A method of detecting a NO x compound in a wound, comprising: providing a sample from a wound, a first retention medium, VCl 3 as a reducing agent, p-diaminodiphenyl sulfone as a chromogenic reagent, N-(1-naphthyl)-ethylenediamine as a developing agent, and HCl as an acid; wherein the chromogenic reagent is capable of reacting with a nitrite compound to form a colored compound; wherein the first retention medium is configured to retain the colored compound; forming a first mixture comprising the sample, the reducing agent, the chromogenic reagent, the developing agent, and the acid under conditions that permit the reaction of a nitrite compound with the chromogenic reagent to form the colored compound; wherein the method comprises reacting the sample in the first mixture at 70 °C for about 10 minutes: wherein the conditions that permit the reaction of a nitrite compound with the chromogenic reagent to form the colored compound simultaneously permit the reduction of a nitrate compound to a nitrite compound; contacting at least a portion of the first mixture with the first retention medium; and detecting the colored compound retained on the first retention medium, wherein the first retention medium comprises a medium with ionic functional groups that interact with ionic groups in the colored compound, thereby capturing and retaining the colored compound on and/or in the retention medium. providing a sample from a wound, a first retention medium, VCl 3 as a reducing agent, p-diaminodiphenyl sulfone as a chromogenic reagent, N-(1-naphthyl)-ethylenediamine as a developing agent, and HCl as an acid; wherein the chromogenic reagent is capable of reacting with a nitrite compound to form a colored compound; wherein the first retention medium is configured to retain the colored compound; wherein the chromogenic reagent is capable of reacting with a nitrite compound to form a colored compound; wherein the first retention medium is configured to retain the colored compound; forming a first mixture comprising the sample, the reducing agent, the chromogenic reagent, the developing agent, and the acid under conditions that permit the reaction of a nitrite compound with the chromogenic reagent to form the colored compound; wherein the method comprises reacting the sample in the first mixture at 70 °C for about 10 minutes: wherein the conditions that permit the reaction of a nitrite compound with the chromogenic reagent to form the colored compound simultaneously permit the reduction of a nitrate compound to a nitrite compound; contacting at least a portion of the first mixture with the first retention medium; and detecting the colored compound retained on the first retention medium, wherein the conditions that permit the reaction of a nitrite compound with the chromogenic reagent to form the colored compound simultaneously permit the reduction of a nitrate compound to a nitrite compound; contacting at least a portion of the first mixture with the first retention medium; and detecting the colored compound retained on the first retention medium, wherein the first retention medium comprises a medium with ionic functional groups that interact with ionic groups in the colored compound, thereby capturing and retaining the colored compound on and/or in the retention medium.