A Specific HPLC Method to Determine Residual HEPES in [68Ga]Ga-Radiopharmaceuticals: Development and Validation

Background: Nowadays, in Nuclear Medicine, clinically applied radiopharmaceuticals must meet quality release criteria such as high radiochemical purity and radiochemical yield. Many radiopharmaceuticals do not have marketing authorization and have no dedicated monograph within European Pharmacopeia (Ph. Eur.); therefore, general monographs on quality controls (QCs) have to be applied for clinical application. These criteria require standardization and validation in labeling and preparation, including quality controls measurements, according to well defined standard operation procedures. However, QC measurements are often based on detection techniques that are specific to a certain chromatographic system. Several radiosyntheses of [⁶⁸Ga]Ga-radiopharmaceuticals are more efficient and robust when they are performed with 2-[4-(2-hydroxyethyl)piperazin-1-yl] ethanesulfonic acid (HEPES) buffer, which is considered as an impurity to be assessed in the QC procedure, prior to clinical use. Thus, Ph. Eur. has introduced a thin-layer chromatography (TLC) method to quantify the HEPES amount that is present in [⁶⁸Ga]Ga-radiopharmaceuticals. However, this is only qualitative and has proven to be unreliable. Here we develop and validate a new high-performance liquid chromatography (UV-Radio-HPLC) method to quantify the residual amount of HEPES in ⁶⁸Ga-based radiopharmaceuticals. Method: To validate the proposed UV-Radio-HPLC method, a stepwise approach was used, as defined in the guidance document that was adopted by the European Medicines Agency (CMP/ICH/381/95 2014). The assessed parameters are specificity, linearity, precision (repeatability), accuracy, and limit of quantification. A range of concentrations of HEPES (100, 80, 60, 40, 20, 10, 5, 3 μg/mL) were analyzed. Moreover, to test the validity and pertinence of our new HPLC method, we analyzed samples of [⁶⁸Ga]Ga-DOTATOC; [⁶⁸Ga]Ga-PSMA; [⁶⁸Ga]Ga-DOTATATE; [⁶⁸Ga]Ga-Pentixafor; and [⁶⁸Ga]Ga-NODAGA-Exendin-4 from different batches that were prepared for clinical use. Results: In the assessed samples, HEPES could not be detected by the TLC method that was described in Ph. Eur. within 4 min incubation in an iodine-saturated chamber. Our developed HPLC method showed excellent linearity between 3 and 100 μg/mL for HEPES, with a correlation coefficient (R²) for calibration curves that was equal to 0.999, coefficients of variation (CV%) < 2%, and percent deviation value of bias from 100% to 5%, in accordance with acceptance criteria. The intra-day and inter-day precision of our method was statistically confirmed and the limit-of-quantification (LOQ) was 3 μg/mL, confirming the high sensitivity of the method. The amount of HEPES that was detected with our developed HPLC method in the tested [⁶⁸Ga]Ga-radiopharmaceuticals resulted well below the Ph. Eur. limit, especially for [⁶⁸Ga]Ga-NODAGA-Exendin-4. Conclusions: The TLC method that is described in Ph. Eur. to assess residual HEPES in [⁶⁸Ga]-based radiopharmaceuticals may not be sufficiently sensitive and thus unsuitable for QC release. Our new HPLC method was sensitive, quantitative, reproducible, and rapid for QCs, allowing us to exactly determine the residual HEPES amount in [⁶⁸Ga]Ga-radiopharmaceuticals for safe patient administration.     

Phase transitions in the tantalum-hydrogen system observed by PAC

The perturbation felt by¹⁸¹Hf probes in a¹⁸¹HfTa lattice loaded with 30 at% hydrogen was observed by PAC as a function of temperature. Three different interactions were identified: 1) Ν_Q1=433 (6) MHz, η=0.45 2) Ν_Q2=142 (9) MHz, η=0.9, and 3) Ν_Q?0, σ=4–14 Μ^?1 which are attributed to the Β^?, ε^? and α-phase in TaH system, respectively.     

Lifetime of electronic states of CO2+

The radiative lifetimes of the $\text{A}\text{?}{}^2\text{Π}{}_{\mathrm{u}}$ and $\text{B}\text{?}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ states of CO₂⁺ were measured by means of the delayed coincidence method. Excitation was performed by a pulsed electron beam incident on CO₂. The results of these measurements are 115 ± 5 nsec for the $\text{A}\text{?}{}^2\text{Π}{}_{\mathrm{u}}$ state and 126 ± 3 nsec for the $\text{B}\text{?}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$ state.     

An ergodic theorem for Schlögl models with small migration

Summary We consider a class of reaction-diffusion processes with state space N^Zd. The reaction part is described by a birth and death process where the rates are given by certain polynomials. The diffusion part is an irreducible symmetric random walk. We prove ergodicity in the case of a sufficiently small migration rate. For the proof we couple two processes and show that the density of the discrepancies goes to zero.     

Magnetic response of microbially synthesized transition metal- and lanthanide-substituted nano-sized magnetites

The magnetic susceptibility (κ_RT) and saturation magnetization (M_S) of microbially synthesized magnetites were systematically examined. Transition metal (Cr, Mn, Co, Ni and Zn)- and lanthanide (Nd, Gd, Tb, Ho and Er)-substituted magnetites were microbially synthesized by the incubation of transition metal (TM)- and lanthanide (L)-mixed magnetite precursors with either thermophilic (TOR-39) or psychrotolerant (PV-4) metal-reducing bacteria (MRB). Zinc incorporated congruently into both the precursor and substituted magnetite, while Ni and Er predominantly did not. Microbially synthesized Mn- and Zn-substituted magnetites had higher κ_RT than pure biomagnetite depending on bacterial species and they exhibited a maximum κ_RT at 0.2 cationic mole fraction (CMF). Other TMs’ substitution linearly decreased the κ_RT with increasing substitution amount. Based on the M_S values of TM- and L-substituted magnetite at 0.1 and 0.02 CMF, respectively, Zn (90.7 emu/g for TOR-39 and 93.2 emu/g for PV-4)- and Mn (88.3 emu/g by PV-4)-substituted magnetite exhibited higher M_S than standard chemical magnetite (84.7 emu/g) or pure biomagnetite without metal substitution (76.6 emu/g for TOR-39 and 80.3 emu/g for PV-4). Lanthanides tended to decrease M_S, with Gd- and Ho-substituted magnetites having the highest magnetization. The higher magnetization of microbially synthesized TM-substituted magnetites by the psychrotroph, PV-4 may be explained by the magnetite formation taking place at low temperatures slowing mechanics, which may alter the magnetic properties compared to the thermophile, through suppression of the random distribution of substituted cations.