Ktl-icon-tai-lieu

AOAC Official Method 995.06 DMalic Acid in Apple Juice

Được đăng lên bởi nasaisme1111-gmail-com
Số trang: 2 trang   |   Lượt xem: 342 lần   |   Lượt tải: 1 lần
37.1.50A

Apple juice is injected onto reverse-phase LC column; D- and
acids, which are enantiomeric α-hydroxy acids, can be efficiently resolved by ligand exchange using a chiral mobile phase consisting of a complex of Cu II and an amino acid such as L-valine. After
chromatographic separation D-malic acid is measured by UV detector
at 330 nm using external standards.

(c) LC mobile phase.16mM L-valine (1.87 g/L) and 8mM copper II acetate (1.60 g/L) adjusted to pH 5.5 with 1M NaOH
(40 g/L). Before addition of L-valine, completely dissolve copper
acetate in H2O. After all reagents are completely dissolved, adjust
pH to 5.5 and filter mobile phase through 0.45 µm membrane filter.
Equilibrate column with mobile phase 20–30 min before use.
(d) Membrane filter.0.45 µm, LC grade, or equivalent.
(e) D-Malic acid standard solutions.(1) 200 mg/100 mL—Dissolve mg D -malic acid (400 mg DL -malic acid) in deionized water and dilute to 100 mL in a volumetric flask.
(2) 100 mg/100 mL.—Pipet 50 mL solution (1) into a 100 mL volumetric flask and dilute to volume with deionized water.
(3) 50 mg/100 mL.—Pipet 25 mL solution (1) into a 100 mL volumetric flask and dilute to volume with deionized water.
(4) 25 mg/100 mL—Pipet 25 mL (2) into a 100 mL volumetric
flask and dilute to volume with deionized water.
(5) 10mg/100 mL—Pipet 10 mL solution (2) into a 100 mL volumetric flask and dilute to volume with deionized water.
(6) 0 mg/100 mL—Use deionized water as the control.
D-and DL-Malic acid are available from Sigma, PO Box 14508,
St. Louis, MO 63178, USA

B. Apparatus and Reagents

C. Determination

AOAC Official Method 995.06
D-Malic Acid in Apple Juice
Liquid Chromatographic Method
First Action 1995
Final Action 1998

(Applicable to determination of 25–200 mg D-malic acid/100 mL in
apple juice.)
See Table 995.06 for the results of the interlaboratory study supporting acceptance of the method.
A. Principle

L-malic

(a) Liquid chromatograph (LC).¾With pump, autosampler or
10 µL fixed loop manual injector, and UV detector. Operating conditions: flow rate, 1.2 mL/min; column temperature, ambient; variable wavelength detector, 330 nm, 1.0 absorbance unit full scale
(AUFS) interfaced to integrator; injection volume, 10 µL. Retention
time for D-malic acid is 6–8 min (see Figure 995.06). Total time of
analysis is 15 min/determination.
(b) LC column.250 × 4.6 mm id, 5 µm particle size, polystyrene divinyl-benzene copolymer. Must provide baseline or near
baseline separation of D...
37.1.50A
AOAC Official Method 995.06
D-Malic Acid in Apple Juice
Liquid Chromatographic Method
First Action 1995
Final Action 1998
(Applicable to determination of 25–200 mg D-malic acid/100 mL in
apple juice.)
See Table 995.06 for the results of the interlaboratory study sup-
porting acceptance of the method.
A. Principle
Apple juice is injected onto reverse-phase LC column; D- and
L-malic acids, which are enantiomeric α-hydroxy acids, can be effi-
ciently resolved by ligand exchange using a chiral mobile phase con-
sisting of a complex of Cu II and an amino acid such as
L-valine. After
chromatographic separation
D-malic acid is measured by UV detector
at 330 nm using external standards.
B. Apparatus and Reagents
(a) Liquid chromatograph (LC).¾With pump, autosampler or
10 µL fixed loop manual injector, and UV detector. Operating con-
ditions: flow rate, 1.2 mL/min; column temperature, ambient; vari-
able wavelength detector, 330 nm, 1.0 absorbance unit full scale
(AUFS) interfaced tointegrator; injection volume, 10 µL. Retention
time for
D-malic acid is 6–8 min (see Figure 995.06). Total time of
analysis is 15 min/determination.
(b) LC column.250 × 4.6 mm id, 5 µm particle size, polysty-
rene divinyl-benzene copolymer. Must provide baseline or near
baseline separation of
D-malic acid as shown in Figure 995.06.
(c) LC mobile phase.16mM
L-valine (1.87 g/L) and 8mM cop-
per II acetate (1.60 g/L) adjusted to pH 5.5 with 1M NaOH
(40 g/L). Before addition of
L-valine, completely dissolve copper
acetate in H
2
O. After all reagents are completely dissolved, adjust
pH to 5.5 and filter mobile phase through 0.45 µm membrane filter.
Equilibrate column with mobile phase 20–30 min before use.
(d) Membrane filter.0.45 µm, LC grade, or equivalent.
(e)
D-Malic acid standard solutions.(1) 200 mg/100 mL—Dis-
solve mg
D-malic acid (400 mg DL-malic acid) in deionized wa-
ter and dilute to 100 mL in a volumetric flask.
(2) 100mg/100 mL.—Pipet 50 mLsolution(1)into a 100 mLvol-
umetric flask and dilute to volume with deionized water.
(3) 50 mg/100 mL.—Pipet 25 mL solution (1) into a 100 mL vol-
umetric flask and dilute to volume with deionized water.
(4) 25 mg/100 mL—Pipet 25 mL (2) into a 100 mL volumetric
flask and dilute to volume with deionized water.
(5) 10mg/100 mL—Pipet 10 mLsolution (2)into a 100mL volumet-
ric flask and dilute to volume with deionized water.
(6) 0 mg/100 mL—Use deionized water as the control.
D-and DL-Malic acid are available from Sigma, PO Box 14508,
St. Louis, MO 63178, USA
C. Determination
Set UV detector at 330 nm. Inject 10 µL each of DL-malic acid
standard solutions, B(e),onto LC column.Preparestandard curve by
plotting
D-malic acid absorbance peak area vs D-malic acid concen-
trations in standard solutions.Ifcurve is not linear,preparenew stan-
dard solutions and curve. Run duplicate 10 µL injections for each
apple juice. Read
D-malic acid concentration in test injections from
standard curve. Average duplicate values.
Reference: J. AOAC Int. 79, 50(1996).
© 2000 AOAC INTERNATIONAL
Table 995.06 Interlaboratory study results for determination of
D-malic acid in apple juice by liquid chromatography
Sample
Mean
a
,
mg/100 mL N
b
True value
c
,
mg/mL
s
r
s
R
RSD
r
, % RSD
R
, %
r
d
R
e
A—
f
11 0——————
B—
g
11 3——————
C 28.7
(29.7)
h
11 26 1.0
(0.9)
2.2
(4.4)
3.5
(3.0)
7.7
(14.8)
2.80
(2.52)
6.16
(12.32)
D 81.7
(78.4)
11 77 1.3
(2.3)
7.0
(15.5)
1.6
(2.9)
8.6
(19.8)
3.64
(6.44)
19.6
(43.3)
E 121.7 11 121 1.9 14.3 1.6 11.7 5.32 40.04
F 158.7 11 162 2.2 17.1 1.4 10.8 6.16 47.88
G 187.7
(182.5)
11 188 1.9
(5.7)
15.7
(18.2)
1.0
(3.1)
8.4
(10.0)
5.32
(15.96)
43.96
(50.96)
a
Mean of average duplicate value obtained by all participating laboratories.
b
No. of mean observations.
c
Amount of D-malic acid added to test sample.
d
r = 2.8 × s
r
.
e
R = 2.8 × s
R
.
f
Sample not spiked with D-malic acid.
g
Negligible amount of D-malic acid present; results not evaluated.
h
Values in parenthesis calculated including outliers.
AOAC Official Method 995.06 DMalic Acid in Apple Juice - Trang 2
AOAC Official Method 995.06 DMalic Acid in Apple Juice - Người đăng: nasaisme1111-gmail-com
5 Tài liệu rất hay! Được đăng lên bởi - 1 giờ trước Đúng là cái mình đang tìm. Rất hay và bổ ích. Cảm ơn bạn!
2 Vietnamese
AOAC Official Method 995.06 DMalic Acid in Apple Juice 9 10 275