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Robert H. Byrne - One of the best experts on this subject based on the ideXlab platform.

  • Achieving accurate spectrophotometric pH measurements using unpurified Meta-cresol purple
    Marine Chemistry, 2017
    Co-Authors: N.k. Douglas, Robert H. Byrne
    Abstract:

    Abstract For best accuracy, spectrophotometric characterizations of seawater pH are obtained using a purified pH-sensitive dye—usually Meta-cresol purple (mCP) for typical ranges of seawater pH. In recognition of practical limitations, though, a straightforward method is here proposed to improve measurements made using unpurified mCP. The user first determines, for a particular lot of unpurified mCP, the absorbance contribution of indicator impurities at 434 nm (434Aimp). Correction for this contribution is then mathematically applied to the measurements of seawater pH. We tested this approach using six unpurified lots of mCP and, for comparison, purified mCP in a synthetic experimental solution over the pH range 7.25–8.25. The 434Aimp correction yielded substantial improvements in pH accuracy: on the order of 0.005 at low pH (~ 7.25) and 0.01 or more at higher pH (~ 8.25). The pH accuracy achieved by the corrective model was also examined relative to the Global Ocean Acidification Observing Network (GOA-ON) “weather” and “climate” goals for pH measurements (uncertainties of ± 0.02 and ± 0.003, respectively). When previously published algorithms (appropriate for purified mCP) were used, none of the unpurified dyes met the more stringent “climate” goal in waters of pH > 7.6. With the algorithms proposed here (i.e., incorporating the lot-specific 434Aimp correction), three of the six lots came into “climate” compliance over the full experimental pHT range and two additional lots achieved “climate” compliance up to pH ~ 8.0. This protocol offers a simple, user-determined correction to significantly improve the accuracy of pH measurements made with unpurified mCP.

  • Purification and Characterization of Meta-cresol Purple for Spectrophotometric Seawater pH Measurements
    2015
    Co-Authors: Xuewu Liu, Mark C. Patsavas, Robert H. Byrne
    Abstract:

    Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, Meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:pHT=−log(K2Te2)+log(R−e11−Re3e2)where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances, λ1A and λ2A, used to calculate R are measured at wavelengths (λ) of 434 and 578 nm. This characterization is appropriate for 278.15 ≤ T ≤ 308.15 and 20 ≤ S ≤ 40

  • Purification of Meta-cresol purple and cresol red by flash chromatography: Procedures for ensuring accurate spectrophotometric seawater pH measurements
    Marine Chemistry, 2013
    Co-Authors: Mark C. Patsavas, Robert H. Byrne, Xuewu Liu
    Abstract:

    Abstract Impurities in sulphonephthalein indicator salts can result in significant errors in seawater pH determinations. To ensure suitable measurement accuracy and intercomparability on a global basis, impurities must be removed from all indicators used for oceanographic CO 2 system analyses. Previous work has described an effective HPLC (high-performance liquid chromatography) procedure for purification of Meta-cresol purple, but the technique is labor-intensive, with each HPLC run producing only a small batch of purified indicator. This work describes the use of flash chromatography to more efficiently produce large batches of purified Meta-cresol purple (mCP) and cresol red (CR), the preferred indicators for direct water column determinations of seawater pH. Several batches of unrefined mCP and CR of independent origin were prepared by flash chromatography. Indicator purity was then assessed in two ways: by (a) HPLC verification and (b) pH measurements of highly buffered solutions. HPLC chromatograms of the various flash-prepared mCPs indicated that the process did not always result in a completely pure product. In terms of performance, however – i.e., pH measurements of highly buffered solutions – no differences were observed between an HPLC-purified reference mCP and the flash-purified mCPs. HPLC examination of the flash-purified CRs indicated that every product was free of detectable impurities. No differences were seen in comparative pH measurements made with the purified CRs. The flash chromatography procedures outlined in this work are suitable for producing bulk quantities of mCP and CR for use in high-precision spectrophotometric pH measurements in seawater.

  • The effect of pressure on Meta-cresol Purple protonation and absorbance characteristics for spectrophotometric pH measurements in seawater
    Marine Chemistry, 2013
    Co-Authors: Alan L. Soli, Brody J. Pav, Robert H. Byrne
    Abstract:

    Abstract The sulfonephthalein indicator Meta-cresol Purple (mCP) is well suited to direct spectrophotometric pH measurements throughout the oceanic water column. In prior work the molar absorbance and proton exchange characteristics of purified mCP were characterized over a wide range of salinities and temperatures, allowing use of the indicator over a broad range of oceanic conditions in the surface ocean. Modern spectrophotometric instrumentation allows direct in situ measurements of seawater pH at depths that create substantial pressure-dependent changes in the physical chemical behavior of mCP. In order to allow use of purified mCP for quantitative pH measurements over essentially the full range of ocean depths, prior calibrations of mCP for measurements of seawater pH were extended to include pressures up to 827 bar. Using purified mCP, seawater pH is measured using the equation pH T = − log K 2 e 2 + log R − e 1 1 − R ⋅ e 3 e 2 where e 1 = − 0.007762 + 4.5174 × 1 0 – 5 T + 1.7 × 1 0 – 6 P e 3 / e 2 = − 0.020813 + 2.60262 × 1 0 – 4 T + 1.0436 × 1 0 – 4 S – 35 + 4.6 × 1 0 – 6 P – log K 2 e 2 = a + b / T + c ln T − d T − 0.05645 / T × P and a = 246.64209 + 0.315971S + 2.8855 × 10− 4S2 b = 7229.23864 − 7.098137S − 0.057034S2 c = 44.493382 − 0.052711S d = 0.0781344. P and T are gauge pressure (bar) and Kelvin temperature, and the coefficients a, b and c are salinity dependent coefficients determined in previous work. The influence of pressure on the properties of mCP is sufficient to cause easily measureable effects at depths less than 100 m.

  • Spectrophotometric calibration of pH electrodes in seawater using purified m-cresol purple.
    Environmental science & technology, 2012
    Co-Authors: Regina A. Easley, Robert H. Byrne
    Abstract:

    This work examines the use of purified Meta-cresol purple (mCP) for direct spectrophotometric calibration of glass pH electrodes in seawater. The procedures used in this investigation allow for simple, inexpensive electrode calibrations over salinities of 20–40 and temperatures of 278.15–308.15 K without preparation of synthetic Tris seawater buffers. The optimal pH range is ∼7.0–8.1. Spectrophotometric calibrations enable straightforward, quantitative distinctions between Nernstian and non-Nernstian electrode behavior. For the electrodes examined in this study, both types of behavior were observed. Furthermore, calibrations performed in natural seawater allow direct determination of the influence of salinity on electrode performance. The procedures developed in this study account for salinity-induced variations in liquid junction potentials that, if not taken into account, would create pH inconsistencies of 0.028 over a 10-unit change in salinity. Spectrophotometric calibration can also be used to expedi...

C Valla - One of the best experts on this subject based on the ideXlab platform.

  • determination of urinary ortho and Meta cresol in humans by headspace spme gas chromatography mass spectrometry
    Journal of Chromatography B, 2005
    Co-Authors: Silvia Fustinoni, Rosa Mercadante, Laura Campo, L Scibetta, C Valla
    Abstract:

    Abstract ortho-cresol (o-C) and Meta-cresol (m-C) are minor urinary Metabolites of toluene, a widely used chemical with neurotoxicological properties. A new assay for their determination in human urine is here proposed. Urinary cresol sulphates and glucuronates are submitted to acid hydrolysis, urine is neutralized, added with o-cresols-d8, and analytes are sampled in the headspace of urine by SPME using a polydimethylsiloxane fiber. Analysis is performed by GC/MS using, for separation, either a SupelcoWax10 (for o-C) or a chiral CP cresol (for o-C and m-C) column. The method is very specific, with a range of linearity 0–5.0 mg/l, within- and between-run precision, as coefficient of variation,

  • Determination of urinary ortho- and Meta-cresol in humans by headspace SPME gas chromatography/mass spectrometry.
    Journal of Chromatography B, 2005
    Co-Authors: Silvia Fustinoni, Rosa Mercadante, Laura Campo, L Scibetta, C Valla
    Abstract:

    Abstract ortho-cresol (o-C) and Meta-cresol (m-C) are minor urinary Metabolites of toluene, a widely used chemical with neurotoxicological properties. A new assay for their determination in human urine is here proposed. Urinary cresol sulphates and glucuronates are submitted to acid hydrolysis, urine is neutralized, added with o-cresols-d8, and analytes are sampled in the headspace of urine by SPME using a polydimethylsiloxane fiber. Analysis is performed by GC/MS using, for separation, either a SupelcoWax10 (for o-C) or a chiral CP cresol (for o-C and m-C) column. The method is very specific, with a range of linearity 0–5.0 mg/l, within- and between-run precision, as coefficient of variation,

  • determination of urinary ortho and Meta cresol in humans by headspace spme gas chromatography mass spectrometry
    Journal of Chromatography B, 2005
    Co-Authors: Silvia Fustinoni, Rosa Mercadante, Laura Campo, L Scibetta, C Valla, V Foa
    Abstract:

    ortho-cresol (o-C) and Meta-cresol (m-C) are minor urinary Metabolites of toluene, a widely used chemical with neurotoxicological properties. A new assay for their determination in human urine is here proposed. Urinary cresol sulphates and glucuronates are submitted to acid hydrolysis, urine is neutralized, added with o-cresols-d8, and analytes are sampled in the headspace of urine by SPME using a polydimethylsiloxane fiber. Analysis is performed by GC/MS using, for separation, either a SupelcoWax10 (for o-C) or a chiral CP cresol (for o-C and m-C) column. The method is very specific, with a range of linearity 0-5.0 mg/l, within- and between-run precision, as coefficient of variation, <15% and <19%, limit of detection of 0.006 mg/l for o-C and 0.007 mg/l for m-C. The procedure is applied to the quantification of cresols in urine from workers exposed to toluene and from subjects belonging to the general population.

Xuewu Liu - One of the best experts on this subject based on the ideXlab platform.

  • Purification and Characterization of Meta-cresol Purple for Spectrophotometric Seawater pH Measurements
    2015
    Co-Authors: Xuewu Liu, Mark C. Patsavas, Robert H. Byrne
    Abstract:

    Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, Meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:pHT=−log(K2Te2)+log(R−e11−Re3e2)where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances, λ1A and λ2A, used to calculate R are measured at wavelengths (λ) of 434 and 578 nm. This characterization is appropriate for 278.15 ≤ T ≤ 308.15 and 20 ≤ S ≤ 40

  • Purification of Meta-cresol purple and cresol red by flash chromatography: Procedures for ensuring accurate spectrophotometric seawater pH measurements
    Marine Chemistry, 2013
    Co-Authors: Mark C. Patsavas, Robert H. Byrne, Xuewu Liu
    Abstract:

    Abstract Impurities in sulphonephthalein indicator salts can result in significant errors in seawater pH determinations. To ensure suitable measurement accuracy and intercomparability on a global basis, impurities must be removed from all indicators used for oceanographic CO 2 system analyses. Previous work has described an effective HPLC (high-performance liquid chromatography) procedure for purification of Meta-cresol purple, but the technique is labor-intensive, with each HPLC run producing only a small batch of purified indicator. This work describes the use of flash chromatography to more efficiently produce large batches of purified Meta-cresol purple (mCP) and cresol red (CR), the preferred indicators for direct water column determinations of seawater pH. Several batches of unrefined mCP and CR of independent origin were prepared by flash chromatography. Indicator purity was then assessed in two ways: by (a) HPLC verification and (b) pH measurements of highly buffered solutions. HPLC chromatograms of the various flash-prepared mCPs indicated that the process did not always result in a completely pure product. In terms of performance, however – i.e., pH measurements of highly buffered solutions – no differences were observed between an HPLC-purified reference mCP and the flash-purified mCPs. HPLC examination of the flash-purified CRs indicated that every product was free of detectable impurities. No differences were seen in comparative pH measurements made with the purified CRs. The flash chromatography procedures outlined in this work are suitable for producing bulk quantities of mCP and CR for use in high-precision spectrophotometric pH measurements in seawater.

Silvia Fustinoni - One of the best experts on this subject based on the ideXlab platform.

  • determination of urinary ortho and Meta cresol in humans by headspace spme gas chromatography mass spectrometry
    Journal of Chromatography B, 2005
    Co-Authors: Silvia Fustinoni, Rosa Mercadante, Laura Campo, L Scibetta, C Valla
    Abstract:

    Abstract ortho-cresol (o-C) and Meta-cresol (m-C) are minor urinary Metabolites of toluene, a widely used chemical with neurotoxicological properties. A new assay for their determination in human urine is here proposed. Urinary cresol sulphates and glucuronates are submitted to acid hydrolysis, urine is neutralized, added with o-cresols-d8, and analytes are sampled in the headspace of urine by SPME using a polydimethylsiloxane fiber. Analysis is performed by GC/MS using, for separation, either a SupelcoWax10 (for o-C) or a chiral CP cresol (for o-C and m-C) column. The method is very specific, with a range of linearity 0–5.0 mg/l, within- and between-run precision, as coefficient of variation,

  • Determination of urinary ortho- and Meta-cresol in humans by headspace SPME gas chromatography/mass spectrometry.
    Journal of Chromatography B, 2005
    Co-Authors: Silvia Fustinoni, Rosa Mercadante, Laura Campo, L Scibetta, C Valla
    Abstract:

    Abstract ortho-cresol (o-C) and Meta-cresol (m-C) are minor urinary Metabolites of toluene, a widely used chemical with neurotoxicological properties. A new assay for their determination in human urine is here proposed. Urinary cresol sulphates and glucuronates are submitted to acid hydrolysis, urine is neutralized, added with o-cresols-d8, and analytes are sampled in the headspace of urine by SPME using a polydimethylsiloxane fiber. Analysis is performed by GC/MS using, for separation, either a SupelcoWax10 (for o-C) or a chiral CP cresol (for o-C and m-C) column. The method is very specific, with a range of linearity 0–5.0 mg/l, within- and between-run precision, as coefficient of variation,

  • determination of urinary ortho and Meta cresol in humans by headspace spme gas chromatography mass spectrometry
    Journal of Chromatography B, 2005
    Co-Authors: Silvia Fustinoni, Rosa Mercadante, Laura Campo, L Scibetta, C Valla, V Foa
    Abstract:

    ortho-cresol (o-C) and Meta-cresol (m-C) are minor urinary Metabolites of toluene, a widely used chemical with neurotoxicological properties. A new assay for their determination in human urine is here proposed. Urinary cresol sulphates and glucuronates are submitted to acid hydrolysis, urine is neutralized, added with o-cresols-d8, and analytes are sampled in the headspace of urine by SPME using a polydimethylsiloxane fiber. Analysis is performed by GC/MS using, for separation, either a SupelcoWax10 (for o-C) or a chiral CP cresol (for o-C and m-C) column. The method is very specific, with a range of linearity 0-5.0 mg/l, within- and between-run precision, as coefficient of variation, <15% and <19%, limit of detection of 0.006 mg/l for o-C and 0.007 mg/l for m-C. The procedure is applied to the quantification of cresols in urine from workers exposed to toluene and from subjects belonging to the general population.

Mark C. Patsavas - One of the best experts on this subject based on the ideXlab platform.

  • Purification and Characterization of Meta-cresol Purple for Spectrophotometric Seawater pH Measurements
    2015
    Co-Authors: Xuewu Liu, Mark C. Patsavas, Robert H. Byrne
    Abstract:

    Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, Meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:pHT=−log(K2Te2)+log(R−e11−Re3e2)where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances, λ1A and λ2A, used to calculate R are measured at wavelengths (λ) of 434 and 578 nm. This characterization is appropriate for 278.15 ≤ T ≤ 308.15 and 20 ≤ S ≤ 40

  • Purification of Meta-cresol purple and cresol red by flash chromatography: Procedures for ensuring accurate spectrophotometric seawater pH measurements
    Marine Chemistry, 2013
    Co-Authors: Mark C. Patsavas, Robert H. Byrne, Xuewu Liu
    Abstract:

    Abstract Impurities in sulphonephthalein indicator salts can result in significant errors in seawater pH determinations. To ensure suitable measurement accuracy and intercomparability on a global basis, impurities must be removed from all indicators used for oceanographic CO 2 system analyses. Previous work has described an effective HPLC (high-performance liquid chromatography) procedure for purification of Meta-cresol purple, but the technique is labor-intensive, with each HPLC run producing only a small batch of purified indicator. This work describes the use of flash chromatography to more efficiently produce large batches of purified Meta-cresol purple (mCP) and cresol red (CR), the preferred indicators for direct water column determinations of seawater pH. Several batches of unrefined mCP and CR of independent origin were prepared by flash chromatography. Indicator purity was then assessed in two ways: by (a) HPLC verification and (b) pH measurements of highly buffered solutions. HPLC chromatograms of the various flash-prepared mCPs indicated that the process did not always result in a completely pure product. In terms of performance, however – i.e., pH measurements of highly buffered solutions – no differences were observed between an HPLC-purified reference mCP and the flash-purified mCPs. HPLC examination of the flash-purified CRs indicated that every product was free of detectable impurities. No differences were seen in comparative pH measurements made with the purified CRs. The flash chromatography procedures outlined in this work are suitable for producing bulk quantities of mCP and CR for use in high-precision spectrophotometric pH measurements in seawater.

  • purification and characterization of Meta cresol purple for spectrophotometric seawater ph measurements
    Environmental Science & Technology, 2011
    Co-Authors: Mark C. Patsavas, Robert H. Byrne
    Abstract:

    Spectrophotometric procedures allow rapid and precise measurements of the pH of natural waters. However, impurities in the acid–base indicators used in these analyses can significantly affect measurement accuracy. This work describes HPLC procedures for purifying one such indicator, Meta-cresol purple (mCP), and reports mCP physical–chemical characteristics (thermodynamic equilibrium constants and visible-light absorbances) over a range of temperature (T) and salinity (S). Using pure mCP, seawater pH on the total hydrogen ion concentration scale (pHT) can be expressed in terms of measured mCP absorbance ratios (R = λ2A/λ1A) as follows:pHT=−log(K2Te2)+log(R−e11−Re3e2)where −log(K2Te2) = a + (b/T) + c ln T – dT; a = −246.64209 + 0.315971S + 2.8855 × 10–4S2; b = 7229.23864 – 7.098137S – 0.057034S2; c = 44.493382 – 0.052711S; d = 0.0781344; and mCP molar absorbance ratios (ei) are expressed as e1 = −0.007762 + 4.5174 × 10–5T and e3/e2 = −0.020813 + 2.60262 × 10–4T + 1.0436 × 10–4 (S – 35). The mCP absorbances...