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Producers of QCMs, where transportation is a necessary component of the supply chain such as between differently located laboratory parts or for proficiency testing schemes, are expected to be familiar with and conform to the requirements of ISO Guides 34 and The layout and structure of this Guide provides general information on the production of QCMs in the main chapters, with specific case studies in the annex. It is expected that the in-house QCM producer will have some knowledge of the type of material to be prepared and be aware of any potential problems due to matrix effects, contamination, etc.
For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document including any amendments applies. NOTE 2 Properties can be quantitative or qualitative e. NOTE 3 Uses may include the calibration of a measurement system, assessment of a measurement procedure, assigning values to other materials, and quality control. Uncertainties for such attributes may be expressed as probabilities.
NOTE 2 In batch certifications, the characterization refers to the property values of the batch. It is not intended to define a new class of reference materials. All quality control materials should meet the requirements of the definition for a reference material 3. QCMs cannot be used to establish metrological traceability of a measurement result.
QCMs should always comply with the basic requirements of any reference material, i. The QCM should be stable for a period of time that is at least as long as that during which it is intended to be used. CRMs produced according to the principles of ISO Guide 34 are essential to establish the concept of metrological traceability in a meaningful manner, and provide the highest standard with respect to reference materials.
There is no requirement for QCMs to have metrologically traceable assigned values; consequently, QCMs should not be used to establish metrological traceability or to estimate uncertainty.
For method validation and uncertainty estimation, QCMs may be used to a limited extent e. When confirming that a measurement process is under statistical control, the acceptability of laboratory performance is generally assessed by comparing either the standard deviation or the range in the individual results for the QCM against a pre-established criterion. If a lack of control of the measurement process is identified, the laboratory in general takes action.
A more in-depth discussion of the uses of quality control materials can be found in ISO Guide 33. Regardless of the intended use, it is necessary to assess homogeneity and stability of a QCM. In general, more pragmatic and less rigorous protocols can be used for stability and homogeneity steps to strike a balance between material development costs on the one hand and the intended use of the material on the other.
The key steps involved in the in-house production of a typical QCM are summarized in the flow chart in Figure 1 and are described in more detail in References  and . The chart also indicates which steps should be carried out in-house, i.
The scope and applicability of a matrix reference material is an important consideration for both the production and use of all reference materials. The matrix of the QCM should be as similar as possible to the matrix of the routine test samples, so that a satisfactory result for the QCM is genuinely indicative of satisfactory results for the test samples.
For example, a freeze-dried food matrix may behave differently during analysis to a similar foodstuff with higher moisture content. The importance of commutability in clinical chemistry has been described.
When commutability of a reference material has not been established the results from different methods cannot be compared with the assigned value to determine whether a bias exists due to measuring actually different analytes.
The properties of the QCM should be as similar as possible to those expected in the test samples. This may require some preliminary screening measurements to be carried out on a number of candidate materials, to enable the most appropriate to be selected. When preparing a QCM, the size of individual units should be based on the likely use, i.
The preparation of the bulk material is an important area that has significant cost implications for the production of QCMs.
It follows that to produce reference materials more cost-effectively the inherent preparation methods need to be as simple and straightforward as possible.
The exact preparation procedures required for a particular QCM will depend on the nature of the matrix and the properties of interest. In general, liquid matrix QCMs are much easier to produce than their solid counterparts.
The main reason for this is that homogeneous liquids can easily be achieved even with fairly rudimentary equipment e. A liquid is easily spiked, filtered or mixed with additives and stabilizers. The corresponding processes for solid materials, milling, grinding, mixing and sieving are much more difficult to accomplish homogeneously, especially for quantities greater than 20 kg. These techniques require a significant investment in major capital equipment when large-scale production is envisaged.
However, some laboratories using QCMs requiring such techniques may have access to appropriate facilities. During preparation of both liquid and solid materials it is important to prevent contamination by substances which can potentially interfere with the intended measurement process e.
Hence, all bottles, vials or flasks to be used for final containment must be carefully cleaned and dried before filling to remove possible contaminants.
Some of the more common processes are described in the following subclauses. Drying of soils and similar matrices may be carried out at ambient or elevated temperature, depending on the properties of interest, since the more volatile components may be partly lost at higher temperatures. Water removal also reduces the likelihood of microbial growth formation, which is a particular problem with biological materials.
Freeze-drying is a technique which is useful with temperature sensitive properties or matrices. For large bulk quantities these processes are slow and can easily take several days to accomplish. Care should be taken not to introduce contamination from the apparatus during the grinding process. The health and safety aspects of grinding large quantities of particulate matter, which may have toxic components, should also be considered.
Particulate materials such as soils, ores, ashes and ground biological materials are passed through a standard sieve to remove large particles that are above a prescribed diameter.
Sieving however changes the matrix composition. If a large fraction is removed by sieving, the analyte concentration may change and the sample may also change in comparison to the composition of regular test samples. Such mixing is carried out after milling, grinding and sieving. Blending of two or more materials with sufficiently similar matrix compositions and differing property values may enable the production of QCMs with a desired property values, a set of similar QCMs covering a range of property values, or the production of QCMs from an existing reference material.
In order to obtain homogeneous mixtures, the materials to be mixed should have similar densities and particle size distributions. Qualification of the filter is critical to avoiding loss of active ingredients. Metals, for example, can precipitate out of neutral or alkaline solutions because of hydrolysis or oxidation and adjustment of the pH of the solution to below 2 counteracts this problem.
Different materials may require other approaches such as addition of antioxidants, preservatives, texture stabilisers, etc. Furthermore, they may contain spores that cause fungal moulds to develop on storage, which could initiate changes in either the composition of the bulk material or the individual units. Such organisms need to be destroyed before the final units are prepared and packaged. Autoclaving is an inexpensive and convenient means of sterilization that is employed for materials, which are temperature resistant.
Autoclaving would normally be done on the bulk material prior to final homogenization and unit preparation. Irradiation can be used on the final packaged units e. Gamma irradiation is a convenient means of sterilization at ambient temperature so changes in matrix composition are less likely than with autoclaving. Dose values need to be determined such that they are effective in removing pathogens but do not adversely affect the material by, for example, raising the temperature to unacceptable value e.
However, gamma irradiation is beyond the means of most laboratories and so an outside contractor should be employed. It is important to consider the impact of any sterilization process on the material, particularly those which degrade at elevated temperatures. The following subclauses describe some of the key considerations for the sub-division process and choice of containers to ensure the QCM is sufficiently homogeneous and stable for its intended purpose.
If unsuitable containers are used, a material may quickly become degraded to the extent that time-consuming and expensive sourcing and preparation work on the bulk material may have to be repeated. The type of container used depends on the inherent stability of the material and the length of time it is required to remain stable. For particularly susceptible materials, two forms of containment e. The following examples serve to illustrate the need for careful consideration of the container and its closure.
Sealed cans, foil pouches or septum-lined crimp-top vials offer more security provided they are correctly closed. High-density polyethylene HDPE bottles with screw-caps are more suitable from the latter point of view, but themselves have the potential problem of loss of water by evaporation through the bottle walls.
This can be minimized by storage in a refrigerator rather than at ambient temperature or by the use of fluorinetreated polyethylene bottles. For example, the iron content of canned foodstuff QCMs may be subject to unpredictable increases on a can-by-can basis, as iron leaches from the can wall into the food matrix.
Bottles whether glass or HDPE containing aqueous acid solutions may also give rise to leaching problems. As a general rule, containers that might interact with the QCM should be carefully evaluated before use by suitable leaching trials. Amber glass gives additional protection against degradation induced by light.
Vials and ampoules should preferably be amber to reduce the impact of light. Some preliminary experimental work, including blank studies, may be required to identify the most suitable container type to use for a particular QCM. The effect of repeated opening and closing of the sample containers may also be assessed if repeated use of the material is anticipated.
Tamper evident closures should be considered if the unit should only be used once. That is, the sub-division process itself, or the time taken to complete the sub-division of a bulk material, should not re-introduce heterogeneity into the material.
This may conceivably occur in a number of ways. Matrices comprising mixtures of liquids of differing volatilities e. Effects of this sort may be minimized by protecting the bulk material from evaporation and by completing the sub-division in as short a time as is consistent with accurate dispensing.
All liquids and solutions should be stirred continuously while individual aliquots are being dispensed.
Consider filtering solutions before dispensing commences if particulates are likely to be present to an extent that could affect the properties of interest. Care should be taken with solid particulate matrices such as soils, sediments, industrial products, etc. Special care should be taken when sampling bulk material from a large drum, to ensure that there is no vertical segregation.
Riffling is a process for representatively subdividing free-flowing powdered materials so that each aliquot receives similar particulate fractions. When operated effectively, riffling minimizes flow segregation and produces units with low between unit variation. Commercial riffling devices are available which can be used to sub-divide such materials without introducing heterogeneity. In food matrices with a high fat content e. As a general principle, sub-division of a bulk material should be completed as quickly as possible to minimize the opportunities for the matrix to revert to heterogeneity.
Where appropriate, steps should be taken to maintain a homogeneous bulk material during the sub-division process. The required level of homogeneity of a QCM is dependent on an understanding of the expected variation of and the amount of sample used in the measurement process under investigation see 7.
In all cases, the level of inhomogeneity should result in a smaller effect on the measurement result than the expected variation of the measurement process or should be below an established criterion value. Once a candidate QCM has been sub-divided into individual aliquots it is important to establish whether there are any variations in its property values between aliquots.
For certain QCM matrices, such as true solutions which have been prepared by procedures such as filtration to remove particulates and thorough mixing, formal homogeneity testing is, in principle, not necessary. Such materials may be formally regarded as being intrinsically homogeneous.
Nevertheless, because of the risk for contamination e. For more complex matrices such as foodstuffs, soils and solid matrices that are inherently heterogeneous, a formal experimental investigation of homogeneity is required. A sufficient number of units, representative of the entire batch of the QCM should be chosen and analysed for selected properties ISO Guide 34. In certain instances, one property can be chosen to represent and quantify the homogeneity of several properties of a similar general type.
This should be based on scientific evidence or on previous experience that certain properties exhibit similar behaviour  or are known to have strong tendency to homogeneous distribution in sample e.
A statistical evaluation of the data is carried out, which entails calculating the observed standard deviation So for the results and the standard deviation due to the analytical method Sa. By subtracting the analytical variation from the observed variation a value for the actual between-unit variation is obtained.
Where the calculated between unit variation is smaller than the analytical variation, the latter is adopted as representing the maximum between unit variation that could be present, but is not detectable because of the precision of the analytical method used to assess homogeneity.
The value adopted as the between unit variation expressed as a standard deviation Sb is used to calculate the contribution any possible heterogeneity makes to the uncertainty of the property value. Homogeneity has two aspects, between-unit homogeneity and within-unit homogeneity. Within-unit homogeneity is reflected in the minimum size of subsample that is representative for the whole unit. It should be confirmed that sample sizes typically used in the day-to-day analysis are larger or at least equal to this size.
Between-unit homogeneity reflects the variation of the average level of the measurand in each unit of the material. This should be tested on the optimum sample size of the method, regardless of the sample size used in day-to-day analysis. For example, between-unit homogeneity can be established using sample intakes of 1 g whereas mg are used in daily practice 9.
The selected units should be representative of the entire production batch and the number of units is dictated by the total number of units produced. For a stock of to 1 units this equates to between 27 and 30 units to be analysed in duplicate. This represents a considerable analytical effort which will be time-consuming and expensive. A study of the impact of reducing the number of units selected for homogeneity assessment of a QCM concluded that in certain circumstances 10 units analysed in duplicate were sufficient.
For the production of a QCM therefore, there may be scope for cost savings by reducing the number of units selected for homogeneity testing, although this should be assessed on a case by case basis. ISO Guide 35 acknowledges the fact that, in some circumstances, it may not be feasible technically or economically to determine the homogeneity of all properties of interest.
Where only selected properties are assessed for homogeneity, these must be representative of the other properties of interest e. The following represents a suitable approach for homogeneity assessment.
The number of samples included in the homogeneity check may be reduced if suitable data are available from previous homogeneity checks on similar samples prepared by the same procedures. The measurements should be carried out in such that measurement drift can be distinguished from any trend in the batch of samples. This can be achieved by measuring the replicates in randomized order or by reversing the order of the replicates.
In principle, homogeneity testing could be dispensed for such materials, which may be considered to be intrinsically homogeneous. However, the process of sub-dividing may introduce heterogeneity such that although the within unit heterogeneity is small, the between unit heterogeneity i. Concentration differences may also result from pumps and transfer lines to the final sample containers even though the bulk material is highly homogeneous, therefore checks for concentration changes in the fill-order and for contamination should always be made.
Adapting example B. In order to achieve this effectively an indication of the property values of the QCM used to monitor the process is needed. It is also necessary to have an indication of the likely variation in values due to heterogeneity between different aliquots. An effective way of determining an indicative property value is to use of the overall mean derived from the homogeneity study.
The range within which the property values may reasonably be expected to lie can be estimated by the deviation from this overall mean value.
This deviation from the mean can be used to establish control chart warning limits. Conventionally, warning and action limits also described as lower and upper action limits are established at twice and three times the standard deviation of the mean respectively. In principle, the approaches described in ISO Guides 34 and 35 apply for stability testing.
However, if the material is not to be transported beyond the confines in which it was prepared, no short term tests for degradation need to be performed. For stability during storage, stability assessment of all properties of the material can be both costly and time-consuming and may not be necessary if sufficient checks are in place to distinguish between an out of specification result due to a faulty test sample, measurement instrument drift or QCM degradation.
However, those responsible for QCM preparation have to be aware of the trade-off between costs for stability testing and the costs incurred by investigating a method drift, which is in reality caused by degradation of material.
It should be pointed out that as QCMs are made for repeated use, investigation of the stability of opened units may be particularly useful. Adequate stability of QCMs is required; so that users can be confident they will not undergo any significant change affecting the property value s during the period of its intended use.
It is likely that for many QCMs, stability for at least several months is required. Careful choice of the container used for the material can address some intrinsic stability issues e. Some materials e. It is likely that the laboratory will have previous experience of the stability of the types of matrix and property values it is preparing as QCMs, or there may be well established background information from similar materials.
Possible actions include use of freshly prepared calibrants, comparison with certified reference materials and frequent sensitivity checks to confirm any deviations or trends in the QCM results. More information can be found in ISO standards on control charts e. Should a formal assessment of stability be deemed necessary, the principles of ISO Guide 35 should be followed.
An example of this approach is given in Annex F Case study 6. The assignment of a formal expiry date is one of the most problematic tasks in reference material production.
It involves making a prediction of the future behavior of a material based on an extrapolation of its past behavior. Any stated expiry date for a QCM should be based upon previous experience of the stability of the types of matrix and property values and any background information.
The stated expiry date should not be regarded as absolute and the analyst using the QCM should follow laboratory procedures in the event of a QCM giving an unexpected result see However, it is recognized that some materials are intrinsically stable and their property values will not be adversely impacted by transportation controlled or otherwise.
Should there be a requirement to transport the material and there is any concern about its stability, a stability assessment following the principles of ISO Guide 35 should be carried out. ISO Guide 31 provides details of the requirements of the contents of certificates and labels for reference materials.
Generally, this entails ensuring that the individual containers are securely closed and are stored away from extremes of heat, light and humidity. Storage in dark conditions at the appropriate temperature e. These instructions should include details on how the material should be stored and handled, including specific instructions for sub-sampling and moisture correction. The minimum sample intake is the smallest sub-sample that is still representative of the whole unit for the target property value.
Frequently, this is estimated as the minimum sample intake from the sub-samples that have been used in the assessment of the homogeneity of the material. The intake stated is therefore a conservative estimate and not the absolute minimum. Nevertheless, users who encounter problems when analysing reference materials should take care that the amount of sub-sample used is above the minimum sample intake. It is therefore important that aliquots are adequately mixed before a new sub-sample is withdrawn.
This can often be achieved by simple shaking of the units. Guidance on uses of such materials is not included in this Guide. The layout and structure of this Guide provides general information on the preparation of QCMs in the main chapters, with specific case studies covering a range of sectors in the annexes. The case studies are not complete "process manuals" but are included to highlight some of the key considerations when preparing QCMs.
The case studies vary in complexity and detail, including sector specific terminology, but provide a range of information for laboratory staff to draw from. It is expected that those involved in QCM preparation will have some knowledge of the type of material to be prepared and be aware of any potential problems due to matrix effects, contamination, etc. Check out our FAQs. ICS 71 This standard was last reviewed and confirmed in Therefore this version remains current. Abstract Preview. General information.
CHF Buy. Buy this standard. Life cycle Now Published. Final text received or FDIS registered for formal approval.
|Call of duty warzone apk + obb download for android||The matrix of the QCM should be as similar as possible to the rownload of the routine test samples, so that a satisfactory result for the QCM is genuinely indicative of satisfactory results for the test samples. Your comments on this draft are invited and will assist in the preparation of the consequent standard. Different materials may require other approaches such as addition of antioxidants, preservatives, texture stabilisers, etc. This Guide provides some general information on read more production of QCMs which is complemented with a number of specific case studies. Adobe acrobat pdf maker free download would normally be guixe on the bulk material prior to final homogenization and unit preparation.|
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