Pertechnetate

The structure of the technetate(VII) ion.

The pertechnetate ion is an oxoanion with the chemical formula TcO⁻
₄. It is often used as a convenient water-soluble source of isotopes of the radioactive element technetium (Tc). In particular it is used to carry the ^99mTc isotope (half-life 6 hours) which is commonly used in nuclear medicine in several nuclear scanning procedures.

A technetate(VII) salt is a compound containing this ion. Pertechnetate compounds are salts of technetic(VII) acid. Pertechnetate is analogous to permanganate but it has little oxidizing power. Pertechnetate has higher oxidation power than perrhenate.

Understanding pertechnate is important in understanding technetium contamination in the environment and in nuclear waste management.

Compounds

Formula	name	crystal structure	cell dimensions (Å)	unit cell volume (Å3)	remarks	references
LiTcO4	lithium pertechnetate
LiTcO4·2H2O	lithium pertechnetate monohydrate
LiTcO4·3H2O	lithium pertechnetate trihydrate			Pt3/mc
NaTcO4	sodium pertechnetate	tetragonal	a = 5.342, c = 1.874	338.91	absorbs water from atmosphere
NaTcO4·H2O	sodium pertechnetate monohydrate
NaTcO4·2H2O	sodium pertechnetate dihydrate
NaTcO4·4H2O	sodium pertechnetate tetrahydrate
KTcO4	potassium pertechnetate	tetragonal	a = 5.647, c = 12.91	411.73	used to prepare radiopharmaceuticals
RbTcO4	rubidium pertechnetate	tetragonal	a = 5.762, c =13.543	449.65
α-CsTcO4	α-caesium pertechnetate	tetragonal	a = 5.898, c = 14.38		high temperature >470K; volatile at high temperatures
β-CsTcO4	β-caesium pertechnetate	orthorhombic	a = 5.737, b = 5.92, c = 14.341	486.38
TlTcO4	thallium pertechnetate	orthorhombic
TlTcO4	thallium pertechnetate	tetragonal			at high temperatures
NH4TcO4	ammonium pertechnetate	tetragonal			technetium may be supplied in this form
AgTcO4	silver pertechnetate	tetragonal

Reactions

• Radiolysis of TcO⁻
  ₄ in nitrate solutions proceeds through the reduction to TcO²⁻
  ₄ which induces complex disproportionation processes:

${\begin{array}{l}{\ce {{TcO4^{-}}+{e^{-}}->TcO4^{2}-}}\\{\ce {2TcO4^{2-}->{TcO4^{-}}+Tc^{V}}}\\{\ce {2Tc^{V}->{TcO4^{2-}}+Tc^{IV}}}\\{\ce {{Tc^{V}}+TcO4^{2-}->{Tc^{IV}}+TcO4-}}\end{array}}$

• Pertechnetate can be reduced by H₂S to give Tc₂S₇.
• Pertechnetate is also reduced to Tc(IV/V) compounds in alkaline solutions in nuclear waste tanks without adding catalytic metals, reducing agents, or external radiation. Reactions of mono- and disaccharides with ^99mTcO⁻
  ₄ yield Tc(IV) compounds that are water-soluble.

Uses

As a ^99mTc carrier

A technetium-99m generator provides the pertechnetate containing the short-lived isotope ^99mTc for medical uses. This compound is generated directly from molybdate held on alumina within the generator (see this topic for detail).

In nuclear medicine

Pertechnetate has a wide variety of uses in diagnostic nuclear medicine. Since technetate(VII) can substitute for iodine in the Na/I symporter (NIS) channel in follicular cells of the thyroid gland, inhibiting uptake of iodine into the follicular cells, ^99mTc-pertechnetate can be used as an alternative to ¹²³I in imaging of the thyroid, although it specifically measures uptake and not organification. It has also been used historically to evaluate for testicular torsion, although ultrasound is more commonly used in current practice, as it does not deliver a radiation dose to the testes. It is also used in labeling of autologus red blood cells for MUGA scans to evaluate left ventricular cardiac function, localization of gastrointestinal bleeding prior to embolization or surgical management, and in damaged red blood cells to detect ectopic splenic tissue.

It is actively accumulated and secreted by the mucoid cells of the gastric mucosa, and therefore, technetate(VII) radiolabeled with technetium-99m is injected into the body when looking for ectopic gastric tissue as is found in a Meckel's diverticulum with Meckel's scans.

Non-radioactive uses

All technetium salts are mildly radioactive, but some of them have explored use of the element for its chemical properties. In these uses, its radioactivity is incidental, and generally the least radioactive (longest-lived) isotopes of Tc are used. In particular, ⁹⁹Tc (half-life 211,000 years) is used in corrosion research, because it is the decay product of the easily obtained commercial ^99mTc isotope, which is its nuclear isomer. In theory, the longest-lived technetium isotope, ⁹⁸Tc (half-life 4.2 million years), would be the optimal isotope for this use.

Solutions of technetate(VII) react with the surface of iron to form technetium dioxide, in this way it is able to act as an anodic corrosion inhibitor.

See also

• Permanganate
• Perrhenate
• Sodium pertechnetate