Loading (50 kb)...'
(continued)
Section 7.2.1 This section is modified to include the analytes listed in Tables 1 and 2 and the labeled compounds listed in Tables 5 and 6 of this attachment.
Section 7.4.5 This section is modified to include the analytes listed in Tables 1 and 2 and the labeled compounds listed in Tables 5 and 6 in the calibration.
Section 8.2 The initial precision and recovery (IPR) requirements are modified to include the analytes listed in Tables 1 and 2 and the labeled compounds listed in Tables 5 and 6 of this attachment. Additional IPR performance criteria are supplied in Table 7 of this attachment.
Section 8.3 The labeled compounds listed in Tables 3 and 4 of this attachment are to be included in the method performance tests. Additional method performance criteria are supplied in Table 7 of this attachment.
Section 8.5.2 The acceptance criteria for blanks includes the analytes listed in Tables 1 and 2 of this attachment.
Section 10.1.2 The labeled compound solution must include the labeled compounds listed in Tables 5 and 6 of this attachment.
Section 10.1.3 The precision and recovery standard must include the analytes listed in Tables 1 and 2 and the labeled compounds listed in Tables 5 and 6 of this attachment.
Section 12.5 Additional QC requirements for calibration verification are supplied in Table 7 of this attachment.
Section 12.7 Additional QC requirements for ongoing precision and recovery are supplied in Table 7 of this attachment.
Table 1_Base/Neutral Extractable Compounds
------------------------------------------------------------------------
Pollutant
-----------------------
Compound CAS
Registry EPA-EGD
------------------------------------------------------------------------
acetophenone 1.................................. 98-86-2 758
aniline 2....................................... 62-53-3 757
-2,3-dichloroaniline 1.......................... 608-27-5 578
-o-cresol 1..................................... 95-48-7 771
pyridine 2...................................... 110-86-1 1330
------------------------------------------------------------------------
CAS = Chemical Abstracts Registry.
EGD = Effluent Guidelines Division.
\1\ Analysis of this pollutant is approved only for the Centralized
Waste Treatment industry.
\2\ Analysis of this pollutant is approved only for the Centralized
Waste Treatment and Landfills industries.
Table 2_Acid Extractable Compounds
------------------------------------------------------------------------
Pollutant
-------------------------
Compound CAS
Registry EPA-EGD
------------------------------------------------------------------------
p-cresol 1.................................... 106-44-5 1744
------------------------------------------------------------------------
CAS = Chemical Abstracts Registry.
EGD = Effluent Guidelines Division.
1 Analysis of this pollutant is approved only for the Centralized Waste
Treatment and Landfills industries.
Table 3_Gas Chromatography 1 of Base/Neutral Extractable Compounds
--------------------------------------------------------------------------------------------------------------------------------------------------------
Retention time 2 Retention time 2
------------------------------------------------ Minimum level EGD ----------------------
EGD No. Compound 3 (µg/ No. Compound Mean EGD
Mean (sec) EGD Ref Relative L) (sec) Ref Relative
------------------------------------------------------------------------------------------------------------------- -------------------------------------------------
758...................... acetophenone 4.......... 818 658 1.003-1.005 10
757...................... aniline 5............... 694 657 0.994-1.023 10
578...................... 2,3-dichloroaniline 4... 1160 164 1.003-1.007 10
771...................... o-cresol 4.............. 814 671 1.005-1.009 10
1330..................... pyridine 5.............. 378 1230 1.005-1.011 10
--------------------------------------------------------------------------------------------------------------------------------------------------------
EGD = Effluent Guidelines Division.
1 The data presented in this table were obtained under the chromatographic conditions given in the footnote to Table 3 of EPA Method 1625B.
2 Retention times are approximate and are intended to be consistent with the retention times for the analytes in EPA Method 1625B.
3 See the definition in footnote 2 to Table 3 of EPA Method 1625B.
4 Analysis of this pollutant is approved only for the Centralized Waste Treatment industry.
5 Analysis of this pollutant is approved only for the Centralized Waste Treatment and Landfills industries.
Table 4_Gas Chromatography 1 of Acid Extractable Compounds
----------------------------------------------------------------------------------------------------------------
Retention time 2
EGD No. Compound ------------------------------------------------ Minimum level
Mean (sec) EGD Ref Relative (µ/L) 3
----------------------------------------------------------------------------------------------------------------
1744.................... p-cresol 4............ 834 1644 1.004-1.008 20
----------------------------------------------------------------------------------------------------------------
EGD = Effluent Guidelines Division.
1 The data presented in this table were obtained under the chromatographic conditions given in the footnote to
Table 4 of EPA Method 1625B.
2 Retention times are approximate and are intended to be consistent with the retention times for the analytes in
EPA Method 1625B.
3 See the definition in footnote 2 to Table 4 of EPA Method 1625B.
4 Analysis of this pollutant is approved only for the Centralized Waste Treatment and Landfills industries.
Table 5_Base/Neutral Extractable Compound Characteristic m/z's
------------------------------------------------------------------------
Primary m/
Compound Labeled Analog z 1
------------------------------------------------------------------------
acetophenone 2............................ d5 105/110
aniline 3................................. d7 93/100
o-cresol 2................................ d7 108/116
2,3-dichloroaniline 2..................... n/a 161
pyridine 3................................ d5 79/84
------------------------------------------------------------------------
m/z = mass to charge ratio.
1 Native/labeled.
2 Analysis of this pollutant is approved only for the Centralized Waste
Treatment industry.
3 Analysis of this pollutant is approved only for the Centralized Waste
Treatment and Landfills industries.
Table 6_Acid Extractable Compound Characteristic m/z's
------------------------------------------------------------------------
Primary m/
Compound Labeled Analog z 1
------------------------------------------------------------------------
p-cresol 2................................ d7 108/116
------------------------------------------------------------------------
m/z = mass to charge ratio.
1 Native/labeled.
2 Analysis of this pollutant is approved only for the Centralized Waste
Treatment and Landfills industries.
Table 7_Acceptance Criteria for Performance Tests
----------------------------------------------------------------------------------------------------------------
Acceptance criteria
---------------------------------------
Initial precision and Labeled Calibration On-going
accuracy section 8.2 compound verification accuracy
EGD No. Compound (µg/L) recovery sec. 12.5 sec. 12.7 R
-------------------------- sec. 8.3 µg/mL) (µg/
s (µg/ and 14.2 P L)
L) X (percent)
----------------------------------------------------------------------------------------------------------------
758.................... acetophenone 1....... 34 44-167 ........... 85-115 45-162
658.................... acetophenone-d 5 1... 51 23-254 45-162 85-115 22-264
757.................... aniline 2............ 32 30-171 ........... 85-115 33-154
657.................... aniline-d 7 2........ 71 15-278 33-154 85-115 12-344
771.................... o-cresol 1........... 40 31-226 ........... 85-115 35-196
671.................... o-cresol-d 7 1....... 23 30-146 35-196 85-115 31-142
1744................... p-cresol 2........... 59 54-140 ........... 85-115 37-203
1644................... p-cresol-d7 2........ 22 11-618 37-203 85-115 16-415
578.................... 2,3-dichloroaniline 1 13 40-160 ........... 85-115 44-144
1330................... pyridine 2........... 28 10-421 ........... 83-117 18-238
1230................... pyridine-d 5 2....... ns 7-392 19-238 85-115 4-621
----------------------------------------------------------------------------------------------------------------
s = Standard deviation of four recovery measurements.
X = Average recovery for four recovery measurements.
EGD = Effluent Guidelines Division.
ns = no specification; limit is outside the range that can be measured reliably.
1 Analysis of this pollutant is approved only for the Centralized Waste Treatment industry.
2 Analysis of this pollutant is approved only for the Centralized Waste Treatment and Landfills industries.
[49 FR 43261, Oct. 26, 1984; 50 FR 692, 695, Jan. 4, 1985, as amended at 51 FR 23702, June 30, 1986; 62 FR 48405, Sept. 15, 1997; 65 FR 3044, Jan. 19, 2000; 65 FR 81295, 81298, Dec. 22, 2000]
Appendix B to Part 136—Definition and Procedure for the Determination of the Method Detection Limit—Revision 1.11
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Definition
The method detection limit (MDL) is defined as the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero and is determined from analysis of a sample in a given matrix containing the analyte.
Scope and Application
This procedure is designed for applicability to a wide variety of sample types ranging from reagent (blank) water containing analyte to wastewater containing analyte. The MDL for an analytical procedure may vary as a function of sample type. The procedure requires a complete, specific, and well defined analytical method. It is essential that all sample processing steps of the analytical method be included in the determination of the method detection limit.
The MDL obtained by this procedure is used to judge the significance of a single measurement of a future sample.
The MDL procedure was designed for applicability to a broad variety of physical and chemical methods. To accomplish this, the procedure was made device- or instrument-independent.
Procedure
1. Make an estimate of the detection limit using one of the following:
(a) The concentration value that corresponds to an instrument signal/noise in the range of 2.5 to 5.
(b) The concentration equivalent of three times the standard deviation of replicate instrumental measurements of the analyte in reagent water.
(c) That region of the standard curve where there is a significant change in sensitivity, i.e., a break in the slope of the standard curve.
(d) Instrumental limitations.
It is recognized that the experience of the analyst is important to this process. However, the analyst must include the above considerations in the initial estimate of the detection limit.
2. Prepare reagent (blank) water that is as free of analyte as possible. Reagent or interference free water is defined as a water sample in which analyte and interferent concentrations are not detected at the method detection limit of each analyte of interest. Interferences are defined as systematic errors in the measured analytical signal of an established procedure caused by the presence of interfering species (interferent). The interferent concentration is presupposed to be normally distributed in representative samples of a given matrix.
3. (a) If the MDL is to be determined in reagent (blank) water, prepare a laboratory standard (analyte in reagent water) at a concentration which is at least equal to or in the same concentration range as the estimated method detection limit. (Recommend between 1 and 5 times the estimated method detection limit.) Proceed to Step 4.
(b) If the MDL is to be determined in another sample matrix, analyze the sample. If the measured level of the analyte is in the recommended range of one to five times the estimated detection limit, proceed to Step 4.
If the measured level of analyte is less than the estimated detection limit, add a known amount of analyte to bring the level of analyte between one and five times the estimated detection limit.
If the measured level of analyte is greater than five times the estimated detection limit, there are two options.
(1) Obtain another sample with a lower level of analyte in the same matrix if possible.
(2) The sample may be used as is for determining the method detection limit if the analyte level does not exceed 10 times the MDL of the analyte in reagent water. The variance of the analytical method changes as the analyte concentration increases from the MDL, hence the MDL determined under these circumstances may not truly reflect method variance at lower analyte concentrations.
4. (a) Take a minimum of seven aliquots of the sample to be used to calculate the method detection limit and process each through the entire analytical method. Make all computations according to the defined method with final results in the method reporting units. If a blank measurement is required to calculate the measured level of analyte, obtain a separate blank measurement for each sample aliquot analyzed. The average blank measurement is subtracted from the respective sample measurements.
(b) It may be economically and technically desirable to evaluate the estimated method detection limit before proceeding with 4a. This will: (1) Prevent repeating this entire procedure when the costs of analyses are high and (2) insure that the procedure is being conducted at the correct concentration. It is quite possible that an inflated MDL will be calculated from data obtained at many times the real MDL even though the level of analyte is less than five times the calculated method detection limit. To insure that the estimate of the method detection limit is a good estimate, it is necessary to determine that a lower concentration of analyte will not result in a significantly lower method detection limit. Take two aliquots of the sample to be used to calculate the method detection limit and process each through the entire method, including blank measurements as described above in 4a. Evaluate these data:
(1) If these measurements indicate the sample is in desirable range for determination of the MDL, take five additional aliquots and proceed. Use all seven measurements for calculation of the MDL.
(2) If these measurements indicate the sample is not in correct range, reestimate the MDL, obtain new sample as in 3 and repeat either 4a or 4b.
5. Calculate the variance (S 2 ) and standard deviation (S) of the replicate measurements, as follows:
where:
X?; i=1 to n, are the analytical results in the final method reporting units obtained from the n sample aliquots and S refers to the sum of the X values from i=l to n.
6. (a) Compute the MDL as follows:
MDL = t(n-1,1-a=0.99) (S)
where:
MDL = the method detection limit
t(n-1,1-a=.99) = the students' t value appropriate for a 99% confidence level and a standard deviation estimate with n-1 degrees of freedom. See Table.
S = standard deviation of the replicate analyses.
(b) The 95% confidence interval estimates for the MDL derived in 6a are computed according to the following equations derived from percentiles of the chi square over degrees of freedom distribution (? 2 /df).
LCL = 0.64 MDL
UCL = 2.20 MDL
where: LCL and UCL are the lower and upper 95% confidence limits respectively based on seven aliquots.
7. Optional iterative procedure to verify the reasonableness of the estimate of the MDL and subsequent MDL determinations.
(a) If this is the initial attempt to compute MDL based on the estimate of MDL formulated in Step 1, take the MDL as calculated in Step 6, spike the matrix at this calculated MDL and proceed through the procedure starting with Step 4.
(b) If this is the second or later iteration of the MDL calculation, use S2 from the current MDL calculation and S2 from the previous MDL calculation to compute the F-ratio. The F-ratio is calculated by substituting the larger S2 into the numerator S2A and the other into the denominator S2B. The computed F-ratio is then compared with the F-ratio found in the table which is 3.05 as follows: if S2A/S2B<3.05, then compute the pooled standard deviation by the following equation:
if S2A/S2B>3.05, respike at the most recent calculated MDL and process the samples through the procedure starting with Step 4. If the most recent calculated MDL does not permit qualitative identification when samples are spiked at that level, report the MDL as a concentration between the current and previous MDL which permits qualitative identification.
(c) Use the Spooled as calculated in 7b to compute The final MDL according to the following equation:
MDL=2.681 (Spooled)
where 2.681 is equal to t(12,1-a=.99).
(d) The 95% confidence limits for MDL derived in 7c are computed according to the following equations derived from precentiles of the chi squared over degrees of freedom distribution.
LCL=0.72 MDL
UCL=1.65 MDL
where LCL and UCL are the lower and upper 95% confidence limits respectively based on 14 aliquots.
Tables of Students' t Values at the 99 Percent Confidence Level
------------------------------------------------------------------------
Degrees
of
Number of replicates freedom tcn-1,.99)
(n-1)
------------------------------------------------------------------------
7............................................... 6 3.143
8............................................... 7 2.998
9............................................... 8 2.896
10.............................................. 9 2.821
11.............................................. 10 2.764
16.............................................. 15 2.602
21.............................................. 20 2.528
26.............................................. 25 2.485
31.............................................. 30 2.457
61.............................................. 60 2.390
00.............................................. 00 2.326
------------------------------------------------------------------------
Reporting
The analytical method used must be specifically identified by number or title ald the MDL for each analyte expressed in the appropriate method reporting units. If the analytical method permits options which affect the method detection limit, these conditions must be specified with the MDL value. The sample matrix used to determine the MDL must also be identified with MDL value. Report the mean analyte level with the MDL and indicate if the MDL procedure was iterated. If a laboratory standard or a sample that contained a known amount analyte was used for this determination, also report the mean recovery.
If the level of analyte in the sample was below the determined MDL or exceeds 10 times the MDL of the analyte in reagent water, do not report a value for the MDL.
[49 FR 43430, Oct. 26, 1984; 50 FR 694, 696, Jan. 4, 1985, as amended at 51 FR 23703, June 30, 1986]
Appendix C to Part 136—Inductively Coupled Plasma—Atomic Emission Spectrometric Method for Trace Element Analysis of Water and Wastes Method 200.7
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1. Scope and Application
1.1 This method may be used for the determination of dissolved, suspended, or total elements in drinking water, surface water, and domestic and industrial wastewaters.
1.2 Dissolved elements are determined in filtered and acidified samples. Appropriate steps must be taken in all analyses to ensure that potential interferences are taken into account. This is especially true when dissolved solids exceed 1500 mg/L. (See Section 5.)
1.3 Total elements are determined after appropriate digestion procedures are performed. Since digestion techniques increase the dissolved solids content of the samples, appropriate steps must be taken to correct for potential interference effects. (See Section 5.)
1.4 Table 1 lists elements for which this method applies along with recommended wavelengths and typical estimated instrumental detection limits using conventional pneumatic nebulization. Actual working detection limits are sample dependent and as the sample matrix varies, these concentrations may also vary. In time, other elements may be added as more information becomes available and as required.
1.5 Because of the differences between various makes and models of satisfactory instruments, no detailed instrumental operating instructions can be provided. Instead, the analyst is referred to the instruction provided by the manufacturer of the particular instrument.
2. Summary of Method
2.1 The method describes a technique for the simultaneous or sequential multielement determination of trace elements in solution. The basis of the method is the measurement of atomic emission by an optical spectroscopic technique. Samples are nebulized and the aerosol that is produced is transported to the plasma torch where excitation occurs. Characteristic atomic-line emission spectra are produced by a radio-frequency inductively coupled plasma (ICP). The spectra are dispersed by a grating spectrometer and the intensities of the lines are monitored by photomultiplier tubes. The photocurrents from the photomultiplier tubes are processed and controlled by a computer system. A background correction technique is required to compensate for variable background contribution to the determination of trace elements. Background must be measured adjacent to analyte lines on samples during analysis. The position selected for the background intensity measurement, on either or both sides of the analytical line, will be determined by the complexity of the spectrum adjacent to the analyte line. The position used must be free of spectral interference and reflect the same change in background intensity as occurs at the analyte wavelength measured. Background correction is not required in cases of line broadening where a background correction measurement would actually degrade the analytical result. The possibility of additional interferences named in 5.1 (and tests for their presence as described in 5.2) should also be recognized and appropriate corrections made.
3. Definitions
3.1 Dissolved—Those elements which will pass through a 0.45 µm membrane filter.
3.2 Suspended—Those elements which are retained by a 0.45 µm membrane filter.
3.3 Total—The concentration determined on an unfiltered sample following vigorous digestion (Section 9.3), or the sum of the dissolved plus suspended concentrations. (Section 9.1 plus 9.2).
3.4 Total recoverable—The concentration determined on an unfiltered sample following treatment with hot, dilute mineral acid (Section 9.4).
3.5 Instrumental detection limit—The concentration equivalent to a signal, due to the analyte, which is equal to three times the standard deviation of a series of ten replicate measurements of a reagent blank signal at the same wavelength.
3.6 Sensitivity—The slope of the analytical curve, i.e., functional relationship between emission intensity and concentration.
3.7 Instrument check standard—A multielement standard of known concentrations prepared by the analyst to monitor and verify instrument performance on a daily basis. (See 7.6.1)
3.8 Interference check sample—A solution containing both interfering and analyte elemelts of known concentration that can be used to verify background and interelement correction factors. (See 7.6.2.)
3.9 Quality control sample—A solution obtained from an outside source having known, concentration values to be used to verify the calibration standards. (See 7.6.3)
3.10 Calibration standards—A series of known standard solutions used by the analyst for calibration of the instrument (i.e., preparation of the analytical curve). (See 7.4)
3.11 Linear dynamic range—The concentration range over which the analytical curve remains linear.
3.12 Reagent blank—A volume of deionized, distilled water containing the same acid matrix as the calibration standards carried through the entire analytical scheme. (See 7.5.2)
3.13 Calibration blank—A volume of deionized, distilled water acidified with HNO3 and HCl. (See 7.5.1)
3.14 Methmd of standard addition— The standard addition technique involves the use of the unknown and the unknown plus a known amount of standard. (See 10.6.1.)
4. Safety
4.1 The toxicity of carcinogenicity of each reagent used in this method has not been precisely defined; however, each chemical compound should be treated as a potential health hazard. From this viewpoint, exposure to these chemicals must be reduced to the lowest possible level by whatever means available. The laboratory is repsonsible for maintaining a current awareness file of OSHA regulations regarding the safe handling of the chemicals specified in this method. A reference file of material data handling sheets should also be made available to all personnel involved in the chemical analysis. Additional references to laboratory safety are available and have been identified(14.7,14.8 and 14.9) for the information of the analyst.
5. Interferences
5.1 Several types of interference effects may contribute to inaccuracies in the determination of trace elements. They can be summarized as follows:
5.1.1 Spectral interferences can be categorized as (1) overlap of a spectral line from another element; (2) unresolved overlap of molecular band spectra; (3) background contribution from continuous or recombination phenomena; and (4) background contribution from stray light from the line emission of high concentration elements. The first of these effects can be compensated by utilizing a computer correction of the raw data, requiring the monitoring and measurement of the interfering element. The second effect may require selection of an alternate wavelength. The third and fourth effects can usually be compensated by a background correction adjacent to the analyte line. In addition, users of simultaneous multi-element instrumentation must assume the responsibility of verifying the absence of spectral interference from an element that could occur in a sample but for which there is no channel in the instrument array. Listed in Table 2 are some interference effects for the recommended wavelengths given in Table 1. The data in Table 2 are intended for use only as a rudimentary guide for the indication of potential spectral interferences. For this purpose, linear relations between concentration and intensity for the analytes and the interferents can be assumed. The Interference information, which was collected at the Ames Laboratory, 1 is expressed as analyte concentration equivalents (i.e., false analyte concentrations) arising from 100 mg/L of the interferent element. The suggested use of this information is as follows: Assume that arsenic (at 193.696 nm) is to be determined in a sample containing approximately 10 mg/L of aluminum. According to Table 2, 100 mg/L of aluminum would yield a false signal for arsenic equivalent to approximately 1.3 mg/L. Therefore, 10 mg/L of aluminum would result in a false signal for arsenic equivalent to approximately 0.13 mg/L. The reader is cautioned that other analytical systems may exhibit somewhat different levels of interference than those shown in Table 2, and that the interference effects must be evaluated for each individual system.
1 Ames Laboratory, USDOE, Iowa State University, Ames Iowa 50011.
Only those interferents listed were investigated and the blank spaces in Table 2 indicate that measurable interferences were not observed for the interferent concentrations listed in Table 3. Generally, interferences were discernible if they produced peaks or background shifts corresponding to 2–5% of the peaks generated by the analyte concentrations also listed in Table 3.
At present, information on the listed silver and potassium wavelengths are not available but it has been reported that second order energy from the magnesium 383.231 nm wavelength interferes with the listed potassium line at 766.491 nm.
5.1.2 Physical interferences are generally considered to be effects associated with the sample nebulization and transport processes. Such properties as change in viscosity and surface tension can cause significant inaccuracies especially in samples which may contain high dissolved solids and/or acid concentrations. The use of a peristaltic pump may lessen these interferences. If these types of interferences are operative, they must be reduced by dilution of the sample and/or utilization of standard addition techniques. Another problem which can occur from high dissolved solids is salt buildup at the tip of the nebulizer. This affects aersol flow rate causing instrumental drift. Wetting the argon prior to nebulization, the use of a tip washer, or sample dilution have been used to control this problem. Also, it has been reported that better control of the argon flow rate improves instrument performance. This is accomplished with the use of mass flow controllers.
5.1.3 Chemical Interferences are characterized by molecular compound formation, ionization effects and solute vaporization effects. Normally these effects are not pronounced with the ICP technique, however, if observed they can be minimized by careful selection of operating conditions (that is, incident power, observation position, and so forth), by buffering of the sample, by matrix matching, and by standard addition procedures. These types of interferences can be highly dependent on matrix type and the specific analyte element.
5.2 It is recommended that whenever a new or unusual sample matrix is encountered, a series of tests be performed prior to reporting concentration data for analyte elements. These tests, as outlined in 5.2.1 through 5.2.4, will ensure the analyst that neither positive nor negative interference effects are operative on any of the analyte elements thereby distorting the accuracy of the reported values.
5.2.1 Serial dilution. If the analyte concentration is sufficiently high (minimally a factor of 10 above the instrumental detection limit after dilution), an analysis of a dilution should agree within 5 percent of the original determination (or within some acceptable control limit (14.3) that has been established for that matrix.). If not, a chemical or physical interference effect should be suspected.
5.2.2 Spike addition. The recovery of a spike addition added at a minimum level of 10X the instrumental detection limit (maximum 100X) to the original determination should be recovered to within 90 to 110 percent or within the established control limit for that matrix. If not, a matrix effect should be suspected. The use of a standard addition analysis procedure can usually compensate for this effect.
Caution: The standard addition technique does not detect coincident spectral overlap. If suspected, use of computerized compensation, an alternate wavelength, or comparison with an alternate method is recommended (See 5.2.3).
5.2.3 Comparison with alternate method of analysis. When investigating a new sample matrix, comparison tests may be performed with other analytical techniques such as atomic absorption spectrometry, or other approved methodology.
5.2.4 Wavelength scanning of analyte line region. If the appropriate equipment is available, wavelength scanning can be performed to detect potential spectral interferences.
6. Apparatus
6.1 Inductively Coupled Plasma-Atomic Emission Spectrometer.
6.1.1 Computer controlled atomic emission spectrometer with background correction.
6.1.2 Radiofrequency generator.
6.1.3 Argon gas supply, welding grade or better.
6.2 Operating conditions—Because of the differences between various makes and models of satisfactory instruments, no detailed operating instructions can be provided. Instead, the analyst should follow the instructions provided by the manufacturer of the particular instrument. Sensitivity, instrumental detection limit, precision, linear dynamic range, and interference effects must be investigated and established for each individual analyte line on that particular instrument. It is the responsibility of the analyst to verify that the instrument configuration and operating conditions used satisfy the analytical requirements and to maintain quality control data confirming instrument performance and analytical results.
7. Reagents and Standards
7.1 Acids used in the preparation of standards and for sample processing must be ultra-high purity grade or equivalent. Redistilled acids are acceptable.
7.1.1 Acetic acid, conc. (sp gr 1.06).
7.1.2 Hydrochloric acid, conc. (sp gr 1.19).
7.1.3 Hydrochloric acid, (1+1): Add 500 mL conc. HCl (sp gr 1.19) to 400 mL deionized, distilled water and dilute to 1 liter.
7.1.4 Nitric acid, conc. (sp gr 1.41).
7.1.5 Nitric acid, (1+1): Add 500 mL conc. HNO3 (sp gr 1.41) to 400 mL deionized, distilled water and dilute to 1 liter.
7.2 Deionized, distilled water: Prepare by passing distilled water through a mixed bed of cation and anion exchange resins. Use deionized, distilled water for the preparation of all reagents, calibration standards and as dilution water. The purity of this water must be equivalent to ASTM Type II reagent water of Specification D 1193 (14.6).
7.3 Standard stock solutions may be purchased or prepared from ultra high purity grade chemicals or metals. All salts must be dried for 1 h at 105°C unless otherwise specified.
(CAUTION: Many metal salts are extremely toxic and may be fatal if swallowed. Wash hands thoroughly after handling.)
Typical stock solution preparation procedures follow:
7.3.1 Aluminum solution, stock, 1 mL=100µg Al: Dissolve 0.100 g of aluminum metal in an acid mixture of 4 mL of (1+1) HCl and 1 mL of conc. HNO3 in a beaker. Warm gently to effect solution. When solution is complete, transfer quantitatively to a liter flask add an additional 10 mL of (1+1) HCl and dilute to 1,000 mL with deionized, distilled water.
7.3.2 Antimony solution stock, 1 mL=100 µg Sb: Dissolve 0.2669 g K(SbO)C4H4O6 in deionized distilled water, add 10 mL (1+1) HCl and dilute to 1,000 mL with deionized, distilled water.
7.3.3 Arsenic solution, stock, 1 mL=100 µg As: Dissolve 0.1320 g of As2O3 in 100 mL of deionized, distilled water containing 0.4 g NaOH. Acidify the solution with 2 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.4 Barium solution, stock, 1 mL=100 µg Ba: Dissolve 0.1516 g BaCl2 (dried at 250°C for 2 hrs) in 10 mL deionized, distilled water with 1 mL (1+1) HCl. Add 10.0 mL (1+1) HCl and dilute to 1,000 with mL deionized, distilled water.
7.3.5 Beryllium solution, stock, 1 mL=100 µg Be: Do not dry. Dissolve 1.966 g BeSO4·4H2O, in deionized, distilled water, add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.6 Boron solution, stock, 1 mL=100µg B: Do not dry. Dissolve 0.5716 g anhydrous H3BO3 in deionized, distilled water and dilute to 1,000 mL. Use a reagent meeting ACS specifications, keep the bottle tightly stoppered and store in a desiccator to prevent the entrance of atmospheric moisture.
7.3.7 Cadmium solution, stock, 1 mL=100 µg Cd: Dissolve 0.1142 g CdO in a minimum amount of (1+1) HNO3. Heat to increase rate of dissolution. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.8 Calcium solution, stock, 1 mL=100 µg Ca: Suspend 0.2498 g CaCO3 dried at 180 °C for 1 h before weighing in deionized, distilled water and dissolve cautiously with a minimum amount of (1+1) HNO3. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.9 Chromium solution, stock, 1 mL=100 µg Cr: Dissolve 0.1923 g of CrO3 in deionized, distilled water. When solution is complete, acidify with 10 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.10 Cobalt solution, stock, 1 mL=100 µg Co: Dissolve 0.1000 g of cobalt metal in a minimum amount of (1+1) HNO3. Add 10.0 mL (1+1) HCl and dilute to 1,000 mL with deionized, distilled water.
7.3.11 Copper solution, stock, 1 mL=100 µg Cu: Dissolve 0.1252 g CuO in a minimum amount of (1+1) HNO3. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.12 Iron solution, stock, 1 mL=100 µg Fe: Dissolve 0.1430 g Fe2O3 in a warm mixture of 20 mL (1+1) HCl and 2 mL of conc. HNO3. Cool, add an additional 5 mL of conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.13 Lead solution, stock, 1 mL=100 µg Pb: Dissolve 0.1599 g Pb(NO3)2 in a minimum amount of (1+1) HNO3. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.14 Magnesium solution, stock, 1 mL=100 µg Mg: Dissolve 0.1658 g MgO in a minimum amount of (1+1) HNO3. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.15 Manganese solution, stock, 1 mL=100 µg Mn: Dissolve 0.1000 g of manganese metal in the acid mixture 10 mL conc. HCl and 1 mL conc. HNO3, and dilute to 1,000 mL with deionized, distilled water.
7.3.16 Molybdenum solution, stock, 1 mL=100 µg Mo: Dissolve 0.2043 g (NH4)2 MoO4 in deionized, distilled water and dilute to 1,000 mL.
7.3.17 Nickel solution, stock, 1 mL=100 µg Ni: Dissolve 0.1000 g of nickel metal in 10 mL hot conc. HNO3, cool and dilute to 1,000 mL with deionized, distilled water.
7.3.18 Potassium solution, stock, 1 mL=100 µg K: Dissolve 0.1907 g KCl, dried at 110 °C, in deionized, distilled water and dilute to 1,000 mL.
7.3.19 Selenium solution, stock, 1 mL=100 µg Se: Do not dry. Dissolve 0.1727 g H2SeO3 (actual assay 94.6%) in deionized, distilled water and dilute to 1,000 mL.
7.3.20 Silica solution, stock, 1 mL=100 µg SiO2: Do not dry. Dissolve 0.4730 g Na2SiO3·9H2O in deionized, distilled water. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.21 Silver solution, stock, 1 mL=100 µg Ag: Dissolve 0.1575 g AgNO3 in 100 mL of deionized, distilled water and 10 mL conc. HNO3. Dilute to 1,000 mL with deionized, distilled water.
7.3.22 Sodium solution, stock, 1 mL=100 µg Na: Dissolve 0.2542 g NaCl in deionized, distilled water. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.23 Thallium solution, stock, 1 mL=100 µg Tl: Dissolve 0.1303 g TlNO3 in deionized, distilled water. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.24 Vanadium solution, stock, 1 mL=100 µg V: Dissolve 0.2297 NH4 VO3 in a minimum amount of conc. HNO3. Heat to increase rate of dissolution. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL with deionized, distilled water.
7.3.25 Zinc solution, stock, 1 mL=100 µg Zn: Dissolve 0.1245 g ZnO in a minimum amount of dilute HNO3. Add 10.0 mL conc. HNO3 and dilute to 1,000 mL deionized, distilled water.
7.4 Mixed calibration standard solutions—Prepare mixed calibration standard solutions by combining appropriate volumes of the stock solutions in volumetric flasks. (See 7.4.1 thru 7.4.5) Add 2 mL of (1+1) HNO3 and 10 mL of (1+1) HC1 and dilute to 100 mL with deionized, distilled water. (See Notes 1 and 6.) Prior to preparing the mixed standards, each stock solution should be analyzed separately to determine possible spectral interference or the presence of impurities. Care should be taken when preparing the mixed standards that the elemelts are compatible and stable. Transfer the mixed standard solutions to a FEP fluorocarbon or unused polyethylene bottle for storage. Fresh mixed standards should be prepared as needed with the realization that concentration can change on aging. Calibration standards must be initially verified using a quality control sample and monitored weekly for stability (See 7.6.3). Although not specifically required, some typical calibration standard combinations follow when using those specific wavelengths listed in Table 1.
7.4.1 Mixed standard solution I—Manganese, beryllium, cadmium, lead, and zinc.
7.4.2 Mixed standard solution II—Barium, copper, iron, vanadium, and cobalt.
7.4.3 Mixed standard solution III—Molybdenum, silica, arsenic, and selenium.
7.4.4 Mixed standard solution IV—Calcium, sodium, potassium, aluminum, chromium and nickel.
7.4.5 Mixed standard solution V— Antimony, boron, magnesium, silver, and thallium.
Note: 1. If the addition of silver to the recommended acid combination results in an initial precipitation, add 15 mL of deionized distilled water and warm the flask until the solution clears. Cool and dilute to 100 mL with deionized, distilled water. For this acid combination the silver concentration should be limited to 2 mg/L. Silver under these conditions is stable in a tap water matrix for 30 days. Higher concentrations of silver require additional HCl.
7.5 Two types of blanks are required for the analysis. The calibration blank (3.13) is used in establishing the analytical curve while the reagent blank (3.12) is used to correct for possible contamination resulting from varying amounts of the acids used in the sample processing.
7.5.1 The calibration blank is prepared by diluting 2 mL of (1+1) HNO3 and 10 mL of (1+1) HCl to 100 mL with deionized, distilled water. (See Note 6.) Prepare a sufficient quantity to be used to flush the system between standards and samples.
7.5.2 The reagent blank must contain all the reagents and in the same volumes as used in the processing of the samples. The reagent blank must be carried through the complete procedure and contain the same acid concentration in the final solution as the sample solution used for analysis.
7.6 In addition to the calibration standards, an instrument check standard (3.7), an interference check sample (3.8) and a quality control sample (3.9) are also required for the analyses.
7.6.1 The instrument check standard is prepared by the analyst by combining compatible elements at a concentration equivalent to the midpoint of their respective calibration curves. (See 12.1.1.)
7.6.2 The interference check sample is prepared by the analyst in the following manner. Select a representative sample which contains minimal concentrations of the analytes of interest but known concentration of interfering elements that will provide an adequate test of the correction factors. Spike the sample with the elements of interest at the approximate concentration of either 100 µg/L or 5 times the estimated detection limits given in Table 1. (For effluent samples of expected high concentrations, spike at an appropriate level.) If the type of samples analyzed are varied, a synthetically prepared sample may be used if the above criteria and intent are met.
7.6.3 The quality control sample should be prepared in the same acid matrix as the calibration standards at a concentration near 1 mg/L and in accordance with the instructions provided by the supplier. The Quality Assurance Branch of EMSL-Cincinnati will either supply a quality control sample or information where one of equal quality can be procured. (See 12.1.3.)
8. Sample Handling and Preservation
8.1 For the determination of trace elements, contamination and loss are of prime concern. Dust in the laboratory environment, impurities in reagents and impurities on laboratory apparatus which the sample contacts are all sources of potential contamination. Sample containers can introduce either positive or negative errors in the measurement of trace elements by (a) contributing contaminants through leaching or surface desorption and (b) by depleting concentrations through adsorption. Thus the collection and treatment of the sample prior to analysis requires particular attention. Laboratory glassware including the sample bottle (whether polyethylene, polyproplyene or FEP-fluorocarbon) should be thoroughly washed with detergent and tap water; rinsed with (1+1) nitric acid, tap water, (1+1) hydrochloric acid, tap and finally deionized, distilled water in that order (See Notes 2 and 3).
Note: 2. Chromic acid may be useful to remove organic deposits from glassware; however, the analyst should be cautioned that the glassware must be thoroughly rinsed with water to remove the last traces of chromium. This is especially important if chromium is to be included in the analytical scheme. A commercial product, NOCHROMIX, available from Godax Laboratories, 6 Varick St., New York, NY 10013, may be used in place of chromic acid. Chromic acid should not be used with plastic bottles.
Note: 3. If it can be documented through an active analytical quality control program using spiked samples and reagent blanks, that certain steps in the cleaning procedure are not required for routine samples, those steps may be eliminated from the procedure.
8.2 Before collection of the sample a decision must be made as to the type of data desired, that is dissolved, suspended or total, so that the appropriate preservation and pretreatment steps may be accomplished. Filtration, acid preservation, etc., are to be performed at the time the sample is collected or as soon as possible thereafter.
8.2.1 For the determination of dissolved elements the sample must be filtered through a 0.45-µm membrane filter as soon as practical after collection. (Glass or plastic filtering apparatus are recommended to avoid possible contamination.) Use the first 50–100 mL to rinse the filter flask. Discard this portion and collect the required volume of filtrate. Acidify the filtrate with (1+1) HNO3 to a pH of 2 or less. Normally, 3 mL of (1+1) acid per liter should be sufficient to preserve the sample.
8.2.2 For the determination of suspended elements a measured volume of unpreserved sample must be filtered through a 0.45-µm membrane filter as soon as practical after collection. The filter plus suspended material should be transferred to a suitable container for storage and/or shipment. No preservative is required.
8.2.3 For the determination of total or total recoverable elements, the sample is acidified with (1+1) HNO3 to pH 2 or less as soon as possible, preferably at the time of collection. The sample is not filtered before processing.
9. Sample Preparation
9.1 For the determinations of dissolved elements, the filtered, preserved sample may often be analyzed as received. The acid matrix and concentration of the samples and calibration standards must be the same. (See Note 6.) If a precipitate formed upon acidification of the sample or during transit or storage, it must be redissolved before the analysis by adding additional acid and/or by heat as described in 9.3.
9.2 For the determination of suspended elements, transfer the membrane filter containing the insoluble material to a 150-mL Griffin beaker and add 4 mL conc. HNO3. Cover the beaker with a watch glass and heat gently. The warm acid will soon dissolve the membrane. Increase the temperature of the hot plate and digest the material. When the acid has nearly evaporated, cool the beaker and watch glass and add another 3 mL of conc. HNO3. Cover and continue heating until the digestion is complete, generally indicated by a light colored digestate. Evaporate to near dryness (2 mL), cool, and 10 mL HCl (1+1) and 15 mL deionized, distilled water per 100 mL dilution and warm the beaker gently for 15 min. to dissolve any precipitated or residue material. Allow to cool, wash down the watch glass and beaker walls with deionized distilled water and filter the sample to remove insoluble material that could clog the nebulizer. (See Note 4.) Adjust the volume based on the expected concentrations of elements present. This volume will vary depending on the elements to be determined (See Note 6). The sample is now ready for analysis. Concentrations so determined shall be reported as “suspended.” (continued)