4.3 Measurement Traceability Over Time
47
by competent and reliable producers, acting in agreement with the requirements of
ISO 17034. Regarding traceability over time, this means that the producer must periodically determine the value of the certified property, and in case any changes occur
must immediately notify its customers or laboratories.
4.4 Compliance with the Requirements of the Reference
Material
An ideal RM (standard) is one that is identical in terms of physical properties and
chemical composition to the test object. Hence it is extremely important that the
producer of an RM specifies as much information as possible in the certificate of
material. Among the important information is the homogeneity of the substance. In
the case of powder materials, the producer should specify the portion of minimum
weighed that provides retaing of certified value. For occlusive matter, used in direct
measurements, without carrying out the sample to a solution, the producer should
provide information about the homogeneity of distribution of the compounds of interest on the surface. Interestingly, some solids that are considered homogeneous when
using a relatively robust measurement technique (e.g., X-Ray Fluorescence; XRF)
do not provide the required homogeneity in the application of measurement techniques with higher surface resolution (Laser Ablation Inductively Coupled Plasma
Mass Spectrometry; LA-ICP-MS:). This applies, among others, to the standard of
various alloys recognized for a long time as homogenous. When using those standards for LA-ICP-MS, the level of homogeneity is no longer sufficient. The situation
is similar to the standards of glass, which are commonly used in the examination
of the glass composition with the XRF technique. When carrying out measurements
using microsampling by laser ablation characterized by a significantly higher surface
resolution, these standards do not guarantee the required homogeneity.
4.5 Metrological Traceability in Practice
Assume that the aim is to determine the total iron content in the sample of dried
leaves of peppermint. The analytical procedure used in the laboratory comprises the
following steps:
– After pre-drying leaves in air conditions and subsequent grinding, weigh approximately 5 g of powder;
– Then dry the sample at a temperature of about 85 °C to a constant weight, so as to
remove moisture;
– After drying, weigh accurately on an analytical balance three parallel sub-samples
of about 1 g each;
47
by competent and reliable producers, acting in agreement with the requirements of
ISO 17034. Regarding traceability over time, this means that the producer must periodically determine the value of the certified property, and in case any changes occur
must immediately notify its customers or laboratories.
4.4 Compliance with the Requirements of the Reference
Material
An ideal RM (standard) is one that is identical in terms of physical properties and
chemical composition to the test object. Hence it is extremely important that the
producer of an RM specifies as much information as possible in the certificate of
material. Among the important information is the homogeneity of the substance. In
the case of powder materials, the producer should specify the portion of minimum
weighed that provides retaing of certified value. For occlusive matter, used in direct
measurements, without carrying out the sample to a solution, the producer should
provide information about the homogeneity of distribution of the compounds of interest on the surface. Interestingly, some solids that are considered homogeneous when
using a relatively robust measurement technique (e.g., X-Ray Fluorescence; XRF)
do not provide the required homogeneity in the application of measurement techniques with higher surface resolution (Laser Ablation Inductively Coupled Plasma
Mass Spectrometry; LA-ICP-MS:). This applies, among others, to the standard of
various alloys recognized for a long time as homogenous. When using those standards for LA-ICP-MS, the level of homogeneity is no longer sufficient. The situation
is similar to the standards of glass, which are commonly used in the examination
of the glass composition with the XRF technique. When carrying out measurements
using microsampling by laser ablation characterized by a significantly higher surface
resolution, these standards do not guarantee the required homogeneity.
4.5 Metrological Traceability in Practice
Assume that the aim is to determine the total iron content in the sample of dried
leaves of peppermint. The analytical procedure used in the laboratory comprises the
following steps:
– After pre-drying leaves in air conditions and subsequent grinding, weigh approximately 5 g of powder;
– Then dry the sample at a temperature of about 85 °C to a constant weight, so as to
remove moisture;
– After drying, weigh accurately on an analytical balance three parallel sub-samples
of about 1 g each;