Difference between revisions of "O2k-Specifications"

Latest revision as of 10:37, 20 April 2021

O2k-Specifications

MitoPedia O2k and high-resolution respirometry: O2k-Open Support

Description

O2k versus multiwell respirometer: O2k stands for Oroboros O2k and high-resolution respirometry, meeting powerful quality criteria securing high output and pioneering state-of-the-art comprehensive OXPHOS analysis of substrate control and coupling control of mitochondrial function. 'High throughput' stands for disposable multiwell systems - expensive, with limited scope and extremely high running costs. In respirometry, high throughput is not equivalent to high output. If you’re using a biased instrument, it doesn’t matter how many measurements you take – you’re aiming at the wrong target (Silver 2012 Penguin Press).

Reference: MiPNet18.10 O2k-Specifications, Flyer with specification summary

MitoPedia O2k and high-resolution respirometry: O2k hardware

» Keywords

» Comprehensive OXPHOS analysis

» High-output, low running costs

» O2k-Publications: Topics

» Power-O2k

» Specifications of the O2k

Combination of interests

Erich Gnaiger is founder and CEO of Oroboros Instruments, and responsible for the development of the O2k in collaboration with the O2k-Team and our partners. A series of methodological publications is the result of positive feedback between his work as faculty staff of the Medical University of Innsbruck, his company initiatives and numerous international cooperations.

Selected references

Comparison of respirometric methods -  Discussion

Horscroft JA, Kotwica AO, Laner V, West JA, Hennis PJ, Levett DZH, Howard DJ, Fernandez BO, Burgess SL, Ament Z, Gilbert-Kawai ET, Vercueil A, Landis BD, Mitchell K, Mythen MG, Branco C, Johnson RS, Feelisch M, Montgomery HE, Griffin JL, Grocott MPW, Gnaiger E, Martin DS, Murray AJ (2017) Metabolic basis to Sherpa altitude adaptation. Proc Natl Acad Sci U S A 114:6382–7. - »Bioblast link«

Lemieux H, Blier PU, Gnaiger E (2017) Remodeling pathway control of mitochondrial respiratory capacity by temperature in mouse heart: electron flow through the Q-junction in permeabilized fibers. Sci Rep 7:2840. - »Bioblast link«

Lemieux H, Subarsky P, Doblander C, Wurm M, Troppmair J, Gnaiger E (2017) Impairment of mitochondrial respiratory function as an early biomarker of apoptosis induced by growth factor removal. bioRxiv doi: https://doi.org/10.1101/151480. - »Bioblast link«

Gnaiger E, Boushel R, Søndergaard H, Munch-Andersen T, Damsgaard R, Hagen C, Díez-Sánchez C, Ara I, Wright-Paradis C, Schrauwen P, Hesselink M, Calbet JAL, Christiansen M, Helge JW, Saltin B (2015) Mitochondrial coupling and capacity of oxidative phosphorylation in skeletal muscle of Inuit and caucasians in the arctic winter. Scand J Med Sci Sports 25 (Suppl 4):126–34. - »Bioblast link«

Harrison DK, Fasching M, Fontana-Ayoub M, Gnaiger E (2015) Cytochrome redox states and respiratory control in mouse and beef heart mitochondria at steady-state levels of hypoxia. J Appl Physiol 119:1210-8. - »Bioblast link«

Makrecka-Kuka M, Krumschnabel G, Gnaiger E (2015) High-resolution respirometry for simultaneous measurement of oxygen and hydrogen peroxide fluxes in permeabilized cells, tissue homogenate and isolated mitochondria. Biomolecules 5:1319-38. - »Bioblast link«

Gnaiger E (2020) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5th ed. Bioenerg Commun:112 pp. »Bioblast link«

Pesta D, Gnaiger E (2012) High-resolution respirometry. OXPHOS protocols for human cells and permeabilized fibres from small biopsies of human muscle. Methods Mol Biol 810:25-58. »Bioblast link«

Votion DM, Gnaiger E, Lemieux H, Mouithys-Mickalad A, Serteyn D (2012) Physical fitness and mitochondrial respiratory capacity in horse skeletal muscle. PLoS One 7: e34890. |»Bioblast link«

Lemieux H, Semsroth S, Antretter H, Höfer D, Gnaiger E (2011) Mitochondrial respiratory control and early defects of oxidative phosphorylation in the failing human heart. Int J Biochem Cell Biol 43:1729–38. - »Bioblast link«

Pesta D, Hoppel F, Macek C, Messner H, Faulhaber M, Kobel C, Parson W, Burtscher M, Schocke M, Gnaiger E (2011) Similar qualitative and quantitative changes of mitochondrial respiration following strength and endurance training in normoxia and hypoxia in sedentary humans. Am J Physiol Regul Integr Comp Physiol 301:R1078–87. - »Bioblast link«

Scandurra FM, Gnaiger E (2010) Cell respiration under hypoxia: facts and artefacts in mitochondrial oxygen kinetics. Adv Exp Med Biol 662:7-25. - »Bioblast link«

Aguirre E, Rodríguez-Juárez F, Bellelli A, Gnaiger E, Cadenas S (2010) Kinetic model of the inhibition of respiration by endogenous nitric oxide in intact cells. Biochim Biophys Acta 1797:557-65. - |»Bioblast link«

Aragonés J, Schneider M, Van Geyte K, Fraisl P, Dresselaers T, Mazzone M, Dirkx R, Zacchigna S, Lemieux H, Jeoung NH, Lambrechts D, Bishop T, Lafuste P, Diez-Juan A, K Harten S, Van Noten P, De Bock K, Willam C, Tjwa M, Grosfeld A, Navet R, Moons L, Vandendriessche T, Deroose C, Wijeyekoon B, Nuyts J, Jordan B, Silasi-Mansat R, Lupu F, Dewerchin M, Pugh C, Salmon P, Mortelmans L, Gallez B, Gorus F, Buyse J, Sluse F, Harris RA, Gnaiger E, Hespel P, Van Hecke P, Schuit F, Van Veldhoven P, Ratcliffe P, Baes M, Maxwell P, Carmeliet P (2008) Deficiency or inhibition of oxygen sensor Phd1 induces hypoxia tolerance by reprogramming basal metabolism. Nat Genet 40:170-80. - »Bioblast link«

Gnaiger E (2008) Polarographic oxygen sensors, the oxygraph and high-resolution respirometry to assess mitochondrial function. In: Mitochondrial Dysfunction in Drug-Induced Toxicity (Dykens JA, Will Y, eds) John Wiley:327-52. - »Bioblast link«

Hütter E, Renner K, Pfister G, Stöckl P, Jansen-Dürr P, Gnaiger E (2004) Senescence-associated changes in respiration and oxidative phosphorylation in primary human fibroblasts. Biochem J 380:919-28. - »Bioblast link«

Kuznetsov AV, Schneeberger S, Seiler R, Brandacher G, Mark W, Steurer W, Saks V, Usson Y, Margreiter R, Gnaiger E (2004) Mitochondrial defects and heterogeneous cytochrome c release after cardiac cold ischemia and reperfusion. Am J Physiol Heart Circ Physiol 286:H1633–41. - »Bioblast link«

Gnaiger E (2001) Bioenergetics at low oxygen: dependence of respiration and phosphorylation on oxygen and adenosine diphosphate supply. Respir Physiol 128:277-97. - »Bioblast link«

Gnaiger E, Méndez G, Hand SC (2000) High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia. Proc Natl Acad Sci U S A 97:11080-5. »Open Access«

Steinlechner-Maran R, Eberl T, Kunc M, Margreiter R, Gnaiger E (1996) Oxygen dependence of respiration in coupled and uncoupled endothelial cells. Am J Physiol Cell Physiol 271:C2053-61. - »Bioblast link«

Gnaiger E, Steinlechner-Maran R, Méndez G, Eberl T, Margreiter R (1995) Control of mitochondrial and cellular respiration by oxygen. J Bioenerg Biomembr 27:583-96. - »Bioblast link«

MitoPedia O2k and high-resolution respirometry: O2k hardware, O2k-Open Support, O2k-Respirometry, O2k-FluoRespirometry

@@ Line 1: / Line 1: @@
-{{MitoPedia
+{{Technical support}}
-|description=From their basic design, multi-well systems are a tool for qualitative high-throughput screening, particularly for pharmacologic testing.  Designed for high-throughput qualitative measurements, they should not be advertised for quantitative measurements.  A high standard of quantitative results cannot be obtained with the present technology offered and advertised.  The problems of high oxygen diffusion are well known, and the large corrections render [[Talk:Rogers_2011_PlosOne#Instrumental_specifications_of_the_XF_multi-well_system_are_missing|non-specified errors in the calculation of background-corrected oxygen flux]].
+__TOC__
-|info=[http://www.oroboros.at/index.php?hrr-versus-multiwell HRR versus multiwell]
+{{MitoPedia without banner
-|type=Respiration
+|abbr=
+|description=[[Image:O2k-Info.png|right|30px|link=Oroboros O2k]]'''O2k versus multiwell respirometer''': '''O2k''' stands for Oroboros O2k and '''[[high-resolution respirometry]]''', meeting powerful quality criteria securing '''high output''' and pioneering state-of-the-art [[Gnaiger_2012_MitoPathways|comprehensive OXPHOS analysis]] of substrate control and coupling control of mitochondrial function. 'High throughput' stands for disposable multiwell systems - expensive, with limited scope and extremely high running costs. In respirometry, high throughput is not equivalent to high output. ''If you’re using a biased instrument, it doesn’t matter how many measurements you take – you’re aiming at the wrong target'' ([[Silver 2012 Penguin Press]]).
+|info= [[MiPNet18.10 O2k-Specifications]], [http://wiki.oroboros.at/images/9/93/Flyer_backside_.png Flyer with specification summary]
 }}
-{{MitoPedia topics|type=Respiration
+{{MitoPedia O2k and high-resolution respirometry
+|mitopedia O2k and high-resolution respirometry=O2k hardware
 }}
-* Discussion: [[Talk:Rogers_2011_PlosOne|Seahorse XF for isolated mitochondria - High throughput without high output?]]
-* [[Talk:Multiwell respirometer|Correspondence]]
+[[File:Questions.jpg|left|40px]]
+<br />
+<div class="toccolours mw-collapsible mw-collapsed">
+::: <span style="font-size:105%; color:##424242">'''» Keywords'''</span>
+<div class="mw-collapsible-content">
+::::» [[Gnaiger 2012 MitoPathways|Comprehensive OXPHOS analysis]]
+::::» [[High-output, low running costs]]
+::::» [[O2k-Publications: Topics]]
+::::» [[Power-O2k]]
+::::» [[Specifications of the O2k]]'''
+</div>
+</div>
+<br />
-==Quantitative respirometry: HRR versus multiwell==
-The OROBOROS [[Oxygraph-2k]] for [[high-resolution respirometry]] (HRR) is the gold standard for highly accurate quantitative measurements, using very low amounts of sample.  Instrumental and methodological approaches require an adequately advanced level of Quality Assurance in research and clinical applications.
+== Combination of interests ==
+:::: [[Gnaiger E|Erich Gnaiger]] is founder and CEO of Oroboros Instruments, and responsible for the development of the O2k in collaboration with the O2k-Team and our partners. A series of methodological publications is the result of positive feedback between his work as faculty staff of the Medical University of Innsbruck, his company initiatives and numerous international cooperations.
-===HRR===
-HRR is the result of long-term expertise in instrumental design, software development, and experimental protocols developed for mitochondrial physiology, clinical and pharmacological applications. Taken together, these developments resulted in new qualitative and quantitative standards summarized as the O2k-Concept.
+== Selected references ==
-The specifications of the OROBOROS O2k are based on the many unique instrumental features:
+ [[Comparison of respirometric methods]] - [[Talk:Comparison of respirometric methods | Discussion]]
-* Critical selection of materials yielding a nearly diffusion-tight chamber,
+::::* Horscroft JA, Kotwica AO, Laner V, West JA, Hennis PJ, Levett DZH, Howard DJ, Fernandez BO, Burgess SL, Ament Z, Gilbert-Kawai ET, Vercueil A, Landis BD, Mitchell K, Mythen MG, Branco C, Johnson RS, Feelisch M, Montgomery HE, Griffin JL, Grocott MPW, Gnaiger E, Martin DS, Murray AJ (2017) Metabolic basis to Sherpa altitude adaptation. Proc Natl Acad Sci U S A 114:6382–7. - [[Horscroft 2017 Proc Natl Acad Sci U S A |»Bioblast link«]]
-Long-term stability and linearity of the polarographic oxygen sensor (POS),
-* Highly automatic but transparent calibration routines and instrumental background correction,
-* Electronically controlled thermal environment with high temperature stability (+-0.001 °C),
-* Limit of detection of respiratory flux: +-1 pmol.s-1.ml-1.
-===Multi-well===
+::::* Lemieux H, Blier PU, Gnaiger E (2017) Remodeling pathway control of mitochondrial respiratory capacity by temperature in mouse heart: electron flow through the Q-junction in permeabilized fibers. Sci Rep 7:2840. - [[Lemieux 2017 Sci Rep |»Bioblast link«]]
-From their basic design, multi-well systems are a tool for qualitative high-throughput screening, particularly for pharmacologic testing.  Designed for high-throughput qualitative measurements, they should not be advertised for quantitative measurements.  A high standard of quantitative results cannot be obtained with the present technology offered and advertised.  Huge oxygen fluxes reported by one group at a mitochondrial physiology meeting (MiPsummer School 2009, Baton Rouge, USA) were explained by a company representative as a "software problem". The absolute oxygen fluxes represent artefacts. More recently, the problems of high oxygen diffusion were recognized, but the large corrections render non-specified errors in the calculation of background-corrected oxygen flux.
+::::* Lemieux H, Subarsky P, Doblander C, Wurm M, Troppmair J, Gnaiger E (2017) Impairment of mitochondrial respiratory function as an early biomarker of apoptosis induced by growth factor removal. bioRxiv doi: https://doi.org/10.1101/151480. - [[Lemieux 2017 bioRxiv 151480 |»Bioblast link«]]
-==Is plastic material compatible with respirometry?==
+::::* Gnaiger E, Boushel R, Søndergaard H, Munch-Andersen T, Damsgaard R, Hagen C, Díez-Sánchez C, Ara I, Wright-Paradis C, Schrauwen P, Hesselink M, Calbet JAL, Christiansen M, Helge JW, Saltin B (2015) Mitochondrial coupling and capacity of oxidative phosphorylation in skeletal muscle of Inuit and caucasians in the arctic winter. Scand J Med Sci Sports 25 (Suppl 4):126–34. - [[Gnaiger 2015 Scand J Med Sci Sports| »Bioblast link«]]
-===HRR===
+::::* Harrison DK, Fasching M, Fontana-Ayoub M, Gnaiger E (2015) Cytochrome redox states and respiratory control in mouse and beef heart mitochondria at steady-state levels of hypoxia. J Appl Physiol 119:1210-8. - [[Harrison 2015 J Appl Physiol |»Bioblast link«]]
-Plastic materials with high oxygen diffusion are eliminated from the chamber in HRR.  The durane glass chambers are closed by PVDF or PEEK stoppers which are as diffusion tight as our titanium stoppers (originally used in O2k Series A and B). The magnetic stirrer bars are coated by PVDF or PEEK.  Viton O-rings for used for sealing the stoppers, and buyl rubber gaskets provide the seals for the oxygen sensors.
+::::* Makrecka-Kuka M, Krumschnabel G, Gnaiger E (2015) High-resolution respirometry for simultaneous measurement of oxygen and hydrogen peroxide fluxes in permeabilized cells, tissue homogenate and isolated mitochondria. Biomolecules 5:1319-38. - [[Makrecka-Kuka 2015 Biomolecules |»Bioblast link«]]
-HRR not only minimizes the effect of backdiffusion by avoiding inappropriate plastic materials, but additionally implements automatic correction for instrumental background flux (see [http://www.oroboros.at/index.php?o2k-specifications O2k-specifications]).
+::::* Gnaiger E (2020) Mitochondrial pathways and respiratory control. An introduction to OXPHOS analysis. 5th ed. Bioenerg Commun:112 pp. »[[Gnaiger 2020 BEC MitoPathways |Bioblast link«]]
+::::* Pesta D, Gnaiger E (2012) High-resolution respirometry. OXPHOS protocols for human cells and permeabilized fibres from small biopsies of human muscle. Methods Mol Biol 810:25-58. [[Pesta 2012 Methods Mol Biol |»Bioblast link«]]
-===Multi-well===
+::::* Votion DM, Gnaiger E, Lemieux H, Mouithys-Mickalad A, Serteyn D (2012) Physical fitness and mitochondrial respiratory capacity in horse skeletal muscle. PLoS One 7: e34890. [[Votion 2012 PLoS One ||»Bioblast link«]]
-Oxygen storage in the plastic material of multiwell plates leads to high oxygen backdiffusion.  Since the problems are well known ([[Gnaiger_1995_JBB]]), specifications should be provided on backdiffusion, and test protocols applied to enable evaluation of such specifications.
+::::* Lemieux H, Semsroth S, Antretter H, Höfer D, Gnaiger E (2011) Mitochondrial respiratory control and early defects of oxidative phosphorylation in the failing human heart. Int J Biochem Cell Biol 43:1729–38. - [[Lemieux 2011 Int J Biochem Cell Biol |»Bioblast link«]]
-At the high surface-to-volume ratio, the problem is not restricted to oxygen diffusion, but all lipid soluble substances partition between the aqueous and plastic phase, such that the surface-attached biological sample is exposed to undefined effective concentrations.
+::::* Pesta D, Hoppel F, Macek C, Messner H, Faulhaber M, Kobel C, Parson W, Burtscher M, Schocke M, Gnaiger E (2011) Similar qualitative and quantitative changes of mitochondrial respiration following strength and endurance training in normoxia and hypoxia in sedentary humans. Am J Physiol Regul Integr Comp Physiol 301:R1078–87. - [[Pesta 2011 Am J Physiol Regul Integr Comp Physiol |»Bioblast link«]]
+::::* Scandurra FM, Gnaiger E (2010) Cell respiration under hypoxia: facts and artefacts in mitochondrial oxygen kinetics. Adv Exp Med Biol 662:7-25. - [[Scandurra 2010 Adv Exp Med Biol |»Bioblast link«]]
-==Accuracy of chamber volume and mixing==
+::::* Aguirre E, Rodríguez-Juárez F, Bellelli A, Gnaiger E, Cadenas S (2010) Kinetic model of the inhibition of respiration by endogenous nitric oxide in intact cells. Biochim Biophys Acta 1797:557-65. - [[Aguirre 2010 Biochim Biophys Acta ||»Bioblast link«]]
-===HRR===
+::::* Aragonés J, Schneider M, Van Geyte K, Fraisl P, Dresselaers T, Mazzone M, Dirkx R, Zacchigna S, Lemieux H, Jeoung NH, Lambrechts D, Bishop T, Lafuste P, Diez-Juan A, K Harten S, Van Noten P, De Bock K, Willam C, Tjwa M, Grosfeld A, Navet R, Moons L, Vandendriessche T, Deroose C, Wijeyekoon B, Nuyts J, Jordan B, Silasi-Mansat R, Lupu F, Dewerchin M, Pugh C, Salmon P, Mortelmans L, Gallez B, Gorus F, Buyse J, Sluse F, Harris RA, Gnaiger E, Hespel P, Van Hecke P, Schuit F, Van Veldhoven P, Ratcliffe P, Baes M, Maxwell P, Carmeliet P (2008) Deficiency or inhibition of oxygen sensor Phd1 induces hypoxia tolerance by reprogramming basal metabolism. Nat Genet 40:170-80. - [[Aragones 2008 Nat Genet |»Bioblast link«]]
-The 2 ml standard chamber volume of the O2k is calibrated at <1% error (depending on calibrated pipettes), when inserting the stopper and filling the capillary at an error of <20 µl.
+::::* Gnaiger E (2008) Polarographic oxygen sensors, the oxygraph and high-resolution respirometry to assess mitochondrial function. In: Mitochondrial Dysfunction in Drug-Induced Toxicity (Dykens JA, Will Y, eds) John Wiley:327-52. - [[Gnaiger_2008_POS |»Bioblast link«]]
-The entire effective volume (excluding the injection capillaries) is and well controlled stirring is provided in the O2k.
+::::* Hütter E, Renner K, Pfister G, Stöckl P, Jansen-Dürr P, Gnaiger E (2004) Senescence-associated changes in respiration and oxidative phosphorylation in primary human fibroblasts. Biochem J 380:919-28. - [[Huetter_2004_Biochem J |»Bioblast link«]]
-===Multi-well===
+::::* Kuznetsov AV, Schneeberger S, Seiler R, Brandacher G, Mark W, Steurer W, Saks V, Usson Y, Margreiter R, Gnaiger E (2004) Mitochondrial defects and heterogeneous cytochrome ''c'' release after cardiac cold ischemia and reperfusion. Am J Physiol Heart Circ Physiol 286:H1633–41. - [[Kuznetsov_2004_Am_J_Physiol_Heart_Circ_Physiol |»Bioblast link«]]
-No information is provided on the accuracy of the chamber volume in a multi-well system (~7 µl for the XF24).  This inaccuracy translates directly to the calculation of oxyge flux in the closed chamber. Similarly, accurate concentrations of titrated substances are not known.
+::::* Gnaiger E (2001) Bioenergetics at low oxygen: dependence of respiration and phosphorylation on oxygen and adenosine diphosphate supply. Respir Physiol 128:277-97. - [[Gnaiger 2001 Respir Physiol |»Bioblast link«]]
-Mixing by moving the sensor/injector part up and down a few times is inadequate. Undefined diffusion layers develop during a measuring cycle.
+::::* Gnaiger E, Méndez G, Hand SC (2000) High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia. Proc Natl Acad Sci U S A 97:11080-5. [[Gnaiger 2000 Proc Natl Acad Sci U S A |»Open Access«]]
-==Flexibility for MultiSensor applications==
+::::* Steinlechner-Maran R, Eberl T, Kunc M, Margreiter R, Gnaiger E (1996) Oxygen dependence of respiration in coupled and uncoupled endothelial cells. Am J Physiol Cell Physiol 271:C2053-61. - [[Steinlechner-Maran_1996_Am J Physiol Cell Physiol |»Bioblast link«]]
+::::* Gnaiger E, Steinlechner-Maran R, Méndez G, Eberl T, Margreiter R (1995) Control of mitochondrial and cellular respiration by oxygen. J Bioenerg Biomembr 27:583-96. - [[Gnaiger 1995 J Bioenerg Biomembr |»Bioblast link«]]
-===How is the chamber volume defined?===
-No information is provided on the accuracy of the chamber volume in a multiwell system.  The actual concentrations of titrated substances, therefore, are not known, in contrast to HRR.
-===Are specifications comparable?===
-No specifications are given on sensitivity (lower limit of detection of oxygen; non-linearity and restricted linear range; detection limit of oxygen flux) in such multiwell systems.  Some advertise that they are so much better than Clark-type electrodes, but no quantitative specifications are provided. There are detailed and unique specifications for the O2k.
-==How are cell number or mitochondrial protein defined?==
+{{MitoPedia O2k and high-resolution respirometry
+|mitopedia O2k and high-resolution respirometry=O2k hardware, O2k-Open Support, O2k-Respirometry, O2k-FluoRespirometry
-How many cells are actually in the closed compartment for measurement of respiration in a well, or which fraction of isolated mitochondria is outside versus inside the chamber?  How can the recorded change in oxygen concentration be converted to respiration per million cells or per mg protein? Without solving these problems, no quantiative measurements of respiration are possible.
+}}
+[[Category:OroboPedia]]
-==Are multiple substrate-uncouplier-inhibitor titrations possible?==
+[[Category:MitoPedia]]
-The number of substances that can be titrated sequentially into a well is limited, such that modern substrate-uncoupler-inhibitor titration (SUIT) protocols cannot be applied in multiwell systems.  Not even inhibitor titrations can be applied if only a single injection is possible through each port into the chamber.
-==How high are the running costs?==
-How many of the wells of a dischargeable plate can actually be used for independent measurements?  Several wells are required for calibration, edge effects may eliminate the use of wells on the sides.  What is the cost of a plate and the cost of a single measurement?  A plate with sensors and injectors can be used once only.  The initial costs and the running costs are extremely high (e.g. expensive dischargeable plates and sensor cartridge for single use only). By comparison, the [http://www.oroboros.at/index.php?low-o2k-running-costs running costs for the OROBOROS O2k] are very very low.
-The OROBOROS O2k can be considered for a moderately high-throughput approach.  Investing the identical amount of money, a large number of O2k chambers provides a unique high-throughput HRR system for quantitative O2k-measurements at low running costs.
-==pH measurement==
-No specifications are given on sensitivity [µpH/s]. The effects of buffers including the bicarbonate system have been ignored.  The rate of acidification is presented in pH units per time, ignoring the log scale of pH.  What is the drift of the pH signal?.  An oxygen flux of 50 pmol/(s ml) corresponds - at an assumed O2 flux to extracellular H+ flux ratio of 1:1 - to a pH change of about 86 µpH/s in a very weak buffer (2 mM).