Dissolved hydrogen analyzer

Details Dissolved hydrogen analyzer Dissolved hydrogen analyzer

1999-03-22

2001-08-21

Warden, Jill (Department: 1743)

Chemical apparatus and process disinfecting, deodorizing, preser

Analyzer, structured indicator, or manipulative laboratory...

Means for analyzing liquid or solid sample

C422S094000, C422S098000, C422S088000, C073S019100, C073S019120

Reexamination Certificate

active

06277329

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to measurement of dissolved molecular hydrogen. In particular, the present invention relates to an apparatus and process for the measurement of hydrogen in water at concentrations as low as on the order of 0.1 nM.
BACKGROUND OF THE INVENTION
Molecular hydrogen present in water in a dissolved form (dissolved hydrogen) is an important indicator of various biological and chemical processes. These processes include in situ bioremrediation of groundwater by engineered methods or by natural attenuation, anaerobic reactors for waste treatment including anaerobic digesters, anaerobic bioprocesses for the manufacture of biochemicals, including fermentation, operation of subsurface, permeable metal-reactive walls for remediation of chlorinated chemicals in groundwater by reductive dehalogenation and corrosion of metals in process systems including boilers. Dissolved hydrogen can be an indicator of the nature, extent, or stability of these processes.
The concentration of dissolved hydrogen can be extremely low. For example, one class of anaerobic bacteria known as iron-reducing bacteria typically demonstrate dissolved hydrogen concentrations in groundwater in the range of 0.1 to 1.0 nM when at steady state (F. H. Chapelle and P. B. McMahon,
J. Hydrology
, 127:85-108 (1991)).
Methods available for measurement of dissolved hydrogen involve direct measurement in the liquid of interest or extraction of dissolved hydrogen into a carrier gas which is then analyzed. Only one method exists for measuring dissolved hydrogen concentrations as low as 0.1 nM and is called the “bubble strip” method (F. H. Chapelle and P. B. McMahon,
J. Hydrology
, 127:85-108 (1991)). This method involves equilibration of a bubble of nitrogen with a flowing stream of groundwater in a gas sampling bulb made from glass. Samples of the gas bubble are injected into a reduction gas analyzer over time until the gas bubble is in equilibrium with the groundwater. The reduction gas analyzer employs chemical reduction of a heated bed of mercuric oxide by hydrogen to form gaseous mercury that is sensed by an ultraviolet detector. Chromatographic separation of hydrogen from other reducing gases is required prior to mercuric oxide reduction. The gaseous hydrogen concentration is then related to the dissolved hydrogen concentration by Henry's law where 0.1 nM dissolved hydrogen approximately correlates to 0.125 ppm of gaseous hydrogen at equilibrium and ambient temperature and pressure. This method is difficult, time-consuming, and expensive to use and has therefore not gained widespread acceptance as an analytical method. Application of the reduction gas analyzer, in combination with hydrogen equilibration over Teflon tubing, to anaerobic digestion in particular is cited as being limited because of its “sophistication, high cost, detection limits, and interference from other solutes” (K. Kuroda, R. G. Silveira, N. Nishio. H. Sunahara, and S. Nagai,
J. Ferment. Boeing
, 71:418-423 (1991)). The gas bubble equilibration method also is greatly subject to operator error, in part because of mass transfer limitations. A. Pauss, G. Andre, M. Perrier, and S. R. Guiot,
Appl. Environ Microbiol
, 56:1636-1644 (1990). Other methods that are available for hydrogen measurement are insensitive at these low concentrations and in environments of interest.
A Clark probe with reversed polarity is capable of hydrogen measurement in gases or liquids. The lower detection limit is 500 ppm in gases (F. J. Hanus, K. R. Carter, and H. J. Evans,
Methods in Enzymology
, 69:731-739 (1980)) and 15 &mgr;g/L (7,500 nM) in water (J. D. Istok, M. D. Humphrey, M. H. Schroth, M. R. Hyman, and K. T. O'Reilly,
Ground Water
, 35:619-631 (1997)). Another electrochemical probe for dissolved hydrogen described by Strong (G. E. Strong and R. Cord-Ruwisch,
BiotechnoL Boeing
, 45:63-68 (1995)) has a detection limit of 30 Pa partial pressure which is equivalent to 240 nM. Ozawa et al. in EP 0096417A1 describe an electrochemical hydrogen sensor that has a sensitivity of 500 nM dissolved hydrogen. Kitamura et al. in EP 0122511 A2 describe a similar electrochemical hydrogen sensor that compensates for oxygen but does not remove its influence and has an insufficient sensitivity in the nM range. Other electrochemical methods employing fuel cells have been described with detection limits of 1 &mgr;M (1,000 nM) (J.-P. Gebeault, J. Van Berlo, and M. Dymarski,
Trans. Amer. Nucl Soc
., 46:612-613 (1984)) and 80 nM. A. Pauss, R. Samson, S. Guiot and C. Beauchemin,
Biotechnol. Bioeng
., 35:492-501 (1990). Hydrogen sulfide and oxygen interfere with the performance of these probes. A. Pauss, R. Samson, S. Guiot and C. Beaucherun,
Biotechnol. Bioeng
., 35:492-501 (1990). In one case, oxygen did not interfere as long as it was present in lower concentrations than hydrogen (N. Hara and D. D. Macdonald,
J. Electrochem. Soc
., 144:4152-4157 (1997)). In the practice of the present invention, very low hydrogen concentrations render this requirement impractical.
Gas chromatography with thermal conductivity detection can be used to detect hydrogen in gases. This method can be used to detect 0.5 nmoles of injected hydrogen (F. J. Hanus, K. R. Carter, and H. J. Evans,
Methods in Enzymology
, 69:731-739 (1980)) which, based on a 1-ml injection, translates to a concentration of 12 ppm in gas or an equilibrium dissolved concentration of 9.6 nM.
An instrument based on thermal conductivity has been developed to measure hydrogen in steam or hydrogen dissolved in water and has an inadequate detection limit of 100 nM (C. R. Wilson, Electric Power Research Institute Report NP-2650 (1982)).
Equilibration of dissolved hydrogen in water with a carrier gas followed by removal of coexisting gases (e.g., oxygen, hydrogen sulfide, carbon dioxide) that can interfere with or dilute hydrogen during analysis has been attempted but not at sufficiently low detection limits. Removal of carbon dioxide from carrier gas equilibrated with rumen fluid followed by gas chromatography resulted in a detection limit of 10 nM (J. A. Robinson, R. F. Strayer, and J. M. Tiedje,
Appl. Environ. Microbiol
, 41:545-548 (1981)). This method is not applicable where carbon dioxide is present in low concentrations.
Mass spectrometry can be used to detect hydrogen in gases or, via use of a membrane system, in liquids (P. Dornseiffer, B. Meyer, and E. Heinzle,
Biotechnol. Bioeng
., 45:219-228 (1995)). Hydrogen concentrations detected in liquids are in the low &mgr;M (1,000 nM) range and accurate measurement can be compromised by biofilm growth on the membrane surface which requires periodic maintenance and cleaning.
A palladium-coated micromirror fiber optic sensor developed by Sandia National Laboratories was shown to be capable of sensing 50 ppm of hydrogen in transformer oil (M. A. Butler, R. Sanchez, and G. R. Dulleck, Sandia Report SAND96-1133. UC-706 (1996)).
Various types of solid state sensors are capable of hydrogen detection. eithley (Cleveland, Ohio) sells a hot wire semiconductor type sensor named CH-H. This sensor contains a platinum wire in a sintered tin oxide semiconductor bead. Hydrogen reacts with oxygen on the platinum wire thereby generating heat. The altered resistance of the platinum wire is sensed in a bridge circuit. This sensor requires the presence of oxygen and is sensitive to approximately 10 ppm hydrogen in gas or an equilibrium dissolved concentration of 8 nM.
Sensors based on the observed change in the electrical resistance of platinum and palladium upon adsorption of hydrogen have been described. These sensors can be immersed in water but have a detection limit of 5,000 nM dissolved hydrogen (C. Liu and D. D. Macdonald,
J. Supercritical Fluids
., 8:263-270 (1995)).
Lundstrom described metal oxide semiconductor (MOS) transistors containing a palladium gate (K. I. Lundstrom, M. S. Shivaraman, and C. M. Svensson,
J. Appl. Physics
., 46:3876-3880 (1975); I. Lundstrom,
Sensors and Actuators
., 1:403-426 (1981)). The sensitivity of these struc

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