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Microwave digestion and atomic absorption analysis of complex plasma-densified composite powders
Surface and Coatings Technology, 70(1994)159—162
159
Technical note Microwave digestion and atomic absorption analysis of complex plasma-densified composite powders Bradley D. Zehr and Judith P. VanKuren Osram Sylvania Inc., Chemical and Metallurgical Products, Hawes Street, Towanda, PA 18848-0504 (USA) (Received September 3, 1993; accepted in final form February 28, 1994)
Abstract The digestion and analysis ofcomplex plasma-densified spray coating metal alloys is carefully looked at, with the goal of laying out a general analysis method. The key points discussed include the choice of acids, containment of volatiles, digestion safety, analysis accuracy, analysis precision and data interpretation.
1. Introduction Complex densified composite powders can be produced by passing agglomerates containing a myriad of materials through a plasma to alloy and/or densify them. These composites powders can be produced to contain unique combinations of metals, alloys, oxides, carbides, borides etc. An alloy is produced when two or more metals are intimately combined by extreme heat approaching 15 000 °C.Composite powders can be used for thermal spray coating applications. By varying the composition of spray coatings and applying an ultrathin coat to parts or surfaces which experience high wear environments, one is able to extend the lifetime of the part substantially. Some applications may attempt to minimize wear due to abrasiveness, chemical attack and/or thermal decomposition [1]. This type of practice may be compared with the use of plastic laminate on particle board composites, which results in a high wearresistant less-expensive countertop. The analysis of plasma-densified powders is required for two reasons. First, it is important to know whether a significant level of contamination is present. Second, it is necessary to know whether the correct combination of metals or other constituents are present after processing. To answer the first question concerning contamination, a spectrographic qualitative technique which requires no sample dissolution may be used. This method must be able to determine whether a significant amount of a large number of possible contaminants are present. It is not
0257—8972/94/S7.OO SSDI 0257-8972(94)02285-X
important to know the quantitative amount, unless a significant amount of a contaminant is found. With regard to what a significant level is, one must base this decision on function and properties of the end product. Quantitative analysis of the metal blend composition is the main point of this work. One avenue of quantitative analysis includes flame atomic absorption spectroscopy (AAS) analysis; however, to exploit this technique, the sample must first be totally dissolved. The dissolution of plasma-densified powders which can contain as many as eight to 12 cations may pose a challenge. The utilization of a pressure control microwave with double-wall vessels has proven advantageous with respect to this challenge.
2. Equipment and instruments A model MDS-2000 CEM (Matthew, NC) microwave with pressure control was utilized in conjunction with perfluoroalkoxy-lined digestion vessels to carry out digestions. For flame AAS analysis, a Perkin—Elmer (Norwalk, CT) model 5100 instrument was used.
3. Results and discussion 3.1. Acids and volatiles A previous publication dealing specifically with the microwave acid digestion method development points out conditions in which specific elements may be volatile during acid digestion [2]. Of the situations in which
© 1994
—
Elsevier Science S.A. All rights reserved
160
B. D. Zehr. J. P. VanKuren
Digestion and analysis of plasma-densiuied composite powders
volatiles are of concern, the use of hydrofluoric acid (HF) is of greatest importance when digesting metal alloys. As seen in Table 1, more than 90% of the metal alloy digestions shown here include HF in the dissolution
When W is present in the metal alloy. HF is needed during the microwave stage. In addition, if HCI is used in the digestion when W is present. a small amount of phosphoric acid (H5P04) is added so as to complex the
and require the determination of B and/or Si. While compiling Table 1, it was noted that two main digestion strategies were used. When W is not present, one is able to avoid the volatility of B or Si by using a two-stage digestion. The first stage involves microwaving the sample with hydrochloric acid (HC1) and nitric acid (HNO3) in a closed vessel. After cooling, HF is added, the sample is diluted, the vessel is capped and the digestion is allowed to reach completion at room temperature. By using this two-stage digestion, the chance of losing B or Si is minimal since the sample is not heated in the presence of HF.
W. avoiding the precipitation of W in the forni of tungsten chloride. Although a shorter microwave sequence could be used in some cases: the alloys shown in Table 1 were digested using a 45 mm hold at 0.358 Pa (125 Ibf in 2) With HF present during the microwaving cycle, it is important that all vessels are totally sealed from the onset of heating to the point at which room temperature is reached after microwaving. In cases were the use of HF can be avoided until after the microwave cycle. containment of gases is not as critical. However, rapid venting may lead to a loss of sample.
TABLE I. Microwave dissolutions
No W present
Alloy matrix
Dissolution agents ml per g of sampiel
Al, Co. Cr. Ti and Y
50 HCI. 20 HNO~,30 drops
Al. B. Co. Cr, Ti and low Y Al. B, Co. Cr. Ti and High Y
B, Cr. Fe, Mo. Ni and Si B. Cr. Fe, Co, Cu. Mn. Mo. Nb, Ni and Si B. Cr, Nb, Ni and Ti B, Co. Cr, Fe. Mo, Nb. Ni. Si and Ti Co. Cr. Cu. Fe, Mo, Mn, Ni and Si Co. Cr. Cu. Fe. Mo. Ni and Si
H~PO4.5 HF 50 HCI. 20 HNO3, 30 drops H~PO4.5 HF 50 HCI. 20 HNO3. 5 H~PO4. microwave. 5 HF (For \. use 50 HCI. 20 HNO~. S H5P04) 25 HCI. 25 HNO~.microwave. 25 HF 50 HCI, 25 HNO3. microwave. 25 HF 10 HCI. 0 H NO~,microwave, 10 HF 10 HCI. 10 HNO~.microwave. 10 HF 25 HCI. 25 HNO3. 25 HF 50 HCI. 50 HNO~.microwave.
Comments
Y remains as YF~if HF ts used
Add HF cold Add HF cold Microwave, cool and add HF
Add HF cold
20 H F
Co. Cr. Fe, Mo, Nb and Si
W present
B, Cr, Fe, Ni, Si and W B, Co, Cr, Fe, Mo, Mn, Ni, Si and W
10 HCI. 10 HNO~.microwave. 10 HF
Microwave, cool and add HF
40 HF. 20 HNO3 25 HF, 25 HNO3. microwave. 0.5H3P04. 25 HCI B. Cr, Fe, Ni, Si and W 40 HF. 40 HNO~.microwave, 40 HCI Co. Cr, Ni and W 20 HF. 10 HNO-1 Co. Cr, Fe, Mn, Mo, Ni. Si and W 50 HF. 50 HNO5. microwave, 1H5P04, 50 l-lCl Cr, Fe. Ni and W 100 HF. (slowly) 50 HNO3 Cu. Fe. Mn, Ni, Si and W 50 HF, 25 HNO3 2( and then holding for 45 mm. Each vessel contained Microwavea conditions 0.1 g sample forload. the above digestions involved a stepwise program to 0.358 Pa 1125 lbf in
B. D. Zehr, J. P. VanKuren
/
161
Digestion and analysis of plasma-densified composite powders
3.2. Digestion safety With regard to safety during the digestion, it is important to follow the comments (1)—(6) in order to avoid vessel failure during pressurization. (1) Microwave only one alloy type at a time, since each alloy type will react at a different rate. (2) Keep sample loads within 5% for vessels to be microwaved together. (3) Before capping the sample, carefully inspect the outer shell of microwave vessels for indications of failure. For example, if the bottom half of the vessel shell shows any stress lines, it should be discarded. If the vessel shell cap begins to show yellowing on the inside due to HNO3 attack, the cap should also be discarded. (4) Use a stepwise microwave program. That is, when microwaving, do not take the vessel straight to the highest pressure; instead, hold the vessel for about 5 mm at several intermediate pressures. (5) Since samples of the same alloy with smaller particle size distributions react more vigorously, pressure monitor the vessel containing the smallest particle size distribution if a difference among the sample set exists. (6) If there is no difference in particle size distribution within the sample set, monitor the vessel containing the largest sample weight.
laboratory ware when taking the digested sample to a set volume or carrying out dilutions. Other publications deal specifically with estimating the accuracy and precision of dilutions [3]. During the third stage of the method, flame AAS instrumental analysis, the accuracy depends on the accuracy of the standards and knowledge of interferences. Sample spikes and/or alternative wavelengths may be used to test for matrix, chemical and/or spectral interferences. The readings can then be corrected, based on spike recoveries. The precision of a flame AAS instrument depends on the instrument set-up and the element of interest. With regard to the precision of individual
TABLE 2. Ni—Ti alloy blend analysis results
Qualitative
Method
Element
Amount
Spectrographic
Ag
0.5—5 ppm
qualitative analysis
Al As B Be Bi Ca Cd Co
0.05—0.5% <500 ppm 1_10% ~1 ppm <5 ppm 5—50 ppm <5 ppm 0.05—0.5%
Fe Ge Mg Mn Mo Ni P Pb Sb Si Sn Sr Ta Th
0.5-5% <1 ppm 1—10 ppm 0.05—0.5% 0.05—0.5% 10-100% <500ppm 50-500 ppm <5ppm
Ti
5—50%
3.3. Analysis accuracy and precision During digestion, the first stage of the method. accuracy and precision are maintained by avoiding the loss of volatiles or loss of sample. At the second stage of the method, sample dilution, it is important to use calibrated Ag _________
B ______________________
co ~ K U
0.5—5%
UI
V
______
_____
Ni
Quantitative 11
Carrier gas fusion analysis
________
AAS analysis
___________________________________ 0
1
2
3
4
% RSD
Fig. 1. To obtain instrument percentage RSD, the instrument was optimized and calibrated before taking ten consecutive readings of a standard in the linear range of the calibration curve. Figure 1 represents only short-term precision and does not include sample preparation nor day-to-day set-up variation,
W
0.05—0.5%
Zn Zr
C N
3.66% 0.024%
0 B Cr Fe Ni Si Ti
0.37% 2.6% 11.6%
3.9% 61.7 3.8% 10.9%
Qualitative and quantitative analysis data are shown for a single Ni—Ti alloy blend.
162
B. D. Zehr, J. P.
VanKuren
/
Digestion and analysis of plasma-densified composite
TABLE 3. Flame atomic absorption spectroscopy percentage relative standard deviation result ranges based on instrument Element
Amount by flame AAS with ±SDbased on instrument RSD (%±SD)
B 2.6±0.079 Cr 11.6±0.29 Fe 3.9±0.036 Ni 61.7±1.2 Si 3.8±0.027 Ti 10.9±0.087 Total range of quantitative analysis based on AAS instrument RSD
Range of amount by flame AAS based on instrument RSD~ 1%)
2.4—2.8 10.7—12.5 3.8—4.0 58.0—65.4 3.7—3.9 10.611.2 94.9—102.3
__________________________________________________
~Sampling and sample preparation variability is not included in the range shown. Also note that carrier gas fusion analysis (C. N and 0) variation is not estimated. The range was calculated using a ±3RSD. The estimated total range of quantitative analysis was calculated by adding the squared individual AAS element SD. taking the square root and then calculating the range using ±3SD.
elements. Fig. 1 shows the relationship between various elements with respect to the relative standard deviation (RSD) at a concentration within the linear portion of the calibration curve. From this information, confidence limits can be estimated for specific elemental analyses. However, the data shown in Fig. 1 do not include sampling and sample preparation variabilits.
powders
accountability to the end user. This may be accomplished by showing the dominating element as balance or normalizing the data to 100%. As an example, Table 2 shows the analytical results of an Nj—Ti alloy. If the quantitative results are added, a total of 98.6% is obtained. Although this type of calculation is often carried out, the analyst. the engineer and the customer must consider variability when interpreting this information. To illustrate this point, the short-term flame AAS instrument RSD (Fig. 1) for the specific elements was used to calculate a range for each of the flame atomic AAS analytical results. Table 3 shows the associated variability for each result. Excluding the variability involved in carrier gas fusion analysis (C. N and 0), the total possible variation in quantitative analysis is calculated and also shown in Table 3. 4. Conclusions Accurate elemental analysis of complex composite powders poses two main areas of concern: sample digestion and instrumental analysis. Regardless of how well the analysis is carried out, variability is included at each step and must be considered when interpreting the analytical data. As a result of this variability, the use of data manipulation techniques may be misleading.
Acknowledgments
3.4. Data interpretation The authors would like to thank Joan Coveleskie, Data interpretation is often carried out by three David Houck and John Schoonover for technical and groups of individuals: (1) the analyst who is concerned editorial aid. with the accuracy and precision of the analytical representation of the sample; (2) the manufacturing engineers who are concerned with how well the product was References produced: (3) the end user who must consider the performance of the product. It is of utmost importance I H Herman, Sd ,4,n, 257 (September 1988) that all three groups have access to all the analytical 2 B D Zehr, .4ni Lab.. 24 (December, 1992) 24 results. Often the data are manipulated to show l00~?4~ 3 B. D. Zehr and M. A. Maryott, Specrrochini. Acta. Sect. B. 48(10( (1993) 1275.
159
Technical note Microwave digestion and atomic absorption analysis of complex plasma-densified composite powders Bradley D. Zehr and Judith P. VanKuren Osram Sylvania Inc., Chemical and Metallurgical Products, Hawes Street, Towanda, PA 18848-0504 (USA) (Received September 3, 1993; accepted in final form February 28, 1994)
Abstract The digestion and analysis ofcomplex plasma-densified spray coating metal alloys is carefully looked at, with the goal of laying out a general analysis method. The key points discussed include the choice of acids, containment of volatiles, digestion safety, analysis accuracy, analysis precision and data interpretation.
1. Introduction Complex densified composite powders can be produced by passing agglomerates containing a myriad of materials through a plasma to alloy and/or densify them. These composites powders can be produced to contain unique combinations of metals, alloys, oxides, carbides, borides etc. An alloy is produced when two or more metals are intimately combined by extreme heat approaching 15 000 °C.Composite powders can be used for thermal spray coating applications. By varying the composition of spray coatings and applying an ultrathin coat to parts or surfaces which experience high wear environments, one is able to extend the lifetime of the part substantially. Some applications may attempt to minimize wear due to abrasiveness, chemical attack and/or thermal decomposition [1]. This type of practice may be compared with the use of plastic laminate on particle board composites, which results in a high wearresistant less-expensive countertop. The analysis of plasma-densified powders is required for two reasons. First, it is important to know whether a significant level of contamination is present. Second, it is necessary to know whether the correct combination of metals or other constituents are present after processing. To answer the first question concerning contamination, a spectrographic qualitative technique which requires no sample dissolution may be used. This method must be able to determine whether a significant amount of a large number of possible contaminants are present. It is not
0257—8972/94/S7.OO SSDI 0257-8972(94)02285-X
important to know the quantitative amount, unless a significant amount of a contaminant is found. With regard to what a significant level is, one must base this decision on function and properties of the end product. Quantitative analysis of the metal blend composition is the main point of this work. One avenue of quantitative analysis includes flame atomic absorption spectroscopy (AAS) analysis; however, to exploit this technique, the sample must first be totally dissolved. The dissolution of plasma-densified powders which can contain as many as eight to 12 cations may pose a challenge. The utilization of a pressure control microwave with double-wall vessels has proven advantageous with respect to this challenge.
2. Equipment and instruments A model MDS-2000 CEM (Matthew, NC) microwave with pressure control was utilized in conjunction with perfluoroalkoxy-lined digestion vessels to carry out digestions. For flame AAS analysis, a Perkin—Elmer (Norwalk, CT) model 5100 instrument was used.
3. Results and discussion 3.1. Acids and volatiles A previous publication dealing specifically with the microwave acid digestion method development points out conditions in which specific elements may be volatile during acid digestion [2]. Of the situations in which
© 1994
—
Elsevier Science S.A. All rights reserved
160
B. D. Zehr. J. P. VanKuren
Digestion and analysis of plasma-densiuied composite powders
volatiles are of concern, the use of hydrofluoric acid (HF) is of greatest importance when digesting metal alloys. As seen in Table 1, more than 90% of the metal alloy digestions shown here include HF in the dissolution
When W is present in the metal alloy. HF is needed during the microwave stage. In addition, if HCI is used in the digestion when W is present. a small amount of phosphoric acid (H5P04) is added so as to complex the
and require the determination of B and/or Si. While compiling Table 1, it was noted that two main digestion strategies were used. When W is not present, one is able to avoid the volatility of B or Si by using a two-stage digestion. The first stage involves microwaving the sample with hydrochloric acid (HC1) and nitric acid (HNO3) in a closed vessel. After cooling, HF is added, the sample is diluted, the vessel is capped and the digestion is allowed to reach completion at room temperature. By using this two-stage digestion, the chance of losing B or Si is minimal since the sample is not heated in the presence of HF.
W. avoiding the precipitation of W in the forni of tungsten chloride. Although a shorter microwave sequence could be used in some cases: the alloys shown in Table 1 were digested using a 45 mm hold at 0.358 Pa (125 Ibf in 2) With HF present during the microwaving cycle, it is important that all vessels are totally sealed from the onset of heating to the point at which room temperature is reached after microwaving. In cases were the use of HF can be avoided until after the microwave cycle. containment of gases is not as critical. However, rapid venting may lead to a loss of sample.
TABLE I. Microwave dissolutions
No W present
Alloy matrix
Dissolution agents ml per g of sampiel
Al, Co. Cr. Ti and Y
50 HCI. 20 HNO~,30 drops
Al. B. Co. Cr, Ti and low Y Al. B, Co. Cr. Ti and High Y
B, Cr. Fe, Mo. Ni and Si B. Cr. Fe, Co, Cu. Mn. Mo. Nb, Ni and Si B. Cr, Nb, Ni and Ti B, Co. Cr, Fe. Mo, Nb. Ni. Si and Ti Co. Cr. Cu. Fe, Mo, Mn, Ni and Si Co. Cr. Cu. Fe. Mo. Ni and Si
H~PO4.5 HF 50 HCI. 20 HNO3, 30 drops H~PO4.5 HF 50 HCI. 20 HNO3. 5 H~PO4. microwave. 5 HF (For \. use 50 HCI. 20 HNO~. S H5P04) 25 HCI. 25 HNO~.microwave. 25 HF 50 HCI, 25 HNO3. microwave. 25 HF 10 HCI. 0 H NO~,microwave, 10 HF 10 HCI. 10 HNO~.microwave. 10 HF 25 HCI. 25 HNO3. 25 HF 50 HCI. 50 HNO~.microwave.
Comments
Y remains as YF~if HF ts used
Add HF cold Add HF cold Microwave, cool and add HF
Add HF cold
20 H F
Co. Cr. Fe, Mo, Nb and Si
W present
B, Cr, Fe, Ni, Si and W B, Co, Cr, Fe, Mo, Mn, Ni, Si and W
10 HCI. 10 HNO~.microwave. 10 HF
Microwave, cool and add HF
40 HF. 20 HNO3 25 HF, 25 HNO3. microwave. 0.5H3P04. 25 HCI B. Cr, Fe, Ni, Si and W 40 HF. 40 HNO~.microwave, 40 HCI Co. Cr, Ni and W 20 HF. 10 HNO-1 Co. Cr, Fe, Mn, Mo, Ni. Si and W 50 HF. 50 HNO5. microwave, 1H5P04, 50 l-lCl Cr, Fe. Ni and W 100 HF. (slowly) 50 HNO3 Cu. Fe. Mn, Ni, Si and W 50 HF, 25 HNO3 2( and then holding for 45 mm. Each vessel contained Microwavea conditions 0.1 g sample forload. the above digestions involved a stepwise program to 0.358 Pa 1125 lbf in
B. D. Zehr, J. P. VanKuren
/
161
Digestion and analysis of plasma-densified composite powders
3.2. Digestion safety With regard to safety during the digestion, it is important to follow the comments (1)—(6) in order to avoid vessel failure during pressurization. (1) Microwave only one alloy type at a time, since each alloy type will react at a different rate. (2) Keep sample loads within 5% for vessels to be microwaved together. (3) Before capping the sample, carefully inspect the outer shell of microwave vessels for indications of failure. For example, if the bottom half of the vessel shell shows any stress lines, it should be discarded. If the vessel shell cap begins to show yellowing on the inside due to HNO3 attack, the cap should also be discarded. (4) Use a stepwise microwave program. That is, when microwaving, do not take the vessel straight to the highest pressure; instead, hold the vessel for about 5 mm at several intermediate pressures. (5) Since samples of the same alloy with smaller particle size distributions react more vigorously, pressure monitor the vessel containing the smallest particle size distribution if a difference among the sample set exists. (6) If there is no difference in particle size distribution within the sample set, monitor the vessel containing the largest sample weight.
laboratory ware when taking the digested sample to a set volume or carrying out dilutions. Other publications deal specifically with estimating the accuracy and precision of dilutions [3]. During the third stage of the method, flame AAS instrumental analysis, the accuracy depends on the accuracy of the standards and knowledge of interferences. Sample spikes and/or alternative wavelengths may be used to test for matrix, chemical and/or spectral interferences. The readings can then be corrected, based on spike recoveries. The precision of a flame AAS instrument depends on the instrument set-up and the element of interest. With regard to the precision of individual
TABLE 2. Ni—Ti alloy blend analysis results
Qualitative
Method
Element
Amount
Spectrographic
Ag
0.5—5 ppm
qualitative analysis
Al As B Be Bi Ca Cd Co
0.05—0.5% <500 ppm 1_10% ~1 ppm <5 ppm 5—50 ppm <5 ppm 0.05—0.5%
Fe Ge Mg Mn Mo Ni P Pb Sb Si Sn Sr Ta Th
0.5-5% <1 ppm 1—10 ppm 0.05—0.5% 0.05—0.5% 10-100% <500ppm 50-500 ppm <5ppm
Ti
5—50%
3.3. Analysis accuracy and precision During digestion, the first stage of the method. accuracy and precision are maintained by avoiding the loss of volatiles or loss of sample. At the second stage of the method, sample dilution, it is important to use calibrated Ag _________
B ______________________
co ~ K U
0.5—5%
UI
V
______
_____
Ni
Quantitative 11
Carrier gas fusion analysis
________
AAS analysis
___________________________________ 0
1
2
3
4
% RSD
Fig. 1. To obtain instrument percentage RSD, the instrument was optimized and calibrated before taking ten consecutive readings of a standard in the linear range of the calibration curve. Figure 1 represents only short-term precision and does not include sample preparation nor day-to-day set-up variation,
W
0.05—0.5%
Zn Zr
C N
3.66% 0.024%
0 B Cr Fe Ni Si Ti
0.37% 2.6% 11.6%
3.9% 61.7 3.8% 10.9%
Qualitative and quantitative analysis data are shown for a single Ni—Ti alloy blend.
162
B. D. Zehr, J. P.
VanKuren
/
Digestion and analysis of plasma-densified composite
TABLE 3. Flame atomic absorption spectroscopy percentage relative standard deviation result ranges based on instrument Element
Amount by flame AAS with ±SDbased on instrument RSD (%±SD)
B 2.6±0.079 Cr 11.6±0.29 Fe 3.9±0.036 Ni 61.7±1.2 Si 3.8±0.027 Ti 10.9±0.087 Total range of quantitative analysis based on AAS instrument RSD
Range of amount by flame AAS based on instrument RSD~ 1%)
2.4—2.8 10.7—12.5 3.8—4.0 58.0—65.4 3.7—3.9 10.611.2 94.9—102.3
__________________________________________________
~Sampling and sample preparation variability is not included in the range shown. Also note that carrier gas fusion analysis (C. N and 0) variation is not estimated. The range was calculated using a ±3RSD. The estimated total range of quantitative analysis was calculated by adding the squared individual AAS element SD. taking the square root and then calculating the range using ±3SD.
elements. Fig. 1 shows the relationship between various elements with respect to the relative standard deviation (RSD) at a concentration within the linear portion of the calibration curve. From this information, confidence limits can be estimated for specific elemental analyses. However, the data shown in Fig. 1 do not include sampling and sample preparation variabilits.
powders
accountability to the end user. This may be accomplished by showing the dominating element as balance or normalizing the data to 100%. As an example, Table 2 shows the analytical results of an Nj—Ti alloy. If the quantitative results are added, a total of 98.6% is obtained. Although this type of calculation is often carried out, the analyst. the engineer and the customer must consider variability when interpreting this information. To illustrate this point, the short-term flame AAS instrument RSD (Fig. 1) for the specific elements was used to calculate a range for each of the flame atomic AAS analytical results. Table 3 shows the associated variability for each result. Excluding the variability involved in carrier gas fusion analysis (C. N and 0), the total possible variation in quantitative analysis is calculated and also shown in Table 3. 4. Conclusions Accurate elemental analysis of complex composite powders poses two main areas of concern: sample digestion and instrumental analysis. Regardless of how well the analysis is carried out, variability is included at each step and must be considered when interpreting the analytical data. As a result of this variability, the use of data manipulation techniques may be misleading.
Acknowledgments
3.4. Data interpretation The authors would like to thank Joan Coveleskie, Data interpretation is often carried out by three David Houck and John Schoonover for technical and groups of individuals: (1) the analyst who is concerned editorial aid. with the accuracy and precision of the analytical representation of the sample; (2) the manufacturing engineers who are concerned with how well the product was References produced: (3) the end user who must consider the performance of the product. It is of utmost importance I H Herman, Sd ,4,n, 257 (September 1988) that all three groups have access to all the analytical 2 B D Zehr, .4ni Lab.. 24 (December, 1992) 24 results. Often the data are manipulated to show l00~?4~ 3 B. D. Zehr and M. A. Maryott, Specrrochini. Acta. Sect. B. 48(10( (1993) 1275.