What is ionic strength and how is it mathematically defined?

Ionic strength (I or µ) is a measure of the total electric field intensity and electrostatic concentration of all ions in an electrolyte solution. It was formulated by Gilbert N. Lewis and Merle Randall in 1921 as: I = 1/2 * Σ(c_i * z_i²), where c_i is the molar concentration (mol/L) of ion i and z_i is the integer electrical charge of ion i. Both cations and anions are included in the summation.

Why does ionic strength depend on the square of ionic charge (z²)?

Ionic strength depends on z² because electrostatic interactions (Coulombic forces) between ions and solvent dipoles scale with the square of their net charge. Consequently, multivalent ions contribute exponentially more to solution non-ideality than monovalent ions. For example, a 0.1 M solution of Al2(SO4)3 has an ionic strength of 1.5 M (15 times its molarity), whereas 0.1 M NaCl has an ionic strength of exactly 0.1 M.

How do you calculate the ionic strength of a mixed electrolyte solution?

To calculate the ionic strength of a mixture of multiple salts, first find the total molar concentration of each individual ion across all dissolved salts. Then evaluate I = 1/2 * [Σ(c_cations * z_cation²) + Σ(c_anions * z_anion²)]. For example, a mixture of 0.1 M NaCl and 0.05 M CaCl2 contains [Na+] = 0.1 M, [Ca²+] = 0.05 M, and [Cl-] = 0.20 M, yielding I = 1/2 * [0.1*(1)² + 0.05*(2)² + 0.20*(1)²] = 1/2 * [0.1 + 0.2 + 0.2] = 0.25 M.

What is the difference between molar concentration and thermodynamic activity (a = γ * c)?

Molar concentration (c) is the physical number of moles per liter. Thermodynamic activity (a) is the 'effective concentration' that governs actual chemical equilibria, reaction rates, electrode potentials, and osmotic pressure. In real solutions, electrostatic shielding reduces the availability of ions, related by the activity coefficient (γ): a_i = γ_i * c_i. In infinitely dilute solutions (I -> 0), γ -> 1 and activity equals concentration.

When should you use the Debye-Hückel Limiting Law vs the Davies Equation?

The Debye-Hückel Limiting Law (log10 γ = -0.509 * z² * √I at 25 °C) is valid only for very dilute solutions where ionic strength I < 0.01 M. The Extended Debye-Hückel equation accounts for finite ion size (a_i) and is accurate up to I ≈ 0.1 M. The Davies equation (log10 γ = -0.509 * z² * [√I / (1 + √I) - 0.3*I]) is an empirical model widely used in chemistry and environmental science for moderate ionic strengths up to I ≈ 0.5 M.

What is the Debye screening length (κ⁻¹) and how does ionic strength affect it?

The Debye screening length (κ⁻¹ or Debye length) is the characteristic thickness of the electrical double layer (diffuse ion cloud) surrounding a charged particle or biological membrane. In aqueous solution at 25 °C, κ⁻¹ ≈ 0.304 / √I nanometers (where I is in mol/L). As ionic strength increases, the Debye length shrinks (e.g., ~3.04 nm in 0.01 M salt vs ~0.77 nm in 0.154 M physiological saline), screening electrostatic repulsion and often causing colloidal or protein aggregation.

How does ionic strength alter the apparent pKa and pH of biological buffers?

Increasing ionic strength decreases the activity coefficients of charged buffer species, shifting the apparent pKa' according to: pKa' = pKa° - (2*z_acid - 1) * A * [√I / (1 + √I)]. For example, in a phosphate buffer (H2PO4⁻ / HPO4²⁻, where z_acid = -1), the apparent pKa shifts from thermodynamic 7.20 in pure water down to ~6.86 in 1X PBS (I ≈ 0.16 M). Formulations must account for this shift to maintain target physiological pH.

What is the ionic strength of standard Phosphate-Buffered Saline (1X PBS)?

Standard 1X PBS (137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4, and 1.8 mM KH2PO4) has a total ionic strength of approximately 162.7 mM (0.1627 M) and an osmolarity of ~300 mOsm/L. The divalent hydrogen phosphate ion (HPO4²⁻, z = 2) contributes 40 mM (1/2 * 10 mM * 2² = 20 mM from HPO4²⁻ plus sodium counterions), making 1X PBS an isotonic mimic of human extracellular fluid.

What is the Mean Ionic Activity Coefficient (γ_±)?

Because positive and negative ions cannot be isolated experimentally, electrochemists measure the mean ionic activity coefficient (γ_±), defined as the geometric mean of individual ion activity coefficients: γ_± = (γ_+^ν_+ * γ_-^ν_-)^(1/ν), where ν = ν_+ + ν_-. For a 1:1 electrolyte like NaCl, γ_± = √(γ_Na+ * γ_Cl-). For a 1:2 electrolyte like CaCl2, γ_± = (γ_Ca²+ * γ_Cl-²)^(1/3).

How does ionic strength affect protein solubility ('salting-in' vs 'salting-out')?

At low ionic strength (I 1.0 M, such as adding ammonium sulfate), salt ions compete with the protein for water molecules, stripping hydration shells and forcing hydrophobic patches to associate, leading to precipitation ('salting-out').

Electrolyte Thermodynamics & Activity Suite • 100% Free

Ionic Strength Calculator

Calculate solution ionic strength ($I = \frac{1}{2}\sum c_i z_i^2$), mean activity coefficients ($\gamma_\pm$ via Debye-Hückel & Davies), Debye screening lengths ($\kappa^{-1}$), and buffer $\text{pK}_a'$ shifts for single and mixed electrolyte solutions.

Benchmark Electrolyte & Buffer Presets 1-Click to auto-populate solution composition

Salt Composition & Mixture

I = ½Σ cᵢzᵢ²

Primary Salt 1: 1:1 Salt (Mult: 1×)

Concentration of Salt 1:

Optional Salt 2 (Mixture): None

Optional Salt 3 (Mixture): None

Thermodynamic Ionic State & Activity Moderate Ionic Strength

Total Solution Ionic Strength ($I$):

0.1000 M

100.0 mM • Osmolarity ≈ 200 mOsm/L

Mean Activity Coefficient ($\gamma_\pm$):

0.7715

Activity $a = 0.0772\,\text{M}$ (77.1% Active)

Debye Length ($\kappa^{-1}$) 0.961 nm

Davies $\gamma$ (|z|=1) 0.778

Ionic Multiplier 1.0×

Debye-Hückel $\gamma$ (Limit)

0.6903

$\log \gamma = -A z^2 \sqrt{I}$

Extended D-H $\gamma$

0.7584

$a_i = 4.0\,\text{Å}$

Apparent $\text{pK}_a'$ Shift

-0.116 pH

$\Delta \text{pK}_a = \text{pK}_a' - \text{pK}_a^\circ$

Individual Ion Electrostatic Contributions ($c_i z_i^2$) Summed $\frac{1}{2}\sum c_i z_i^2$

Ion Species	Valence ($z_i$)	Conc ($c_i$)	$c_i \cdot z_i^2$	Activity ($a_i$)
Na⁺ (Sodium)	+1	0.100 M	0.100 M	0.077 M
Cl⁻ (Chloride)	-1	0.100 M	0.100 M	0.077 M

Physical Principles of Solution Ionic Strength ($I$)

Formulated by Gilbert N. Lewis and Merle Randall in 1921, ionic strength ($I$ or $\mu$) is a fundamental physical property that quantifies the total electrostatic electric field intensity exerted by dissolved ions in an electrolyte solution.

$$I = \frac{1}{2} \sum_{i=1}^{N} c_i z_i^2 = \frac{1}{2} \left( c_1 z_1^2 + c_2 z_2^2 + \dots + c_n z_n^2 \right)$$

where $c_i$ is the molar concentration ($\text{mol/L}$ or $\text{M}$) of ion species $i$, and $z_i$ is the integer net charge number of that ion. Because of the $z_i^2$ term, multivalent ions dominate ionic strength: a $0.05\,\text{M}$ solution of $\text{Al}_2(\text{SO}_4)_3$ exerts an ionic strength of $0.75\,\text{M}$ ($15\times$ its nominal concentration!).

Salt Stoichiometry & Ionic Strength Multiplier Reference Table

Ratio $I / c_{\text{salt}}$

How nominal salt molarity ($c$) converts directly into total solution ionic strength ($I$):

Electrolyte Type	Example Salt	Dissociation Equation	Cation ($z_+$)	Anion ($z_-$)	$I / c$ Multiplier
1:1 Electrolyte	$\text{NaCl, KCl, KNO}_3$	$\text{NaCl} \to \text{Na}^+ + \text{Cl}^-$	+1	-1	1.0 × $c$
1:2 Electrolyte	$\text{CaCl}_2, \text{MgCl}_2$	$\text{CaCl}_2 \to \text{Ca}^{2+} + 2\text{Cl}^-$	+2	-1	3.0 × $c$
2:1 Electrolyte	$\text{Na}_2\text{SO}_4, \text{K}_2\text{SO}_4$	$\text{Na}_2\text{SO}_4 \to 2\text{Na}^+ + \text{SO}_4^{2-}$	+1	-2	3.0 × $c$
2:2 Electrolyte	$\text{MgSO}_4, \text{CuSO}_4, \text{ZnSO}_4$	$\text{MgSO}_4 \to \text{Mg}^{2+} + \text{SO}_4^{2-}$	+2	-2	4.0 × $c$
1:3 Electrolyte	$\text{FeCl}_3, \text{AlCl}_3$	$\text{FeCl}_3 \to \text{Fe}^{3+} + 3\text{Cl}^-$	+3	-1	6.0 × $c$
3:1 Electrolyte	$\text{Na}_3\text{PO}_4, \text{K}_3\text{PO}_4$	$\text{Na}_3\text{PO}_4 \to 3\text{Na}^+ + \text{PO}_4^{3-}$	+1	-3	6.0 × $c$
2:3 Electrolyte	$\text{Al}_2(\text{SO}_4)_3, \text{Fe}_2(\text{SO}_4)_3$	$\text{Al}_2(\text{SO}_4)_3 \to 2\text{Al}^{3+} + 3\text{SO}_4^{2-}$	+3	-2	15.0 × $c$

Activity Coefficients ($\gamma$): Debye-Hückel, Extended & Davies Equations

In real solutions, electrostatic shielding reduces the chemical availability of ions. The effective concentration (activity $a$) is $a_i = \gamma_i \cdot c_i$. Three established models quantify $\gamma_i$:

1. Debye-Hückel Limiting Law

Valid for very dilute solutions ($I < 0.01\,\text{M}$):

$$\log_{10} \gamma_i = -A z_i^2 \sqrt{I}$$

where $A = 0.509\,\text{M}^{-1/2}$ for water at 25 °C.

2. Extended Debye-Hückel

Accounts for finite ion radius $a_i$ ($I < 0.1\,\text{M}$):

$$\log_{10} \gamma_i = -\frac{A z_i^2 \sqrt{I}}{1 + B a_i \sqrt{I}}$$

where $B = 0.328 \times 10^8\,\text{cm}^{-1}\text{M}^{-1/2}$ in water.

3. Davies Equation

Accurate for moderate ionic strength ($I \le 0.5\,\text{M}$):

$$\log_{10} \gamma_i = -A z_i^2 \left( \frac{\sqrt{I}}{1 + \sqrt{I}} - 0.3 I \right)$$

Widely used in water quality and geochemical modeling.

Kielland Hydrated Ion Radii ($a_i$) Parameter Matrix

Kielland (1937) Standard

In the Extended Debye-Hückel equation, the parameter $a_i$ (in $\text{Å} = 10^{-10}\,\text{m}$) represents the effective diameter of the hydrated ion in aqueous solution:

Effective Size $a_i$ ($\text{Å}$)	Cations ($z_+$)	Anions ($z_-$)	Typical Activity $\gamma$ @ 0.05 M
2.5 – 3.0 Å	$\text{Rb}^+, \text{Cs}^+, \text{Tl}^+, \text{Ag}^+, \text{NH}_4^+$	$\text{Cl}^-, \text{Br}^-, \text{I}^-, \text{NO}_3^-, \text{ClO}_4^-$	0.805
3.5 – 4.0 Å	$\text{K}^+, \text{Na}^+, \text{Cd}^{2+}$	$\text{SO}_4^{2-}, \text{HPO}_4^{2-}, \text{IO}_3^-, \text{HCO}_3^-$	0.815 (\|z\|=1) / 0.445 (\|z\|=2)
4.5 – 5.0 Å	$\text{Sr}^{2+}, \text{Ba}^{2+}, \text{Ra}^{2+}, \text{Pb}^{2+}$	$\text{CH}_3\text{COO}^-, \text{Citrate}^{3-}, \text{F}^-, \text{H}_2\text{PO}_4^-$	0.465 (\|z\|=2) / 0.160 (\|z\|=3)
6.0 Å	$\text{Li}^+, \text{Ca}^{2+}, \text{Cu}^{2+}, \text{Zn}^{2+}, \text{Mn}^{2+}, \text{Ni}^{2+}, \text{Co}^{2+}$	$\text{PO}_4^{3-}, \text{P}_2\text{O}_7^{4-}$	0.485 (\|z\|=2) / 0.180 (\|z\|=3)
8.0 – 9.0 Å	$\text{Mg}^{2+}, \text{Be}^{2+}, \text{Al}^{3+}, \text{Fe}^{3+}, \text{Cr}^{3+}, \text{Sc}^{3+}$	—	0.520 (\|z\|=2) / 0.245 (\|z\|=3)
9.0 – 11.0 Å	$\text{H}^+\ (\text{Hydronium } \text{H}_9\text{O}_4^+), \text{Th}^{4+}, \text{Zr}^{4+}, \text{Ce}^{4+}$	—	0.860 (\|z\|=1) / 0.095 (\|z\|=4)

Standard Biological Laboratory Buffer Ionic Strength & Osmolarity

Biochemistry Benchmark

Formulation parameters for standard biological buffers, critical for maintaining protein tertiary structure and physiological osmolarity:

Buffer Formulation	Primary Chemical Components	Molarity ($\text{M}$)	Ionic Strength ($I$)	Debye Length ($\kappa^{-1}$)
1X PBS (pH 7.4)	$137\,\text{mM NaCl}, 2.7\,\text{mM KCl}, 10\,\text{mM Na}_2\text{HPO}_4, 1.8\,\text{mM KH}_2\text{PO}_4$	0.1515 M	162.7 mM (0.163 M)	0.75 nm
10X PBS Stock	$1.37\,\text{M NaCl}, 27\,\text{mM KCl}, 100\,\text{mM Na}_2\text{HPO}_4, 18\,\text{mM KH}_2\text{PO}_4$	1.515 M	1,627 mM (1.63 M)	0.24 nm
1X TBS (pH 7.6)	$50\,\text{mM Tris-HCl}, 150\,\text{mM NaCl}$	0.200 M	178.0 mM (0.178 M)	0.72 nm
1X TAE (Electrophoresis)	$40\,\text{mM Tris}, 20\,\text{mM Acetic Acid}, 1\,\text{mM EDTA}$	0.061 M	15.2 mM (0.015 M)	2.47 nm
1X TBE (Electrophoresis)	$89\,\text{mM Tris}, 89\,\text{mM Boric Acid}, 2\,\text{mM EDTA}$	0.180 M	35.4 mM (0.035 M)	1.62 nm
20X SSC (Hybridization)	$3.0\,\text{M NaCl}, 0.3\,\text{M Sodium Citrate}\ (\text{Na}_3\text{C}_6\text{H}_5\text{O}_7)$	3.300 M	4,800 mM (4.80 M)	0.14 nm

Colloidal Stability (DLVO Theory) & Protein Salting-Out Kinetics

1. Electrical Double Layer (EDL) & DLVO Theory

Colloidal and nanoparticle stability is governed by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, balancing electrostatic double-layer repulsion against van der Waals attraction. Increasing ionic strength compresses the Debye length ($\kappa^{-1} \propto 1/\sqrt{I}$), collapsing the energy barrier and causing rapid flocculation at the Critical Coagulation Concentration (CCC):

$$\text{CCC} \propto \frac{1}{z^6} \quad \text{(Schulze-Hardy Rule)}$$

Thus, trivalent ions ($\text{Al}^{3+}$) are $3^6 / 1^6 = 729\times$ more potent coagulants than monovalent ions ($\text{Na}^+$).

2. Protein Salting-In vs. Salting-Out (Cohn Equation)

In structural biology, protein solubility ($S$) as a function of ionic strength is described by the Cohn equation:

$$\log_{10} S = \beta - K_s \cdot I$$

where $\beta$ is intrinsic solubility and $K_s$ is the salting-out constant. Kosmotropic anions follow the Hofmeister series: $$\text{SO}_4^{2-} > \text{HPO}_4^{2-} > \text{acetate} > \text{Cl}^- > \text{NO}_3^- > \text{ClO}_4^-$$ Ammonium sulfate $(\text{NH}_4)_2\text{SO}_4$ is standard for fractional protein precipitation because $\text{SO}_4^{2-}$ strips hydration shells at $I > 2\,\text{M}$.

Step-by-Step Worked Case Studies: 1X PBS, Al₂(SO₄)₃ & CaCl₂ Activity

Case 1: 1X PBS Buffer Biology

Composition: $137\,\text{mM NaCl} + 2.7\,\text{mM KCl} + 10\,\text{mM Na}_2\text{HPO}_4 + 1.8\,\text{mM KH}_2\text{PO}_4$:

$[\text{Na}^+] = 137 + 20 = 157\,\text{mM}$
$[\text{HPO}_4^{2-}] = 10\,\text{mM} \implies 10 \times 2^2 = 40\,\text{mM}$
$I = \frac{1}{2}[157(1) + 2.7(1) + 1.8(1) + 139.7(1) + 40] = \mathbf{162.7\,\text{mM}}$

Case 2: 0.05 M Al₂(SO₄)₃ 2:3 Salt

Dissociation: $\text{Al}_2(\text{SO}_4)_3 \to 2\text{Al}^{3+} + 3\text{SO}_4^{2-}$:

$[\text{Al}^{3+}] = 2 \times 0.05 = 0.10\,\text{M}$ ($z=3$)
$[\text{SO}_4^{2-}] = 3 \times 0.05 = 0.15\,\text{M}$ ($z=2$)
$I = \frac{1}{2}[0.10(3^2) + 0.15(2^2)] = \frac{1}{2}[0.9 + 0.6] = \mathbf{0.750\,\text{M}}$

Case 3: 0.10 M CaCl₂ Activity Davies Eq

Given: $c = 0.10\,\text{M} \implies I = 3 \times 0.10 = 0.30\,\text{M}$:

$\sqrt{I} = \sqrt{0.30} = 0.5477$
Davies $\gamma(\text{Ca}^{2+}, z=2) = \mathbf{0.347}$
Active Conc $a_{\text{Ca}^{2+}} = 0.347 \times 0.10 = \mathbf{0.0347\,\text{M}}$

Frequently Asked Questions (FAQ)

Authoritative answers to common questions about calculating solution ionic strength, activity coefficients, Debye screening lengths, and buffer pKa shifts.

Effective Size \(a_i\) (\(\text{Å}\))	Cations (\(z_+\))	Anions (\(z_-\))	Typical Activity \(\gamma\) @ 0.05 M
2.5 – 3.0 Å	\(\text{Rb}^+, \text{Cs}^+, \text{Tl}^+, \text{Ag}^+, \text{NH}_4^+\)	\(\text{Cl}^-, \text{Br}^-, \text{I}^-, \text{NO}_3^-, \text{ClO}_4^-\)	0.805
3.5 – 4.0 Å	\(\text{K}^+, \text{Na}^+, \text{Cd}^{2+}\)	\(\text{SO}_4^{2-}, \text{HPO}_4^{2-}, \text{IO}_3^-, \text{HCO}_3^-\)	0.815 (\|z\|=1) / 0.445 (\|z\|=2)
4.5 – 5.0 Å	\(\text{Sr}^{2+}, \text{Ba}^{2+}, \text{Ra}^{2+}, \text{Pb}^{2+}\)	\(\text{CH}_3\text{COO}^-, \text{Citrate}^{3-}, \text{F}^-, \text{H}_2\text{PO}_4^-\)	0.465 (\|z\|=2) / 0.160 (\|z\|=3)
6.0 Å	\(\text{Li}^+, \text{Ca}^{2+}, \text{Cu}^{2+}, \text{Zn}^{2+}, \text{Mn}^{2+}, \text{Ni}^{2+}, \text{Co}^{2+}\)	\(\text{PO}_4^{3-}, \text{P}_2\text{O}_7^{4-}\)	0.485 (\|z\|=2) / 0.180 (\|z\|=3)
8.0 – 9.0 Å	\(\text{Mg}^{2+}, \text{Be}^{2+}, \text{Al}^{3+}, \text{Fe}^{3+}, \text{Cr}^{3+}, \text{Sc}^{3+}\)	—	0.520 (\|z\|=2) / 0.245 (\|z\|=3)
9.0 – 11.0 Å	\(\text{H}^+\ (\text{Hydronium } \text{H}_9\text{O}_4^+), \text{Th}^{4+}, \text{Zr}^{4+}, \text{Ce}^{4+}\)	—	0.860 (\|z\|=1) / 0.095 (\|z\|=4)

Ionic Strength Calculator

Salt Composition & Mixture

Activity Coefficient Engine

Biological Buffer System

Physical Principles of Solution Ionic Strength (\(I\))

Salt Stoichiometry & Ionic Strength Multiplier Reference Table

Activity Coefficients (\(\gamma\)): Debye-Hückel, Extended & Davies Equations

Kielland Hydrated Ion Radii (\(a_i\)) Parameter Matrix

Standard Biological Laboratory Buffer Ionic Strength & Osmolarity

Colloidal Stability (DLVO Theory) & Protein Salting-Out Kinetics

Step-by-Step Worked Case Studies: 1X PBS, Al₂(SO₄)₃ & CaCl₂ Activity

Frequently Asked Questions (FAQ)

Electrolyte Type	Example Salt	Dissociation Equation	Cation (\(z_+\))	Anion (\(z_-\))	\(I / c\) Multiplier
1:1 Electrolyte	\(\text{NaCl, KCl, KNO}_3\)	\(\text{NaCl} \to \text{Na}^+ + \text{Cl}^-\)	+1	-1	1.0 × \(c\)
1:2 Electrolyte	\(\text{CaCl}_2, \text{MgCl}_2\)	\(\text{CaCl}_2 \to \text{Ca}^{2+} + 2\text{Cl}^-\)	+2	-1	3.0 × \(c\)
2:1 Electrolyte	\(\text{Na}_2\text{SO}_4, \text{K}_2\text{SO}_4\)	\(\text{Na}_2\text{SO}_4 \to 2\text{Na}^+ + \text{SO}_4^{2-}\)	+1	-2	3.0 × \(c\)
2:2 Electrolyte	\(\text{MgSO}_4, \text{CuSO}_4, \text{ZnSO}_4\)	\(\text{MgSO}_4 \to \text{Mg}^{2+} + \text{SO}_4^{2-}\)	+2	-2	4.0 × \(c\)
1:3 Electrolyte	\(\text{FeCl}_3, \text{AlCl}_3\)	\(\text{FeCl}_3 \to \text{Fe}^{3+} + 3\text{Cl}^-\)	+3	-1	6.0 × \(c\)
3:1 Electrolyte	\(\text{Na}_3\text{PO}_4, \text{K}_3\text{PO}_4\)	\(\text{Na}_3\text{PO}_4 \to 3\text{Na}^+ + \text{PO}_4^{3-}\)	+1	-3	6.0 × \(c\)
2:3 Electrolyte	\(\text{Al}_2(\text{SO}_4)_3, \text{Fe}_2(\text{SO}_4)_3\)	\(\text{Al}_2(\text{SO}_4)_3 \to 2\text{Al}^{3+} + 3\text{SO}_4^{2-}\)	+3	-2	15.0 × \(c\)

Buffer Formulation	Primary Chemical Components	Molarity (\(\text{M}\))	Ionic Strength (\(I\))	Debye Length (\(\kappa^{-1}\))
1X PBS (pH 7.4)	\(137\,\text{mM NaCl}, 2.7\,\text{mM KCl}, 10\,\text{mM Na}_2\text{HPO}_4, 1.8\,\text{mM KH}_2\text{PO}_4\)	0.1515 M	162.7 mM (0.163 M)	0.75 nm
10X PBS Stock	\(1.37\,\text{M NaCl}, 27\,\text{mM KCl}, 100\,\text{mM Na}_2\text{HPO}_4, 18\,\text{mM KH}_2\text{PO}_4\)	1.515 M	1,627 mM (1.63 M)	0.24 nm
1X TBS (pH 7.6)	\(50\,\text{mM Tris-HCl}, 150\,\text{mM NaCl}\)	0.200 M	178.0 mM (0.178 M)	0.72 nm
1X TAE (Electrophoresis)	\(40\,\text{mM Tris}, 20\,\text{mM Acetic Acid}, 1\,\text{mM EDTA}\)	0.061 M	15.2 mM (0.015 M)	2.47 nm
1X TBE (Electrophoresis)	\(89\,\text{mM Tris}, 89\,\text{mM Boric Acid}, 2\,\text{mM EDTA}\)	0.180 M	35.4 mM (0.035 M)	1.62 nm
20X SSC (Hybridization)	\(3.0\,\text{M NaCl}, 0.3\,\text{M Sodium Citrate}\ (\text{Na}_3\text{C}_6\text{H}_5\text{O}_7)\)	3.300 M	4,800 mM (4.80 M)	0.14 nm