An implementation and using of a simple radiochemical purity assessment method of [^99mTc]-etifenin

Summary

Introduction:
Methods for a radiochemical purity (RCP) assessment of [^99mTc]technetium-etifenin mentioned in a patient information leaflet (PIL) of ROTOP – EHIDA 20,0 mg kit are too tedious or less available. A currently valid method of the Czech Pharmacopoeia (Ph. Boh.) stated in its Supplement 2015 is more complicated too. A simplest (currently non-pharmacopoeial) method was stated in Ph. Boh. 2009 – Supplement 2011 and therefore this one has been verified and introduced to a common practice.

Subjects and methods:
A radiochromatography with scintillation detector NaI(Tl) attached to a multichannel analyzer MCA-1000G. A stationary phase was ITLC-SA (9 × 1 cm), a mobile phase was 0,9% NaCl, a path length was 7 cm. To find out a radioactivity distribution the strip was cut into 0,5cm ones. For RCP assessment the strip was cut only into three pieces in optimized points.

Results:
A retardation factor (R_F) of [^99mTc]-etifenin R_F = 0,75 (compared to 0,5 stated in Ph. Boh. 2009 – Supplement 2011) was determined by a radioactivity distribution measurement. R_F of [^99mTc]technetium in colloidal form and [^99mTc]pertechnetate ion were 0–0,1 and 0,9–1, respectively. For RCP assessment the strips were cut at points accordant with R_F = 0,1 and R_F = 0,9. Average RCP was calculated from 15 values and was (96,8 ± 1,1) %, average [^99mTc]technetium in colloidal form and [^99mTc]pertechnetate ion were (1,6 ± 0,4) % and (1,6 ± 0,9) %, respectively.

Conclusion:
The RCP assessment method according to Ph. Boh. 2009 – Supplement 2011 is applicable. A developed chromatogram can´t be cut into thirds as [^99mTc]-etifenin isn´t in the middle of the chromatogram (as mentioned in Ph. Boh. 2009 – Supplement 2011) but around the point corresponding R_F = 0,75. A cutting of the strip into three pieces at points accordant with R_F = 0,1 and R_F = 0,9 is convenient. The method is then reliable and RCP values were always satisfactory (minimum value 95,0 %).

Key words:
[^99mTc]technetium-etifenin, [^99mTc]technetium-EHIDA, N-(2,6-diethylacetanilido)iminodiacetic acid, [(2,6-diethylphenylcarbamoyl)methyl]iminodiacetic acid, radiochemical purity, [^99mTc]technetium in colloidal form, [^99mTc]pertechnetate ion