1. A method for estimating the number of nuclei of a preselected isotope in a molecular species from an NMR spectrum of a sample containing said molecular species as a predominant substance, said NMR spectrum comprising a plurality of signal peaks corresponding to said nuclei, the method comprising the steps of: a) selecting from said plurality of signal peaks a set of included signal peaks that fulfill an inclusion criterion; b) ordering said set of included signal peaks according to a preselected signal ordering criterion to obtain a set of corresponding ordered signal peaks; c) determining the integral of each one of said ordered signal peaks to obtain a corresponding set of ordered integrals; d) defining a set of mutually non-identical positive integers that do not exceed a preselected highest integer and ordering said set according to a preselected number ordering criterion to obtain a set of ordered integers; e) starting an outer iteration cycle by selecting the first one of said ordered integrals to obtain a selected integral; f) starting an inner iteration cycle by assigning to a running number the value of the first one of said ordered integers; g) calculating a scaling factor given by the ratio of said running number to said currently selected integral; h) multiplying with said scaling factor each one of said ordered integrals to produce a set of scaled integrals; i) rounding each one of said scaled integrals to the nearest integer value to produce a set of integerized scaled integrals; j) calculating the sum of said set of integerized scaled integrals to produce a candidate total number of nuclei; k) retrievably storing a result set corresponding to the instant inner iteration cycle, said stored result set containing at least said candidate total number of nuclei; l) starting a further inner iteration cycle by setting the running number equal to the next one of said ordered integers, then assigning said running number to said selected integral and repeating steps g) to l) until all of said ordered integers have been processed; m) starting a further outer iteration cycle by selecting the next one of said ordered integrals and repeating steps f) to m) until all ordered integrals have been processed; n) determining from the plurality of said stored result sets the number of occurrences of each one of said candidate total numbers of nuclei; o) determining the highest number of occurrences; p) forming a set consisting of all the candidate total numbers of nuclei that have a number of occurrences equal to said highest number of occurrences; and q) obtaining an estimated total number of nuclei by taking the lowest one from said set of candidate total numbers of nuclei.