Review Ho & Gao
Table 3. Stability evaluations for surrogate matrix tissue method. Categories
Solution
Stability type Bench-top Long-term Other†
Homogenate/surrogate Bench-top
Freeze–thaw Long-term Other
Extract (Whole) tissue
Autosampler Other
Bench-top
Freeze–thaw Long-term Other†
In surrogate matrix In tissue NA NA NA ✓ ✓ ✓ ✓ ✓ ✓
NA NA NA ✓
importantly introduces risk to analytical accuracy and precision due to the batch to batch variation.
Establishing surrogate matrix validity In order to obtain accurate results, the validity of surrogate matrix must be established prior to sample analysis. Interestingly, this seeming obvious fact has not received due attention. To our knowledge, there have not been any writings that summarize the com- mon methodologies for establishing the validity of a surrogate matrix. Many authors omit this topic in their manuscripts completely. When the topic is discussed in the manuscript, it is always under one of the assay per- formance headings, such as calibration, linearity, pre- cision and accuracy, recovery and matrix effect. In the following paragraphs, we summarize the four common methodologies reported in the literature and describe each in some detail. We hope the summary will help one to select the most suitable method for establishing surrogate matrix validity. Method 1: comparing the slopes of calibration
curves. Under this method, calibration curves are pre- pared in surrogate matrix and authentic tissue homog- enate and the slopes of the calibration curve of each matrix are compared [2]. Similar slopes (i.e., paral- lel curves) indicate similar recovery, which indicates that the surrogate matrix is suitable. An example for this method can be found in the validation of the LC–MS/MS method for the determination of tes- tosterone (T) and dihydrotestosterone (DHT) in rat prostate tissue via compound derivatization [17]. As shown in Table 4, the slopes of T- and DHT-derivatives were very similar between the matrix and the solvent
2422 Bioanalysis (2015) 7(18)
NA NA NA ✓ ✓ ✓ ✓ ✓ ✓ – – –
✓
†Other stability may include analyst stability under thermal and photo conditions and derivatization product stability. ✓: Should be evaluated; NA: Not applicable.
proving the surrogate matrix is valid. In most cases, once the similarity of the slope was demonstrated, the assay precision and accuracy are evaluated in surrogate matrix only [11,29]. In certain cases, no further precision and accuracy experiments were performed since the results of the calibration curve do infer some knowl- edge of assay precision and accuracy [4]. This method uses a limited amount of authentic tissue to establish the validity the surrogate matrix. In addition, it gener- ates information on linearity, precision and accuracy in authentic tissue. We consider it is a good approach for limited authentic tissue and time. The shortcoming of this method is that there are no generally agreed upon acceptance criteria to determine how similar a slope is sufficient. One approach is to use the student t-test to assess the slope similarity statistically [29]. The accep- tance criteria for this method are certainly an area that requires further research. Method 2: evaluating the accuracy of QC samples.
Under this method, the calibration curve is prepared in surrogate matrix but QC samples are prepared in surrogate matrix and in authentic tissue homogenate. Acceptable accuracy for QC prepared in both matri- ces indicates the surrogate matrix is suitable. Teunis- sen used this method for simultaneous analysis of 2-amino-1-methyl-6-phenylimidazo[4–5-b]pyridine (PhIP) and its main metabolite 2-hydroxyamino- 1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH- PhIP) in brain, kidney, liver, small intestinal content, small intestinal tissue, spleen and testis from mice [27]. The surrogate matrix for the tissue homogenate was 4% BSA. Since both analytes are not endogenous, the assay accuracy is easily confirmed by spiking PhIP and
future science group
In solvent ✓ ✓ ✓
NA NA NA NA NA NA NA NA NA NA
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154