Analysis of Inorganic Acids

ICE-Borate column was used as the separator, which is an lonPac ICE-ASl column being especially conditioned for borate analysis. 

In addition to borate and carbonate, fluoride can also be analyzed by ion-exclusion chromatography. Again, both conductivity detection modes may be 

The heteropoly acid formed in the reaction of orthosilicate with sodiiun molybdate can also be used for a chemical reaction with luminol (5-amino-2,3-dihydrophthalazine-l,4-dione) in alkaline solution to yield 3-aminophthalate in an excited electronic state that returns to the ground state with the emission of chemiluminescence light [19]. Sakai et al. [20] applied this form of chemiluminescence detection for the analysis of orthosilicate in seawater. 

In addition to a couple of inorganic acids, a wealth of organic acids may be separated by using the separator columns listed in Table 5.1. A selection of the ana-lyzable compoimds with their pAa values is listed by elution order in Table 5.3. 

As mentioned in Section 5.5, fully dissociated acids elute within the void volume due to Dorman exclusion. The retention behavior of weak organic acids, on the other hand, may be predicted on the basis of the following criteria  

The separator columns listed in Table 4-1 (see Section 4.2) allow the separation of a variety of inorganic acids. While strong inorganic acids elute within the void volume because of Donnan exclusion, weak inorganic acids are more strongly retained. This includes the hardly dissociated boric acid (pATa = 9.23), which is detected by measuring 

0 2 4 6 8 rate 1 mL/min detection photometry at 410 nm after reaction with so- 

Minutes dium molybdate injection volume 50 pL solute concentration 20 ppm 

In combination with an amperometric detection, ion-exclusion chromatography is suitable for the determination of sulfite and arsenite. Both ions can be oxidized at a Pt working electrode and, thus, can be selectively and very sensitively detected. Fig. 4-5 displays the chromatogram of a 10-ppm arsenite standard that was obtained with an oxidation potential of +0.95 V. 

High selectivities are also obtained by combining ion-exclusion chromatography with photometric detection after derivatization of the column effluent with suitable reagents. As a typical example, Fig. 4-6 shows the chromatogram of a 20-ppm silicate standard obtained by derivatization with sodium molybdate in acid solution and subsequent photometric detection at 410 nm. Orthophosphate may also be detected under these conditions. Because of its different acid strength it elutes prior to silicate, so that this method is very selective for the determination of both anions. 

For sensitive borate detection, a large excess of mannitol is added to a meth-anesulfonic add eluant to increase the borate conductance via complexation. Recently, a spedal concentrator column (Trace Borate Concentrator, TBC-1) was developed for the ultra-trace analysis of borate. The stationary phase of this concentrator is functionalized with a ds-diol, on which borate is selectively retained. Minimum detection limits in the lower ng/L range are obtained when pre-con-centrating large sample volumes, so that this method is suitable for the trace 

60 mmol/L mannitol flow rate 1 mL/min detection suppressed conductivity regenerant 25 mmol/LTMAOH -h 15 mmol/L mannitol concentrator column TBC-1 pre-concentrated volume 160 mL solute concentration 500 ng/L borate (as boron) (1). 

1 mL/min detection pulsed amperometry on a platinum working electrode injection volume 50 pL analytes (1) unknown, (2) mannitol, and (3) sulfite. 

Ion-exclusion chromatography is also suited for the determination of cyanide, which can be oxidized on a silver working electrode at low potential. Nitric acid (c = 0.1 mol/L) is used as the eluant Because an alkaline medium is required for 

1 mol/L nitric acid flow rate 0.8 mL/min detection amperometry on a silver working electrode oxidation potential OV suppressor AMMS-ICE regenerant 0.5 mol/L NaOH injection volume 50 pL solute concentration 10 mg/L cyanide (1). 

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Inorganic Analysis Acid-base titrimetry is a standard method for the quantitative analysis of many inorganic acids and bases. Standard solutions of NaOH can be used in the analysis of inorganic acids such as H3PO4 or H3ASO4, whereas standard solutions of HCl can be used for the analysis of inorganic bases such as Na2C03. 

The electrical conductivity detector is probably the second most commonly used in LC. By its nature, it can only detect those substances that ionize and, consequently, is used frequently in the analysis of inorganic acids, bases and salts. It has also found particular use in the detection of those ionic materials that are frequently required in environmental studies and in biotechnology applications. The detection system is the simplest of all the detectors and consists only of two electrodes situated in a suitable detector cell. An example of an electrical conductivity detector sensing cell is shown in figure 13. 

Although many quantitative applications of acid-base titrimetry have been replaced by other analytical methods, there are several important applications that continue to be listed as standard methods. In this section we review the general application of acid-base titrimetry to the analysis of inorganic and organic compounds, with an emphasis on selected applications in environmental and clinical analysis. First, however, we discuss the selection and standardization of acidic and basic titrants. 

Ultimately, a single sampling device was designed which collected both the vaporous and particulate forms of inorganic acids with subsequent analysis by ion chromatography. 

Lukac, S. Chromatography method using 2 columns for analysis of inorganic gases and Cj—C2-hydrocarbons formed by radiolysis of acetic acid. Chromatographia 3, 359(1970). 

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