CN104807770A - Method for detecting caffeine in tea leaves - Google Patents
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- CN104807770A CN104807770A CN201510197084.7A CN201510197084A CN104807770A CN 104807770 A CN104807770 A CN 104807770A CN 201510197084 A CN201510197084 A CN 201510197084A CN 104807770 A CN104807770 A CN 104807770A
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Abstract
The invention relates to a method for detecting caffeine in tea leaves, and belongs to the technical field of detection. The method comprises the following steps: preparing a test solution, making a standard curve of caffeine, and calculating results. The method has the advantages that through the adoption of the method to detect the content of caffeine in the tea leaves, the repeatability of the detection result is good, and the error can reach the requirement of national standard.
Description
Technical field
The invention belongs to detection technique field, be specifically related to a kind of method detecting caffeine in tealeaves.
Background technology
Tea Caffeine belongs to alkaloid, it is the one of tealeaves purine base, bitter, there is medical value and health value, generally in tealeaves, account for 2.0% ~ 5.0% of dry matter content, many reaches more than 6.0%, is one of main chemical compositions of composition tealeaves flavour, measures that its content is how many to play an important role for excellent time to measurement tea leaf quality.In tealeaves, caffeine has multiple detection method, comprise iodimetric titration, gravimetric method, ultraviolet spectrophotometry, nitriding, colourimetry, vapor phase method, high performance liquid chromatography, chromatography and near infrared spectroscopy etc., that comparatively commonly uses at present has two kinds: high performance liquid chromatography, ultraviolet spectrophotometry.
High performance liquid chromatography, requires that experiment condition is relatively high, ultraviolet spectrophotometry because of its have easy, fast feature and by great majority detect unit adopted.Ultraviolet spectrophotometry utilizes caffeine solution to have a maximum absorption peak at ultraviolet region wavelength 274nm place, with basic lead acetate as precipitation agent, the materials such as removing Tea Polyphenols, protein and pigment, then the ultraviolet light of 274nm wavelength is directly used, measure extract optical density numerical value, calculate caffeine content.The method adopting ultraviolet spectrophotometry to calculate caffeine content is described in the inspection of GB/T8312-2002 Tea Caffeine, the wherein preparation of test solution: take 3g (accurately to 0.001g) and grind sample in 500mL conical flask, add the distilled water 450mL that boils, move into lixiviate 45min in boiling water bath (every 10min shake once) immediately.Filtration under diminished pressure while hot immediately after lixiviate, filtrate moves in 500mL volumetric flask, residue a small amount of hot distilled water washing 2 ~ 3 times, and filtrate is filtered in above-mentioned volumetric flask, after cooling with distilled water diluting to scale.The typical curve range of linearity made during existing determined by ultraviolet spectrophotometry Tea Caffeine is narrower, concentration of standard solution setting, to make the not too science such as reference with reagent blank.The range of linearity is narrow, and when the caffeine content of Tea Samples is larger, measured absorbance corresponding concentration often exceeds the range of linearity, and error is larger.Detect with the existing range of linearity, Tea Caffeine content maximal value about 4.0%, and in fact very most of Tea Caffeine content is more than 4.0%, concentration of standard solution range set not science, traditionally testing result repeatability is bad.
Summary of the invention
The object of this invention is to provide a kind of method detecting caffeine in tealeaves, the content range that the method can detect is wide, and reproducible, testing result is closer to actual value.
The technical solution used in the present invention is a kind of Tea Caffeine detection method of content, comprises the following steps:
A, peparation: take 3g (accurately to 0.001g) and grind sample in 500mL conical flask, add the distilled water 450mL that boils, move into immediately in boiling water bath, lixiviate 45min (every 10min shake once), filtration under diminished pressure while hot immediately after lixiviate, filtrate moves in 500mL volumetric flask, residue a small amount of hot distilled water washing 2 ~ 3 times, and filtrate is filtered in above-mentioned volumetric flask, after cooling with distilled water diluting to scale, make reagent blank while Specimen Determination;
B, accurately to draw test solution 10mL with transfer pipet and move in 100mL volumetric flask, add 4mL0.01mol/L hydrochloric acid and 1mL basic lead acetate solution, be diluted with water to scale, mixing, leave standstill clarification filtration, obtain filtrate, accurately draw this filtrate 25mL, inject 50mL volumetric flask, add 0.1mL 4.5mol/L sulfuric acid solution, be diluted with water to scale, mixing, leave standstill clarification filtration.Use 10mm cuvette, at wavelength 274nm place, make reference with typical curve 0 pipe, measure absorbance (A);
The making of c, caffeine typical curve
Caffeine standard solution: take 100mg caffeine (purity is not less than 99%) and be dissolved in 100mL water as mother liquor.Accurate absorption 5mL mother liquor, in 100mL volumetric flask, adds water to scale and shakes up as caffeine working fluid (1mL working fluid is containing caffeine 50ug).
Draw 0 respectively, 0.5,1,3,5,7,10mL caffeine working fluid in one group of 25mL volumetric flask, respectively add 1.0mL hydrochloric acid, be diluted with water to scale, mixing, uses 10mm quartz cuvette, at wavelength 274nm place, make reference with typical curve 0 pipe, measure absorbance (A).By the absorbance that records and corresponding caffeine concentration drawing standard curve;
D, result calculate
In tealeaves, caffeine content is with dry mass fraction representation, is calculated as follows
In formula:
C
2---the corresponding content of caffeine that the absorbance (A) that sample records checks in from caffeine typical curve, deducts the value after the content of the caffeine that absorbance that reagent blank records checks in from caffeine typical curve;
L
3---test solution total amount mL;
M
2---sample dosage g;
M
2---sample dry rate %.
GB/T8312-2002 ultraviolet spectrophotometry detects in the method for caffeine content in tealeaves, the method for making of typical curve for respectively " draw 0,1,2,3,4,5,6mL caffeine working fluid is in one group of 25mL volumetric flask; respectively add 1.0mL hydrochloric acid; be diluted with water to scale; mixing ", then at wavelength 274nm place, make reference with blank reagent solution, measure absorbance.Draw the typical curve of caffeine standard working solution making according to this uptake, the absorbance that 6mL caffeine working fluid records is about 0.600, but the absorbance of most of sample is higher than 0.600, and its concentration is not in this curve ranges.According to the typical curve that this method makes, because caffeine working fluid uptake is less, the corresponding caffeine concentration of the absorbance that sample records is not in the typical curve range of linearity.According to actual needs, the uptake of caffeine working fluid is made an adjustment, be adjusted to " draw 0,0.5,1,3,5,7,10mL ".According to the typical curve that this uptake makes, the concentration corresponding to absorbance of current institute test sample product is all in this curve ranges.
GB/T8312-2002 ultraviolet spectrophotometry detects in the method for caffeine content in tealeaves, and the concentration of caffeine working fluid is 0.05mg/mL, and being drawn in 25mL volumetric flask concentration after constant volume by standard method is 0.002mg/mL.With this concentration value production standard curve, different samples checks in different absorbances (see table 1) on typical curve.
Table 1 sample absorbance and caffeine content (mg/mL)
As can be seen from Table 1, according to national standard method make typical curve, sample absorbance in certain interval range by corresponding same concentration value.The absolute difference of interval endpoint is minimum is 0.039, is 0.058 to the maximum.In same interval, any absorbance caffeine content result of calculation is identical.As the 13rd interval, absorbance is minimum is 0.777, is 0.827 to the maximum, difference 0.050, and corresponding concentration value is 0.016mg/mL, and the caffeine content calculated is all 5.7%.At interval two ends, absorbance lower limit corresponding concentration value is close to a upper interval upper concentration value; Absorbance upper limit corresponding concentration value is close to next interval limit concentration value.The every 100g of the caffeine content that these two concentration values calculate differs 0.3g or 0.4g.As the 14th interval, absorbance is minimum is 0.828, close with the 13rd interval maximum absorbance 0.827, only difference 0.001, but the concentration of both correspondences is respectively 0.017mg/mL and 0.016mg/mL, the caffeine content of calculating is 6.1% and 5.7%, difference 0.4%; Absorbance is 0.874 to the maximum, close with the 15th interval minimum absorbance 0.877, also be only differ 0.001, but the concentration of both correspondences is respectively 0.017mg/mL and 0.018mg/mL, the caffeine content calculated is 6.1% and 6.4%, difference 0.3%, all substandard requirement of repeatability (repeatability of standard-required is that every 100g is no more than 0.2g).The present invention does not change the concentration of working fluid when production standard curve, and concentration value is increased 1000 times, namely changes concentration measurement unit, mg/mL is changed into μ g/mL.With this concentration value production standard curve, the concentration value on the absorbance that sample records and typical curve substantially can one_to_one corresponding (see table 2).
Table 2 sample absorbance and caffeine content (μ g/mL)
| Project | Absorbance | Concentration (μ g/mL) | Caffeine content (%) | Remarks |
| 1 | 0 | 0.026 | 0 | Sample 1 |
| 2 | 0.068 | 1.437 | 0.5 | Sample 2 |
| 3 | 0.098 | 2.045 | 0.7 | Sample 2 |
| 4 | 0.555 | 11.312 | 4.0 | Sample 3 |
| 5 | 0.559 | 11.393 | 4.1 | Sample 3 |
| 6 | 0.623 | 12.690 | 4.5 | Sample 4 |
| 7 | 0.632 | 12.873 | 4.6 | Sample 4 |
| 8 | 0.663 | 13.501 | 4.8 | Sample 5 |
| 9 | 0.669 | 13.623 | 4.9 | Sample 5 |
| 10 | 0.720 | 14.649 | 5.2 | Sample 6 |
| 11 | 0.732 | 14.871 | 5.3 | Sample 6 |
| 12 | 0.839 | 17.070 | 6.1 | Sample 7 |
| 13 | 0.846 | 17.212 | 6.2 | Sample 7 |
As can be seen from Table 2, concentration value measurement unit changes latter made typical curve, even if the absorbance difference less (in table listed minimum only have 0.004) that same sample records, corresponding concentration value also has difference.As project 2 and project 3, absorbance difference 0.030, to check in by this curve caffeine content that concentration value calculates be 0.5% and 0.7% (note: when calculating caffeine content be mg/mL by unit reduction), and every 100g differs 0.2g; And for example project 4 and project 5, absorbance difference 0.004, checking in by this curve the caffeine content that concentration value calculates is 4.0% and 4.1%, and every 100g differs 0.1g, all meets the repeatability required by standard.
GB/T8312-2002 ultraviolet spectrophotometry detects in the method for caffeine content in tealeaves, and in formula, C2 is " according to the absorbance (A) that sample records, the corresponding content of caffeine from caffeine typical curve checks in ".Detect the environmental baseline such as air, humidity in practical operation in chemical examination, experiment agents useful for same, experimental implementation error etc. have impact to experimental result, general all needs in an experiment does experiment blank to eliminate the impact of this class, so require in this method do reagent blank and reduce reagent blank value when result calculates, to make testing result closer to actual value.
Beneficial effect of the present invention is: adopt the inventive method to detect the content of caffeine in tealeaves, testing result is reproducible, the requirement that error can be up to state standards, and result is closer to actual value.
Embodiment
For making those skilled in the art understand detection method of the present invention and technique effect in detail, introduce application of the present invention and technique effect further with concrete detection example below.
(1) instrument and apparatus: UV detector, analytical balance (sensibility reciprocal 0.0001g).
(2) reagent and solution: agents useful for same is for analyzing pure (AR), and water is distilled water.
Basic lead acetate solution: take 50g basic lead acetate, add water 100mL, and hold over night is inclined and supernatant liquid filtering.
Hydrochloric acid: 0.01mol/L solution, gets 0.9mL concentrated hydrochloric acid, and dilute with water 1L, shakes up.
Sulfuric acid: 4.5mol/L solution, gets concentrated sulphuric acid 250mL, is diluted with water to 1L, shake up.
Caffeine titer: take 100mg caffeine (purity is not less than 99%) and be dissolved in 100mL water, as mother liquor, accurately draws 5mL and adds water to 100mL as working fluid (1mL working fluid is containing caffeine 50 μ g).
(3) determination step:
A, peparation: take 3g (accurately to 0.001g) and grind sample in 500mL conical flask, add the distilled water 450mL that boils, move in boiling water bath immediately, lixiviate 45min (every 10min shake once).Filtration under diminished pressure while hot immediately after lixiviate.Filtrate moves in 500mL volumetric flask, residue a small amount of hot distilled water washing 2 ~ 3 times, and filtrate is filtered in above-mentioned volumetric flask, after cooling with distilled water diluting to scale, make reagent blank while Specimen Determination.
B, accurately to draw test solution 10mL with transfer pipet and move in 100mL volumetric flask, add 4mL 0.01mol/L hydrochloric acid and 1mL basic lead acetate solution, be diluted with water to scale, mixing, leave standstill clarification filtration, obtain filtrate.This filtrate of accurate absorption 25mL, injects 50mL volumetric flask, adds 0.1mL 4.5mol/L sulfuric acid solution, be diluted with water to scale, and mixing leaves standstill clarification filtration.Use 10mm cuvette, at wavelength 274nm place, make reference with typical curve 0 pipe, measure absorbance (A).
The making of c, caffeine typical curve
Draw 0 respectively, 0.5,1,3,5,7,10mL caffeine working fluid in one group of 25mL volumetric flask, respectively add 1.0mL hydrochloric acid, be diluted with water to scale, mixing, uses 10mm quartz cuvette, at wavelength 274nm place, make reference with typical curve 0 pipe, measure absorbance (A).By the absorbance that records and corresponding caffeine concentration drawing standard curve.
(4) result calculates
In tealeaves, caffeine content is with dry mass fraction representation, is calculated as follows
In formula:
C
2---according to the absorbance (A) that sample records, from the corresponding content of caffeine that caffeine typical curve checks in, deduct the content of the caffeine that absorbance that reagent blank records checks in from caffeine typical curve;
L
3---test solution total amount mL;
M
2---sample dosage g;
M
2---sample dry rate %.
For verifying technique effect of the present invention, selected sample 1-3, as research object, adopts former method (existing national standard method) and the inventive method (new method) to carry out detection and analyzes.
Sample 1
Former method caffeine content is higher than new method 0.47%; The difference of former method two Duplicate Samples measured values, more than 0.2g, does not meet repeated requirement, and the difference of new method two Duplicate Samples measured values is not more than 0.2g.
Sample 2
Former method caffeine content is higher than new method 0.64%; Concentration value corresponding to former method absorbance is outside standard curve range, and concentration value corresponding to new method absorbance is in standard curve range; The difference of two Duplicate Samples measured values, more than 0.2g, does not meet repeated requirement, and the difference of new method two Duplicate Samples measured values is not more than 0.2g.
Sample 3
Former method caffeine content is higher than new method 0.72%; Concentration value corresponding to former method absorbance is outside standard curve range, and concentration value corresponding to new method absorbance is in standard curve range; The difference of two Duplicate Samples measured values, more than 0.2g, does not meet repeated requirement, and the difference of new method two Duplicate Samples measured values is not more than 0.2g.
Visible, measure caffeine in tealeaves by the inventive method, compared with former method, survey the caffeine content of Tea Samples all in standard curve range, the repeated requirement that measured Tea Samples caffeine result is all up to state standards, result is closer to actual value.
Finally it should be noted that, above embodiment is the unrestricted technical scheme of the present invention in order to explanation only, although with reference to above-described embodiment to invention has been detailed description, those skilled in the art are to be understood that, still can modify to the present invention or equivalent replacement, and not departing from any modification or partial replacement of the spirit and scope of the present invention, it all should be encompassed in right of the present invention.
Claims (1)
1. detect a method for caffeine in tealeaves, it is characterized in that, comprise the following steps:
A, peparation: take 3g and grind sample in 500mL conical flask, add the distilled water 450mL that boils, move into immediately in boiling water bath, lixiviate 45min, filtration under diminished pressure while hot immediately after lixiviate, filtrate moves in 500mL volumetric flask, residue a small amount of hot distilled water washing 2 ~ 3 times, and filtrate is filtered in above-mentioned volumetric flask, after cooling with distilled water diluting to scale, obtain test solution; Reagent blank is made while Specimen Determination;
B, accurately to draw above-mentioned test solution 10mL with transfer pipet and move in 100mL volumetric flask, add 4mL0.01mol/L hydrochloric acid and 1mL basic lead acetate solution, be diluted with water to scale, mixing, leave standstill clarification filtration, obtain filtrate, accurately draw this filtrate 25mL, inject 50mL volumetric flask, add 0.1mL 4.5mol/L sulfuric acid solution, be diluted with water to scale, mixing, leave standstill clarification filtration; Use 10mm cuvette, at wavelength 274nm place, make reference with typical curve 0 pipe, measure absorbance;
The making of c, caffeine typical curve
Caffeine standard solution: take 100mg caffeine and be dissolved in 100mL water as mother liquor; Accurate absorption 5mL mother liquor, in 100mL volumetric flask, adds water to scale and shakes up, obtain caffeine working fluid;
Draw 0 respectively, 0.5,1,3,5,7, the above-mentioned caffeine working fluid of 10mL in one group of 25mL volumetric flask, respectively add 1.0mL hydrochloric acid, be diluted with water to scale, mixing, uses 10mm quartz cuvette, at wavelength 274nm place, make reference with typical curve 0 pipe, measure absorbance; By the absorbance that records and corresponding caffeine concentration drawing standard curve;
D, result calculate
In tealeaves, caffeine content is with dry mass fraction representation, is calculated as follows
In formula:
C
2---the corresponding content of caffeine that the absorbance that sample records checks in from caffeine typical curve, deducts the value after the content of the caffeine that absorbance that reagent blank records checks in from caffeine typical curve;
L
3---test solution total amount mL;
M
2---sample dosage g;
M
2---sample dry rate %.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112198131A (en) * | 2020-10-13 | 2021-01-08 | 福建省农业科学院茶叶研究所 | Ultraviolet absorption spectrum detection method for caffeine content in tea |
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| KR20110106112A (en) * | 2010-03-22 | 2011-09-28 | 강원대학교산학협력단 | Use of near-infrared reflectance spectroscopy for estimating caffeine and individual catechines contents in green tea leaves |
| CN102680416A (en) * | 2012-04-19 | 2012-09-19 | 江苏大学 | Method and device for fast detecting caffeine content of summer and autumn tea |
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2015
- 2015-04-23 CN CN201510197084.7A patent/CN104807770A/en active Pending
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| US20020192834A1 (en) * | 2001-03-23 | 2002-12-19 | Sand Bruce J. | Analysis of caffeine |
| US20040115092A1 (en) * | 2002-12-17 | 2004-06-17 | Paul Starr | Caffeine detector |
| US20080095912A1 (en) * | 2006-10-21 | 2008-04-24 | Emmett Loughran | Portable caffeine detector and method of detecting caffeine in a beverage |
| KR20110106112A (en) * | 2010-03-22 | 2011-09-28 | 강원대학교산학협력단 | Use of near-infrared reflectance spectroscopy for estimating caffeine and individual catechines contents in green tea leaves |
| CN102128791A (en) * | 2010-12-09 | 2011-07-20 | 福建省农业科学院土壤肥料研究所 | Method for determining content of tea caffeine |
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| Title |
|---|
| MARIO ARANDA ET AL: "Simultaneous Determination of Caffeine, Ergotamine and Metamizol in Solid Pharmaceutical Formulation by HPTLC–UV-FLD with Mass Confirmation by Online HPTLC–ESI-MS", 《JOURNAL OF CHROMATOGRAPHIC SCIENCE》 * |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112198131A (en) * | 2020-10-13 | 2021-01-08 | 福建省农业科学院茶叶研究所 | Ultraviolet absorption spectrum detection method for caffeine content in tea |
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Application publication date: 20150729 |