C30J_RS_Topic_1_Samples_and_Sampling - Topic 1: Samples and...

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Sampling Objective : to take from an object (the population) an amount of material (the sample) that can be analysed in a “laboratory” in such a way that the analytical result for the sample is of such quality that it represents the concentration of the analyte in the object. Topic 1: Samples and Sampling. What is the “object”? A compound prepared in the lab. – be sure it is the product and not the product and some reactant? Product with a boiling chip? Ketchup made in a factory. – within one factory shift? The whole day’s production? The production from one batch of ingredients? Bauxite to be processed. – From one pit? Feed to the processing plant (from several pits)? From the total deposit (all pits in the approved mining area)? Pesticides in fish. – the whole fish, the intestines, the flesh? Nutrients in coastal waters – avoid areas where rivers or other fresh waters are mixing with the marine waters. Must clearly define the goal of the study and therefore the “object” that is the focus of that study. If you don’t define the object carefully the sampling cannot be correct. If the sampling is wrong then the analyses are a waste of time and money.
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Solids
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Liquids
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Gases
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Sampling Objective : to take from an object (the population) an amount of material (the sample) that can be analysed in a “laboratory” in such a way that the analytical result for the sample is of such quality that it represents the concentration of the analyte in the object. object homogeneous heterogeneous Static dynamic discontinuous eg: well mixed gases, liquids or solutions, pure metals. eg: ores in soils or rocks. minimal change with time. Consistently changing with time: eg: reactive solutions or gases; settling suspensions. Change temporally and/or spatially in undefined ways – eg: plumes Samples a) Pure substances b) “Complex” mixtures continuous
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Sampling for analyses. object Composite via spacial and/or temporal increments Discrete sample(s) analyses Gross sample(s) storage Parts of the object Representative part of the object Quality control samples Representative parts of the sample. Sub-samples Related samples •co-located (replicates) Spiked in field •Field blanks/control site sample(s) Laboratory sub-samples •duplicates spiked •blanks •{RMs} (x ± y)units The analytical result(s) can only be as good as the sample(s) collected. Vogel Chapter 5; Kebbekus and Mitra Chapter 2.
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ISO 17025 5.7 – Sampling. 5.7.1. “The laboratory shall have a sampling plan and procedures for sampling …”. “The sampling plan and sampling procedure shall be available at the location …” … “ Sampling plans shall, whenever reasonable , be based on appropriate statistical methods.” “The sampling plan shall address the factors to be controlled to ensure the validity of … results.” Sampling Protocols 5.7.3. “The laboratory shall have procedures for recording relevant data and operations relevant to sampling …(sampling procedure used, sampler
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This note was uploaded on 02/23/2011 for the course CHEMISTRY C30J taught by Professor Vaugnrattray during the Spring '11 term at University of the West Indies at Mona.

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C30J_RS_Topic_1_Samples_and_Sampling - Topic 1: Samples and...

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