A Certified Spiking Solution^® of routinely tested Carnitine and Acetylcarnitine at a concentration of 10 mg/mL. Acylcarnitines are biomarker for many inborn errors of metabolism that cause several metabolic diseases and are routinely tested in newborn screening programs. This multi-component mix is suitable for critical quantitative applications in research and clinical environments including: for use in preparation of controls, calibrators, and linearity standards for LC-MS/MS assays; as system tuning/suitability standards; linearity verification; and internal proficiency testing. The stable, quantitative solution format provides significant benefits to the user such as convenience of use, material savings, and increased efficiency of labor. Certified concentration values for each component provides increased efficiency from less time remaking pools due to dilution errors or rerunning samples.