U.S. patent application number 14/145454 was filed with the patent office on 2014-10-30 for raman spectroscopy method of measuring melamine contents in dairy products having different matrixes.
The applicant listed for this patent is Nuctech Company Limited, Tsinghua University. Invention is credited to Zhiqiang CHEN, Jianping GU, Qingping HUANG, Hongqiu WANG, Zhiming WANG, Yumin YI, Jianhong ZHANG, Li ZHANG, Ziran ZHAO.
Application Number | 20140320855 14/145454 |
Document ID | / |
Family ID | 51767742 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140320855 |
Kind Code |
A1 |
CHEN; Zhiqiang ; et
al. |
October 30, 2014 |
RAMAN SPECTROSCOPY METHOD OF MEASURING MELAMINE CONTENTS IN DAIRY
PRODUCTS HAVING DIFFERENT MATRIXES
Abstract
A raman spectroscopy method of measuring melamine contents in
dairy products having different matrixes. The method includes: (a)
establishing a database of characteristic curves of dairy products
having different matrixes; (b) taking several copies of the dairy
products having one certain unknown matrix and adding melamine
standard solutions having different concentrations therein, to
obtain a series of dairy product samples in which the relative
concentrations of the melamine are known; (c) performing raman
spectrum testing analysis and obtaining corresponding
characteristic peak intensities to obtain a slope of the
characteristic curve showing variation of the characteristic peak
intensities with the relative concentrations of the melamine; (d)
searching the database of step (a) using the slope of the
characteristic curve of the dairy product samples to find a
matching characteristic curve, and (e) calculating concentration of
melamine in the dairy products by using the matched characteristic
curve and the characteristic peak intensity.
Inventors: |
CHEN; Zhiqiang; (Beijing,
CN) ; ZHANG; Li; (Beijing, CN) ; ZHANG;
Jianhong; (Beijing, CN) ; WANG; Hongqiu;
(Beijing, CN) ; ZHAO; Ziran; (Beijing, CN)
; GU; Jianping; (Beijing, CN) ; WANG; Zhiming;
(Beijing, CN) ; HUANG; Qingping; (Beijing, CN)
; YI; Yumin; (Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tsinghua University
Nuctech Company Limited |
Beijing
Beijing |
|
CN
CN |
|
|
Family ID: |
51767742 |
Appl. No.: |
14/145454 |
Filed: |
December 31, 2013 |
Current U.S.
Class: |
356/301 |
Current CPC
Class: |
G01N 21/65 20130101 |
Class at
Publication: |
356/301 |
International
Class: |
G01N 21/65 20060101
G01N021/65 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2013 |
CN |
201310155894.7 |
Claims
1. A Raman spectroscopy method of measuring melamine contents in
dairy products having different matrixes, comprising the following
steps: (a) establishing a database of characteristic curves of the
dairy products having different matrixes; (b) taking several copies
of dairy products to be detected having a certain unknown matrix,
and adding melamine standard solutions having different
concentrations into the several copies respectively, to obtain a
series of such dairy product samples in which the relative
concentrations of the melamine are known; (c) performing Raman
spectrum testing analysis on the dairy product samples and
obtaining corresponding characteristic peak intensities, so that a
slope of the characteristic curve showing variation of the
characteristic peak intensities of the dairy product samples with
the relative concentrations of the melamine is obtained; (d)
carrying out a search in the database established in the step (a)
by using the slope of the characteristic curve of the dairy product
samples, so as to find out a characteristic curve matched with it;
and (e) calculating concentration of the melamine in the dairy
products to be detected by using the matched characteristic curve
and the characteristic peak intensity of the dairy product to be
detected.
2. The Raman spectroscopy method of claim 1, wherein, in step (b),
after adding the melamine standard solutions into the dairy
products to be detected, a water, an organic solvent or a salt is
added into the dairy products to be detected, and then they are
uniformly mixed, centrifugally treated, and finally a clear liquid
thereof is taken to be ready for measurement.
3. The Raman spectroscopy method of claim 2, wherein, a
nanomaterial reinforcing agent is added into the clear liquid, and
uniformly mixed with the clear liquid to form the sample of the
dairy products.
4. The Raman spectroscopy method of claim 1, wherein, in step (c),
the process of obtaining the characteristic peak intensity further
comprises: performing background subtraction processing on the
obtained raman spectrum of the dairy product sample, in order to
obtain a smooth raman spectrum; obtaining the characteristic peak
intensity of the characteristic peak, by dividing a corresponding
peak area at a raman shift of a first characteristic peak in the
raman spectrum by a corresponding peak area at a raman shift of a
second characteristic peak.
5. The Raman spectroscopy method of claim 4, wherein, the raman
shift of the first characteristic peak is approximately 707
cm.sup.-1; and the raman shift of the second characteristic peak is
approximately 935 cm.sup.-1.
6. The Raman spectroscopy method of claim 1, wherein, step (a)
includes measuring the concentrations of the melamine in a series
of the dairy product samples having the same matrix using high
performance liquid chromatography, liquid chromatography-mass
spectrometry, or gas chromatography-mass spectrometry; obtaining
characteristic peak intensities of the dairy product samples having
the same matrix by Raman spectroscopy, so that a characteristic
curve showing variation of the characteristic peak intensities of
the dairy product having such matrix with the melamine
concentration is established; and establishing a database of the
characteristic curves of the dairy products having different
matrixes, by measuring the characteristic curves of the dairy
products having different matrixes.
7. The Raman spectroscopy method of claim 2, wherein, the water
comprises deionized water, or distilled water; the organic solvent
comprises alcohol or acetone, and the salt comprises kalium
chloride, or sodium chloride.
8. The Raman spectroscopy method of claim 3, wherein, the
nanomaterial reinforcing agent comprises any one of metal
nanoparticles, metal nanowires, metal nanoclusters, carbon
nanotubes, carbon nanoparticles, or a combination thereof with a
size in the range of 1-1000 nm.
9. The Raman spectroscopy method of claim 8, wherein, the metal
comprises any one of gold, silver, copper, magnesium, aluminium,
iron, cobalt, nickel, palladium, and platinum, or a combination
thereof.
10. The Raman spectroscopy method of claim 1, wherein, in step (c),
the slope of the characteristic curve is determined based on a
differential method or linear fitting method, in accordance with
variation of the characteristic peak intensities with the
concentrations of the melamine.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Chinese Patent
Application No. 201310155894.7 filed on Apr. 28, 2013 in the State
Intellectual Property Office of China, the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the field of detecting
melamine content in dairy products, and more particularly, to the
method of detecting melamine content in dairy products having
different matrixes.
[0004] 2. Description of the Related Art
[0005] Chinese government-issued regulations "Method of Detecting
Melamine in Raw Milk and Dairy Products" (GB/T 22388-2008),
regulate three methods of detecting melamine in raw milk, in dairy
products, and in milk contained products, i.e., high performance
liquid chromatography (HPLC), liquid chromatography-mass
spectrometry (LC-MS/MS), as well as gas chromatography-mass
spectrometry [including GC-MS, GC-MS/MS]. Although these methods
can facilitate accurate qualitative analysis and quantitative
analysis, they can only be performed in labs, due to limitations
such as complicated operations, harsh operating conditions, high
cost of consumptive materials, and low detecting speed, or the
like.
[0006] One patent application filed by the China Academy of
Inspection and Quarantine has been published with a publication
number of CN101477051, entitled with "Raman Spectroscopy for Quick
Field Detecting Melamine in the Liquid Milk and Reagent Kit". The
above described patent application discloses one method to
quantitatively detect melamine contents in liquid milk using raman
spectroscopy. This method mainly studied characteristic curves
showing variation of characteristic peak intensity of the raman
spectrum of the fresh milk with concentration of the melamine
therein, and adopted such characteristic curves and the raman
spectrum of the fresh milk to be detected. This can detect the
melamine more quickly, and obtain a relatively good detection
result with respect to the contents of the melamine in the fresh
milk. However, when detecting other kinds of liquid milks, there
are some differences between their characteristic curves and those
of the fresh milks, since compositions of various different liquid
milks will vary. If a quantitative calculation is still done with
the characteristic curve of the fresh milks, then it would cause
large deviation of the calculation results from the real values.
Real measurement indicates that such a method will cause a
relatively large measuring deviation upon detecting various liquid
milks available on the market. This is mainly because the liquid
milks have different compositions and these different matrixes will
largely affect the measurement of the raman spectroscopy.
Therefore, one of main difficulties for quantitative detection of
the melamine in dairy products with raman spectroscopy is to remove
interferences caused by different matrixes in the dairy products
being measured.
[0007] In view of this, there is indeed a need for a quantitative
analysis method for quickly and/or accurately detecting melamine
content in dairy products having different matrixes.
SUMMARY OF THE INVENTION
[0008] In view of the above shortages in the prior art, an object
of the present invention is to alleviate at least one aspect of the
above problems and defects.
[0009] Concerning the above, one objective of the present invention
is to establish a testing and data analyzing method to avoid
interferences from the different matrixes in dairy products by
using raman spectroscopy, and to achieve the quantitative detection
of melamine in the dairy products having different matrixes by
using raman spectroscopy.
[0010] In accordance with one aspect of the present invention, it
provides a raman spectroscopy method of measuring melamine contents
in dairy products having different matrixes, comprises the
following steps:
[0011] (a) establishing a database of characteristic curves of the
dairy products having different matrixes;
[0012] (b) taking several copies of dairy products to be detected
having one certain unknown matrix, and adding melamine standard
solutions with different concentrations into the several copies
respectively, to obtain a series of such dairy product samples in
which the relative concentrations of the melamine are known;
[0013] (c) performing raman spectrum testing analysis on the dairy
product samples and obtaining corresponding characteristic peak
intensities, so that a slope of the characteristic curve showing
variation of the characteristic peak intensities of the dairy
product samples with the relative concentrations of the melamine is
obtained;
[0014] (d) carrying out a search in the database established in the
step (a) by using the slope of the characteristic curve of the
dairy product samples, so as to find a characteristic curve matched
with it; and
[0015] (e) calculating concentration of the melamine in the dairy
products to be detected by using the matched characteristic curve
and the characteristic peak intensity of the dairy product to be
detected.
[0016] Further, in the step (b), after adding the melamine standard
solutions into the dairy products to be detected, a water, an
organic solvent or a salt is added into the dairy product to be
detected, and then they are uniformly mixed, centrifugally treated,
and finally, a clear liquid thereof is taken to be ready for
measurement.
[0017] In addition, a nanomaterial reinforcing agent is added into
the clear liquid, and uniformly mixed with the clear liquid to form
the dairy product samples.
[0018] In another embodiment, in step (c), the process of obtaining
the characteristic peak intensity further comprises:
[0019] performing background subtraction processing on the obtained
raman spectrum of the dairy product sample, in order to obtain a
smooth raman spectrum;
[0020] obtaining the characteristic peak intensity of the
characteristic peak, by dividing a corresponding peak area at a
raman shift of a first characteristic peak in the raman spectrum by
a corresponding peak area at a raman shift of a second
characteristic peak.
[0021] Specifically, the raman shift of the first characteristic
peak is approximately 707 cm.sup.-1; and the raman shift of the
second characteristic peak is approximately 935 cm.sup.-1.
[0022] In a further embodiment, step (a) includes measuring the
concentrations of the melamine in a series of the dairy product
samples having the same matrix, by means of high performance liquid
chromatography, liquid chromatography-mass spectrometry, or gas
chromatography-mass spectrometry;
[0023] obtaining characteristic peak intensities of the dairy
product samples having the same matrix by raman spectroscopy, so
that a characteristic curve showing variations of the
characteristic peak intensities of the dairy product having such
matrix with the melamine concentration is established; and
[0024] establishing a database of the characteristic curves of the
dairy products having different matrixes, by measuring the
characteristic curves of the dairy products having different
matrixes.
[0025] In an embodiment, the water comprises deionized water, or
distilled water; the organic solvent comprises alcohol or acetone,
and the salt comprises kalium chloride, or sodium chloride.
[0026] In an embodiment, the nanomaterial reinforcing agent
comprises any one of metal nanoparticles, metal nanowires, metal
nanoclusters, carbon nanotubes, carbon nanoparticles, or a
combination thereof, with a size in the range of 1-1000 nm.
[0027] In an embodiment, the metal comprises any one of gold,
silver, copper, magnesium, aluminium, iron, cobalt, nickel,
palladium, and platinum, or a combination thereof.
[0028] In one further embodiment, in step (c), the slope of the
characteristic curve is determined based on the differential method
or linear fitting method, in accordance with variation of the
characteristic peak intensities with the concentrations of the
melamine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] These and other aspects and advantages of the present
invention can become apparent and readily understood from the
description of the preferred embodiments in combination with the
accompanying figures below.
[0030] FIG. 1 is a schematic view showing a part of an established
database including characteristic curves of the dairy products
having different matrixes in accordance with an embodiment of the
present invention;
[0031] FIGS. 2a-2c are views of raman spectra for three liquid milk
samples detected by a method in accordance with an embodiment of
the present invention, wherein the liquid milk samples each are
formed by adding melamine standard solutions with different
concentrations into the liquid milk having a certain matrix;
[0032] FIG. 3 is a schematic view showing characteristic curves of
the liquid samples to be detected as shown in FIGS. 2a-2c, obtained
by calculation in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Technical solutions of the present invention will be
described hereinafter in more detail by the way of embodiments with
reference to accompanying drawings, wherein the same or like
reference numerals refer to the same or like elements throughout
the specification. The explanation of the embodiments of the
present invention with reference to the accompanying drawings is
intended to interpret the general inventive concept of the present
invention, rather than being construed as limiting the present
invention.
[0034] The main concept of the present invention is: performing
raman spectroscopy measurement and analysis of dairy products
having the same matrix, with known concentration of melamine;
establishing characteristic curves of the corresponding raman
spectroscopy peak intensities vs. the melamine concentrations of
the dairy products having the same matrix; studying and analyzing
the characteristic curves of the corresponding raman spectroscopy
peak intensities vs. the melamine concentrations of the dairy
products having a plurality of different matrixes, so as to
establish a database of the characteristic curves; performing a
plurality of raman spectroscopy measurements of the dairy product
to be detected by using relative methods, so as to determine a
slope of the characteristic curve; establishing the characteristic
curve of the dairy product to be detected in combination with the
database; and using the obtained characteristic curve to calculate
the contents of the melamine in the dairy products to be
detected.
[0035] A raman spectroscopy method of detecting a content of
melamine in dairy products having different matrixes in accordance
with the present invention, comprises the following steps:
[0036] 1) Preparation of samples having known melamine
concentrations: the concentration of the melamine in the dairy
products can be measured by means of the above described national
standard measuring method (for example, HPLC, LC-MS/MS, GC-MS,
GC-MS/MS); a series of samples having known melamine concentrations
can be obtained by adding melamine standard solutions having
different concentrations.
[0037] 2) Raman spectroscopy measurement: after taking a certain
amount of samples, a certain amount of water, or chemicals such as
organic solvents, salts or the like can be added into the samples.
After uniformly mixing, a centrifugal treatment is performed and
the obtained clear liquid is ready for detection. A certain amount
of the clear liquid is mixed with one nanomaterial reinforcing
agent, and the raman spectrum of the obtained mixture can be
measured by a raman spectrometer.
[0038] 3) analysis of characteristic peak intensities: obtaining a
characteristic peak intensity of one certain characteristic peak in
the raman spectrum, i.e., a relative intensity of a signal (or peak
area) at a raman shift of the certain characteristic peak with
respect to a signal (or peak area) at a raman shift of another
characteristic peak.
[0039] 4) establishing characteristic curve: as for the dairy
products having the same matrix, establishing the characteristic
curve showing variation of the characteristic peak intensities with
the concentration changes of the melamine;
[0040] 5) establishing database: with respect to the dairy products
having different matrixes, the corresponding characteristic curves
are established, so as to constitute the corresponding database (as
shown in FIG. 1, the zero point or 0 ppm of the melamine
concentration as shown in FIG. 1 indicates the milk sample is
really free of melamine);
[0041] 6) relative measurement: after taking multiple samples of
the dairy product to be detected, and respectively adding melamine
standard solutions with different concentrations into the samples,
a series of samples of the dairy product to be detected having
different matrixes can be obtained wherein the relative
concentrations of the melamine have been known, and in accordance
with the step 2), the raman spectrum (as shown in FIGS. 2a-2c) of
each sample to be detected can be measured and then the
characteristic peak intensities thereof are obtained;
[0042] 7) Quantitative analysis: the characteristic curve
corresponding to the dairy product to be detected can be
established by using the database established by the step 5) and
the characteristic peak intensities of the raman spectrum obtained
by the relative measurement in the step 6) (see FIG. 3). In
combination with the characteristic curve and the characteristic
intensities of the raman spectrum of the sample to be detected, the
concentration of the melamine in the sample can be quantitatively
calculated.
[0043] With the above relative measurement and data analysis method
as described, the quantitative measurement to the melamine contents
in the dairy products can be achieved. When the content of the
melamine is above 2.5 mg/kg, the detection rate of recovery is
80%.about.110%, and the relative standard deviation is less than
10%.
[0044] In the present invention, the step of establishing the
database consisting of the characteristic curves of the dairy
products having different matrixes specifically comprises: the
concentrations of the melamine in a series of dairy product samples
having the same matrix are measured by the method regulated by the
national government, such as HPLC, LC-MS/MS, GC-MS and GC-MS/MS;
the characteristic peak intensities of the above samples are
obtained by the raman spectroscopy, so that the characteristic
curve showing variation of the characteristic peak intensities of
the dairy product having the same matrix with the concentration of
the melamine is established; and then by detecting and obtaining
the characteristic curves of the dairy products having different
matrixes, the database of the characteristic curves for the dairy
products having different matrixes can be established.
[0045] In an embodiment of the present invention, the nanomaterial
reinforcing agent applied in the step 2) may include any one of
metal nanoparticles, nanowires, nanoclusters, carbon nanotubes,
carbon nanoparticles, or a combination thereof with the size in the
range of 1-1000 nm. The metal nanoparticles, nanowires, or
nanoclusters include the nanoparticles, nanowires, or nanocluster
made of any one of gold, silver, copper, magnesium, aluminium,
iron, cobalt, nickel, palladium, and platinum, or a combination
thereof.
[0046] In addition, in step 2), the water may include deionized
water, or distilled water; and the organic solvent includes alcohol
or acetone, or the like, the salt may include kalium chloride, or
sodium chloride, and so on.
[0047] In step 3), the process of obtaining the characteristic peak
intensities may include: performing background subtraction
processing on the obtained raman spectrum of the dairy product
sample in order to obtain a smooth raman spectrum; obtaining a
characteristic peak intensity of the characteristic peak, by
dividing a corresponding peak area at a raman shift of a first
characteristic peak in the raman spectrum by a corresponding peak
area at a raman shift of second characteristic peak. In an
embodiment, the raman shift of the first characteristic peak is
approximately 707 cm.sup.-1; and the raman shift of the second
characteristic peak is approximately 935 cm.sup.-1.
[0048] In an example of the present invention, the process of
obtaining the slope of the characteristic curve is as follows: the
slope of the characteristic curve is determined by a differential
method or linear fitting method, based on variation of the
characteristic peak intensities with the concentrations of the
melamine.
[0049] As compared with the method mentioned in the regulations of
"GB/T 22388-2008", the present invention obtains the following
advantages, such as simple pre-processing of the samples, low cost
of the consumable materials for testing, and quick field detection.
With respect to other raman spectroscopy reported in the prior art,
the biggest advantage of the present invention removes the
interferences of the detection with the matrixes. The present
method is not limited to detection of one certain dairy product,
but can be applied to more than 20 kinds of liquid dairy products
sold in the current market. It can achieve the quantitative
detection, the measuring limit of 2.5 mg/kg, and good repetition
(quantitative analysis, RSD.ltoreq.10%).
[0050] In an embodiment, a method of the present invention
includes:
[0051] Step 1: a plurality of copies of 500 .mu.L liquid milk
having known melamine concentrations are put into a plurality of
centrifuge tubes respectively. And then, one of 50 .mu.L melamine
standard solutions having different concentrations and 800 .mu.L
absolute ethyl alcohol are added into each of the centrifuge tubes.
After whirling 10 seconds, the tube is placed within a centrifugal
machine. After being in centrifuge treatment for 12 minutes under
the rotation speed of 14000 rpm, the clear liquid in an upper layer
is taken and ready for detection.
[0052] Step 2: a 430 .mu.L solution containing nano silver
reinforcing agent (the concentration thereof may be 100 mg/L, and
the nano silver materials or particles may have sizes in the range
of 30-150 nm) and the clear liquid of milk of 200 .mu.L as
described above are added into a test bottle, and they are evenly
mixed by whirling.
[0053] Step 3: a raman spectrometer having a laser light source
with an emitting wavelength of 785 nm as shown in the prior art, is
used to detect the raman spectrum of the mixed solution, wherein
the laser power is 450 w, the integration time is 1 s, an average
spectrum is obtained by continually scanning at 15 times.
[0054] Step 4: the characteristic peak intensity, i.e., the
relative intensity of the raman signal of the characteristic peak
at the raman shift of approximately 707 cm.sup.-1, is obtained by
dividing the peak area of the corresponding peak at a raman shift
of 707 cm.sup.-1 of the characteristic peak by the peak area of the
corresponding peak at a raman shift of 935 cm.sup.-1 of the
characteristic peak.
[0055] Step 5: with respect to the liquid milk samples having
different melamine contents, the characteristic curve showing a
linear relationship of the relative intensity of the characteristic
peak at the raman shift of approximately 707 cm.sup.-1 with the
concentration of the melamine is established.
[0056] Step 6: with respect to the liquid milk samples having
different matrixes, the characteristic curves thereof are
established respectively, thereby constituting a database of the
characteristic curves of the liquid milks having different
matrixes. FIG. 1 depicts the characteristic curves showing
variation of the raman characteristic peak intensities of six
liquid milks having different matrixes (for example, milks 1-6)
with the concentration of the melamine.
[0057] Step 7: firstly, taking out several copies of the liquid
milk having a certain unknown matrix, and then adding different
concentrations of the melamine standard solutions into it, finally
obtaining a series of the liquid milk samples to be detected having
the certain unknown matrix, the relative concentration of the
melamine therein being known.
[0058] Specifically, in the present embodiment, three copies of the
liquid milk of 500 .mu.L may be taken, and 50 .mu.L water, 15 ppm
melamine standard solution and 35 ppm melamine standard solution
may be added into the three copies respectively, in the same manner
as discussed in steps 1 and 2 for preparing the liquid milk samples
to be detected (that is, the liquid milks having the known melamine
concentrations in steps 1 and 2 are replaced by equal volumes of
the liquid milks to be detected, while keeping other parameters,
conditions or processing orders constant). Assuming the melamine
concentration of the liquid milk to be detected is X, the melamine
concentrations of the three samples are considered as X, X+1.5 ppm,
X+3.5 ppm.
[0059] Step 8: With respect to the slope of the characteristic
curve of the liquid milk to be detected, a search is performed
within the established database, so as to find the characteristic
curve matched with it.
[0060] Specifically, the raman spectrum of each sample to be
detected is measured by the methods as described in the above
steps, thereby obtaining the characteristic peak intensity, and the
characteristic curve of the liquid milk to be detected. See FIGS.
2a-2c which illustrate the raman spectra showing the raman peak
intensity and raman shift of the liquid milk to be detected.
[0061] By using the corresponding method as described in step 3,
the raman spectra of the three liquid milk samples to be detected
are obtained, as shown in FIGS. 2a, 2b, 2c. The calculated
characteristic peak intensities (the relative intensity of the
raman signal at the characteristic peak raman shift of 707
cm.sup.-1) are respectively 0.691, 1.030, 1.426, thereby obtaining
the corresponding relationship between the melamine concentration
and the characteristic peak intensity, as shown in Table 1:
TABLE-US-00001 TABLE 1 showing the relationship between the
relative concentrations of the melamine in the liquid milk to be
detected and the characteristic peak intensity thereof Relative
concentration Characteristic Sample number of the melamine (ppm)
peak intensity Sample 1 X 0.691 Sample 2 X + 1.5 1.030 Sample 3 X +
3.5 1.426
[0062] The slope of the corresponding characteristic curve is
calculated by using the relative concentration of the melamine and
the characteristic peak intensity. The value of X can be supposed
as any value, and a linear fitting method is applied to the above
three sets of data (the fitted curve of FIG. 3 is obtained in the
case of X=0). After such fitting, the obtained slope is 0.21. After
searching in the database for the corresponding slope, the
corresponding characteristic curve is y=0.21x+0.37.
[0063] Step 9: The concentration of the melamine in the liquid milk
to be detected is calculated quantitatively by using the
characteristic curve and the characteristic peak intensity of the
raman spectrum of the liquid milk to be detected. The
characteristic peak intensity of the liquid milk to be detected is:
Y=0.691. By using the characteristic curve, the melamine
concentration of the liquid milk sample to be detected is
calculated as 1.53 ppm. By comparison, it is found that the
calculated value (by the above method) is very close to the
actually measured value of 1.50 ppm (which is measured by the
detection method regulated by the National Rule of Law as described
above).
[0064] By measuring the samples in accordance with the above
method, it is found that when the melamine content is less than or
equal to 2.5-5 ppm, the recovery rate is within 80%-110%, and the
relative standard deviation is less than 10%. With respect to step
7, as such, several samples of the liquid milks having unknown
matrixes in which the relative concentration of the melamine is
known, can be measured, so as to determine the melamine
concentration in the liquid dairy products having unknown
matrixes.
[0065] Although some embodiments of the general inventive concept
are illustrated and explained, it will be appreciated by those
skilled in the art that modifications and variations may be made in
these embodiments without departing from the principles and spirit
of the general inventive concept of the disclosure, the scope of
which is defined in the appended claims and their equivalents.
* * * * *