« SEPARATIONS AND PURIFICATIONS
boundaries of analytical instrumentation. For this reason, developing sensitive methods with lower detection and quantitation limits (QL) are critical in ensuring patient safety and conserving the sample especially in early stages of development.
For each of the 9 selected metals, the limit of detection (LOD) and limit of quantitation (LOQ) were evaluated based on the signal-to- noise (S/N) ratio and percent recovery. The S/N is a key attribute that helps verify the reliability of the measured signal and is that the signal is distinct from the background noise. The percent recovery is also important as it verifi es the accuracy of the method at low levels. The LOD and LOQ were evaluated by testing each element of interest’s standard solution. The results for each element are shown in Table 5. The QL for each specifi ed metal is based on the sample size used. The LOQ of the method is below 3 ppm (μg/g) for each element based on a 20-mg sample size with percent recoveries ranging from 92% to 108% for all elements, with the exception of palladium at the 363.470-nm emission line. The percent recovery of palladium at 363.470 nm is lower than 340.458 nm (82% vs 104%) and the LOQ is higher (20 ppm vs 2.6 ppm) based on the 20-mg sample, due to a lower sensitivity at 363.470 nm. However, the LOQ of palladium can be lowered if desired by increasing the sample size and by choosing an alternative emission line of 340.458 nm, which is more sensitive and specifi c. This emphasizes the importance of evaluating multiple lines during method development. The experimental results demonstrate the adequacy of the method for this intended use in agreement with the ICH guidelines for residual elements.
Repeatability and System Precision
Repeatability and precision are important parameters that should be minimally evaluated in the pharmaceutical industries. These measure the degree of closeness of analytical results between replicate measurements of a sample and between samples originating from the same homogeneous sample over a short interval of time. Repeatability adds to the adequacy of the method for its intended use.
Repeatability of the method was evaluated using triplicate standard preparations at 3 levels for each specifi ed metal assessed. Usually, the levels bracket the nominal concentration for each specifi ed metal. System precision was evaluated by analyzing a single preparation of the standard at a nominal concentration, usually with 6 measurements. Repeatability was assessed from the relative standard deviation (RSD) of the analytical results obtained from independent preparations of standard solution at multiple levels. Tables 6 and 7 show the results of the repeatability study. The RSD at each level and overall levels were below 20% for all samples demonstrating the adequacy of the method for intended use.
Stability of Standard Solutions
It is important to assess the stability of standard solutions used in the release testing of API as it determines the duration of its use and hence the number of samples that can be analyzed. Occasionally, it can be helpful in out-of-trend and or out-of-specifi cation investigations. The stability of standard solution containing the elements of interest
Table 6. Repeatability of 1 µg/mL (ppm) Standard Concentration on Primary Wavelength
Element Concentration 1 µg/mL (ppm) Element
Zn Wavelength (λ).
Prep 1, Run 1 Prep 1, Run 2 Prep1, Run 3 Mean
Std. Dev. %RSD
Prep 2, Run 1 Prep 2, Run 2 Prep2, Run 3 Mean
Std. Dev. %RSD
Prep 3, Run 1 Prep 3, Run 2 Prep3, Run 3 Mean
Std. Dev. %RSD
Overall Average Overall Std. Dev Overall %RSD
213.857 1.091 1.163 1.052 1.045
0.0067 0.64
1.000 1.008 1.011 1.007
0.0058 0.57
0.994 1.000 1.045 1.013
0.0277 2.74
1.021 0.023 2.24
Fe
238.204 1.092 1.132 1.033 1.034
0.0150 1.45
0.989 0.977 1.025 0.997
0.0250 2.51
1.031 0.989 1.028 1.016
0.0237 2.33
1.016 0.025 2.42
Ru
240.272 1.042 1.078 1.060 1.050
0.0100 0.96
1.010 1.017 1.016 1.014
0.0041 0.40
1.002 1.006 1.043 1.017
0.0224 2.21
1.027 0.021 2.06
V
290.880 1.102 1.142 1.048 1.037
0.0097 0.94
0.987 0.997 1.001 0.995
0.0069 0.69
0.984 0.987 1.030 1.001
0.0259 2.59
1.011 0.024 2.41
Pt
265.945 0.963 1.024 1.037 1.037
0.0137 1.32
0.994 0.985 1.031 1.003
0.0245 2.44
1.036 0.994 1.031 1.020
0.0229 2.24
1.020 0.023 2.30
Mo
202.031 1.048 1.091 1.028 1.021
0.0110 1.08
0.963 0.959 0.979 0.967
0.0103 1.07
0.951 0.959 0.999 0.970
0.0255 2.63
0.995 0.046 4.58
Mn
257.610 1.084 1.159 0.876 1.016
0.0112 1.11
0.952 0.963 0.969 0.962
0.0087 0.90
0.959 0.969 1.015 0.981
0.0301 3.07
0.969 0.042 4.38
Cu
324.752 0.990 1.051 1.041 1.034
0.0074 0.72
0.973 0.981 0.995 0.983
0.0113 1.15
0.988 0.974 1.026 0.996
0.0266 2.67
1.004 0.027 2.72
Cr
267.716 1.090 1.150 1.028 1.017
0.0098 0.97
0.974 0.980 0.979 0.978
0.0032 0.32
0.966 0.970 1.013 0.983
0.0260 2.65
0.993 0.023 2.33
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