Little is known about Markus Heinrich Grauel. He was known as a cellist at the Prussian Hofkapelle of Friedrich II, and as a composer as well. Out of his oeuvre, only a sonata for violin and harpsichord, a violin and a cello concerto, and 2 viola concertos in the keys of E-flat major and C major are known today. As for the 3rd viola concerto in E-flat major, which is currently located at Berlin's Sing-Akademie in two manuscripts, one of which naming [Grauel] (Signature: SA 2685), the other one naming [Graun] as the author (Signature: SA 2725), recent findings suggest Johann Gottlieb Graun, concertmaster of the Prussian Hofkapelle as the likely author (Grau-Werkverzeichnis under Cv:XIII:116; this concerto has appeared with Ortus in 2015: http://www.ortus-musikverlag.de/en/sing-akademie-archiv/om204).
Part of his dissertation to acquire the title Doctor of Musical Arts (D.M.A.), Griffin F. Browne presented in 2013, the first comprehensive study on Grauel's life and work, under the title [Violoncello Concerto in A Major by Markus Heinrich Graul: A Performance Edition], focussing predominantly on his cello concerto and the Grauel sources in the archive of Berlin's Sing-Akademie, however without consulting the original sources.
Furthermore, there is an article written by Marshall Fine, which appeared in 2015 in the [Journal of the American Viola Society], vol. 31/1, S. 31-38: "The Viola Concertos of J. G. Graun and M. H. Graul Unconfused". The composers Grauel and Graun are compared stylistically. It is unfortunate that Fine, who refers to Browne, wrongfully assumes that the mentioned viola concerto GraunWV Cv:XIII:116 was written by Grauel, and that the anonymously handed on viola concerto (Signature: Mus.329) is a work by Johann Gottlieb Graun (following the first edition of Walter Lebermann's concerto with Simrock in 1976) - all of which has meanwhile been classified as a misallocation. In regards to the writer and chronology, Fine's conclusions are hardly comprehensible. Furthermore, he does not consider the entirety of available sources.