352
C. Sarzanini
Inorganic selenium species were determined by ion-pairing reversed-phase (silica
C18) microscale-liquid chromatography (eluent: methanol-water-TBA, flow rate
50 fll min-I) and a direct injection nebulizer (DIN) coupled with ICP-MS (detection
limits of 10-20 ng mrl) (Houck et al.1991). A similar ion-pair chromatographic separation with an ICP-MS detector using an ultrasonic nebulizer gave detection limits
between 0.17 and 0.76 ng ml- I for TMSe, Se(IV) and Se(VI) (Yang and Jiang 1995).
Se(IV) and Se(VI) species were also separated (Shum and Houck 1993) on an anion
exchange micro column (eluent flow rate 100 fll min-I) with a DIN-ICP-MS detection
system. Isotope ratio measurements on chromatographically separated species of Se
gave detection limits of 7-8 ng mrl for both of the species. A two-step eluent switching procedure (25 mM K2S04 eluent switching to 200 mM after 200 s at flow rate
2.0 ml min-I), with an anion exchange column, enabled the separation of inorganic
selenium species in aqueous samples (Pitts et al. 1995). Detection of analytes, after online microwave reduction and hydride generation, was performed with an atomic fluorescence detector. The method provided detection limits of 0.2 and 0.3 ng mrl within
1.5 and 2.0% RSD for selenite and selenate respectively. Speciation of eight selenium
compounds has also been obtained with a strong cation-exchange column by interfacing the chromatographic system with an ICP-MS by high pressure hydraulic nebulizer (Goessler et al. 1997).
Mercury species, methyl-, ethyl- and inorganic mercury, are both neutral and ionic,
and their ion chromatographic separation as cysteine complexes was developed
(Sarzanini et al. 1994). Eluent composition (acetic acid, sodium perchlorate and cysteine) was optimized with respect to the separation procedure and to the reductive
reaction (N aBH4) which permits the detection of mercury with cold vapour AAS. Online preconcentration procedures were also investigated using both C I8 and ion exchange micro columns. The detection limits, for 100 ml samples, were 2,10 and 4 ng for
Hg, CH3Hg and C2HSHg respectively. Enrichment and separation of methyl-, ethyl-,
methoxyethyl-, ethoxyethyl-, phenyl- and inorganic Hg complexes were also performed
with pyrrolidine dithiocarbamate (PDC). An RP C18 column was used coupled with
an acetonitrile-water buffered eluent. Analytes were determined by ultraviolet, postcolumn oxidation, cold vapour atomic absorption spectrometry (UV-PCO-CVAAS)
(Falter and Scholer 1994,1995). The preconcentration (300 ml samples) of mercurychelates on a micro column (Hypersil-ODS RP C18) gave detection limits of 0.5 ng rl.
ICP-MS detection through ultrasonic nebulization was enabled for methyl-, ethyl- and
inorganic mercury by their separation on a C18 reversed phase column with a methanol-acetonitrile-2-mercaptoethanol eluent containing ammonium acetate (Huang and
Jiang 1993). Detection limit values (0.4-0.8 ppb) 10 times lower than those obtained
with LC-ICP-MS with a conventional nebulizer, and comparable to those for LC-ICPMS with cold vapour generation, were obtained.
The determination of chromium speciation by ion-pair chromatography has been
optimized (Posta et al. 1993). The separation of Cr(VI)-Cr(I1I) was performed on an
RP C18 column by using a TBA-acetate, ammonium acetate, phosphoric acid and
methanol based eluent. This eluent composition also enhanced the sensitivity of detection obtained by coupling HPLC to a flame AAS by a high pressure capillary with
hydraulic high pressure nebulization. Detection limits of 0.02 and 0.03 mg rl for Cr(VI)
and Cr(I1I) respectively were lowered to 0.5 flg rl for Cr(VI) after a preconcentration
step. An anion chromatographic separation (polymer-based anion exchanger, eluent:
C. Sarzanini
Inorganic selenium species were determined by ion-pairing reversed-phase (silica
C18) microscale-liquid chromatography (eluent: methanol-water-TBA, flow rate
50 fll min-I) and a direct injection nebulizer (DIN) coupled with ICP-MS (detection
limits of 10-20 ng mrl) (Houck et al.1991). A similar ion-pair chromatographic separation with an ICP-MS detector using an ultrasonic nebulizer gave detection limits
between 0.17 and 0.76 ng ml- I for TMSe, Se(IV) and Se(VI) (Yang and Jiang 1995).
Se(IV) and Se(VI) species were also separated (Shum and Houck 1993) on an anion
exchange micro column (eluent flow rate 100 fll min-I) with a DIN-ICP-MS detection
system. Isotope ratio measurements on chromatographically separated species of Se
gave detection limits of 7-8 ng mrl for both of the species. A two-step eluent switching procedure (25 mM K2S04 eluent switching to 200 mM after 200 s at flow rate
2.0 ml min-I), with an anion exchange column, enabled the separation of inorganic
selenium species in aqueous samples (Pitts et al. 1995). Detection of analytes, after online microwave reduction and hydride generation, was performed with an atomic fluorescence detector. The method provided detection limits of 0.2 and 0.3 ng mrl within
1.5 and 2.0% RSD for selenite and selenate respectively. Speciation of eight selenium
compounds has also been obtained with a strong cation-exchange column by interfacing the chromatographic system with an ICP-MS by high pressure hydraulic nebulizer (Goessler et al. 1997).
Mercury species, methyl-, ethyl- and inorganic mercury, are both neutral and ionic,
and their ion chromatographic separation as cysteine complexes was developed
(Sarzanini et al. 1994). Eluent composition (acetic acid, sodium perchlorate and cysteine) was optimized with respect to the separation procedure and to the reductive
reaction (N aBH4) which permits the detection of mercury with cold vapour AAS. Online preconcentration procedures were also investigated using both C I8 and ion exchange micro columns. The detection limits, for 100 ml samples, were 2,10 and 4 ng for
Hg, CH3Hg and C2HSHg respectively. Enrichment and separation of methyl-, ethyl-,
methoxyethyl-, ethoxyethyl-, phenyl- and inorganic Hg complexes were also performed
with pyrrolidine dithiocarbamate (PDC). An RP C18 column was used coupled with
an acetonitrile-water buffered eluent. Analytes were determined by ultraviolet, postcolumn oxidation, cold vapour atomic absorption spectrometry (UV-PCO-CVAAS)
(Falter and Scholer 1994,1995). The preconcentration (300 ml samples) of mercurychelates on a micro column (Hypersil-ODS RP C18) gave detection limits of 0.5 ng rl.
ICP-MS detection through ultrasonic nebulization was enabled for methyl-, ethyl- and
inorganic mercury by their separation on a C18 reversed phase column with a methanol-acetonitrile-2-mercaptoethanol eluent containing ammonium acetate (Huang and
Jiang 1993). Detection limit values (0.4-0.8 ppb) 10 times lower than those obtained
with LC-ICP-MS with a conventional nebulizer, and comparable to those for LC-ICPMS with cold vapour generation, were obtained.
The determination of chromium speciation by ion-pair chromatography has been
optimized (Posta et al. 1993). The separation of Cr(VI)-Cr(I1I) was performed on an
RP C18 column by using a TBA-acetate, ammonium acetate, phosphoric acid and
methanol based eluent. This eluent composition also enhanced the sensitivity of detection obtained by coupling HPLC to a flame AAS by a high pressure capillary with
hydraulic high pressure nebulization. Detection limits of 0.02 and 0.03 mg rl for Cr(VI)
and Cr(I1I) respectively were lowered to 0.5 flg rl for Cr(VI) after a preconcentration
step. An anion chromatographic separation (polymer-based anion exchanger, eluent: