CHAPTER 18 • Metals Analysis by High Performance Liquid Chromatography
349
1993).A C2-bonded silica microcolumn, loaded with a dithiocarbamate-cetyltrimethylammonium ion pair, enabled the retention of metal ions and their complexation. Elution on an ODS analytical column was optimized by adding cetyltrimethylammonium
(CTA) bromide to a CH 3 CN-H20 mixture, owing to the relative instability of the CdDEDTC anionic complex which was eluted as a neutral ion pair.
On the basis of previous studies (Zhao and Fu 1990), a selective pre concentration
method with a cation exchange resin for RP-HPLC of the CO-5-Br-PADAP has been
more recently developed (Uehara et al.1994). Co complex, in aqueous solution, is readily
oxidized to the Co(I1I)-5-Br-PADAP inert cationic complex which is retained on a sulfonated XAD-4 resin. Co is detected spectrophotometrically (588 nm) after elution onto
a C18 analytical column (Capcell SG-120) with a methanol-water eluent to which EDTA
and TBA have been added and without 5-Br-PADAP. The absence of 5-Br-PADAP
favours the dissociation, e.g. of Cu and Zn chelates, and other metal ions eluted later,
like Fe and Ni, do not interfere. The detection limit for Co in water samples is reported
to be 5.9 ng rl.
A feature of these techniques is the high selectivity obtainable by a proper choice
of ligand and chromatographic parameters. The method developed for Fe(II) determination in aerosol, rainwater and seawater (remote marine aerosol) is an example
(Yi et al. 1992). A solid phase extraction on Sep-Pak C18 cartridges loaded with 3-(2pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p'-disulfonic acid (ferrozine, FZ) enabled the
separation from matrix and pre concentration of Fe(II) as Fe(II)-FZ cation complex.
The complex and FZ were eluted with methanol, and excess ligand was separated by
ion pair-reversed phase LC. In this way Fe(I1I), Ni(II), Co(II) and Cu(II) interferences
were removed, and a detection limit of 5.6 ng rl was obtained.
The detection limits of the whole IIC procedure, based on metal ion precomplexation
with Plasmocorinth B (Sarzanini et al. 1993a), were lowered by coupling a preconcentration step. This last was performed by eluting samples through a hydrophobic
micro column (C18) after carrying out the ion-pair reaction directly on the sample. The
procedure gave enrichment factors up to 900 willi detection limits between 15-90 ng rl
(Sarzanini et al. 1993b).
The above mentioned highly cross-linked macroporous PS-DVB resin containing
the iminodiacetate functional group that allows operation at high pressure without
physical degradation (MetPac CC-1 column, Dionex) (Siriraks et al. 1990) seems a good
example of the column switching technique involving a preconcentration step and
selective matrix removal. At pH 5.2-5.6 polyvalent metal ions are selectively concentrated into MetPac CC-1, alkali metals and anions are not retained, and a selective elution of alkali earth metals can be achieved using ammonium acetate. Lanthanides and
heavy metals, with the exception of chromium, are eluted with acid into a cation exchange column, acting as interface before the analytical column, to which the above
are successively driven with a PDCA or an oxalate complexing eluent. UV-VIS spectrophotometric detection is accomplished after post-column derivatization (PAR), and
detection limits (Fe, Cu, Ni, Zn, Co, Mn, Cd, Pb) range from 0.2 to 1 flg rl (Siriraks et al.
1990; Dionex 1990). The procedure was successfully used for metal ion determination
in seawater from the Venice Lagoon, and with 60 ml sample preconcentration the detection limits for Cu, Ni, Zn, Co and Mn were lowered to 0.05-0.1 flg rl (Caprioli and
Torcini 1993). A modification of the above mentioned procedure performed metal
recovery from MetPac CC-1 resin with the same eluent used for the ion chromato-
349
1993).A C2-bonded silica microcolumn, loaded with a dithiocarbamate-cetyltrimethylammonium ion pair, enabled the retention of metal ions and their complexation. Elution on an ODS analytical column was optimized by adding cetyltrimethylammonium
(CTA) bromide to a CH 3 CN-H20 mixture, owing to the relative instability of the CdDEDTC anionic complex which was eluted as a neutral ion pair.
On the basis of previous studies (Zhao and Fu 1990), a selective pre concentration
method with a cation exchange resin for RP-HPLC of the CO-5-Br-PADAP has been
more recently developed (Uehara et al.1994). Co complex, in aqueous solution, is readily
oxidized to the Co(I1I)-5-Br-PADAP inert cationic complex which is retained on a sulfonated XAD-4 resin. Co is detected spectrophotometrically (588 nm) after elution onto
a C18 analytical column (Capcell SG-120) with a methanol-water eluent to which EDTA
and TBA have been added and without 5-Br-PADAP. The absence of 5-Br-PADAP
favours the dissociation, e.g. of Cu and Zn chelates, and other metal ions eluted later,
like Fe and Ni, do not interfere. The detection limit for Co in water samples is reported
to be 5.9 ng rl.
A feature of these techniques is the high selectivity obtainable by a proper choice
of ligand and chromatographic parameters. The method developed for Fe(II) determination in aerosol, rainwater and seawater (remote marine aerosol) is an example
(Yi et al. 1992). A solid phase extraction on Sep-Pak C18 cartridges loaded with 3-(2pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p'-disulfonic acid (ferrozine, FZ) enabled the
separation from matrix and pre concentration of Fe(II) as Fe(II)-FZ cation complex.
The complex and FZ were eluted with methanol, and excess ligand was separated by
ion pair-reversed phase LC. In this way Fe(I1I), Ni(II), Co(II) and Cu(II) interferences
were removed, and a detection limit of 5.6 ng rl was obtained.
The detection limits of the whole IIC procedure, based on metal ion precomplexation
with Plasmocorinth B (Sarzanini et al. 1993a), were lowered by coupling a preconcentration step. This last was performed by eluting samples through a hydrophobic
micro column (C18) after carrying out the ion-pair reaction directly on the sample. The
procedure gave enrichment factors up to 900 willi detection limits between 15-90 ng rl
(Sarzanini et al. 1993b).
The above mentioned highly cross-linked macroporous PS-DVB resin containing
the iminodiacetate functional group that allows operation at high pressure without
physical degradation (MetPac CC-1 column, Dionex) (Siriraks et al. 1990) seems a good
example of the column switching technique involving a preconcentration step and
selective matrix removal. At pH 5.2-5.6 polyvalent metal ions are selectively concentrated into MetPac CC-1, alkali metals and anions are not retained, and a selective elution of alkali earth metals can be achieved using ammonium acetate. Lanthanides and
heavy metals, with the exception of chromium, are eluted with acid into a cation exchange column, acting as interface before the analytical column, to which the above
are successively driven with a PDCA or an oxalate complexing eluent. UV-VIS spectrophotometric detection is accomplished after post-column derivatization (PAR), and
detection limits (Fe, Cu, Ni, Zn, Co, Mn, Cd, Pb) range from 0.2 to 1 flg rl (Siriraks et al.
1990; Dionex 1990). The procedure was successfully used for metal ion determination
in seawater from the Venice Lagoon, and with 60 ml sample preconcentration the detection limits for Cu, Ni, Zn, Co and Mn were lowered to 0.05-0.1 flg rl (Caprioli and
Torcini 1993). A modification of the above mentioned procedure performed metal
recovery from MetPac CC-1 resin with the same eluent used for the ion chromato-