Leucomalachite Green-Phenolphthalein Test - Lab Report Example

The change in pH is detected by phenolphthalein, and the solution turns pink quickly, or leuchomalachite green, which turns the solution green (Houck and Siegel, 2010; Tobe et al., 2007).

            However, there are a few considerations in using these substrates. First, because phenolphthalein is a pH indicator, phenolphthalein reacts with any basic solution. It is thus important that the addition of LMG or PPT prior to the addition of hydrogen peroxide does not yield a color change. This ensures that any change in the solution results from the reaction of hemoglobin with hydrogen peroxide. Second, when the phenolphthalein is exposed too long in the solution, spontaneous oxidation occurs causing the colorimetric reaction to occur (Houck and Siegel, 2010). The color change indicating the presence of blood must thus be quick. Third, substances in fruits and vegetables may act like a peroxidase (Tobe et al., 2007). 

MATERIALS AND METHODS

            Sample FS-26-07 was tested for the presence of blood using leuchomalachite green (LMG) and phenolphthalein (PPT). Two set-ups were prepared. Each set-up consists of three spot plates each containing a strip of 1) positive control, 2) negative control, or 3) FS-26-07. The spot plates in the first set-up were added with two drops of LMG, while those of the second set-up was added with the same amount of PPT. The spot plates were then added with hydrogen peroxide. Colorimetric changes were noted.

RESULTS

Table 1. Colorimetric change upon addition of Leucomalachite green

sample

Color change after addition of leucomalachite green

Color change after the addition of hydrogen peroxide

Positive control (blood)

No observable change

Green

Negative control (blank)

No observable change

No observable change

Sample (FS-26-07)

No observable change

No observable change

Table 2. Colorimetric change upon addition of Phenolphthalein

sample

Color change after the addition of phenolphthalein

Color change after the addition of hydrogen peroxide

Positive control (blood)

No observable change

pink

Negative control (blank)

No observable change

No observable change

Sample (FS-26-07)

No observable change

No observable change

CONCLUSION

            Because the results of leucomalachite green-phenolphthalein test on FS-26-07 were the same as that of the negative control, it is thus conclusive that the sample does not contain blood.