TEST METHOD: Preparing to analyse
Revised: 3 July 2007 (pretests, dilutions & calibrations expanded)
Best practice in analysis begins with appropriate analytical preparation.
TASK SAFETY REQUIREMENTS
Delta dress code applies
SPECIFIC JOB STEPS
Unpack container of samples and look for analysis request, chains of custody or other documentation.
Make a note of client details and special instructions, including information on return of sampling containers, eskies, ice packs, chains of custody, preferred testing methods etc.
Make a note of which tests are required and the quantity of the sample.
Is there enough sample to conduct all tests separately? If not, are there some tests that can be run sequentially on samples without affecting later tests? For example, SG and temperature may be read with a hydrometer and thermometer prior to other tests. Be aware that reading pH with a meter should be conducted AFTER other tests such as EC and SG, as the reference electrode in the meter contains KCl.
What analytical equipment will you need? If you need an oven, spectrophotometer or scales, these require warming up. Turn them on now.
Lay out a page in the lab notebook. Record details above and list the tests in the order you will conduct them.
Consider the samples. What do you know about them? Do you know enough about the sample matrix to determine the dilutions required to prevent interferences from affecting the method you plan to use? If not, what tests will you need to conduct to determine the level of interferences? You may need to analyse first for the interference you suspect, take an EC/pH reading, and/or run the samples along with some matrix spikes.
If a hydrometer reading suggests a water sample is saline, consider the source of the water. An indication of the likely ionic composition of seawater-derived brines may be obtained from the tables in Baseggio's "The Composition of Seawater and its Concentrates" Similar concentrations are frequently found in Australian underground waters, which are often marine-derived. When you receive brines of unknown composition, check whether there are any 'typical analyses' available for the material, either from the client or from government agencies. In South Australia PIRSA and DLWBC have online databases that contain information from groundwater bores across the state.
Using the methods you have available, will any dilutions be small enough to still provide a useful minimum practical quantation level? You may need to utilose a quick 'dip test' such as the Merck phosphate strips to characterise the sample, allowing you to estimate appropriate dilutions. Reference tables with typical wastewater characteristics can be found on the bookcase. Use these to assist you in estimating the range of less common analytes.
When doing titrations, use the information obtained from your consideration of the samples to determine what sample size you need to test and what approximate volume of titre and size of burette will be appropriate for the sample.
Determine if the samples need additional preparation before they can be tested (eg water or acid extraction for soils, and digestions for some water parameters).
Get out the test method documentation (including any extraction/digestion processes) and become familiar with all its requirements. Read it right through and consider what you will need to do in each step.
Lay out the equipment and reagents for the first analysis.
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