{"id":1161,"date":"2024-04-11T14:18:12","date_gmt":"2024-04-11T11:18:12","guid":{"rendered":"https:\/\/sisu.ut.ee\/lcms_method_validation\/self-test-5-4c\/"},"modified":"2024-04-11T14:18:12","modified_gmt":"2024-04-11T11:18:12","slug":"self-test-5-4c","status":"publish","type":"page","link":"https:\/\/sisu.ut.ee\/lcms_method_validation\/self-test-5-4c\/","title":{"rendered":"Self-test 5.4C"},"content":{"rendered":"
\n

<\/p>\n\n\n\n

\n
\n\t\t\t

1. <\/span>Sometimes calibration graph is used for estimating matrix effect. This approach additionally gives possibility to estimate if matrix effect is concentration dependent.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Standard<\/strong><\/td>\nSample<\/strong><\/td>\n<\/tr>\n
C (mg\/kg)<\/strong><\/td>\nSignal<\/strong><\/td>\nC (mg\/kg)<\/strong><\/td>\nSignal<\/strong><\/td>\n<\/tr>\n
0.045514<\/td>\n4729453<\/td>\n0.054981<\/td>\n2479148<\/td>\n<\/tr>\n
0.09502<\/td>\n10239100<\/td>\n0.094095<\/td>\n2829679<\/td>\n<\/tr>\n
0.125402<\/td>\n14069331<\/td>\n0.131234<\/td>\n5879648<\/td>\n<\/tr>\n
0.175325<\/td>\n16628949<\/td>\n0.179036<\/td>\n6189080<\/td>\n<\/tr>\n
0.225785<\/td>\n20635051<\/td>\n0.232482<\/td>\n8489240<\/td>\n<\/tr>\n
0.281598<\/td>\n23964984<\/td>\n0.28458<\/td>\n11626711<\/td>\n<\/tr>\n
0.335968<\/td>\n29837123<\/td>\n0.327439<\/td>\n11796479<\/td>\n<\/tr>\n
0.386379<\/td>\n30453933<\/td>\n0.371094<\/td>\n15791685<\/td>\n<\/tr>\n
0.481088<\/td>\n37769230<\/td>\n0.487316<\/td>\n21413804<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u00a0<\/p>\n

Question 1: <\/strong>Estimate matrix effect based on calibration graph slopes!<\/p>\n

Please give the answer in percents with one decimal place and please use dot as decimals separator (i.e. please give 91.7% and not 0.917; 91,7% or 91.765%).<\/p>\n

Answer: <\/p>\n

Question 2: <\/strong>Is the matrix effect independent of analyte concentration? <\/div><\/div>\t\t\t\t\t

\t\t \n\t\t\t\t\t\t\"Loading...\"\u00a0Loading...\t\t\t\t\t<\/div>\t\n\t\t\t

Question 1 of 3<\/p><\/div>

\n\t\t\t
2. <\/span>Glyphosate was analyzed in the lake water with high organic content. The analyses contained sample purification and concentration with solid phase extraction (SPE). However there was a strong suspicion that a strong matrix effect may occur. To test this suspicion a blank sample extract was treated with SPE and the obtained extract was deviated into small parts. Each part was spiked with analyte on a known concentration level (similar to matrix matched calibration). Also the standard solutions at the same concentration levels were prepared. After the LC-MS analyses following results were obtained:
\r\n
c (\u00b5g\/L)<\/strong><\/td>Signal, standard<\/strong><\/td>Signal, spiked sample<\/strong><\/td><\/tr>
2<\/td>15931<\/td>6002<\/td><\/tr>
5<\/td>35198<\/td>15171<\/td><\/tr>
10<\/td>73501<\/td>25734<\/td><\/tr>
15<\/td>115041<\/td>37313<\/td><\/tr>
20<\/td>129941<\/td>55175<\/td><\/tr>
50<\/td>361007<\/td>124671<\/td><\/tr><\/tbody><\/table>\u00a0
\r\n
\r\nCalculate the matrix effect based on the calibration graph slopes.
\r\n
\r\nPlease give the answer in percents with one decimal place.<\/div><\/div>

<\/p><\/div><\/div>\t\t\t\t\t

\t\t \n\t\t\t\t\t\t\"Loading...\"\u00a0Loading...\t\t\t\t\t<\/div>\t\n\t\t\t

Question 2 of 3<\/p><\/div>

\n\t\t\t

3. <\/span>Standard addition is one possibility to account for matrix effect. However it assumes that matrix effect is a proportional effect independent of the analyte concentration. In order to control this assumption analyst prepared both standards and post-extraction spiked samples at analyte concentration of 10 and 2.5 mg\/kg.<\/p>\n

Following results were observed:<\/p>\n\n\n\n\n\n\n
Standard 10 mg\/kg<\/strong><\/td>\nSample 10 mg\/kg<\/strong><\/td>\nStandard 2.5 mg\/kg<\/strong><\/td>\nSample 2.5 mg\/kg<\/strong><\/td>\n<\/tr>\n
7832180<\/td>\n6964080<\/td>\n2406174<\/td>\n827948<\/td>\n<\/tr>\n
7718368<\/td>\n6722779<\/td>\n2434535<\/td>\n854663<\/td>\n<\/tr>\n
7822817<\/td>\n7387993<\/td>\n2586852<\/td>\n764868<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u00a0<\/p>\n

Question 1: <\/strong>Estimate matrix effect for 10 mg\/kg and 2.5 mg\/kg from the measured signals.<\/p>\n

Please give the answer\u00a0in percents with one decimal place<\/span> and please use dot as decimals separator (i.e. please give 91.7% and not 0.917; 91,7% or 91.765%).<\/p>\n

Matrix effect (10 mg\/kg)\u00a0 \u00a0 \u00a0 \u00a0 <\/p>\n

Matrix effect (2.5 mg\/kg)\u00a0 \u00a0 \u00a0 \u00a0<\/p>\n

Question 2: <\/strong>Can standard addition be used in this case in order to account for matrix effect? \u00a0<\/div><\/div>\t\t\t\t\t

\t\t \n\t\t\t\t\t\t\"Loading...\"\u00a0Loading...\t\t\t\t\t<\/div>\t\n\t\t\t

Question 3 of 3<\/p><\/div>

\n\t
\n\t\t\"Loading...\"\u00a0Loading...\t<\/div>\n<\/div>\n\n
\n\t\n\t\t\t
\n\t\t
<\/div>\t\t
<\/div>\t\t
<\/div>\t\t \n\t\t \t \t\t
\n\t\t<\/div>\n\t\t<\/div>\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\t\t<\/form>\n\t

\u00a0<\/p>\n<\/div>\n\n