# Analysis of Total-Forms of Cyanotoxins Microcystins in Biological Matrices: A Methodological Review
## 2 Quantification of Total MC by the MMPB Method
### Limitations and Difficulties Faced during the MMPB Method
#### 2.5.2 Variability of the Overall Conversion Process  
The review of the literature on the MMPB method has shown that the conversion yields strongly differ among matrices (i.e., cyanobacterial matrices, sediments, and animal matrices). The yields for cyanobacterial matrices and sediments are around 80%, and those for animal matrices range from 4% for dog hair to 114% for a golden retriever (_Canis lupus familiaris_) vomit sample [86]. Even for the same protocol, significant variability can be observed depending on the matrices and for the same animal species depending on the organs, probably in relation to the levels of lipids and proteins in the tissues and the associated efficiency of MMPB extraction. Three times higher yields were thus observed on trout liver compared to trout muscle [29], while in the study by [PERSON] et al. [86], the oxidation yield for dog hair was only 4%, while this yield was 114% for dog vomit samples. When considering the performance of the different steps taken one by one, a strong disparity can be observed. The study by [PERSON] et al. [29] thus proposes the yield of the method for the intestinal tissue of rainbow trout but also the yield of the various stages of the method: 25% for the oxidation step, 93% for filtration, and 27% for the SPE + evaporation step. Globally, the MMPB protocol provides an overall yield of 6%. Switching to another type of tissue, gills provide better yields in terms of oxidation (67%) but much lower yields for SPE and evaporation (18%), giving a final overall yield of the method of 12% (it is to be specified that for the gill matrix, the filtration yields have not been specified). Even with an optimized protocol, switching from one animal matrix to another can have an impact on the yield and shows how important the matrix effect can be. These results can be compared to the study by [PERSON] et al. [70], also providing the yields of their step-by-step MMPB method on two matrices: sediments and clams at two spike levels of MC-LR (100 and 500 ug/L). The protocol begins with a lipid extraction step with average yields of 96% for sediments and clams. The main losses estimated in this method occurred during the conversion step of MC-LR to MMPB, with average conversion rates of 75% for sediments and 64% for clams. It should be noted that this study distinguishes between conversion and oxidation yields without making this distinction explicit, which could lead to confusion when comparing the yields of this method to another. Much higher yields than the method used by [PERSON] et al. [29] were observed in the method used by [PERSON] et al. [70] during the oxidation and SPE steps, with average yields for sediments of 91% and 91%, respectively, and for claims of 91% and 91%, respectively. Thus, the step that seems to generate the most loss is oxidation, with yields ranging from 25% to 60% for intestinal tissue and gills, respectively, in [PERSON] et al. [29], and a yield of about 91% for sediments and claims in [PERSON] et al. [70].