A comparison of SepPak and high-performance liquid chromatography as techniques for measuring the radiochemical purity of 99mTc-MAG3.

OBJECTIVE: To compare high-performance liquid chromatography and SepPak as techniques for measuring the radiochemical purity of 99mTc-MAG3. METHODS: Samples of 99mTc-MAG3 (n = 20) with radiochemical purities in the range 43-98% were prepared and analysed by both techniques. RESULTS: The correlation between the results from the two techniques was excellent (r = 1.00) and the differences between the results were not statistically significant (P > 0.05). CONCLUSION: Both techniques are suitable for measuring the radiochemical purity of 99mTc-MAG3.

99Tcm-MAG3: problems with radiochemical purity testing.

The radiochemical purity (RCP) of 99Tcm-MAG3 was determined using solid-phase extraction (SPE), high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). The difference between the HPLC and SPE methods was highly significant (P < 0.001), yielding values for RCP of 94.4 +/- 1.4% and 86.0 +/- 5.1% [corrected] respectively (mean +/- s). Further qualitative analysis of the SPE fractions obtained, was carried out using HPLC and TLC. The unexpected presence of 99Tcm-MAG3 in one of the fractions was observed together with the appearance of hydrophilic impurities in the hydrophobic extract. This lack of specificity may be the reason for the discrepancy between the SPE and HPLC methods. Use of the SPE method leads to an underestimation of the RCP of 99Tcm-MAG3 and, indeed, had we been relied solely on this method of analysis, we would have had to reject most kits we prepared. In a separate study, we compared a TLC method with HPLC. Differences were found to be highly significant (P < 0.001), yielding values of 98.3 +/- 0.6% and 95.8 +/- 0.9% respectively. Comparison of the data points showed that TLC gave consistently higher RCP yield than HPLC. This elevated value was found to be due to the inability of the TLC method to separate 99Tcm-lipophilic impurity, seen on HPLC, from the 99Tcm-MAG3. Therefore, use of this TLC method leads to an overestimation of the RCP of 99Tcm-MAG3.

The influence of temperature and alkaline pH on the labeling of free and conjugated MAG3 with technetium-99m.

Benzoyl-protected mercaptoacetyltriglycine (S-benzoyl MAG3) is radiolabeled by tartrate transchelation at elevated temperatures or basic pH. The object of this investigation was to establish whether the same 99mTc labeled species are formed when S-acetyl (S-acetyl MAG3)-conjugated compounds are radiolabeled by tartrate transchelation at ambient temperature and neutral pH in contrast to labeling at 95 degrees C and pH 11. S-acetyl MAG3 was conjugated to biocytin and to the amine-derivitized oligomers DNA and PNA. Along with free S-acetyl MAG3, these were radiolabeled under the different conditions. Although labeling efficiencies were always lower when labeled at ambient temperature and neutral pH relative to labeling at 95 degrees C or pH 11 (free S-acetyl MAG3 could not be labeled at all), size exclusion and reverse phase HPLC showed no difference with labeling conditions in the radiochemical profiles for labeled DNA and biocytin. In the case of DNA, a cysteine challenge also failed to demonstrate a difference. However, in the case of PNA, some important differences were observed in the size exclusion HPLC radiochromatograms. In addition, PNA labeled at ambient temperature and neutral pH was less stable to transchelation to cysteine. In conclusion, S-acetyl MAG3 conjugated compounds may be radiolabeled at ambient temperature and neutral pH. In most cases, the radiochemical species produced appear to be identical to those formed when labeling is accomplished at 95 degrees C or pH 11.

Anomalies in hepatobiliary excretion of technetium-99m-MAG3 preparations.

Technetium-99m-MAG3 is accepted as a renal tubular function agent. However, sporadic liver and gall bladder visualisation during its clinical use is clearly a disadvantage. HPLC-purified 99mTc-MAG3 samples exhibited appreciable hepatobiliary uptake (7%), and an elevated level of such uptake was observed in unpurified kit preparations, which was stated to be associated with the excretory property of the radiolabeled kit impurities. To verify this we attempted to quantitate the hepatobiliary uptake of the kit preparations with that of its radiolabeled components. The contribution of each component toward hepatobiliary uptake of the sample was calculated from their abundance in the chelate mixture and the individual biodistribution of the isolated components. However, the anticipated hepatobiliary uptake of different preparations of 99mTc-MAG3 calculated in this way was always lower than that of the experimental value determined directly. Further work is needed to explain the anomaly.

Effects of generator eluate age on the radiochemical purity of fractionated 99Tcm-MAG3.

The fractionation of US mercaptoacetyltriglycene (MAG3) cold kits provides an economical way of preparing 99Tcm-MAG3. However, our nuclear pharmacy noted that fractionated 99Tcm-MAG3 kits sometimes failed radiochemical purity (RCP) testing (i.e. RCP < 90%) when a 99Tcm eluate of older age was used. The purpose of this study was to evaluate the effects of eluate age on the radiochemical purity of fractionated 99Tcm-MAG3 kits. Each of four US MAG3 cold kits was initially diluted with 10 ml N2-purged 0.9% NaCl solution and subdivided into 10 aliquots of 1 ml MAG3 solution and overlayered with N2. The 40 fractionated MAG3 vials were immediately frozen at -20 degrees C for storage. Fractionated MAG3 kits were reconstituted with 1 ml of approximately 111 GBq 99Tcm eluate from a long-ingrowth generator (i.e. > or = 72 h) every hour during the 6 h post-elution period. The RCP of each 99Tcm-MAG3 preparation was determined using the recommended Sep-Pak C18 column chromatography 1, 2, 3, 4, 5 and 6 h post-reconstitution. All fractionated MAG3 kits prepared with 99Tcm eluates 4 h post-elution or less maintained an average RCP value of 96.3 +/- 2.5% (n = 144) throughout the 6 h evaluation period following preparation. However, 99Tcm eluates 5 and 6 h post-elution resulted in kit failure rates of 16.7% (1/6) with RCP = 89.3%, and 50% (3/6) with RCP = 88.2, 83.9 and 87.1%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)