Eluent molybdate

Eluent for TLC was 8 4 1 AcOEt/MeOH/H20. Substrates and products were visualized at 254 nm and with the molybdic reagent ((NH4)eMo7024 4H2O, 42 g Ce(S04)2, 2 g H2SO4 concentrated, 62 mL made up to 1 L with deionized water). 

Fig. 3-75. Separation of polarizable anions on an Ion Pac AS4A separator column. - Eluent 0.0017 mol/L NaHC03 + 0.0018 mol/L Na2C03 + 100 mg/L p-cy-anophenol flow rate 2 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations a) 20 ppm each of iodide, thiocyanate, and thiosulfate, b) 20 ppm each of tungstate, molybdate, and chromate.

Fig. 3-104. Separation of polyphosphonic acids upon application of phosphorus-specific detection. - Separator column IonPac AS7 eluent 0.17 mol/L KC1 + 0.0032 mol/L EDTA, pH 5.1 flow rate 0.5 mL/min detection photometry at 410 nm after hydrolysis and derivatization with vana-date/molybdate injection 50 pL, l-hydroxyethane-l,l-diphosphonic acid (HEDP), aminotris-(methylenephosphonic acid) (ATMP), ethylenediamine-tetramethylenephosphonic acid (EDTP), l,l-diphosphonopropane-2,3-dicarboxylic acid (DPD), and 2-phosphonobutane-l,2,4-tricarboxylic add (PBTC) (taken from [84]).

Fig. 3-127. Separation of various inorganic anions with an isoconductive eluent. - Separator column Waters IC-PAK Anion eluent see Table 3-23 (eluent switching at the time of injection) detection direct conductivity injection volume 100 pL solute concentrations 1 ppm fluoride (1), 2 ppm carbonate (2) and chloride (3), 4 ppm nitrite (4), bromide (5), and nitrate (6), 6 ppm orthophosphate (7), 4 ppm sulfate (8) and oxalate (9), 10 ppm chromate (10), and molybdate (11) (taken from [135]).

Fig. 5-24. Separation of molybdate and its thia-substituted derivatives. - Separator column Ion Pac NS1 (10 pm) eluent 0.002 mol/L TBAOH + 0.001 mol/L Na2C03 / acetonitrile (75 25 v/v) flow rate 1 mL/min detection suppressed conductivity injection volume 50 pL solute concentrations 50 mg/L (NH4)2Mo04, 200 mg/L (NH4)2MoOS3, and (NH4)2MoS4 (taken from [37]).

Fig. 8-2. Simultaneous analysis of weak and strong inorganic acids. — Separator column IonPac AS4A eluent 0.0017 mol/L NaHC03 + 0.0018 mol/L Na2C03 flow rate 1 mL/min detection (A) suppressed conductivity, (b) photometry at 410 nm after post-column reaction with sodium molybdate injection volume 50 pL solute concentrations 3 ppm fluoride, 4 ppm chloride, 10 ppm nitrite and bromide, 20 ppm nitrate, 10 ppm orthophosphate, 25 ppm sulfate, and 27 ppm orthosilicate.

Chromatography. Separations by ion exchange column chromatography were performed according to ASTM methods (10,11). The Technicon AutoAnalyzer (Bran and Luebbe) (12,13) was employed for analysis of the eluent from ASTM method D 2761 (11-13). ASTM method D 501 was followed as written, using the ammonium molybdate colorimetric analysis of the hydrolyzed fractions. 

The retention times of sample anions become longer as the operating pH becomes more acidic and the net positive charge on the ion exchanger increases. Figure 3.4 plots the retention factor as a function of eluent pH for several sample anions. Thiocyanate and molybdate are very strongly retained, even at moderately acidic pH values. 

A sodium molybdate eluent with indirect detection at 250 nm was found to provide an excellent separation and a very sensitive detection of inorganic anions. The separa-... 

Figure 6.17. Separation of 7 common anions on a latex-coated column with a sodium molybdate eluent run at 0.75 mL/min. Indirect spectropbotometric detection was used at 250 nm with 0.05 a.u.f.s. Peaks 1 = ethylsulfonate 2 = propylsulfonate 3 = chloride 4 = nitrite 5 = bromide 6 = nitrate 7 = sulfate (10-20 ppm each anion). (From Ref. [18] with permission).

Its basic form has been used successfully for the collection of Cr(lII) [36], and cadmium [37] fnrni urine. In a detailed study on the behavior of various oxyanions on activated alumina (acidic) Cook et al.[35] have shown that while arsenate, chromate, molybdate, phosphate, selenate, and vanadate were all well retained on the sorbent, only chromate and molybdate could be reasonably well eluted using IM NH4OH, or stronger alkali solutions. About 80% of phosphate and selenate could be eluted using IM KOH, whereas arsenate and vanadates may be de-sorbed only by using stronger eluents such as 5M KOH. 

Indirect spectral detection requires the use of a strongly absorbing anion in the eluent. Eluents containing molybdate, p-hydroxybenzoate or phthalate have been used successfully. 

Figure 6.19 Separation of anions on a latex-coated anion-exchange column of very low exchange capacity (27 peq g ). Eluent 4 mM sodium molybdate. Detection Indirect UV at 250 nm. Peaks l=ethylsufonate, 2=propylsulfonate, 3=chlor-ide, 4=nitrite, 5=bromide, 6=nitrate, 7=sulfate (from Ref. [25] with permission).

Figure 5.14 Analysis of orthosilicate after photometry at 410 nm after reaction with derivatization with sodium molybdate. Separa- sodium molybdate injection volume 50 pL tor column lonPac ICE-AS1 eluent 05 mmol/L peak 20mg/L SI (as SiCI, 1).

US EPA Method 326.0 allows the combination of suppressed conductivity detection and postcolumn derivatization for UV absorbance detection, as schematically depicted in Figure 8.45. A volume of sample (225 pL) is introduced into an ion chromatography system. After separation and eluent suppression, standard anions and oxyhalide ions are measured using conductivity detection. The suppressed effluent from the conductivity detector is then combined with an acidic solution of potassium iodide (0.26 mol/L) containing a catalytic amoimt of ammonium molybdate tetrahydrate (43 pmol/L). The mixture is heated in the knitted reaction coil to 80 °C to facilitate complete reaction. The formed triiodide is measured by its UV absorption at 352 nm. Because KI is photosensitive, the KI/Mo PCR solution develops a light yellow color with time, even when stored under helium. Therefore, the PCR reservoir has to be protected from light by covering it with aluminum foil and should be pressimzed with helium. Under... 

Use of ascorbate solution as both an eluent and a reducing agent following by molybdate derivatization... 

---