Accred Qual Assur (2003) 8:21–24 DOI 10.1007/s00769-002-0549-9 © Springer-Verlag 2003 G. Anand Kumar H.S. Sahoo S.K. Satpathy G. Swarnabala Received: 3 April 2002 Accepted: 4 September 2002 G. Anand Kumar · H.S. Sahoo S.K. Satpathy · G. Swarnabala (✉) VIMTA Labs Ltd, Hyderabad – 500 051, India e-mail: [email protected] Tel.: +91-40-7264141 Fax: +91-40-7263657 Interlaboratory quality audit program for potable water – assessment of method validation done on inductively coupled plasma atomic emission spectrometer (ICP-AES) Abstract In an effort to assess the method validation done using ICPAES in our laboratory for potable water, an Environmental Laboratory Approval Program organized by New York State Department of Health, Wadsworth Center providing the reference material has been undertaken for 14 trace elements and seven other chemical constituents. The certified means for the reference material and the results obtained in our laboratory are compared. The comparisons helped us assess the quality of our work. All the data from the inductively coupled plasma atomic emission spectrometer (ICPAES) fall into the ranges specified. Introduction Certain major, minor and trace elements tend to accumulate causing toxicity in potable water. The quantitative measurement of these elements helps in diagnosis and treatment of a range of disorders. Proficiency testing materials, when studied by an analytical method, help in method improvement and validation and lead to better results, increasing the confidence of the analysts in reporting the data to the customers. Due to the complex nature of the material in question, its variable compositions of the elements, the need to validate the method of analysis is mandatory on the part of the analyst. So the analysis can be authenticated with the help of studies on proficiency testing materials, thus increasing the confidence level for values reported. In an effort to meet this demand, we have procured proficiency testing material of potable water from the Environmental Laboratory Approval Program being conducted by New York State Department of Health, Wads- These data are intended to depict the quality of chemical analysis being conducted in our laboratory and to increase the level of confidence of our clientele in accepting our test reports. It should be further noted that while the technique may not be new, the model is new and the simultaneous detection of elements required validation for those of our clientele who are only familiar with sequential AAS and AES. Keywords ICP-AES · Environmental Laboratory Approval Program – New York Department of Health, Wadsworth Center · Trace elements · Potable water worth Center. The chief of this institute has initiated the collaborative analysis program for analyzing the reference material for subsequent certification, with respect to major, minor and trace element concentrations. The whole study is used to analyze the waters of all kinds [1–6] such as drinking water – IS: 10500/1991, packaged natural drinking water – IS: 13428/1998, packaged drinking water – IS: 14543/1998, and water for quality tolerances for processed food industry – IS: 4251/1967. The characterization of these materials includes different sample preparation methods and analytical techniques being used by all the laboratories worldwide. Our laboratory is participating from India with NABL accreditation. We have determined 14 constituents by ICP-AES and seven by classical methods for the present study. The aim of this paper is to highlight the potential of ICP-AES in the generation of accurate analytical data for several trace elements in potable water samples and increase the confidence level of the customers who send us these Interlaboratory quality audit program for potable water – assessment of method validation done on ICP-AES Table 1 Validation data for potable water reference materials – Environmental Laboratory Approval Program analyzed for the following elements by ICPAES Sat, Satisfactory; Unsat, unsatisfactory. Table 2 Validation data for potable water reference materials – Environmental Laboratory Approval Program analyzed for the following chemical parameters on ICP-AES TDS, Total dissolved salts; Sat, satisfactory. 113 Parameter (µg/L) Result APHA method Study mean Accept. limits Score Ag As Ba Be Cd Cr Cu Fe Mn Ni Pb Sb Se Zn 87.0 57.3 777 8.74 10.0 99.0 300 541 70.5 219 31 45.95 130.0 479 3120 3120 3120 3120 3120 3120 3120 3120 3120 3120 3120 3120 3120 3120 82.2 51.1 817.0 7.42 8.59 88.4 328.0 523.0 74.20 240.0 33.80 39.30 48.50 479.0 73.8–90.5 44.8–57.3 696.0–942.0 6.6–8.94 6.9–10.4 75.1–102.0 293.0–359.0 478.0–568.0 68.50–79.80 201.0–273.0 23.60–43.80 27.40–51.0 37.80–56.60 439.0–518.0 Sat Sat Sat Sat Sat Sat Sat Sat Sat Sat Sat Sat Unsat Sat Parameter (mg/L) Result APHA method Study mean Accept. limits Score Na Nitrite Chloride Fluoride NO3 as N Sulfate TDS 12.6 1.52 62.9 5.1 7.94 44.4 228 3500 4500 4500 4500 4500 4500 2540 12.50 1.51 59.10 5.46 7.91 48.4 244.0 11.30–13.70 1.28–1.74 55.10–63.10 4.94–6.04 7.19–8.79 43.4–53.4 162.0–326.0 Sat Sat Sat Sat Sat Sat Sat samples. Since the programme had all the constituents determined, the data for the classical methods is also presented for completeness. Experimental follows: the ampoule temperature is adjusted to 20 °C prior to analysis. Approximately 900 mL of reagent water is added to a 1-L volumetric flask. Reagent grade nitric acid (5.0 mL) is added to the volumetric flask. The flask is swirled to mix. Ampoule ID no. is recorded. The ampoule is broken and 10 mL of the sample is transferred to the flask using a pipette. Then the flask is filled to mark with Milli-Q water and thoroughly shaken. The 14 elements are measured and the data are tabulated in Table 1. Instrumentation The ICP-AES used is a Varian-Radial Vista (Varian Instruments, Australia) associated with a microcomputer, software operating parameters, etc. as given in reference . Materials The water sample is obtained from the Environmental Laboratory Approval Program. We have used ICP-AES multi-element Reference Standard supplied by E. Merck with Lot. No: 0C030033 for standard calibration. These standards have certified data obtained from NIST as third-generation traceability, assuring reasonable accuracy in the estimations (Certificate of Analysis, Certipur – Reference Material; 11355 ICP multielement standad IV made from NIST standards reference materials, Lot No. 0C030033. Dr. Harald Untenecker, Central Analytical Laboratory, Merck). An echellogram showing all the elements is attached. Standard preparation Aqueous standards are prepared from 1000 ppm E. Merck standard reference material supplied with NIST traceability. The standards are made up using 18 MΩ Milli-Q water with 1% v/v high quality nitric acid 65%-Fluka Chemie. The following calibration standards for a five-point calibration curve have been made keeping in view the need to cover the range of 10, 2, 1, 0.1, and 0.01-ppm concentrations: Std. 1: Ag, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Std. 2: Be. Std. 3: As, Se, and Sb. Rinse and calibration blank solutions were prepared from 18 MΩ Milli-Q water with 5% HNO3 as per the instructions provided by the approval program. Sample procedure Methods used for chemical analysis To minimize the possibility of change in concentration, the ampoule is opened just before the analysis. The sample is prepared as All the chemical analysis procedures are adopted from APHA methods . These are specified in Table 2 along with the analyte. 114 G.A. Kumar et al. Fig. 1 Echellogram showing all the 23 elements in the standard along with the wavelengths. The wavelengths for all the 23 elements are: Ag Bi Co Fe Li Ni Zn 328.068 223.061 238.892 238.204 670.783 231.604 213.857 Al Ca Cr Ga Mg Pb 396.152 317.933 267.716 294.363 279.553 220.353 B Cd Cr In Mn Sr 249.772 214.439 357.868 230.606 257.610 407.771 Ba Cd Cu K Na Tl 455.403 226.502 327.395 766.491 589.592 190.794 Results and discussion ICP-AES offers rapid, multi-element determinations. Its sensitivity is lower than that of either ICP-MS or AA-GTA, but it can handle higher levels of total dissolved solids than ICP-MS and is much faster than AA-GTA. The results obtained are in comparison with all the equipment used by about 100 laboratories that are participating in the Environmental Laboratory Approval Program. The quality of the performance relating to equipment as well as the analyst in such international collaborative programs implies the use of certified reference materials for calibration and control samples to ensure a certain level of traceability of the measurements and finally the degree of assurance of reliability. The use of reference standards for calibration minimized several analytical errors. However, our working standards also gave results very similar to the reference standards. The results obtained for the study in question are summarized in Tables 1 and 2. The organizers collected the assigned value for individual elements and provided us the mean or range of the submitted data for over 100 laboratories using highly reliable statistical procedures. The table gives the result, mean, method, range and reliability of the parameter in question. A careful observation of these data provides the precision with which the experimental work has been conducted in the present study. Figure 1 shows the Echellogram of 23 elements in the reference standard along with the wavelengths. A typical example of the requirements for IS: 14543/1998 (4) are Ba, 1.0; Cu, 0.05; Fe, 0.1; Mn, 0.1; Zn, 5.0; Ag, 0.01; Al, 0.03; Se, 0.01; Ca, 75.0; Mg, 30.0; Na, 200.0; Hg, 0.001; Cd, 0.01; As, 0.05; Pb, 0.01; Cr, 0.05; Ni, 0.02; Sb, 0.005; B, 5.0 µg/L separately. Routinely all the samples are checked for the requirements before reporting. VISTA software has a built in program with USEPA requirements [9, 10] for the aspirating of standard reference solution; instrument check standard solution; interference check standard solution and QC standard solution for the laboratory QC control. Continuing calibration verification is done every ten analytical samples run on Auto Sampler, a facility that is not available when using the manual runs of the samples. We have adopted the Varian instruments instructions to calibrate the equipment to find the instrument detection limits and the method detection limits. The former values were obtained by aspirating on consecutive three days for all the standards and the latter values were obtained for consecutive seven runs on the same day for all the standards. These are also reconfirmed using “CHEMSW” software program available for the calculation of detection limits. The original “K-style” glass concentric nebulizer is used to obtain the raw-data with best possible sensitivity. For our method validation, we have adopted a seven-point calibration range for almost all the elements ranging between 10–0.01 mg/L. The accuracy in the recovery of the standards ranged from 95%–105% with a precision at 1 µg/L as ±12%. Matrix spiking results in the recoveries range between 75%–%125% as per USEPA/APHA. Vapour-generation accessory (VGA 77), is used for Hg measurements. Three standards 0.001; 0.005, and 0.01 µg/L are used for linearity or calibration. Stannous chloride (25%) and HCl (Fluka) are being used for the reduction in the cold-vapour generation. Conclusions It may be concluded that the observed data for 13 elements (except for the selenium) and the seven other constituents specified for potable water are in concurrence with all the laboratories whose data is submitted to Environmental Laboratory Program, New York State Department of Health. [After the constructive criticism from the reviewers, the unsatisfactory results for the Ag, Cd, Sb and Se elements were repeated. Cd values have improved by changing the wavelength from 217 to 226 nm. For antimony we have used a new standard and the value improved. For silver the number of washings before aspiration was tripled and the result improved. The selenium range is still not very satisfactory, but our efforts to improve upon this are in progress and we are positive about it.] The method detection limits, RSD’s, and the instru- Interlaboratory quality audit program for potable water – assessment of method validation done on ICP-AES mental detection limits obtained for our instrument and also the method validation done using this data confirms the validity of the method being adopted. Thus the use of instruments simultaneously for routine analysis imparts a high degree of excellence to the data being reported. 115 Acknowledgements G.S. is grateful to Dr. S. P. Vasireddi, Founder, Chairman and Managing Director, VIMTA Labs Ltd for giving permission to publish this work. We would like to thank the Environmental Laboratory Approval Program organized by New York State Department of Health, Wadsworth Center for permitting us to publish these data. References 1. APHA (2000) Standard methods for the examination of water and waste water analysis, 20th edn. APHA. 2. (1991) IS 10500 – Drinking water 3. (1998) IS 13428 – Packaged natural mineral water 4. (1998) IS 14543 – Packaged drinking water (other than the packaged natural mineral water) 5. (1992) IS 1070 – Reagent-grade water 6. (1967) IS 4251 – Quality tolerances from water for processed food industry 7. Satyanarayana KVS, Ravi Kumar Ch, Swarnabala G (2002) Atomic Spectrosc (submitted) 8. APHA (2000). Methods – 3120, 3500, 4500 and 2540. In: Standard methods for the examination of water and waste water analysis, 20th edn. APHA 9. USEPA (1994) Determination of metal and trace elements in water and wastes by inductively coupled plasma–atomic emission Sspectrometry – Method 200.7, USEPA, Environmental Monitoring and Support Laboratory, Cincinnati, OH, May 1994. USEPA Washington, DC 10. Bridger S, Knowles M (2000) ICPAES at work – ICP-29. A complete method for environmental samples by simultaneous axially viewed ICP-AES following USEPA guidelines. Varian Australia Pty Ltd.