Sample Submission Protocol ICP Analysis The Spectro CIROS7 inductively coupled argon plasma–optical emission spectrometer (ICP‐OES) is a direct‐reading emission system which uses a radio‐frequency generated plasma as an emission source for elemental analysis. Elements in solution are simultaneously analyzed through a series of charge‐coupled device detectors that are arrayed on a Rowland circle in a Pashen‐Runge optics system. The principles familiar to atomic absorption/emission spectrophotometry (AAS) operation are applicable to the ICP, the main differences being the emission source and the multi‐element integrations are obtained through a computer processor. The ICP is an excellent analytical tool for elemental analysis, not only because of simultaneous data acquisition, greatly shortening the time required for thorough sample analysis, but also due to amplified linear range and sensitivity. The argon plasma has higher temperature than even the hottest flame (~10,000 K) and creates a non‐reactive environment for close to complete excitation of atoms with little interference. The plasma is also viewed end‐on (axial), which provides for method detection limits that can approach those obtained by graphite furnace AAS (Appendix II). Analytical ICP services are available for University and Experiment Station personnel and to any requestors outside these institutions with proper approval. An ICP Analysis Request form can be obtained from either the ICP supervisor (Dr. Essington, Rm. 213 Biosystems Engineering & Environmental Science) or the ICP operator (Melanie Stewart, Rm. 340 or 314 Ellington Plant Science Building). This form must be completed and submitted to Dr. Essington or Ms. Stewart before samples will be accepted for analysis. After a request for services has been received and analyses scheduled, samples may be submitted to the Soil Chemistry lab (Rm 314, Ellington Plant Science Building) for analysis. The operator will process the samples and the analytical data will be returned to the requestor through the ICP operator. This bulletin outlines complete procedures for requesting services and preparing and submitting samples. This bulletin also details what to expect from the ICP analytical service team. Summary of Sample Submission and Analysis Protocol 1.
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Contact the ICP supervisor or operator to arrange for analysis and obtain an ICP Analysis Request form. The following information will be needed: a.
Number of samples b.
Elements of interest and their anticipated concentrations c.
Sample matrix composition d.
Sample submission date e.
Project title and account number Submit complete ICP Analysis Request form to the ICP supervisor or operator and confirm scheduling for ICP analysis with the ICP operator. 1
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Submit samples and matrix (300 mL per 100 samples) to Rm. 314 on the scheduled submission date. Obtain analytical results from ICP operator. Sample Submission Protocol A. Requesting Service 1.
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Any member of the faculty/staff of the Institute of Agriculture can request service by contacting the ICP supervisor or operator. Other departments within the University system may also request service. However, such requests require an interdepartmental agreement cleared through the ICP supervisor. It is required that faculty/staff requesting ICP service meet with the ICP supervisor or operator to discuss ICP capabilities and sample characteristics. Information, such as sample matrix and salt content, elements of interest, anticipated elemental concentrations, and the number of samples is required by the ICP operator to facilitate analysis. An ICP Analysis Request form is available from the ICP supervisor or operator. This form must be completed by the requestor and submitted to the ICP supervisor or operator in advance of sample submission to facilitate scheduling and the ordering of supplies. When requesting analyses, the requestor is asked to provide the research project and supervisor name (if requestor is a student). A portion of the cost associated with ICP analysis is borne by the BESS Department (a portion of the operator time, instrument service contract). However, the cost of consumables (e.g., Argon gas, standards, and sample tubes) is borne by the requestor. The requestor may purchase the consumables directly, or an account number may be provided to the ICP operator. The ICP operator is responsible for communicating the material and supply needs to the requestor. B. Available Methods and Elements 1.
The ICP in the BESS Department is capable of simultaneously analyzing more than 30 elements in solution. Solids and solutions containing particulates will not be analyzed. There are a variety of extraction and digestion methods available to bring analytes into solution. The extraction/digestion method employed is ultimately dictated by the research objectives, elements of interest, and the sample preservation techniques used. The ICP lab has experience in analyzing several matrices (Appendix I). The ICP supervisor can also offer suggestions as to the appropriate extraction/digestion techniques and stabilization methods to employ. 2
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Sample cleanup and preparation (extraction/digestion, filtration) are normally not the responsibility of the ICP operator. It is strongly recommended that aqueous samples be filtered through 0.2 µm filter (or minimally a 0.45 µm filter) prior to submission. It is also strongly recommended that aqueous samples be stored at 4°C while awaiting analysis. DO NOT freeze or add chemical stabilizers, as these actions will result in the formation of sparingly soluble and microcrystalline precipitates (altering the chemical nature of the solution). Detection limits vary for each element analyzed and for each matrix. For some elements it may be desirable to use a more sensitive analytical technique (such as colorimetry for P, graphite furnace AAS for select metals, or hydride generation AAS for Hg, As, and Se), as dictated by the research project goals. Please refer to Appendix II for the ICP quantitative detection limits (method detection limits) for the elements. The linear response range for ICP is generally 100 times the standard concentration. However, excessive elemental concentrations cause problems. If requestor is interested in both major and trace elements in a single solution, it is strongly recommended that a full‐strength sample (for trace element analysis) and a diluted sample (for major element analysis) are submitted for each solution of interest. The analysis of samples by ICP takes time. Under optimal conditions, the length of time required for a submission will depend on several factors, including sample matrix, and the number of elements requested and their concentrations. Normally, sample throughput is approximately 80 to 100 samples per day. The ICP is a finely tuned analytical instrument that requires the simultaneous and unwavering operation of several interdependent systems. In order to maintain peak performance, down‐time is occasionally required for preventative maintenance. Invariably, individual systems fail. If instrument operation cannot be restored by the operator, via phone consultation with the manufacturer, a service visit will be scheduled. As per the instrument’s service contract, Spectro will respond to our request as soon as practicable. However, and under the best of conditions, instrument operation may not be restored for several weeks. So, if the analysis of samples is delayed, be patient! In general, routine maintenance results in approximately 5 days of instrument down‐time per month. C. Sample Submission 1.
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Samples are scheduled for analysis on a first come, first served basis. The ICP operator will be able to provide a general estimate of when the analyses will be completed. Samples must be in standard 17 x 100 mm culture tubes for placement in autosampler racks and should be submitted 24 h in advance of analysis. 3
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The condition of the samples is the responsibility of the requestor. Only liquids are analyzed. The solutions must be free of particulates. Samples that contain particulates will be returned to requestor for further clarification. The ICP cannot distinguish between elements that are truly dissolved and those that are particulate. If particulates are not removed before analysis, their elemental composition will skew the results. Make sure samples are in clean containers; specific information on the type of vials which fit autosampler racks is available upon request. The ICP lab does not normally provide containers. Good laboratory practices and statistically correct data acquisition require the requestor to submit at least one extractant blank, preferably a blank which has been carried through the extraction procedure. The volume of blank required is 300 mL per every 100 samples. As many blanks as deemed necessary to estimate background contamination may be run, although blank solutions are primarily used in making standards. EPA procedures also require spikes and standards to be carried through extracting procedures ‐ a standard agriculture soil sample is available from Rm. 314 if the requestor wishes to check a procedure. The ICP operator routinely analyzes a certified soil extract standard as part of the overall quality control/quality assurance program (QA/QC). However, it is strongly recommended that requestors submit blind blanks, spikes, and standards for further quality assurance. In general, the requestor should incorporate a QA/QC sample every 5 to 10 unknowns. The samples will be loaded onto autosampler racks in numerical order from lowest to highest. The numbering system generated by the ICP autosampler is simple, starting with "1" ‐ no custom numbering of samples is done. Therefore it is necessary for the requestor to keep track of sample identification, and to label the submitted samples as 1, 2, 3, 4, … n. Notes regarding sample loading will be kept by the ICP operator if it is determined that confusion may occur. During the analyses, the ICP operator may have concerns associated with ICP response that may require input from the requestor (e.g., elemental concentrations outside linear range or causing carryover problems). The requestor or other responsible individual should remain available to respond to the operator=s queries. Occasionally it may be necessary to dilute samples to bring elemental concentrations into the analytical range of the ICP. Generally, dilutions are the responsibility of the requestor. After analysis, the samples and containers used to transport the samples will be returned to requestor, unless otherwise directed. Do not dispose of samples until the analytical results have been reviewed and found to be acceptable; store them at 4°C. 4
D. Data Reporting 1.
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Data will be reported to the requestor when the analyses are completed and the ICP operator is confident of the quality. The length of time necessary to complete the analysis of submitted samples depends on a myriad of factors, including the number of samples in the queue before submission, the number of samples, the number of elements requested and the sample matrix, the need for dilutions, and a great many instrument intangibles. Requestor will receive the results in an Excel spreadsheet. Elemental concentrations in the submitted samples will be reported in units of mg L–1. This is the elemental concentration in the samples provided to the ICP operator. Any corrections, such as dilution factors or unit conversions (mg L–1 to mg kg–1), are the responsibility of the requestor. The ICP operator also retains an electronic copy of the data. Problems with the data are possible. The ICP operator inspects the quality control checks as samples are analyzed, and recalibrates the ICP and reruns samples as required. The ICP supervisor also inspects the data before distributing the results. However, it is the responsibility of the requestor to review the data and, if necessary, request a repeat analysis. It should be noted that rarely are the analytical results in error. Nearly all inconsistencies in reported data can be traced to improper sampling or handling (e.g., drying soil samples in an oven prior to extraction, algal growth on moist samples before extraction, freezing liquid samples as a preservative method). Repeated analyses are done only if it is deemed absolutely necessary by the ICP supervisor, not to facilitate data fitting or expectations. Errors in analytical results can have several sources. Several metrics may be employed to establish the quality of analytical data, or to trigger repeat analyses. In general, relative errors of analysis of < 20% are acceptable for analytical analyses (particularly for commercial laboratories). This means that a 10 mg L–1 standard sample will pass QA/QC if the analytical measurement lies between 8 and 12 mg L–1. Normally, QA/QC for the BESS ICP is generally < 4% relative standard error (depending on the element of interest). Now, if the 10 mg L–1 sample was generated through the total dissolution of a soil (using aqua regia, HF, and boric acid), the dilution factor necessary to convert from mg L–1 to mg kg–1 (back to a soil basis) would be 250× (0.05 L volume of digestate to 0.0002 kg soil). Therefore, a 4% error of analysis for a 10 mg L–1 digestate would translate to a 200 mg kg–1 error range for the elemental analysis of the soil (10 ± 0.4 mg L–1= 2,500 ± 100 mg kg–1). On top of this error, every step in the sample handling process, from field soil sampling to extraction to final dilution, imparts error (see Appendix III for typical errors associated with the ICP total elemental analysis of east Tennessee soils). 5
E. Additional Services 1.
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The extraction or total dissolution of mineral matter (e.g., soil, geologic material) or the digestion of solutions may be conducted on a limited basis (the ICP lab does not currently have the facilities to digest plant material). Requests for sample processing must be cleared through the ICP supervisor. It is expected that Institute of Agriculture personnel will utilize their respective departmental facilities, and will not require sample processing. Once approved, turn‐around time for sample processing and analysis is usually no less then two weeks, with usual times ranging from two to four weeks. Complete instructions for extraction procedure must be discussed with the ICP supervisor. The personnel, materials, and supplies cost associated with sample preparation will be the responsibility of the faculty member that request service. Occasionally, rapid turnaround for chemical analysis is required. The ICP supervisor will honor requests for rapid turnaround only if such a request is a result of the experimental design employed by the requestor. Ideally, this should be discussed with the ICP supervisor during the research planning stage. If sufficiently forewarned, rapid turnaround samples can be planned in advance and treated as normal submissions. However, requests for rapid turnaround that result from poor planning will not be honored. The soil sample extraction/dissolution methods that may be performed by the ICP operator are generally those indicated in Appendix I. The Archae is a weak double acid extraction commonly used by pedoarchaeologist. The Mehlich I and III extractions are used for establishing the soil fertility status of P and K (the need to fertilize). The BaCl2 and NH4OAc extractions are used to determine cation exchange capacity, base saturation, or soil exchange phase composition. The total elemental content of inorganic matrices (soils or mineral separates) is determined be dissolving the material in an aqua regia–HF solution (Total method). The Chang method is an extraction technique that provides a measure of the total elemental content of soil, but does not involve the total dissolution of the matrix. Other sample preparation methods may also be performed by the ICP operator, with approval from the ICP supervisor. 6
Appendix I Methods Most of the methods prescribed here can be referenced in many soil and plant analysis texts, most notably SSSA Book Series No. 5 "Methods of Soil Analysis, Part 3 – Chemical Methods" edited by D.L. Sparks et al., "Plant Analysis Handbook" by J.B. Jones, B. Wolf, and H.A. Mills (Micro‐Macro Publ.), and the USEPA SW‐846 analytical and sampling methods (http://www.epa.gov/epawaste/). The number of matrices and methods that can be run is limited to avoid confusion for the ICP operator. Methods listed below are most often used. Samples which are extracted in a different matrix than those listed, or requiring elements to be analyzed that are not usually run in the method, must have prior clearance from the ICP supervisor before submission, as method development is required. Method Matrix Elements Archae 0.16N HNO3 + 0.6N HCl Al As B Ba Ca Cd Co Cr Cu Fe K Mg Mn Mo Na Ni P Pb S Se Si Sr Ti Zn Zr BaCl2 0.1M CaCl2 Al Ca Co Cu Fe K Li Mg Mn Na Sr Ti Zn Chang 4M HNO3 Al As B Ba Ca Cd Ce Co Cr Cu Fe Hf K La Mg Mn Mo Na Nd Ni P Pb S Se Si Sr Ti Zn Zr Mehlich I 0.025M H2SO4 + 0.05M HCl Ca Cu Fe K Mg Mn Na P Zn Mehlich III 0.2N CH3COOH + 0.25N Ca Cu K Mg Mn Na P Zn NH4NO3 + 0.015N NH4F + 0.013N HNO4 + 0.001M EDTA NH4OAc 1N (pH 7.0) NH4OAc Ca K Mg Na Total 0.58M HF + 0.20M HNO3 + Al As Ba Ca Cd Ce Co Cr Cu Fe Hf K La 0.45M HCl + 0.16M H3BO4 Mg Mn Mo Na Nd Ni P Pb S Se Si Sr Ti Zn Zr 7
Appendix II Elemental Detection Limits† Element Detection Limit Low (µg L‐1) Method Detection Limit (µg L‐1) Al 0.09 1 As 3 3 B 0.9 2 Ba 0.04 4 Ca 0.05 0.5 Cd 0.3 2.5 Ce – 2.5 Co 0.3 2.5 Cr 0.6 2.5 Cu 1 1 Fe 0.5 2 Hg 0.8 – K 2 5 La – 2.5 Mg 0.02 0.5 Mn 0.05 0.5 Mo 0.8 5 Na 1 10 Nd – 2.5 Ni 0.08 2.5 P 3 20 Pb 2 5 Rb – 2 S 5 20 Sb – 3 Se 4 10 Si 3.3 5 Sr 0.04 2.5 Ti 0.3 5.5 V 0.6 2.5 Zn 0.4 5 Zr – 3 †Detection Limit Low represents the manufacturer’s estimate of sensitivity (normally three times the standard deviation of the baseline for the analysis of a single element in an aqueous solution containing only a simple salt of that element). The Method Detection Limit is three times the standard deviation of the baseline for the analysis of the element in a multi‐element mixture in an aqua regia–HF–boric acid solution (total analysis digestate). 8
Appendix III Errors of Analysis† Element %RSE Element %RSE Al 2.81 Mn 3.37 As 19.1 Na 2.27 Ba 4.50 Nd 4.01 Ca 3.94 Ni 9.45 Cd 5.68 P 3.30 Ce 3.79 Rb 3.83 Co 5.36 Se 13.8 Cr 8.79 Si 6.15 Cu 3.79 Sr 3.21 Fe 3.16 Ti 5.36 K 2.52 V 3.02 La 5.15 Zn 3.14 Mg 3.36 Zr 4.07 †Relative standard error (RSE) is the standard deviation of replicate analyses divided by the mean elemental content and the square root of the number of replicates. For the above data, the %RSE is the average of 68 soil samples; the replicates are soil subsamples; and the number of replicates ranges from 3 to 8. The data were taken from Essington, M.E., G.V. Melnichenko, M.A. Stewart, and R.A. Hull. 2009. Soil metals analysis using laser‐induced breakdown spectroscopy (LIBS). Soil Sci. Soc. Am. J. 73:xxx‐yyy. 9