Chromate indirect detection

Chromate, TTAB, borate CZE system with indirect detection Inorganic anions 52... 

Adamantane carboxylic acids 13, CM-/3, Me-p A-reciprocal 66 indirect detection (sodium chromate)... 

A generic CE method has been validated 118( for this testing. The method uses an electrolyte, which contains chromate to provide the background UV signal at 254 nm for indirect detection. A cationic surfactant is added which forms a double-layer coating... 

BGE gives a peak in the direction of reduced absorbance when a sample ion passes through the detector. The absorbing reagent, which is sometimes called a visualization reagent, should have a mobility that matches those of the sample ions as closely as possible. Chromate is often used for the indirect detection of anions and a proton-ated amine cation, such as benzylamine, for detection of cations. 

Chromate at a concentration of around 5 mM has been used very successfully for indirect detection of common inorganic anions at a wavelength of 254 nm. A now classic separation of some 30 anions in a single run is illustrated in Fig. 10.2. More recently, Shamsi and Danielson have proposed naphthalenedisulfonate (NDS) and naphthalenetrisulfonate (NTS) for indirect detection of inorganic and organic anions... 

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.)...

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.

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). 

Indirect UV is the most common mode for the detection of inorganic anions and cations by CE. Pyromellitic acid or chromate are the most... 

I.6. Capillary electrophoresis [55] Simultaneous analysis of silicate with other ions (nitrite, nitrate, phosphate) is carried out by capillary electrophoresis with an indirect UV detection. The separation is achieved in a fused silica capillary filled with an electrolyte solution containing sodium chromate and an electro-osmotic flow modifier, trimethyltetrade-cylammonium bromide. 

Probes currently employed in the indirect UV detection of amino acids include p-aminosalicylic acid, benzoic acid, phthalic acid, sodium chromate, 4-(N,N -dimethylamino)benzoic acid, 1,2,4,-benzenetricar-boxylic acid (trimellitic acid), 1,2,4,5-benzenetetracar-boxylic acid (pyromellitic acid), and quinine sulfate. Several of these probes are employed in combination with metal cations and cationic surfactants, which are incorporated into the electrolyte solution as modifiers of the electro-osmotic flow. 

A CE method with indirect UV detection has been validated for eight anions and two electrolyte systems pyromellitic acid - - hexamethonium hydroxide and chromate- -TTAB. The detection limits are between 1 and 3 mg 1 the repeatability and reproducibility of the measurement differ for different compounds and amounts to 5%, except for fluoride and phosphate. Linear calibration curves have been obtained within a concentration range between 1 and lOmgl. ... 

The elegant isotope separation of Lucy and McDonald was successfully repeated somewhat later in the author s (JF) laboratory. The following conditions were employed for the separation in Figure 11.7 -20 kV, pH 9.2 using a very dilute buffer containing 3 mM borate and 6 mM chromate for indirect spectrophoto-metric detection... 

Indirect UV detection using a chromate chromophore, [187] 30 s hydrostatic injection... 

Improved detection sensitivity may also be achieved if a UV-absorbent salt, such as sodium chromate, is included in the buffer and indirect UV absorption is performed. Using this approach, minimum detectable concentrations of ions such as phosphate of <100 pg (3.2 pM) can be achieved using sample injection times of 30 s [128]. 

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