How climate change is changing the laboratory
How a 2 °C shift is a whole world of difference for analyses
Two degrees Celsius: that is the target the political leaders have set. Many experts are already predicting that even this seemingly small global temperature change will have enormous impact on our environment.
We want to set up a different scenario here that asks the question: what does a difference of 2 °C actually signify in instrumental analysis? In a thought experiment, we therefore remove all means of temperature control from the analysis devices in the laboratory and look to see how big – or indeed how little – an impact an ambient temperature increase from 20 °C to 22 °C has on the measurement result.
When enzymes go haywire: biochemical analysis in climate change
The warming has a most dramatic impact on enzymatic reactions. Almost every clinical laboratory uses enzymes to identify glucose, cholesterol and other relevant biomolecules. The enzyme reactions largely follow what’s known as the Q₁₀ rule: this states that enzyme activity doubles with every ten degree increase in temperature.
This relationship between reaction speed and temperature is also known as van’t Hoff’s Law, after Jacobus Henricus van ’t Hoff, the Dutch Chemist who formulated it in 1884 (expanded in 1889 by Svante Arrhenius to become the Arrhenius equation).
A two degree rise in temperature increases enzyme activity by almost 15 percent. This has consequences for medical tests, such as establishing blood sugar levels. A glucose assay that gives a correct reading of 100 mg/dl at 20 °C, for instance, would measure as high as 115 mg/dl at 22 °C. In diabetes diagnostics, this could be the difference between “healthy” and “in need of treatment”.
A shake-up for pH values
The pH value is also sensitive to temperature changes. Buffer solutions that are intended to keep pH values stable show that even a change of just a few degrees can cause a temperature-related drift.
The temperature dependency of the pH value is primarily down to the self-ionisation of water. This shifts towards the ionic product as an endothermic reaction when temperature rises, causing the pH value to fall (increase in H⁺ concentration).
H₂O ⇌ H⁺ + OH⁻
Buffer systems are also temperature-dependent because of the dissociation constant Ka, as evidenced by the van’t Hoff equation:
dln(Ka)/dT = ΔH°/(RT²)
As well as temperature-dependent dissociation of the buffer and the self-ionisation of the water, the ionic activity is also subject to temperature dependency.
As per the equation for activity coefficient γ, the following applies:
log γ = -A(T) × z² × √I / (1 + B(T) × a × √I)
The Debye-Hückel parameters A and B here are dependent on the permittivity ε(T) and density ρ(T) of the water, which are themselves temperature-dependent. However, the influence this factor has on the pH-value is negligible.
All these influences are very labour-intensive to calculate in detail. For small temperature changes, however, they can get close in linear terms, which in practice is indicative of a simplified equation of the temperature dependency:
pH(T) = pH(T₀) + α × (T – T₀)
Where α is the temperature coefficient that is calculated specifically for a buffer system (normally specified by the manufacturer). Consequently, the change in pH for a typical phosphate buffer at a temperature change of 2 °C is as follows:
pH(20 °C) = 7,0000
pH(22 °C) = 7,0000 + (-0,0028/°C × 2°C) = 6, 9944
which in turn gives
H⁺ concentration at i 20 °C: 10⁻⁷ mol/l = 1,000 × 10⁻⁷ mol/l
H⁺ concentration at 22 °C: 10⁻⁶’⁹⁹⁴⁴ mol/l = 1,013 × 10⁻⁷ mol/l
This equates to a percentage change of +1.3%.
A phosphate buffer with a pH of 7.0 at 20 °C drops to pH 6.994 at 22 °C. Though this may sound very little, it signifies a 1.3 increase in the concentration of hydrogen ions, determined by the logarithmic interplay of the pH scale (changing the pH value by 1 results in the hydrogen ion concentration changing by a factor of 10). The high measurement requirements of certain analyses means even a deviation such as this could have consequences, for example if it is a precipitation reaction or a biochemical reaction that is pH-sensitive.
IN THE SPOTLIGHT: acidification of the oceans
Although only a thought experiment inside the lab, this effect is already being seen today in the world’s oceans: the pH-value is getting notably lower. However, this is not down to the temperature dependency of the pH value, but a result of the fact that warmer water absorbs less CO₂ from the atmosphere – with dramatic consequences for the marine ecosystem.
Der Anstieg des CO₂-Gehalts des Meerwassers samt pH-Abfall ist dabei hauptsächlich eine Folge des CO₂-Partialdruckanstiegs in der Atmosphäre. Da sich mit steigender Temperatur immer weniger CO₂ in den Ozeanen löst und das Meer als Pufferspeicher entfällt, nimmt der CO₂-Gehalt in der Atmosphäre bei anhaltender Produktion immer schneller zu. Hierdurch wird die Differenz zwischen CO₂-Gehalt in der Atmosphäre und im Wasser immer größer, der CO₂-Partialdruck erhöht sich. Durch diese Differenz wird CO₂ gleichsam in das Ozeanwasser ‚hineingedrückt‘ – mit den bekannten Folgen der Übersäuerung der Meere.
Since industrialisation began, the average surface temperature of the world’s oceans has risen by around 1 °C, while the pH value of the oceans has fallen from around 8.2 to 8.1 – a seemingly small change with massive consequences. This 0.1 change in pH equates to an almost 30 percent increase in acid concentration [1].
The mechanism behind this is easily explained: atmospheric CO₂ dissolves in sea water and forms carbonic acid through an equilibrium reaction [3]:
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
More CO₂ means more H⁺ ions and, in turn, a lower pH value. What impact does this change have? Corals may struggle to build up their carbonate skeleton (calcium carbonate CaCO₃ is sensitive to acids), meaning their exoskeletons become thinner and more fragile [2].
The shells of pteropods (a type of sea snail), for instance, are up to 37 percent thinner in acidic water than in less acidic seawater [4]. In especially acidic regions of the ocean, these organisms are already showing signs of dissolution on their shells [4, 5].
By the year 2100, the ocean’s pH value could fall by a further 0.3 to 0.4 [6] – which would equate to acid concentrations of two or three times current levels. What that means for entire food chains, which often start with shell-forming organisms, is something only marine biologists can explain. According to experts’ estimates, this poses a particular threat to cold-tempered coral reefs and polar sea regions [6].
While the temperature (and therefore the pH value) can be controlled in the laboratory, the world’s oceans have no such defence against the changing climate. The acidification of the oceans is one of the greatest ecological challenges of our time and it is plain to see it cannot be ignored: every tenth of a degree saved counts when it comes to global warming.
Chromatography precision declines
In high-performance liquid chromatography (HPLC), a temperature difference of just 2 °C causes a notable shift in retention times. This is primarily a result of the partition equilibrium between the stationary and mobile phase, which changes with the temperature. The van’t Hoff equation describes this as follows:
ln(k’) = -ΔH°/(RT) + ΔS°/R + ln Φ
Where k’ is the retention factor, ΔH° the standard enthalpy of the analyte partition between the phases, ΔS° is the corresponding entropy change, R is the gas constant, T the absolute temperature and Φ the phase ratio of the columns.
The formula shows a reverse temperature dependency: that is to say, higher temperatures lead to lower retention factors and, in turn, shorter retention times. As a rule of thumb for small analyte molecules, the retention reduces falls by two percent for every degree the temperature increases. [7]
Parallel to the partition equilibrium, the viscosity of the solvent also changes: it falls by 2.2 percent, which reduces the column pressure and influences the subsequent separation. For a pharmaceutical company checking the purity of medication, variations such as these would have a profound impact. Quantitative assessments would be systematically incorrect and the method validation would have to be completely revised.
Conductivity measurements drift away
The electrical conductivity of solutions increases in a linear relationship with temperature – by approximately two percent per degree. Consequently, a two-degree warming means an increase of four percent.
A saline solution of 1000 µS/cm at 20 degrees suddenly shows 1040 µS/cm at 22 degrees. In water analysis, for example this would lead to false readings for ion concentration. Drinking water limit values could appear exceeded, when in actual fact nothing in the composition has changed.
When reference electrodes give false values
Not even electrochemistry is spared the effects. The Nernst equation – at the heart of all electrochemical measurements – incorporates the temperature in its figures: E = E₀ + (RT/nF) × ln(Q).
The Nernst factor RT/F increases from 58.85 mV per decade at 20 °C to 59.16 mV at 22 °C. That equates to an increase of 0.53% – enough for pH electrodes to systematically display false values.
Conclusion
The thought experiment shows: temperature is a critical quality factor in many areas of analysis. Even a difference of just two degrees Celsius can result in significant change, whether in terms of enzyme reactions, pH values or other temperature-dependent factors, such as electrical conductivity, viscosity or ion solubility.
In laboratory work, precise temperature measurement, adjustment calculus in the systems and exact temperature control are necessary to ensure analytical results are always reproducible. This is why it is important to have measuring devices regularly maintained and to check their calibration or recalibrate them.
Sources:
[1] American Scientist: Ocean acidification: the other climate change issue – https://www.americanscientist.org/article/ocean-acidification-the-other-climate-change-issue
[2] Woods Hole Oceanographic Institution: Scientists identify how ocean acidification weakens coral skeletons – https://www.whoi.edu/press-room/news-release/scientists-identify-how-ocean-acidification-weakens-coral-skeletons/
[3] Ocean Acidification ICC: Why ocean acidification is called climate change’s evil twin – https://news-oceanacidification-icc.org/2024/12/25/why-ocean-acidification-is-called-climate-changes-evil-twin/
[4] NCBI PMC: Pteropod shell thinning in natural CO₂ gradients – https://pmc.ncbi.nlm.nih.gov/articles/PMC7814018/
[5] Coast Adapt: Ocean acidification and its effects – https://coastadapt.com.au/ocean-acidification-and-its-effects
[6] European Environment Agency: Ocean acidification indicators – https://www.eea.europa.eu/en/analysis/indicators/ocean-acidification
[7] https://www.chromatographyonline.com/view/how-much-retention-time-variation-normal-0
Calculations
Enzyme activity
Formula:
v(T) = v₀ × Q₁₀((T-T₀)/10 °C)
- v(T) = velocity at temperature T
- v₀ = initial velocity at reference temperature T₀
- Q₁₀ = temperature coefficient (for enzymes this is typically 2)
- T = new temperature
- T₀ = reference temperature
- /10 °C, because Q₁₀ is defined as applying to increments of 10 °C
Example calculation:
v₀ = 100 U/ml at 20 °C; mit U = enzyme activity>> 1 Unit = 1 μmol substrate min-1
v(22°C) = 100 U/ml × 2((22 °C-20 °C)/10 °C)
v(22°C) = 114,9 U/ml >> Percentage change: +14.9%
Electrical conductivity
Formula:
κ(T) = κ(T₀) × [1 + α × (T – T₀)]
where α ≈ 0,02/°C for most aqueous solutions
Example calculation:
initial conductivity: 1.000 µS/cm bei 20 °C
κ(22°C) = 1.000 µS/cm × [1 + 0,02 × (22 – 20)]
κ(22°C) = 1.000 µS/cm × [1 + 0,04] = 1.040 µS/cm
Percentage change: +4.0%
Nernst voltage
Formula:
E = E₀ + (RT/nF) × ln(Q)
- R = 8,314 J/(mol·K), F = 96.485 C/mol
- RT/F at 20°C = 25,69 mV, at 22°C = 25,86 mV
Example calculation:
where n = 1 (monovalent ions):
RT/F at 20 °C: 25,69 mV
RT/F at 22 °C: 25,86 mV
Nernst factor (59,16 mV/Dekade at 25°C):
at 20 °C: 58.85 mV/decade
at 22 °C: 59.16 mV/decade
Percentage change: +0.53%
Viscosity
Formula (Arrhenius-type equation):
η(T) = η₀ × exp[B × (1/T – 1/T₀)]
With factor B = Ea(water)/R = 7870 J/mol / 8314 J/(mol·K) = 946.9 K
Example calculation:
T₀ = 293,15 K (20 °C), T = 295,15 K (22 °C)
η₀ = 1,002 mPa·s (water at 20 °C)
η(22°C) = 1,002 mPa·s × exp[946,9 K × (1/295,15 K – 1/293,15 K)]
η(22°C) = 1,002 mPa·s × exp(-0,0219)
η(22°C) = 1,002 mPa·s × 0,978 = 0,980 mPa·s
Percentage change: -2.2%
