GB 5009.1-2025National food safety standard - Physical and chemical testing - General principles (English PDF)

1 Scope

This standard lays down the basic principles and requirements for physical and chemical testing under the national food safety standards.

This standard applies to physical and chemical testing under the national food safety standards.

2 Terms and definitions

2.1 Method validation. The experimental activity of providing objective and valid evidence that a particular analytical method meets the stated requirements.

2.2 Reference standard. A substance, or a solution of it, having a defined property or value and possessing homogeneity, stability and traceability.

2.3 Sample. One product, or a group of products, taken from the same batch and able to give information about that batch.

2.4 Test portion. A sample that has been prepared so that it can be used for one or several tests.

2.5 Sample reduction. The operation of reducing a sample by a specified method while keeping it representative.

3 General requirements for physical and chemical testing

3.1.1 Testing staff shall have received the corresponding education or training in physical and chemical testing, shall have the corresponding ability, and shall be able to understand and correctly carry out the test.

3.1.2 They shall have a command of laboratory chemical safety practice and shall observe the relevant safety measures and rules during testing, so that their own safety is assured.

3.1.3 Staff who carry out tests involving the sense of smell shall not have an olfactory impairment, and staff who carry out tests involving colour discrimination shall not have a colour vision impairment.

3.2.1 The working area, the general layout, the facilities and equipment and the environmental controls of the laboratory shall meet the needs of the testing work.

3.2.2 The laboratory area shall be physically separated from the office area, and the sample preparation area should be effectively separated from the instrument area.

3.2.3 The temperature, humidity, ventilation, cleanliness, illumination, noise and vibration of the laboratory shall meet the working requirements and shall not affect the accuracy of the test results.

3.2.4 An emergency shower, an eyewash unit and similar emergency facilities shall be placed in a conspicuous position in the laboratory, and a first-aid kit shall be provided as needed.

3.3.1.1 A suitable method shall be chosen according to the scope of application and the performance characteristics of the test method standard and the relevant provisions.

3.3.1.2 Where two or more test methods with the same scope of application meet the requirements, the laboratory may choose which to use according to the actual situation.

3.3.2.1 Before a test method is used, the laboratory shall validate the method it intends to use against the intended purpose.

3.3.2.2 Where the procedure of the test method is the same for all the sample matrices to which it applies, validation shall be carried out on at least one representative sample matrix; where the test method has optional steps, the steps that are to be used shall be validated.

3.3.2.3 For a qualitative method, the detection limit and the specificity shall in principle be validated.

3.3.2.4 For a quantitative method, the detection limit, the limit of quantification, the trueness and the repeatability shall in principle be validated.

3.3.2.5 The validation of the method performance parameters is carried out with reference to GB 5009.295, GB 31604.59 or similar standards.

3.3.2.6 The performance characteristics of the test method after validation by the laboratory shall not be poorer than those laid down in the test method standard, or shall meet the requirements of the intended purpose.

3.4.1.1 The water and the reagents used in the test shall meet the requirements of the test method standard. Chemical reagents of different grades shall be chosen according to the test method and the accuracy required of the result. Key reagents that affect the result shall meet the relevant requirements.

3.4.1.2 Where the test method does not state a concentration, sulfuric acid, nitric acid, hydrochloric acid and ammonia solution mean the commercially available reagent grade concentrations (see Annex A).

3.4.1.3 Reagent storage containers are generally reagent bottles of hard glass; strong alkaline solutions and solutions of inorganic elements should be kept in polyethylene reagent bottles, and light-sensitive reagents shall be kept in brown or black reagent bottles.

3.4.1.4 Ways of expressing solution concentration: a) the mixing ratio by mass of several solid reagents, or by volume of liquid reagents, may be written as (1+1), (4+2+1) and so on; b) the concentration of a solution may be expressed as a mass fraction or a volume fraction, for example a mass (or volume) fraction of 0.75 or a mass (or volume) fraction of 75 per cent; mass fraction and volume fraction may also be expressed as micrograms per gram and as millilitres per cubic metre respectively; c) the concentration may also be expressed as a mass concentration, in grams per litre or a suitable submultiple such as milligrams per millilitre; d) where a solution is prepared by diluting another particular solution, the following convention shall be used: 1) diluted V1 to V2 means that a volume V1 of the particular solution is diluted in some way so that the total volume of the final mixture is V2; 2) diluted V1 plus V2 means that a volume V1 of the particular solution is added to a volume V2 of solution.

3.4.2.1 The reference standard chosen shall meet the requirements of the test method standard as to purity or grade. A product with a certificate of reference material should be chosen, the certificate carrying information on metrological traceability, the assigned value and the uncertainty.

3.4.2.2 Where there is no reference standard for the target analyte, a high-purity chemical with clearly stated purity may be used.

3.4.2.3 The preparation and dilution of standard solutions shall be recorded so that traceability is assured; the record shall state the name of the reference standard, its mass or volume, the solvent, the volume made up or the dilution volume, the storage conditions and the expiry date.

3.4.2.4 The expiry date of a standard solution shall be adequately supported and, where necessary, stability testing shall be carried out in accordance with GB 5009.295, GB 31604.59 or similar standards.

3.4.2.5 Intermediate standard solutions and standard working solutions shall be prepared by stepwise dilution, and a single dilution step should not exceed a factor of 100.

3.4.2.6 As a rule the mass of reference standard to be weighed out shall be calculated from the actual purity.

3.4.3.1 The performance of the test materials shall meet the provisions of the test method standard.

3.4.3.2 Test materials shall be treated and their performance checked as required by the test method standard.

3.5.1 Before instruments and equipment are used it shall be confirmed that their performance parameters meet the technical requirements of the test method standard.

3.5.2 Instruments and equipment shall be kept under suitable environmental conditions and shall be cleaned, maintained and serviced periodically, so that their working performance and safe operation are assured.

3.5.3 Measuring ware, temperature-controlled equipment and detection instruments that affect the accuracy of the result shall all meet the requirements for metrological traceability management.

3.5.4 The accuracy of the volume delivered by the measuring ware used in the test, such as burettes, one-mark pipettes, graduated pipettes, volumetric flasks, micropipettes and colorimetric tubes, shall meet the national standard accuracy requirements for that item of volumetric glassware.

3.5.5 Measuring ware and vessels shall be thoroughly cleaned before use; the preparation and use of the common washing solutions are given in Annex B.

4 Requirements for samples and test portions

4.1.1 Sampling shall follow the principles of representativeness and randomness.

4.1.2 Sampling shall take account of the date of production, the shelf life and the batch number or batch of the product.

4.1.3 The amount sampled shall be enough for testing, for re-testing and for retention.

4.1.4 Sampling equipment shall be of inert material and shall not contaminate the sample or otherwise affect it adversely.

4.1.5 During sampling and transport, adverse effects of ambient temperature, humidity and light on the sample and on the target analyte shall be avoided, for example spoilage, uptake of moisture, loss of water, breakage and cross-contamination.

4.1.6 Where the test method has particular requirements for sampling and transport, those requirements govern.

4.2.1 Basic requirement. Sample reduction and the preparation of the test portion shall keep the sample representative and shall avoid cross-contamination, spoilage of the sample, change in its moisture content and change in the target analyte.

4.2.2 Sample reduction. Except where the whole sample is used to prepare the test portion, sample reduction should follow these principles: a) liquid, semi-fluid and semi-solid samples: a homogeneous sample is shaken or stirred and a portion taken; a non-homogeneous sample is taken at several points and combined; b) powdered and granular samples: mixed, then reduced by quartering, by a sample divider, or by taking and combining several portions; c) solid samples of small individual size, numerous and hard to mix: taken at random from several points; d) solid samples of large individual size and small in number: divided symmetrically or into equal parts.

4.2.3 Preparation of the test portion. According to the requirements of the test, the corresponding part of the reduced or unreduced sample is made into a test portion as follows: a) food samples: ground, homogenized or mixed until uniform; b) food contact material samples: prepared in accordance with GB 31604.1 and GB 5009.156.

4.3.1 The test portion shall be put in a clean, sealed container of inert material; the container may be a wide-mouth glass jar, a polyethylene bottle or a bag, according to the nature of the test portion and of the target analyte.

4.3.2 The test portion shall be kept in a suitable environment, so that it does not spoil or become contaminated, and shall be tested within the stated period.

4.3.3 The test portion shall carry a clear unique identification.

5 Testing requirements

5.1 Basic requirement. The analytical steps laid down in the test method standard shall be followed, and protective measures shall be taken against the unsafe factors of the work (poisoning, explosion, corrosion, burns, static electricity and the like).

5.2.1.1 Weighing means a weighing operation carried out with a balance; measuring out means the quantitative taking of a liquid with a measuring cylinder, a measuring cup, a bottle-top dispenser and the like; pipetting means the taking of a liquid with a one-mark pipette, a graduated pipette, a pipettor and the like.

5.2.1.2 When weighing, measuring out or pipetting, the precision of the mass or volume shall meet the requirements of the test method standard.

5.2.1.3 The accuracy required of a weighing is expressed by the number of significant figures. Weigh out 5.0 g means weighing accurately to between 4.95 g and 5.05 g; weigh out 5 g (to the nearest 0.01 g) means a weighing precision of +/- 0.01 g, the weighed amount preferably being kept between 4.50 g and 5.50 g; weigh out accurately means a weighing operation carried out on a balance with a precision of 0.0001 g; where the amount to be weighed is given as about so much, the amount weighed shall not depart from the stated amount by more than +/- 10 per cent.

5.2.2 Making up to volume. The operation of diluting the solution in a vessel up to the graduation mark when a solution of a given concentration is prepared in a volumetric flask or similar vessel.

5.2.3 Spiking. For the internal standard method or for a recovery test, the spike shall be added after the test portion has been taken and before the extraction solvent is added; after spiking, the portion should be left to stand for a time under suitable conditions before extraction.

5.2.4 Constant mass. When an operation to constant mass is carried out under the conditions laid down in the standard, the difference between the masses weighed after two successive drying or ignition operations shall not exceed the range laid down in the test method standard. Where the test method standard gives no clear provision, the difference between the masses weighed after two successive drying or ignition operations shall not exceed +/- 1.0 mg. The last weighed value is the one used in the calculation.

5.2.5 Distillation. For target analytes with a high boiling point or that are thermally unstable, vacuum distillation or steam distillation should be used. Before distillation, the tightness of the system shall be checked, so that the target analyte is not lost during distillation and so that no safety incident arises from escaping distillate. The liquid in the distillation flask shall not exceed two thirds of its capacity and should not be less than one third. The heating temperature shall be slightly above the boiling point of the target analyte. The condensing system and the receiving system shall match the distillation rate. When distillation is finished, heating shall be stopped first and, once the system has come down to about room temperature, the condensing system shall be stopped.

5.2.6.1 Where the target analyte is present in the test portion wholly or partly in bound or conjugated form, a hydrolysis step is needed to release it before extraction or clean-up. The hydrolysing agents commonly used include acids, alkalis and enzyme preparations.

5.2.6.2 In hydrolysis, note that different kinds of test portion may consume different amounts of hydrolysing agent; the amount of hydrolysing agent shall be suitably in excess, the effect of the sample matrix shall be taken fully into account and the hydrolysis conditions strictly controlled, so that hydrolysis is complete.

5.2.7 Carbonization. Where the test portion has to be carbonized, this may be done on an electric furnace or a hotplate. During carbonization an open flame shall be avoided, so that fine ash particles are not carried away by the air current and the target analyte lost.

5.2.8 Ashing. Test portions that have to be ashed shall generally be ashed at the temperature required for the element to be determined, until the ash is a white or greyish-white loose granulate or powder; the ashing time may be extended where necessary.

5.2.9 Digestion. Digestion shall follow the provisions of the test method standard, with strict control of the amount of digestion reagent, the digestion temperature, the digestion pressure and the digestion time. Note that different kinds of test portion may need different digestion conditions; test portions that differ widely in nature should not be digested in the same batch.

5.2.10.1 Extraction should be carried out two to three times to assure the extraction efficiency, and more times where necessary; the volume of extraction solvent should be not less than the volume of the sample.

5.2.10.2 During extraction, unintended loss of the target analyte through emulsification and the like shall be avoided.

5.2.11 Clean-up. During liquid-liquid extraction clean-up, unintended change in the target analyte through emulsification and the like shall be avoided. Where commercial solid-phase extraction cartridges, dispersive matrix materials and the like are used for clean-up, the clean-up material shall be the same as, or equivalent to, the one laid down in the test method standard, and shall be conditioned before loading where necessary.

5.2.12 Derivatization. In derivatization, note that different kinds of test portion may consume different amounts of derivatizing reagent; the amount of reagent shall be suitably in excess, the reaction time shall be long enough, and the effect of the sample matrix shall be taken fully into account.

5.2.13.1 Concentration shall avoid taking the residue to dryness, too high a temperature and too long a time, all of which affect the stability of the target analyte adversely.

5.2.13.2 Where several test solutions are concentrated at the same time, cross-contamination shall be avoided.

5.2.13.3 In vacuum concentration the pressure shall be controlled carefully, so as to avoid bumping.

5.2.13.4 For target analytes that are highly volatile, a keeper may be added to reduce their loss during concentration.

5.2.14 Reconstitution. When the concentrated residue is redissolved, a reconstitution solvent of the same composition as the standard working solution should be chosen, so that the measurement system stays consistent.

5.3.1 Before testing, the state of the instrument shall be adjusted in accordance with the test method standard so that its performance meets the requirements of the test.

5.3.2 The measurement conditions for the test solution should be the same as for the standard solution, and the qualitative or quantitative measurement shall follow the test method standard.

5.3.3 Where a single-point calibration is used, the concentration of the target analyte in the test solution shall be close to that of the standard solution; where a calibration curve is used, the concentration of the target analyte in the test solution shall lie within the linear range.

5.3.4 Where the concentration of the test solution lies outside the linear range of the calibration curve and the test method standard gives no clear provision, the quantification should be repeated by weighing out a new portion, by preparing a new calibration curve, or by diluting the test solution, with method verification where necessary.

5.3.5 A solvent calibration curve should be the first choice for quantification. Where the method has a marked matrix effect that cannot be removed by clean-up or by internal standard quantification, a matrix-matched calibration curve or a matrix spiked calibration curve may be used, and the blank background value of the matrix shall be assessed, so as to avoid a bias caused by a blank matrix that does not match the sample matrix.

5.3.6 The concentration of the standard solution, the concentration of the isotope-labelled standard solution and the range of the calibration curve may be adjusted moderately according to the actual testing need. For the internal standard method, the internal standard concentration in the standard solution should be the same as that in the test solution. Method verification shall be carried out where necessary.

5.3.7 During measurement, the stability of the test equipment shall be monitored as necessary.

5.4.1 A blank test means a run of the same batch using exactly the same analytical steps, reagents and amounts (apart from the amount of standard titration solution in a titration), but without the test portion.

5.4.2 The result of the blank test is used chiefly to subtract the background or to check whether contamination has occurred during the test.

5.4.3 Subtraction of the reagent blank is limited to subtracting the background content of the target analyte unavoidably introduced by the reagents or during the test.

5.5.1 When samples are tested, suitable quality control methods such as duplicate samples, spike recovery, blind sample testing and control charts shall be used to monitor the validity of the results.

5.5.2 At least one quality control method shall be chosen for each test batch.

5.5.3 Where the quality control result does not meet the expected requirement, the test results of that batch are void.

6 Expression of test results

6.1 The calculation of the measured value and the significant figures shall follow the rules for rounding of numerical values.

6.2 The number of decimal places or of significant figures kept in the test result shall meet the relevant provisions of the test method standard.

6.3 The unit of the measured value of the sample shall be a statutory unit of measurement; the expression of quantities and units is given in Annex C.

6.4 Where the analytical result is expressed as not detected, the value of the detection limit shall be stated.

7 Requirements for raw test records

The laboratory shall record the key data of the testing process together with information on the test method, the equipment and the environment; electronic records and paper records are equally valid. The main content of the record includes, but is not limited to: a) the test method used and, where there are several optional methods or optional steps, a clear record of the method and the steps chosen; b) all the data generated during the test that enter into the calculation of the result, and the test result; c) information on the instruments and equipment closely connected with the metrological traceability of the result; d) the environmental conditions for which the test method has explicit or particular requirements; e) the quality control results.

8 Other requirements

8.1 Provisions in a test method standard marked as for reference, see, or informative annex may be followed as appropriate according to the circumstances of the test.

8.2 Where a relevant national food safety standard contains a special provision, that provision governs.

A Annex A (informative) Table of concentrations of common acids and alkalis

Table A.1 gives, for each commonly used acid or alkali reagent, its relative molecular mass, its content as a mass fraction in per cent, its relative density and its concentration in moles per litre. The values are: glacial acetic acid, 60.05, 99.5, 1.05, 17 (acetic acid); acetic acid, 60.05, 36, 1.04, 6.3 (acetic acid); formic acid, 46.02, 90, 1.20, 23 (formic acid); hydrochloric acid, 36.46, 36 to 38, about 1.18, 12 (hydrogen chloride); nitric acid, 63.02, 65 to 68, 1.39 to 1.40, 16 (nitric acid); perchloric acid, 100.5, 70, 1.67, 12 (perchloric acid); phosphoric acid, 98.00, 85, 1.70, 15 (phosphoric acid); sulfuric acid, 98.08, 96 to 98, about 1.84, 18 (sulfuric acid); ammonia solution, 17.03, 25 to 28, about 0.90, 15 (ammonia monohydrate).

B Annex B (informative) Preparation and use of common washing solutions

B.1 Potassium dichromate and sulfuric acid solution (100 g/L): weigh out 100 g of potassium dichromate (chemically pure) into a 1000 mL beaker, add 100 mL of water and warm gently to dissolve it. Cool the beaker in a water bath, then add sulfuric acid (chemically pure) slowly, stirring with a glass rod as it is added so that the acid does not splash out; a precipitate forms at first and dissolves again once a certain amount of acid has been added; add sulfuric acid until the total volume of the solution is 1000 mL. This washing solution is strongly oxidizing, but acts fairly slowly and has to be in direct contact with the vessel for several minutes to several hours to take effect; after the washed article has been taken out, rinse it thoroughly with tap water seven to ten times and finally rinse three times with pure water.

B.2 Soap washing solution, alkaline washing solution and synthetic detergent washing solution: made up to a given concentration, used chiefly for washing off fats and organic matter.

B.3 Potassium hydroxide and ethanol washing solution (100 g/L): take 100 g of potassium hydroxide, dissolve it in 50 mL of water and add ethanol to 1000 mL. This washing solution is suited to washing off greasy soiling, resins and the like.

B.4 Acidic oxalic acid or acidic hydroxylamine washing solution: weigh out 10 g of oxalic acid or 1 g of hydroxylamine hydrochloride and dissolve it in 10 mL of hydrochloric acid solution (1+4). This washing solution can remove oxidizing substances. For an oxidizing agent soiling a vessel, the acidic oxalic acid solution acts fairly slowly, while the acidic hydroxylamine solution acts quickly and cleans easily.

B.5 Nitric acid washing solution: commonly used at a volume ratio of (1+9) or (1+4), chiefly for soaking and cleaning the vessels used in the determination of metal ions. They are generally soaked overnight, then taken out, rinsed with tap water and rinsed again with deionized water.

B.6 Detergent for washing machines: it combines several cleaning mechanisms, such as dissolving power, solubilization, wetting and emulsification, hydrolysis and oxidation, and it shall have good material compatibility, low foaming, easy rinsing and sound environmental behaviour.

B.7 Vessels that have been washed shall be kept from being contaminated again.

C Annex C (informative) Common quantities, units and their symbols

Table C.1 lists the quantities commonly used in physical and chemical testing, the symbol of each quantity and the names and symbols of the units in which it is expressed. The entries are: the dependent variable X, whose unit depends on the test objective; mass m, in kilograms, grams, milligrams, micrograms and nanograms; amount of substance n, in moles, millimoles and micromoles; volume V, in litres, millilitres, microlitres and nanolitres; mass fraction w, in grams per 100 grams, grams per kilogram, milligrams per kilogram and micrograms per kilogram; mass concentration rho, in grams per litre, milligrams per litre and micrograms per litre; molar concentration c, in moles per litre, millimoles per litre and micromoles per litre; length l, width b, height h and thickness delta, each in metres, decimetres, centimetres and millimetres; area A, in square metres, square decimetres, square centimetres and square millimetres; time t, in days, hours, minutes and seconds; relative density d, dimensionless; energy E, in kilojoules, joules and electronvolts; pressure P, in atmospheres, torr, millimetres of mercury and pascals; temperature T, in degrees Celsius and kelvins; relative molecular mass Mr, dimensionless; voltage V, in volts; wavelength lambda, in nanometres; centrifugal force F, as a multiple of the acceleration due to gravity; and rotational speed n, in revolutions per minute.