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Elemental Analysis Manual: Section 4.4A Inductively Coupled Plasma-Atomic Emission Spectrometric Determination of Elements in Food Using Microwave Assisted Digestion

Appendix A - Supplemental Information on In-house Method Validation

Version 1 (June 2008)
Authors: William R. Mindak
Stephen G. Capar

GLOSSARY


Validation experiments of EAM 4.4 were perform using a CEM Corporation model MDS 2000 microwave digestion system with TFM Teflon lined Heavy Duty Vessels and an Applied Research Laboratories (ARL) Model 3580 inductively coupled plasma atomic emission spectrometer. Both a pneumatic nebulizer (ARL Maximum Dissolved Solids Nebulizer) and an ultrasonic nebulizer (CETAC U-5000 AT) were used. In-house validation results have been published1.

4.4A.1 ANALYTICAL LIMITS

Analytical limits were estimated by the analysis of method blanks and the results are summarized in 4.4A Table 1.

Note: When the method validation was conducted, the protocol at the time required ASQL and LOQ be calculated based on 10 times the standard deviation of the blank. The values reported in this appendix thus reflect "10×σ" values rather than the current protocol of "30×σ".

4.4A Table 1. Estimated Analytical Limits

  Pneumatic NebulizerUltrasonic Nebulizer
ElementSymbolASDL
(mg/L)
LODa
(mg/kg)
LOQa
(mg/kg)
ASDL
(mg/L)
LODa
(mg/kg)
LOQa
(mg/kg)
AluminumAl0.0540.820.00740.10.3
ArsenicAs0.086240.00220.030.08
BariumBa0.00330.050.20.0110.20.4
BoronB0.0210.30.80.00400.050.2
CadmiumCd0.0230.30.90.000390.0050.02
CalciumCa0.638301.12040
ChromiumCr0.13250.00350.050.2
CobaltCo0.0210.30.80.000370.0050.02
CopperCu0.00790.10.30.000710.0090.03
IronFe0.00830.20.30.00380.050.2
LeadPb0.17360.00320.040.2
MagnesiumMg0.16260.52720
ManganeseMn0.00990.20.40.0000790.0010.003
MolybdenumMo0.0270.410.000810.020.03
NickelNi0.0660.930.00150.020.06
PhosphorusP0.16260.00480.060.2
PotassiumK1.120400.0530.72
SeleniumSe0.24390.00860.20.4
SodiumNa0.12250.872040
StrontiumSr0.00190.030.070.0270.41
ThalliumTl0.16260.00310.040.2
VanadiumV0.0140.20.50.000430.0060.02
ZincZn0.0230.30.80.00130.020.05

a Based on 10×σ of method blanks, 4 g analytical portion, and 50 mL analytical solution.

4.4A.2 REFERENCE MATERIAL RESULTS

Reference Material Results

The results of replicate analyses of RMs (0.5 g to 1 g analytical portions) were used to assess accuracy and precision. Pneumatic and ultrasonic nebulization were assessed using independently prepared sets of RMs. RM recoveries were calculated based on available certified, informational, or consensus values for analytical results above LOQ.

Pneumatic nebulization

Results for 9 RMs analyzed using pneumatic nebulization are listed in 4.4A Table 2. At least one RM recovery was attainable for each element except chromium, cobalt, molybdenum, nickel, selenium, and thallium. RM recoveries were acceptable (80-120%) for arsenic, boron, cadmium, calcium, copper, lead, magnesium, manganese, phosphorus, potassium, vanadium, and zinc. As expected, aluminum RM recoveries were low especially materials containing appreciable levels of silicon. Low recovery of aluminum appears to be associated with incomplete dissolution of samples containing silica and requires the use of hydrofluoric acid to obtain complete recovery especially for plant materials2-3. Aluminum RM recoveries for 3 of 4 RMs were low (about 68%) and two of these were plant materials and the other, oyster tissue, has about 0.11% silicon4. Aluminum recovery from the fourth RM (dogfish liver; DOLT-2) was acceptable. Barium RM recoveries for 2 of 4 RMs were low. The barium recovery from oyster tissue (79%) is based on a consensus value (n = 4) with a relative standard deviation of about 14% but this variability does not fully account for the somewhat low recovery. The barium recovery from non-fat milk powder (42%) is also based on a consensus value (n=2) without an estimate of variability. Iron RM recovery for 1 (non-fat milk powder) of 9 RMs was high (121%). The iron concentration was near the LOQ (2 mg/kg) and, as expected had a high RSD (12%). Sodium RM recovery for 1 (orchard leaves) of 7 RMs was low (70%). The sodium level of this RM (58 mg/kg) was much lower than the other RMs and was somewhat near the LOQ (20 mg/kg) but the RSD of measurements was good (2%). This low recovery may indicate a MBK correction problem. Strontium RM recovery for 1 (non-fat milk powder) of 5 RMs was high (121%). This strontium recovery is based on a consensus value (n=2) without an estimate of variability. Molybdenum could not be measured above the LOQ in any RM but was measurable at "trace" level in one RM (rice flour). RSD for this level was good (8%) and the mean level is in close agreement with the reference value. Nickel also could not be measured above LOQ in any RM but was measurable at "trace" levels in two RMs (spinach and lobster). The RSD for nickel measured in spinach RM was good (4%) and the mean level is in close agreement with the reference value. However, the RSD measured in lobster RM was poor (41%) as expected for this "trace" level near the LOD and the mean level was not in agreement with the reference value. Arsenic could only be measured above the LOQ in one RM. However, arsenic was found in 5 other RMs at "trace" levels and all these concentrations were in fairly good agreement to the reference values which may indicate a high estimate of the arsenic LOQ. Precision of replicate analysis (measured as RSD) was 15% or less for all element concentration measurements above LOQ. The somewhat poor precision for aluminum in dogfish muscle is probably due to non-homogeneity. In general, the RM recoveries using microwave digestion and pneumatic nebulization are good except for aluminum and no assessment can be made for chromium, cobalt, molybdenum, nickel, selenium, and thallium due to lack of data.

4.4A Table 2. Reference Material Results Using Pneumatic Nebulizationa (1 of 3)

 Oyster Tissue
(NIST 1566)
 Rice Flour
(NIST 1568)
 Trace Elements inSpinach
(NIST 1570)
ElementRef.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
Aluminum255b172467 2.8b<3-- 8705930.368
Arsenic13.4(13.5)13- 0.41<5-- 0.15<5--
Barium4.9b3.9379 0.3b(0.19)3- 14.6b14.73101
Boron8.0b7.4493 0.64b<1-- 28.0b26193
Cadmium3.5(3.79)4- 0.029<2-- 1.39b<2--
Calcium15001340389 140148490 1350012500293
Chromium0.69<7-- 0.06b<7-- 4.6<7--
Cobalt0.35b<1-- 0.02<1-- 1.49b<1--
Copper6364.72103 2.22.16498 1212.21102
Iron195194399 8.79.083104 550513193
Lead0.48<9-- 0.045<9-- 1.2<9--
Magnesium12801230396 474b4792101 8500b7980194
Manganese17.516.5494 20.120.10.3100 165160197
Molybdenum0.20b<2-- 1.62b(1.72)8- 0.31b<2--
Nickel1.03<4-- 0.14b<4-- 5.6b(6.2)4-
Phosphorus7600b7300696 1620b1580398 55004970190
Potassium96909600199 112011403102 3560033000193
Selenium2.1<20-- 0.4<20-- 0.043b<20--
Sodium510054001106 6(19.1)24- 13900b145001104
Strontium10.3610.1298 0.19b(0.22)11- 8786.3299
Thallium≤ 0.005c<8-- <0.002b<8-- 0.03c<8--
Vanadium2.6b2.33390 0.006b<0.7-- 1.2b(1.3)5-
Zinc852764790 19.419.55100 5045390

4.4A Table 2. Reference Material Results Using Pneumatic Nebulizationa (2 of 3)

 Orchard Leaves
(NIST 1571)
 Non-Fat Milk Powder
(NIST 1549)
 Dogfish Muscle (NRCC
DORM-1)
ElementRef.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
Aluminum330b224468 2c<3-- nv14.916-
Arsenic10-12.35- 0.00193b<5-- 17.7(17.8)9-
Barium43b44.41103 2.2b0.93142 nv(0.27)36-
Boron3330191 1.98b-2.16- nv<1--
Cadmium0.11<2-- 0.00052-- 0.086<2--
Calcium2090017100482 13000123000.195 nv13005-
Chromium2.6<7-- 0.0026<7-- 3.6<7--
Cobalt0.16b<1-- 0.0041c<1-- 0.049<1--
Copper1212.83107 0.7-0.862- 5.225.235100
Iron300257286 1.782.1512121 63.666.33104
Lead4540.8691 0.019<9-- 0.4<9--
Magnesium62005260385 120012000.2100 12101190498
Manganese9179.9288 0.26<0.5-- 1.32(1.52)8-
Molybdenum0.3<2-- 0.34c<2-- nv<2--
Nickel1.3<4-- 0.10b<4-- 1.2<4--
Phosphorus21001790385 10600110000.3104 nv101003-
Potassium1470013800294 16900170000.4101 1590015200596
Selenium0.08<20-- 0.11<20-- 1.62<20--
Sodium8258270 497055400.5111 800081405102
Strontium36b34.9197 3.1b3.70.2121 nv8.58-
Thallium0.041b<8-- 0.00052b<8-- nv<8--
Vanadium0.51b<0.7-- 0.005b<0.7-- nv<0.7--
Zinc2524296 46.144.8197 21.318.1485

4.4A Table 2. Reference Material Results Using Pneumatic Nebulizationa (3 of 3)

 Dogfish Liver
(NRCC DOLT-1)
 Dogfish Liver
(NRCC DOLT-2)
 Lobster Hepatopancreas
(NRCC TORT-1)
ElementRef.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
Aluminumnv(5)16- 25.225.46101 nv35.58-
Arsenic10.1(11.5)8- 16.6(14.1)7- 24.628.23114
Bariumnv(0.19)14- nv0.610- nv3.983-
Boronnv<2-- nv<2-- nv5.4511-
Cadmium4.184.662111 20.819.4193 26.325.4396
Calciumnv4834- nv5212- 89507930589
Chromium0.4<8-- 0.37<8-- 2.4<8--
Cobalt0.157<2-- 0.24<2-- 0.42<2--
Copper20.820.1197 25.827.71107 439429198
Iron712693197 110310100.491 1861914103
Lead1.36<10-- 0.22<10-- 10.4(9.3)20-
Magnesium11001020293 nv7841- 225023803106
Manganese8.728.45197 6.885.910.286 23.422.2395
Molybdenumnv<2-- nv<2-- 1.5<2--
Nickel0.26<4-- 0.2<4-- 2.3(4.7)41-
Phosphorusnv98203- nv83300.3- 879088205100
Potassium101009200191 nv83800.3- 10410107003103
Selenium7.34<20-- 6.06<20-- 6.88<20--
Sodium726072400.3100 nv76300.3- 3670036300299
Strontiumnv4.74- nv4.532- 1131132100
Thalliumnv<9-- nv<9-- nv<10--
Vanadiumnv<0.8-- nv<0.8-- 1.4(1.42)9-
Zinc92.582.5489 85.877.60.390 177154587

a Mean result based on 3 analyses except 5 analyses for Oyster Tissue, Dogfish Muscle (DORM-1), and Lobster Hepatopancreas. NIST=National Institute of Standards and Technology, NRCC=National Research Council of Canada, nv=no value available. Mean results in ( ) are "trace" levels and mean results below the LOD are listed as < LOD.
b Reference value not certified; consensus value7.
c Reference value not certified; informational value provided by certifying organization.

Ultrasonic nebulization

Results for 9 RMs analyzed using ultrasonic nebulization are listed in 4.4A Table 3 (only oyster tissue and dogfish muscle were not the same analytical solutions analyzed using pneumatic nebulization). At least one RM recovery is attainable for each element except thallium. RM recoveries were acceptable (80-120%) for arsenic, barium, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, phosphorus, potassium, sodium strontium, vanadium and zinc. Aluminum RM recoveries for 2 of the 8 RMs were poor. The aluminum recovery from oyster tissue was low (65%) probably for the reasons discussed above. The aluminum recovery from bovine liver was very high (344%) and cannot be readily explained but could be due to the reference value (1.7 mg/kg) and the level found (5.8 mg/kg) being near the LOQ (2 mg/kg) or a contamination problem. A low (68%) nickel RM recovery for 1 (dogfish muscle) of 4 RMs cannot be readily explained. Selenium RM recoveries of all 4 RMs were high (mean 156%). All these RMs have an LOQ of 2 mg/kg and have reference values between 2 and 3 mg/kg, which may indicate that the estimated LOQ is too low or there is not sufficient correction of spectral background emission. Replicate analysis precision (measured as RSD) was 15% or less for all element concentration measurements above LOQ except for chromium in mussel (85%) and soy powdered infant formula (52%), and selenium in whole egg powder (22%). Extremely high variability was observed for chromium and many divergent results were excluded from performance assessment. The cause of this variability was not thoroughly investigated but environmental contamination or spectral interference is suspected. Chromium reference values for all RMs except dogfish muscle were below LOQ. The somewhat high selenium variability for whole egg powder is probably due a low estimated LOQ. Boron was not detected (<0.3 mg/kg) in soy powdered infant formula having a reference value of 0.60 mg/kg. Although the reference value is below the LOQ (1 mg/kg) trace levels should have been detected which may indicate that the estimated LOD may be too low. The trace vanadium result for total diet RM is a factor of 10 lower than a consensus value (n=1) without an estimate of variability indicating the low creditability of the value. A more recent publication by one of the same authors whose work provided the consensus value reported a vanadium concentration for the Total Diet RM of 0.037 mg/kg (mean of 2 analyses)5 which more closely agrees with the trace result. Cobalt was not detected (<0.03 mg/kg) in dogfish muscle having a reference value of 0.049 mg/kg. Although the reference value is below the LOQ (0.07 mg/kg) trace levels should have been detected which may indicate that the estimated LOD may be too low.

4.4A Table 3. Reference Material Results Using Ultrasonic Nebulizationa (1 of 3)

 Oyster Tissue
(NIST 1566)
 Bovine Liver
(NIST 1577a)
 Rice Flour
(NIST 1568a)
ElementRef.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
Aluminum255b166565 1.7b5.815344 4.45.36120
Arsenic13.4142105 0.047<0.2-- 0.29(0.36)21-
Barium4.9b3.9180 0.08b<0.9-- nv<0.7--
Boron8.0b7.2690 0.84b<0.4-- 0.54c(0.44)11-
Cadmium3.53.653104 0.440.4546103 0.022(0.044)44-
Calcium15001430295 120(153)5- 118(151)14-
Chromium0.69<0.4e-- 0.2b(0.79)21- nv<0.3e--
Cobalt0.35b0.317591 0.210.205798 0.018d<0.03e--
Copper63632100 158149394 2.42.51105
Iron195184394 194175390 7.47.61103
Lead0.48(0.54)10- 0.135<0.3e-- <0.010d<0.2--
Magnesium12801150290 600554392 560483186
Manganese17.516.8396 9.99.45495 2020.32102
Molybdenum0.20b(0.16)2- 3.53.693105 1.461.621111
Nickel1.030.91588 0.71b(0.30)e21- nv(0.31)24-
Phosphorus7600b81703108 11100116004105 153017503114
Potassium96908830391 99608600386 12801220395
Selenium2.12.87134 0.71(0.99)44- 0.38<0.6--
Sodium510051402101 24302370298 6.6<60--
Strontium10.3610.72103 0.138<3-- nv<2--
Thallium≤0.005d<0.2-- 0.003d<0.3-- nv<0.2--
Vanadium2.6b2.44394 0.099(0.068)25- 0.007d<0.03--
Zinc852788492 123115493 19.419.3499

4.4A Table 3. Reference Material Results Using Ultrasonic Nebulizationa (2 of 3)

 Total Diet
(NIST 1548)
 Whole Egg Powder
(NIST 8415)
 Dogfish Muscle
(NRCC DORM-1)
ElementRef.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
Aluminum33d392119 5406046112 nv11.47-
Arsenic0.104b<0.2-- 0.01d<0.2-- 17.718.63105
Bariumnv(1.3)1- 3d3.65119 nv<0.7--
Boron2.61c2.23786 0.41<0.4-- nv0.875-
Cadmium0.028(0.041)32- 0.005d<0.04-- 0.0860.1035120
Calcium17401680297 248025804104 nv13903-
Chromium0.5b<0.4-- 0.37(0.78)34- 3.64.3e10119
Cobaltnv(0.043)12- 0.012(0.044)e96- 0.049<0.03e--
Copper2.62.682103 2.72.865106 5.225.2111100
Iron32.630.6394 112104393 63.659193
Lead0.05d<0.3-- 0.061<0.3-- 0.4(0.43)17-
Magnesium556494289 305295497 12101070488
Manganese5.24.88294 1.781.75499 1.321.17388
Molybdenum0.27d0.38110 0.2470.269105 nv(0.18)2-
Nickel0.43b(0.27)32- nv<0.2-- 1.20.811368
Phosphorus324035902111 10010106004106 nv113-
Potassium60605950298 319031401498 1590013700286
Selenium0.245<0.7-- 1.392.222162 1.622.849175
Sodium625065602105 377039008103 80007930299
Strontiumnv(3.8)5- 5.63(6.8)6- nv9.11-
Thalliumnv<0.3-- nv<0.3-- nv<0.2--
Vanadium0.49b(0.048)17- 0.4590.53612117 nv(0.044)17-
Zinc30.829.9397 67.566.6599 21.318584

4.4A Table 3. Reference Material Results Using Ultrasonic Nebulizationa (3 of 3)

 Mussel
(NIES No.6)
 Cocoa Powder
(FDA CP)
 Soy Powder Infant Formula
(FDA SPIF)
ElementRef.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
 Ref.
Value
(mg/kg)
Mean
Result
(mg/kg)
RSD
(%)
RM
Rec
(%)
Aluminum220d218599 50.145.2690 12.512.68101
Arsenic9.29.61105 nv<0.2-- nv<0.2--
Bariumnv<0.8-- nv14.75- nv<0.9--
Boron12.9c12.2195 28.628.4999 0.6<0.3--
Cadmium0.820.8491104 0.390.3661294 nv(0.081)74-
Calcium13001260297 171015201389 62005640791
Chromium0.63(0.88)e85- 0.92<0.4-- nv(0.91)52-
Cobalt0.37d0.307683 1.1641.061391 nv<0.03--
Copper4.95.3112108 41.743.65104 9.38.77794
Iron158147493 1311131086 100d95.8696
Lead0.910.831191 0.117d<0.3-- nv<0.3--
Magnesium21001750283 599059501099 485438490
Manganese16.315392 54.246.71186 2.672.28785
Molybdenumnv0.843- nv0.353- nv0.2913-
Nickel0.930.871394 12.4d10.41284 nv(0.26)e4-
Phosphorus7700d82202107 8070822011102 3900d43104111
Potassium54005270398 1875018300898 566056902101
Selenium1.5d2.39152 nv<0.6;-- nv<0.7--
Sodium100009640396 19<60-- 235024004102
Strontium17d18.53109 18.3d205107 nv(3.2)16-
Thalliumnv<0.2-- nv<0.3-- nv<0.3--
Vanadiumnv0.5623- 0.096(0.079)11- 0.1610.17212107
Zinc106100295 79.270.71589 60d52.7788

a Mean result based on 3 analyses except 4 analyses for Rice Flour, Whole Egg Powder, and Mussel. NIST=National Institute of Standards and Technology, NRCC=National Research Council of Canada, NIES=National Institute for Environmental Studies of Japan, FDA=Food and Drug Administration, nv=no value available. Cocoa Powder and Soy Powdered Infant Formula are FDA in-house reference materials. Mean results in ( ) are "trace" levels and mean results below the LOD are listed as < LOD.
b Reference value not certified; consensus value7.
c Reference value not certified; value based on prompt gamma-ray activation analysis8-9.
d Reference value not certified; informational value provided by certifying organization.
e Excluded one highly divergent analytical result due to spectral interference or environmental contamination.

4.4A.3 FOOD RESULTS

The results of replicate FAP analyses of foods were used to assess analyte recovery and matrix induced interference. Foods were analyzed using ultrasonic nebulization. All foods were portions of FDA Total Diet Study market basket 1994-4 prepared and analyzed for 14 elements under FDA's Total Diet Study program6 enabling comparison of analytical results for some elements.

FAP recovery

Results for 20 foods analyzed using ultrasonic nebulization are listed in 4.4A Table 4. FAPs were analyzed for all elements except calcium, magnesium, phosphorus, potassium and sodium. FAP recoveries for all foods were acceptable (80-120%) for arsenic, barium, cadmium, chromium, copper, iron, manganese, molybdenum, nickel, strontium thallium, and vanadium. Aluminum FAP recovery was low for 3 foods: peanut butter (44%), pancakes (62%), and broccoli (73%). Low FAP recoveries for pancakes and broccoli are attributed to fortification at less than 1 times the native level. Low FAP recovery for peanut butter cannot be explained with confidence but appears to be contamination or an instrument anomaly that caused the result of the unfortified analytical portion to be high (12.0 mg/kg). An aluminum concentration of 6.61 mg/kg for this peanut butter was determined by neutron activation analysis. Using this result for the unfortified analytical portion produces a 95% FAP recovery for the ICP-AES aluminum fortification result. This acceptable FAP recovery suggests that the unfortified aluminum results for peanut butter are erroneously high. Boron FAP recovery was high for 1 food: prune juice (123%). This high recovery may be attributed to fortification at less than 1 times the native level. Cobalt FAP recovery was low for 1 food: corn (67%). This low recovery cannot be explained. Lead FAP recovery was slightly low for 2 foods: pork bacon (74%) and broccoli (79%). These low recoveries cannot be readily explained. The high sodium concentration of the pork bacon may have hindered the ultrasonic nebulization but the other analyte FAP recoveries are acceptable. For broccoli, other analyte FAP recoveries are on the low end of the acceptable range (except selenium), which may indicate an inaccurate fortification. Selenium FAP recoveries are slightly high for 2 foods: spaghetti (122%) and haddock (121%). These high recoveries cannot be readily explained. A high bias on RM selenium results was also observed as mentioned above. In addition, most selenium FAP recoveries were on the high end of the acceptable range (average of acceptable FAP recoveries was 112%). These results indicate that insufficient correction of spectral background emission may be the cause of the slightly high bias on selenium results. Zinc FAP recovery was low for 1 food: fruit flavored cereal (69%). This low recovery may be attributed to fortification at less than 1 times the native level.

Precision

The precision of replicate analysis of unfortified portions (measured as RSD; 4.4A Table 4) was 15% or less for all element concentration measurements above LOQ except for cadmium in spaghetti (19%), calcium in haddock (30%), copper in cheddar cheese (16%), iron in cheddar cheese (19%) and mayonnaise (17%), nickel in prune juice (16%), potassium in mayonnaise (17%), and selenium in haddock (20%). Imprecision due to concentration measurements being near the LOQ and unknown sample homogeneity may explain the results for cadmium in spaghetti (LOQ 0.02 mg/kg), copper in cheddar cheese (LOQ 0.2), iron in mayonnaise (LOQ 2 mg/kg), and selenium in haddock (LOQ 0.8 mg/kg). Imprecision of calcium in haddock may be explained by non-homogeneity caused by haddock bone fragments and the relatively low level of calcium (LOQ 90 mg/kg). Imprecision due to levels being near the LOQ could not explain the slightly poor precision of iron in cheddar cheese (LOQ 0.7 mg/kg), nickel in prune juice (LOQ 0.05 mg/kg) or potassium in mayonnaise (LOQ 20 mg/kg). Non-homogeneity may be the cause of the imprecision for iron in cheddar cheese. An extremely divergent aluminum result was obtained for 1 of the 3 replicates of unfortified pork bacon, beef, and haddock. These results ranged from a factor of about 2 to 5 higher than the other replicates and were excluded from the calculations. The cause of this variability was not thoroughly investigated but environmental contamination is suspected. Extremely divergent chromium results were obtained for 1 of 3 replicates of unfortified pork bacon, 1 of 3 replicates of fortified pork bacon, and 2 of 3 replicates of fortified tuna. Most of these results were negative values indicating spectral interference that may have affected background correction. An extremely divergent lead result was obtained for 1 of 3 replicates of unfortified pork bacon, tuna, and corn. These results ranged from a factor of about 70 to 300 higher than the other replicates and were excluded from the calculations. The cause of this variability was not thoroughly investigated but environmental contamination is suspected.

Comparison to Total Diet Study

FDA Total Diet Study results for market basket 1994-4 were available for comparison for all elements except barium, boron, chromium, molybdenum, strontium, and thallium. The Total Diet Study uses (1) a nitric-perchloric-sulfuric acid digestion and inductively coupled plasma atomic emission spectrometry to measure calcium, copper, iron, magnesium, manganese, phosphorus, potassium sodium and zinc, (2) the same digestion and hydride generation atomic absorption spectrometry to measure arsenic and selenium and (3) a dry ash mineralization and graphite furnace atomic absorption spectrometry to measure cadmium, lead, and nickel. Aluminum, cobalt, and vanadium results were only available for 3 foods (determined by instrumental neutron activation analysis as part of Total Diet Study independent quality assurance activity) and nickel was not available for 1 food. A majority of the results were in agreement with Total Diet Study results (4.4A Table 4). Direct comparisons were made when both results were above LOQ and results were considered in agreement if within ±20% of Total Diet Study result. No cobalt, lead, selenium or vanadium comparisons were available. Two of 3 aluminum results are in agreement and the high result for peanut butter discussed above is probably due to environmental contamination. The 2 arsenic comparisons and 1 cadmium comparison were in agreement. Fourteen of the 15 calcium comparisons agreed. The slightly low and imprecise calcium result for haddock is probably due to non-homogeneity and the relatively low concentration (LOQ 90 mg/kg). All 4 copper comparisons agreed. Eleven of 13 iron comparisons agreed. The iron results for prune juice and broccoli were about 25% lower than the Total Diet Study result. Both Total Diet Study results are near the LOQ (2 and 3 mg/kg, respectively), which may account for the discrepancy. Iron fortification recoveries for these foods were good. Seventeen of 18 magnesium comparisons agreed. The magnesium result for prune juice was about 25% lower than the Total Diet Study result. No reasonable explanation for this discrepancy was found. All 8 manganese comparisons agreed. Only 3 of 6 nickel comparisons agreed. Nickel results for peanut butter, pancakes, and fruit flavored cereal were 25% to 50% higher than Total Diet Study results. No reasonable explanation for this discrepancy was found. Nickel fortification recoveries for these foods were good. Eighteen of 19 phosphorus comparisons agreed. The phosphorus result for peanut butter was about 25% higher than the Total Diet Study result. No reasonable explanation for this discrepancy was found. Twelve of 20 potassium comparisons agreed. Potassium results for prune juice, broccoli, sweat potato, spaghetti, beer, beef and haddock were 21% to 27% lower than Total Diet Study results. No reasonable explanation for this discrepancy was found. Potassium result for mayonnaise was about 85% higher than the Total Diet Study result. The potassium level in mayonnaise was relatively low compared to other foods and measurement precision was at the high end of the acceptable range indicating that the LOQ for mayonnaise (20 mg/kg) may be under estimated. In addition, the Total Diet Study potassium result was near the estimated LOQ (40 mg/kg). All 19 sodium comparisons agreed. Fifteen of 16 zinc comparisons agreed. The zinc result for prune juice was about 30% lower than the Total Diet Study result. The Total Diet Study zinc result was near the LOQ (1 mg/kg), which may explain the disagreement.

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (1 of 7)

 Evaporated milk (8) Cheddar cheese (12) Pork bacon (20)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum<0.2-2.688- (0.6)287.395- (1.3)e51192-
Arsenic<0.05-5.397<0.01 <0.2-1593<0.02 <0.2-2387<0.02
Barium<0.3-1.1103- (1)182.993- <1-4.5101-
Boron0.7185.390- (0.47)201596- (0.69)422395-
Cadmium<0.009-0.5398<0.002 <0.03-1.594<0.003 <0.04-2.391(0.004)
Calcium17705--2040 62205--7480 (120)13--84
Chromium<0.2-2.691- <0.3-7.397- <0.5e-1192e-
Cobalt<0.009-1.188- <0.03-2.990- <0.04-4.588-
Copper<0.02-2.689<0.25 0.35167.392(0.401) 0.9611193(0.886)
Iron0.4562685(0.713) 1.51197387(2.53) 8.030.3113868.74
Lead<0.07-5.395<0.007 <0.2-1585<0.014 <0.3e-2374(0.014)
Magnesium1578--194 2387--283 (182)10--181
Manganese0.024125.386<0.3 0.18281589<0.4 0.12262387<0.4
Molybdenum<0.02-1.192- (0.13)232.992- <0.07-4.592-
Nickel<0.04-2.690<0.025 <0.09-7.391<0.05 <0.2-1187<0.05
Phosphorus19006--1700 48903--4840 34203--3390
Potassium24405--2860 7339--736 32606--2940
Selenium<0.2-111140.04 <0.5-291130.217 <0.8-451020.295
Sodium70210--786 53407--6240 174006--17500
Strontium(1.6)202.695- 6.2117.398- <3-11100-
Thallium<0.07-1187- <0.2-2988- <0.3-4585-
Vanadium<0.01-0.5385- <0.03-1.593- <0.04-2.392-
Zinc6.34111916.9 32.39298636 19.86458322.3

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (2 of 7)

 Tuna (canned in oil) (32) Eggs (boiled) (37) Peanut butter (47)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum(0.9)25.691- (0.38)23395- 12811446.61g
Arsenic0.868111010.966 <0.07-698<0.01 <0.2-21102(0.021)
Barium<0.6-2.2100- (0.64)41.2100- 3.624.295-
Boron(0.6)161190- (0.2)51695- 16.20.12193-
Cadmium(0.028)201.11050.022 <0.02-0.6105<0.002 (0.099)42.11050.067
Calcium(100)15--78 5232--506 5924--499
Chromium<0.3-5.6118f- (0.25)293102- <0.5-1197-
Cobalt<0.02-2.297- <0.02-1.297- <0.04-4.2810.031g
Copper0.4515.690(0.403) 0.581395(0.55) 4.66111924.48
Iron7.93356928.38 16.61309416.9 19.911069519.5
Lead<0.2e-1186(0.011) <0.1-695<0.007 <0.3-21106<0.014
Magnesium2423--251 1142--109 16501--1580
Manganese0.26541194<0.3 0.2721695<0.3 13.91219413
Molybdenum<0.05-2.299- 0.0846695- 1.324.298-
Nickel(0.08)235.696(0.041) <0.05-398<0.025 1.24711980.931
Phosphorus16104--1490 20802--1870 39805--3230
Potassium19302--2070 11802--1170 54902--5500
Selenium(0.88)2221140.613 (0.48)9121100.375 <0.8-421160.118
Sodium32003--3530 12002--1180 42603--4160
Strontium<2-5.6111- (0.86)63103- (5.5)311101-
Thallium<0.2-2294- <0.1-1295- <0.3-4296-
Vanadium<0.03-1.197- <0.02-0.6100- <0.04-2.198<0.12g
Zinc4.45922944.4 12.22129112 261428725.2

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (3 of 7)

 Corn (54) White bread (58) Pancakes (68)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum(0.21)61.891<0.052g 2.324.21012.32g 61.343.762-
Arsenic<0.04-3.795<0.01 <0.1-8.5100<0.02 <0.09-7.3100<0.01
Barium<0.2-0.73101- (1.2)21.7103- (0.65)51.599-
Boron0.6133.793- (0.47)128.599- 1.447.398-
Cadmium(0.009)240.37102(0.004) (0.041)60.851030.021 <0.02-0.731020.011
Calcium(32)8--23 5772--578 13802--1330
Chromium<0.1-1.893- <0.3-4.2107- <0.2-3.7103-
Cobalt<0.007-0.73670.0011g <0.02-1.71100.0073g <0.02-1.592-
Copper0.280.41.891<0.25 1.0734.296(1.07) 0.933.795(0.746)
Iron2.461890(2.93) 29.52429131.5 14.22379014.1
Lead<0.06e-3.790<0.007 <0.2-8.593<0.01 <0.2-7.385(0.012)
Magnesium1892--183 2122--206 3162--292
Manganese0.88423.792(0.855) 4.3628.5944.46 3.0617.3902.8
Molybdenum(0.031)20.7395- 0.1631.798- 0.331.594-
Nickel(0.044)331.893<0.025 (0.17)74.2950.124 0.2953.7910.191
Phosphorus6832--613 11701--1040 41402--3540
Potassium16001--1730 11501--1160 23401--2150
Selenium<0.2-7.3110<0.01 <0.4-171150.146 <0.4-151160.123
Sodium<20---<7 49001--5180 46201--4470
Strontium<0.5-1.8110- (2.5)84.2104- (1.3)63.7102-
Thallium<0.06-7.391- <0.2-1794- <0.2-1590-
Vanadium<0.008-0.3796<0.0047g <0.02-0.85101<0.12g (0.021)280.7396-
Zinc3.517.3873.92 5.56217935.83 6.99415866.79

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (4 of 7)

 Fruit flavored cereal (72) Prune juice (103) Lemonade (105)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum257.2102- 0.44101.397- (0.09)110.76100-
Arsenic<0.2-14101<0.01 <0.03-2.6103<0.01 <0.02-1.5100<0.01
Barium<0.7-2.9101- (0.28)120.5299- <0.08-0.3110-
Boron<0.3-1497- 4.882.6123- 0.3281.597-
Cadmium(0.057)71.41070.018 <0.005-0.26109<0.001 <0.003-0.15105<0.001
Calcium7034--645 8311--98 321--28.8
Chromium(0.38)687.2107- (0.17)1231.393- <0.04-0.76109-
Cobalt(0.068)92.999- <0.005-0.52100- <0.003-0.3100-
Copper1.0157.2980.96 0.1781.396(0.213) 0.0610.7697<0.2
Iron21457281201 2.31913983.2 0.2727.696<0.5
Lead<0.2-14102(0.01) <0.04-2.696<0.005 <0.03-1.597<0.004
Magnesium2735--249 9411--126 174--17.2
Manganese6.91314956.56 0.6692.6100(0.862) 0.04111.597<0.2
Molybdenum0.2332.9100- (0.01)240.5299- <0.006-0.3101-
Nickel0.5547.2980.441 0.1161.31010.113 <0.01-0.76100<0.014
Phosphorus13703--1160 18813--192 263--(22.5)
Potassium11603--1090 17609--2350 2294--262
Selenium<0.6-291100.055 <0.1-5.2115<0.01 <0.06-3103<0.01
Sodium51403--5300 (16)11--(16.9) (14)0.1--(12.9)
Strontium<2-7.2119- (0.7)111.3104- (0.25)30.76104-
Thallium<0.2-2998- <0.04-5.297- <0.02-398-
Vanadium0.09361.4101- (0.008)840.2699- <0.003-0.15104-
Zinc15952969157 0.9495.2991.3 0.1113393<0.2

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (5 of 7)

 Broccoli (113) Sweet potato (140) Spaghetti and meatballs (142)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum1.340.673- (0.4)102.4100- 6.462288-
Arsenic<0.02-1.290<0.01 <0.06-4.894(0.011) <0.04-3.995<0.01
Barium0.3440.2483- 2.230.9797- (0.44)20.7896-
Boron1.731.291- 1.524.893- 0.8443.997-
Cadmium0.013100.12880.014 (0.013)390.481000.01 0.024190.39970.019
Calcium2804--331 2641--275 3075--332
Chromium<0.03-0.691- <0.2-2.4106- <0.09-2102-
Cobalt0.01720.2483- (0.025)100.9794- <0.007-0.7891-
Copper0.2810.686(0.295) 1.2622.4951.27 1.010.32900.961
Iron3.6746814.69 3.55324913.93 10.60.5208611.2
Lead<0.02-1.279<0.007 <0.08-4.891<0.007 <0.06-3.988<0.007
Magnesium922--107 1792--199 1465--168
Manganese1.3451.2861.6 8.424.8928.85 1.6553.9871.8
Molybdenum0.02310.2485- (0.046)80.9796- 0.09870.7893-
Nickel0.1720.6840.167 0.1962.4940.127 0.119291(0.078)
Phosphorus4391--441 5991--558 7794--724
Potassium8583--1170 34704--4450 16004--2090
Selenium<0.05-2.4117<0.01 <0.2-9.7109<0.01 <0.2-7.81220.094
Sodium1242--116 2350.1--237 20203--2190
Strontium2.410.685- 2.842.4100- (1.6)2298-
Thallium<0.02-2.481- <0.08-9.792- <0.06-7.887-
Vanadium(0.004)340.1289- <0.01-0.4899- <0.008-0.3997-
Zinc1.5252.4801.79 2.5239.7902.73 8.3847.8849.01

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (6 of 7)

 Mayonnaise (166) Beer (198) Beef (baby food) (205)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum(1.3)81296- (0.17)20.7684- (0.41)e42.493-
Arsenic<0.3-24100<0.02 <0.02-1.594<0.01 <0.05-4.893<0.01
Barium<2-4.8106- <0.09-0.31103- <0.3-0.96101-
Boron(1.1)92496- 0.3341.593- (0.28)334.893-
Cadmium<0.05-2.4107<0.007 <0.003-0.15101<0.001 <0.009-0.48104<0.002
Calcium<200---83.7 452--52.8 -529--40.6
Chromium<0.7-12110- <0.04-0.76108- <0.2-2.4106-
Cobalt<0.05-4.8100- <0.003-0.3192- <0.009-0.9696-
Copper(0.1)191297<0.34 (0.018)50.7688<0.17 0.4222.492(0.428)
Iron2.261712196(2.61) (0.06)137.688<0.5 14.41249115
Lead<0.4-2497<0.035 <0.03-1.587<0.004 <0.08-4.894<0.007
Magnesium<70---(13.3) 501--62.9 1241--141
Manganese0.07242498<0.4 0.08811.590<0.2 0.05224.893<0.3
Molybdenum<0.1-4.8103- 0.02470.3193- <0.02-0.9697-
Nickel<0.2-12100- <0.02-0.7694<0.014 <0.04-2.497(0.06)
Phosphorus2612--276 1591--159 12300.05--1170
Potassium18317--98.3 2051--281 16701--2200
Selenium<1-48115(0.029) <0.07-3.1115<0.01 <0.2-9.6115(0.03)
Sodium51902--4930 351--41.6 3931--427
Strontium<4-12110- (0.2)30.7695- <0.7-2.4104-
Thallium<0.4-4898- <0.03-3.190- <0.07-9.694-
Vanadium<0.06-2.4103- 0.0320.1595- <0.01-0.4898-
Zinc1.4914893(1.98) <0.01-3.184<0.2 32.429.68332.2

4.4A Table 4. Food Fortification Results Using Ultrasonic Nebulizationa (7 of 7)

 Haddock (243) Pears (canned) (255)
ElementUnfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
 Unfort.
Resultb
(mg/kg)
 
RSD
(%)
Fort.
Level
(mg/kg)
Fort.
Recc
(%)
TDS
Resultd
(mg/kg)
Aluminum0.85e73.387- (0.19)51.197-
Arsenic5.9126.7956.59 <0.03-2.294<0.01
Barium<0.4-1.3102- 0.3440.44101-
Boron0.7986.796- 1.922.291-
Cadmium<0.02-0.67101<0.002 <0.004-0.22103<0.002
Calcium20430--269 463--45.2
Chromium<0.2-3.3105- (0.06)591.1105-
Cobalt<0.02-1.395- <0.004-0.4498-
Copper0.2593.394<0.29 0.3821.196(0.413)
Iron1.5423391(1.64) 6.52211926.39
Lead<0.1-6.790<0.01 (0.041)122.2920.032
Magnesium3456--400 382--40
Manganese0.34106.792(0.41) 0.97922.2941.03
Molybdenum<0.03-1.397- <0.008-0.4498-
Nickel(0.06)283.393<0.036 (0.044)111.196(0.042)
Phosphorus25002--2300 673--68.4
Potassium30606--3860 5331--650
Selenium(0.82)20131210.503 <0.09-4.4107<0.01
Sodium14401--1460 452--41.3
Strontium(1.7)403.3102- (0.36)91.1103-
Thallium<0.09-1393- <0.04-4.496-
Vanadium(0.034)620.6797- <0.005-0.22101-
Zinc4.24213864.58 0.434.492(0.447)

a Foods from FDA Total Diet Study market basket 1994-4 with food number in ( ) next to food name.
b Mean result based on 3 analyses (6 analyses for calcium, magnesium, phosphorus, potassium, and sodium) except 2 analyses (5 analyses for calcium, magnesium, phosphorus, potassium, and sodium) for evaporated milk or as indicated. Mean results in ( ) are "trace" levels and mean results below the LOD are listed as <LOD.
c Mean result based on 3 analyses except 4 analyses for haddock or as indicated. Calcium, magnesium, phosphorus, potassium and sodium not fortified.
d FDA Total Diet Study market basket 1994-4 results6 (n=1) except nickel results from FDA Kansas City District laboratory validation report10 or other source as indicated. Results in ( ) are "trace" levels and results below LOD are listed as <LOD.
e Mean result based on 2 analyses.
f Result of 1 analysis.
g Result by neutron activation analysis11.

4.4A.4 CONCLUSION

The in-house validation results for analysis of foods using microwave decomposition and element detection using ICP-AES indicate the following elements can be reliably measured at concentrations above LOQ: arsenic, barium, boron, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, phosphorus, potassium, sodium, strontium, vanadium and zinc. Thallium appears to be reliably measured but accuracy assessment is hindered by the lack of appropriate reference materials. The following elements appear prone to laboratory environmental contamination and therefore require extensive assessment of contamination control: aluminum, chromium, and lead. Aluminum concentrations using the method do not account for aluminum bound to silicates. Selenium concentrations may have been biased high in this study. Use of ICP-AES for determination of selenium in foods requires a thorough assessment of that background correction was effective.


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