyphenated techniques used for species analysis [48; 49]. There is a large number of ion chromatography methods applied for the determination of metal and metalloids [50]. These methods can be divided into off-line and on-line ones. In the case of the off-line method, metal complexes are formed before the separation to create stable complexes and to avoid decomposition during separation, or a ligand must be added to the eluent.