{"id":45,"date":"2024-04-04T00:39:48","date_gmt":"2024-04-03T21:39:48","guid":{"rendered":"https:\/\/sisu.ut.ee\/lcms_method_validation\/54-quantitative-estimation-matrix-effect-recovery-process-efficiency\/"},"modified":"2024-04-04T00:41:46","modified_gmt":"2024-04-03T21:41:46","slug":"54-quantitative-estimation-matrix-effect-recovery-process-efficiency","status":"publish","type":"page","link":"https:\/\/sisu.ut.ee\/lcms_method_validation\/54-quantitative-estimation-matrix-effect-recovery-process-efficiency\/","title":{"rendered":"5.4 Quantitative estimation of matrix effect, recovery and process efficiency"},"content":{"rendered":"<p>\r\n\tQuantitative estimation of the ionization suppression is possible with post-extraction addition methods\u00a0as is explained in the following videos. The first video explains the principles of evaluating a matrix effect and also touches upon its relations with recovery and process efficiency:\r\n<\/p>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>Calculating matrix effect, recovery and process efficiency\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=23248\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=23248<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a data-url=\"https:\/\/www.youtube.com\/watch?v=J1O1bD7gEy4\" href=\"https:\/\/www.youtube.com\/watch?v=J1O1bD7gEy4\" target=\"_blank\" title=\"\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=J1O1bD7gEy4<\/a>\r\n<\/h5>\r\n\r\n<h5 class=\"media-title\" style=\"text-align: center\">\r\n\t\u00a0\r\n<\/h5>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<p style=\"text-align: left\">\r\n\tThe second video explains evaluating a matrix effect, recovery and process efficiency in practice:\r\n<\/p>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>Practical evaluation of matrix effect, recovery\u00a0and process efficiency\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=23476\" style=\"text-align: center;font-family: inherit;font-weight: 600\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=23476<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a class=\"OWAAutoLink\" href=\"https:\/\/www.youtube.com\/watch?v=vwRVkhZ8GiY\" id=\"LPlnk342758\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=vwRVkhZ8GiY<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t\u00a0\r\n<\/h5>\r\n\r\n<p>\r\n\tFor this approach, the analyte standard solution with a known concentration is prepared in the solvent and analyzed with LC-ESI-MS giving the peak area (signal) <em>S<\/em><sub>standard<\/sub>. Also a blank sample extract is prepared and spiked with the analyte at the same concentration level and ia thereafter analyzed giving the\u00a0peak area (signal) <em>S<\/em><sub>sample<\/sub>. The ionization suppression\/enhancement effect can be calculated:\u00a0\r\n<\/p>\r\n\r\n<h6 style=\"text-align: center\">\r\n\t<img loading=\"lazy\" decoding=\"async\" width=\"808\" height=\"106\" class=\"alignnone wp-image-415\" style=\"width: 400px;height: 52px\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture3.png\" title=\"picture3.png\" alt=\"eq1\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture3.png 808w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture3-300x39.png 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture3-768x101.png 768w\" sizes=\"auto, (max-width: 808px) 100vw, 808px\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (Eq 1)\u00a0\r\n<\/h6>\r\n\r\n<p>\r\n\t<em>ME<\/em><sub>ionization<\/sub> value of\u00a0100% indicates no effect, less than 100% indicates an ionization suppression and <em>ME<\/em><sub>ionization<\/sub> over 100% indicates an\u00a0ionization enhancement due to the coeluting sample compounds. From this definition, though most often used in the LC-MS literature, some possible misunderstandings can arise. The expression \u201creduce matrix effect\u201d does not mean reduced value of %ME, but a <em>ME<\/em><sub>ionization<\/sub> value becoming closer to 100%.\r\n<\/p>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>Calculating matrix effect based on signals\u00a0\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=24822\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=24822<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"https:\/\/www.youtube.com\/watch?v=XZALDnUV9xs&amp;t=32s\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=XZALDnUV9xs&amp;t=32s<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<br>\u00a0\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>Calculating matrix effect based on concentrations\u00a0\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=24818\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=24818<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a data-url=\"https:\/\/youtu.be\/3B9sdDoGx18?si=XwojR_j872wDGx7T\" href=\"https:\/\/youtu.be\/3B9sdDoGx18?si=XwojR_j872wDGx7T\" target=\"_blank\" title=\"\" rel=\"noopener\">https:\/\/youtu.be\/3B9sdDoGx18?si=XwojR_j872wDGx7T<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t\u00a0\r\n<\/h5>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>Calculating matrix effect based on slopes\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=24821\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=24821<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"https:\/\/www.youtube.com\/watch?v=WJ9-O4gJxlk\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=WJ9-O4gJxlk<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t\u00a0\r\n<\/h5>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<p>\r\n\tSometimes also the positive\/negative <em>ME<\/em><sub>ionization<\/sub> scale is used, where 0% denotes no effect, values above 0% indicate\u00a0an ionization enhancement and below 0% a suppression. The corresponding equation is:\r\n<\/p>\r\n\r\n<h6 style=\"text-align: center\">\r\n\t<img loading=\"lazy\" decoding=\"async\" width=\"976\" height=\"108\" class=\"alignnone wp-image-416\" style=\"width: 400px;height: 44px\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture4.png\" title=\"picture4.png\" alt=\"Eq2\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture4.png 976w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture4-300x33.png 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/picture4-768x85.png 768w\" sizes=\"auto, (max-width: 976px) 100vw, 976px\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 (Eq 2)\u00a0\u00a0\r\n<\/h6>\r\n\r\n<p>\r\n\tInstead of comparing the peak areas, calibration graph slopes can be compared [ref 26].\r\n<\/p>\r\n\r\n<p>\r\n\tA similar approach is described in the most recent FDA validation guideline. In this approach, two calibration graphs are constructed, one in the solvent and the other one\u00a0in the post-extraction spiked samples\u00a0(i.e. sample extracts obtained from sample preparation). This approach is usable also in the case when blank matrix is unavailable.\r\n<\/p>\r\n\r\n<p>\r\n\tSeveral aspects have to be kept in mind:\r\n<\/p>\r\n\r\n<p>\r\n\t(a)<em>\u00a0\u00a0\u00a0 <\/em>The intercepts of both calibration graphs have to be negligible so that the ionization suppression\/enhancement would not depend on the analyte concentration. Unfortunately, the latter is not always true.\r\n<\/p>\r\n\r\n<p>\r\n\t(b)\u00a0\u00a0\u00a0 Before using an approach based on the slope, linearity of the method needs to be studied. In the literature, this approach for ionization suppression\/enhancement is often used and sometimes also combined with <em>F<\/em>\u2013 and <em>t<\/em>-test or ANOVA to evaluate the statistical significance of the obtained matrix effect values.\r\n<\/p>\r\n\r\n<p>\r\n\t(c)\u00a0\u00a0\u00a0 All of the calculations described above\u00a0can be done either in the\u00a0signal scale or concentration scale. The obtained results are fairly similar if the samples used for the ionization suppression\/enhancement study are within the linear range and the intercept of the calibration graph is negligible. If these requirements are not fulfilled, it is more useful, from the method point of view, to use the concentration-based calculations.\r\n<\/p>\r\n\r\n<p>\r\n\tIf signal- or concentration-based calculations are used (not slope-based), the number of samples and replicates used for the suppression\/enhancement assessment during validation becomes an issue. Often several replicates are\u00a0run\u00a0at one or more concentration levels.\r\n<\/p>\r\n\r\n<p>\r\n\t(d)\u00a0 \u00a0\u00a0It has been often shown that matrix effects depend\u00a0on the sample source (eg different variety of fruit [ref 27]). It is therefore also recommended to use different matrices for suppression\/enhancement evaluation. In the literature the number of matrices used varies a lot.\r\n<\/p>\r\n\r\n<p>\r\n\t(e) \u00a0 \u00a0In the literature [ref 28, ref 29]\u00a0it has been observed that ionization suppression\/enhancement may strongly vary from day to day and it cannot be estimated once during the method optimization\/validation and then be used later for result correction.\r\n<\/p>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<h2>\r\n\t<strong>Reducing matrix effect<\/strong>\r\n<\/h2>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<strong><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div><\/strong>Reducing matrix effect\u00a0\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=23288\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=23288<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"https:\/\/www.youtube.com\/watch?v=Oh3eZKYpa6g\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=Oh3eZKYpa6g<\/a><br>\u00a0\r\n<\/h5>\r\n\r\n<p>\r\n\tWhenever possible and practical, ionization suppression (matrix effect) should be eliminated or significantly reduced. If it is not possible to reduce the\u00a0ionization suppression to the level of being insignificant, it should be taken into account when\u00a0calculating\u00a0the results. Several approaches have been suggested and tested for reducing the ionization suppression effect, mainly focusing on the ESI ionization source. In broad terms the approaches can be categorized as based on (a) the sample preparation, (b) the instrumental modifications and (c) the modifications in LC method:\r\n<\/p>\r\n\r\n<p>\r\n\t(a) Less than ideal sample preparation may be viewed as the main reason of occurrence of ionization suppression. In case of a perfect sample preparation combined with the perfect chromatographic separation \u2013 leading to the chromatogram where the analyte is completely separated from all of the matrix components \u2013 ionization suppression would not occur and would not have to be considered. Unfortunately, perfect sample preparation methods are not available in most cases. A number of literature sources address choosing the most effective sample preparation method from the matrix effect point of view. In LC-MS solid phase extraction (SPE), liquid-liquid extraction (LLE), precipitation\/centrifugation or combinations of these as well as other methods are used for the sample preparation.\r\n<\/p>\r\n\r\n<p>\r\n\tDifferent sample preparation techniques have been compared and for example found that for phenacetin and caffeine determination in endogenous plasma, protein precipitation is the least favourable technique for LC-ESI-MS analyses while LLE was the most favourable [ref 30]. Additionally, LLE has been found to be more effective sample preparation technique than SPE for methadone determination, because the latter tends to concentrate not only the analyte but also the matrix compounds similar to the analyte (i.e. potentially co-eluting from HPLC with the analyte) [ref 30]. The reason probably being\u00a0that for LLE a larger selection of extracting solvents is available and therefore more freedom in varying selectivity is achievable. On the other hand, in the case of SPE, a solid phase similar to the HPLC stationary phase is often used (often both are low polarity C18 or C8 phases) and therefore a little additional\/different selectivity is obtained during sample preparation. Additionally, it has been shown that sample pre-concentration may significantly increase ionization suppression.\r\n<\/p>\r\n\r\n<p>\r\n\t(b) The main instrumental modification that can be\u00a0considered is using a non-ESI ion source, such as APCI instead of ESI, since ionization in the APCI source has been demonstrated to be less affected by the matrix effects [ref 31, ref 32, ref 33, ref 34]. Also, switching the ESI source from positive to negative ionization mode or reducing the flow rate of the effluent have also been demonstrated to be efficient in some cases [ref 35]. Unfortunately, there are numerous analytes for which neither the use of\u00a0APCI nor switching to\u00a0negative mode ESI are suitable.\u00a0Furthermore, among the different LC-MS ion sources, ESI in general tends to have the lowest limits of detection [ref 36].\r\n<\/p>\r\n\r\n<p>\r\n\t(c) The two main LC-method-related matrix effect reduction possibilities are improvement of the chromatographic separation, e.g. with ultra-high performance liquid chromatography (UPLC\/UHPLC), and sample dilution. Both have been used by numerous authors. Dilution has been shown to significantly reduce the ionization suppression [ref 37]. However, it is often impossible to dilute the sample sufficiently so that the ionization suppression will completely disappear, because the analyte concentration may fall below the limit of quantification. In such cases, the so-called extrapolative dilution approach [ref 37]\u00a0has been found useful, which consists in diluting the sample as far as possible and if the suppression is still present then extrapolating the analyte concentration mathematically to infinite dilution.\r\n<\/p>\r\n\r\n<p>\r\n\tThe following video presents a practical discussion on these issues:\r\n<\/p>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>Accounting for matrix effect\u00a0\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"http:\/\/www.uttv.ee\/naita?id=23308\" target=\"_blank\" rel=\"noopener\">http:\/\/www.uttv.ee\/naita?id=23308<\/a>\r\n<\/h5>\r\n\r\n<h5 style=\"text-align: center\">\r\n\t<a href=\"https:\/\/www.youtube.com\/watch?v=5lonQCdmcis\" target=\"_blank\" rel=\"noopener\">https:\/\/www.youtube.com\/watch?v=5lonQCdmcis<\/a>\r\n<\/h5>\r\n\r\n<p>\r\n\t\u00a0\r\n<\/p>\r\n\r\n<p>\r\n\tSometimes it is too difficult (and therefore impractical) or impossible to remove all of the matrix effect, therefore, approaches accounting for the matrix effect have also been developed. Most of them fall either into the category of internal standard usage or matrix-matched calibration [ref 38].\r\n<\/p>\r\n<br><div class=\"wp-block-group attached-files-group is-layout-constrained wp-block-group-is-layout-constrained\"><div class=\"wp-block-file\"><a href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/5.4_evaluating_matrix_effect.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">5.4_evaluating_matrix_effect.pdf<\/a><\/div><div class=\"wp-block-file\"><a href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/matrix_effect_unsolved.xlsx\" target=\"_blank\" rel=\"noreferrer noopener\">matrix_effect_unsolved.xlsx<\/a><\/div><div class=\"wp-block-file\"><a href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/130\/matrix_effect_resolved.xlsx\" target=\"_blank\" rel=\"noreferrer noopener\">matrix_effect_resolved.xlsx<\/a><\/div><\/div>","protected":false},"excerpt":{"rendered":"<p>Quantitative estimation of the ionization suppression is possible with post-extraction addition methods\u00a0as is explained in the following videos. The first video explains the principles of evaluating a matrix effect and also touches upon its relations with recovery and process efficiency: &#8230;<\/p>\n","protected":false},"author":60,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"class_list":["post-45","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/pages\/45","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/users\/60"}],"replies":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/comments?post=45"}],"version-history":[{"count":2,"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/pages\/45\/revisions"}],"predecessor-version":[{"id":891,"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/pages\/45\/revisions\/891"}],"wp:attachment":[{"href":"https:\/\/sisu.ut.ee\/lcms_method_validation\/wp-json\/wp\/v2\/media?parent=45"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}