UV indirect detection

UV detection may also be performed indirectly. This method is called indirect photometric chromatography (IPC). Introduced independently by Small et al. [65] and by Cochrane and Hillman [66] in 1982, a UV-absorbing eluant is utilized for the determination of UV-transparent ions. In case of anion analysis, the anion exchanger being used is equilibrated with a UV-active eluant Na E . According to Fig. 7-35 (A), a constant signal at the detector ouflet is observed at a constant flow rate and an appropriate absorption wavelength. If a sample Na S  

The precise measurement of eluant ion absorption is also extremely important in indirect photometric detection. It is known from classical spectrophotometry [67] that the photometric error is only small in an absorbance range between 0.2 

The principle of indirect photometric detection can also be applied to ion-pair chromatography provided the counter ion of the ion-pair reagent exhibits the respective absorption properties. For example, N-methyloctylammonium-p-tolu-enesulfonate was utilized as an ion-pair reagent to analyze chloride and sulfate [68] upon application of indirect photometric detection. The corresponding chromatogram is shown in Fig. 7-38. 

In summary, it must be pointed out that indirect photometric detection is characterized by a higher sensitivity than non-suppressed conductivity detection, while it is markedly less sensitive than suppressed conductivity detection. The use of indirect photometric detection is preferred for the determination of major 

In summary, it must be pointed out that indirect photometric detection is characterized by a higher sensitivity than nonsuppressed conductivity detection, 

---

Alcohol sulfates can be characterized by HPLC. Their molecular structure does not permit a direct UV detection but an indirect UV detection of the alcohol sulfate is possible [285]. The detection can be made by the change in UV absorbance of the mobile phase, either by using an ion exchange column contain-... 

It must be remembered, however, that not aU compounds absorb UV radiation. In these circumstances, the use of indirect UV detection, in which a UV-active... 

There are two methods that are commonly employed to overcome this situation, i.e. (a) derivatization of the analyte to introduce a chromophore, and (b) the use of indirect UV detection. 

Figure 10 Capillary ion analysis of 30 anions 1 = thiosulfate, 2 = bromide, 3 = chloride, 4 = sulfate, 5 = nitrite, 6 = nitrate, 7 = molybdate, 8 = azide, 9 = tungstate, 10 = monofluorophosphate, 11 = chlorate, 12 = citrate, 13 = fluoride, 14 = formate, 15 = phosphate, 16 = phosphite, 17 = chlorite, 18 = galactarate, 19 = carbonate, 20 = acetate, 21 = ethanesulphonate, 22 = propionate, 23 = propanesulphonate, 24 = butyrate, 25 = butanesulphonate, 26 = valerate, 27 = benzoate, 28 = D-glutamate, 29 = pentane-sulphonate and 30 = D-gluconate. Experimental conditions fused silica capillary, 60 cm (Ld 52 cm) x 50 p i.d., voltage 30 kV, indirect UV detection at 254 nm, 5 mM chromate, 0.5 mM NICE-Pak OFM Anion-BT, adjusted to pH 8.0, with 100 mM NaOH. (From Jones, W. R. and Jandik, R, /. Chromatogr., 546, 445,1991. With permission.)...

Beck, W. and Engelhardt, H., Capillary electrophoresis of organic and inorganic cations with indirect UV detection, Chromatographia, 33, 313, 1992. 

Since the early 1990s an increasing number of papers has been devoted to the application of CE for the analysis of both inorganic cations [906-915] and low-molecular-mass anions [915-922]. Standard CE methods have been developed and validated for determining inorganic anions (e.g. chloride, sulfate and nitrate), small carboxylic acids and metal ions that all have limited or no UV absorbance. In those situations, short UV wavelengths (190 nm) or indirect UV detection should be used. Such methods might be extended to metallic... 

Figure 3.12 Metabolic profiling by capillary electrophoresis, (a) Comparative carbohydrate profiles of M. truncatula tissue obtained using 4-aminobenzonitrile derivatization, capillary electrophoresis with a 150 mM borate buffer, pH = 9, and on-column UV detection at 214 nm. (b) Anion profile from M. truncatula using capillary electrophoresis and indirect UV detection. The separation buffer was 5 mM K2C1O4, 1% Waters OFM-Anion BT, pH 8.0.

Fig. 17.12. The determination of typical anions using indirect UV detection. Conditions 10 mM sodium chromate, 2.30 mM cetyltrimethylammonium bromide, 60 cm fused silica capillary (effective length 52 cm) x 75 pm I.D., injection 5 s at 35mbar, 20°C, -15 kV (reversed polarity) resulting in a current of approximately 30 pA, detection UV 254 nm.

B. Lagane, M. Treilhou and F. Couderc, Capillary electrophoresis theory, teaching approach and separation of oligosaccharides using indirect UV detection. Biochem. Mol. Biol. Educ. 28 (2000) 251-255. 

For ions that are UV transparent, detection is possible through the use of indirect detection. A wide variety of different eluent systems have been described in the literature. Eluents commonly used for indirect UV detection are similar to those used in non-suppressed conductivity detection phthalate and p-hydroxybenzoic acid along with other... 

Kit solution for the determination of toxic anions (e.g., arsenate, arsenite, azide, or cyanide) and other inorganic and organic anions with indirect UV detection... 

Kit for the separation of low-molecular mass organic cations like alkali metal ions, alkaline earth metal ions, and alkyl amines. Indirect UV detection is applied. 

Geiser, L., Varesio, E., and Veuthey, J.-L. (2003). Simultaneous analysis of metabisulfite and sulfate by CE with indirect UV detection. Application to and validation for a pharmaceutical formulation. J. Pharm. Biomed. Anal. 31(6), 1059—1064. 

Mardones, C., Vizioli, N., Carducci, C., Rios, A., and Valcarcel, M. (1999). Separation and determination of carnitine and acyl-carnitines by capillary electrophoresis with indirect UV detection. Anal. Chim. Acta 382, 23—31. 

Ackermans, M. T., Everaerts, F. M., and Beckers, J. L. (1992). Determination of aminoglycoside antibiotics in pharmaceuticals by capillary zone electrophoresis with indirect UV detection coupled with micellar electrokinetic capillary chromatography.. Chromatogr. 606, 229—235. 

Nickerson, B. (1997). The determination of a degradation product in clidinium bromide drug substance by capillary electrophoresis with indirect UV detection.. Pharm. Biomed. Anal. 15, 965-971. 

Lurie, I. S. (1996). The analysis of cations and anions in illicit heroin using capillary electrophoresis with indirect UV detection. J. Capillary Electrophor. 3, 237-242. 

One of the characteristics of many of these ions is that they are UV transparent, while most CE instruments are equipped with a UV detector. Eor this reason, a special technique called indirect UV detection is often applied. 

In most cases, indirect UV detection is used because existing commercial instruments are generally equipped with such detector. However, many of these ions may be detected at 185 or 200 nm, provided their concentration is high enough (above lOOpg/mL). 

I. Buffers for Anions and Organic Acids with Indirect UV Detection... 

We have seen that a BGE for analysis of anions and organic acids needs to have (a) a pH above the p A 2 of the analyte, (b) a sufficient buffering effect, and (c) a co-ion as a probe for indirect UV detection, with mobility close to that of the analytes of interest. Furthermore, care should be taken to reverse the EOF of the capillary and to work in the anodic or reverse mode. 

FIGURE 9 Separation of chloride, sulfate, and nitrate at 40pg/mL with 5 mM chromate, 0.5 mM TTA-OH, 1.0 mM borate as BGE. Chlorate is used as internal standard. Linearity between I and 4pg/mL with an = 0.999 for all analytes. Indirect UV detection at 254nm (lOnm bandwidth). 

FIGURE 10 Separation of ammonium, potassium, caicium, sodium, magnesium, and iithium at 20pg/mL with iSmM imidazoie, 2mM i8-crown-6 and 33 mM acetic acid as BGE. Linearity between 2 and 20 mg/L with an R >0.999 for aii anaiytes. indirect UV detection at 205 nm (iOnm bandwidth). 

FIGURE I I Separation of (I) trimethylamine, (2) morpholine, (3) isopropylamine, (4) tertbutylamine, and (5) cyclohexylamine with 20 mM aminopyridine, l7mM malic acid, l7mM l8-crown-6 as BGE. The capillary was first rinsed with a polyanion solution, followed by a polycation solution to coat the capillary. Indirect UV detection at 200 nm (filter). 

In an overview on CE for pharmaceutical applications, Altria describes the analysis of ionic salts, organic acids, and also water purity, which may have deleterious effects on synthetic processes. In her review, Natishan " also included indirect UV detection when performing pharmacokinetic studies. 

---