Biomedical Engineering Reference
In-Depth Information
of acetic acid, furfural, methanol, and other substances. The chromatographic
conditions are described as follows: Innovax column; 30 kPa column pressure; split
ratio 1:100; gas nitrogen carrier; inlet temperature of 250
ı
C; detector temperature
of 280
ı
C; temperature program: initial temperature 60
ı
C(2min),7.5
ı
C
min
1
to
200
ı
C, holding for 2 min, 0.1
L injection volume, direct injection.
(2) Furan aldehydes
At present, it has been reported that the furan aldehydes furfural and HMF are
determined by chromatography and spectrophotometry.
The chromatography methods include GC [
69
] and liquid-phase chromatogra-
phy. The liquid chromatographic method has been widely used in recent years.
Levin et al. [
70
] measured the HMF content in milk by liquid chromatographic
techniques. For this examination, 5 mL 0.15 M oxalic acid solution was added to
a 15-mL sample. This was mixed and put into a boiling water bath for 25 min.
The mixture was cooled to room temperature; 3 mL 40 % TCA (trichloroacetic
acid) was added and sufficiently shaken. Then, it was centrifuged (2,000
g
,15min).
The supernatant was collected. Next, 10 mL of 4 % TCA was added to the
precipitate. The mixture was centrifuged, and the supernatant was collected. Two
centrifugal supernatants were merged, and the volume was measured. Then, the
total supernatants were filtered by a microfiltration membrane (0.45
m) and
detected by HPLC. Chromatographic conditions were as follows: column resolve
C18 column (150
4.0 mm); mobile phase was 0.1 M pH 3.6 sodium acetate
buffer: methanol
D
92:10, 0.1 M pH 3.8 sodium acetate buffer: methanol
D
92:10;
UV detector 280-nm detection wavelength; 20-
L injection volume.
Compared with the chromatographic method, spectrophotometry produces a
colorimetric measurement error because of the presence of both furfural and HMF,
so it cannot detect the true content. The result also is relatively high. Chang et al.
[
71
] proposed using 2-thiobarbituric acid (TBA) as a derivative of the reagents
to determine the contents of HMF and furfural in cellulose hydrolyzates by first-
derivative spectrophotometry. An appropriate amount of standard solution or sample
solution was added to a 25-mL volumetric flask, together with 8.5 mL concentrated
hydrochloric acid and 7 mL 0.03 M TBA solution. The mixture was placed in a
40
ı
C water bath for 30 min. At the end of the reaction, it was cooled to room
temperature. Then, it was adjusted to a constant volume and shaken to uniformity.
The blank was the same amount of hydrochloric acid without TBA standard solution
or a sample solution. The sample was scanned in the wavelength range of 370-
510 nm. The first-derivative spectra were recorded.
Then, 20 mg
mL
1
furfural and HMF standard solution were prepared as a series
of mixed standard solution. The first-order derivative spectrum diagram of each
mixed standard solution was scanned and recorded according to the analysis steps.
Peak values at 412- and 428-nm wavelengths were measured, respectively, with
a zero-crossing measurement method. Then, take peak value as the y axis and take
concentration as x axis. A standard curve equation was obtained by linear regression
and used to calculate the content of these two components in mixture. Zhang et al.
[
72
] proposed a rapid determination method for furfural and HMF content based
